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  • 1
    Electronic Resource
    Electronic Resource
    Syntheses of Batzelline A, Batzeline B, Isobatzelline A, and Isobatzelline B (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1173-1183 
    Details
    ISSN: 1434-193X
    Keywords: Marine alkaloids ; Pyrroloquinoline ; Total synthesis ; Heterocycles ; Alkaloids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Batzellines A and B (1a, b) and isobatzellines A and B (2a, b) are 1,3,4,5-tetrahydropyrrolo[4,3,2-de]quinoline-containing marine alkaloids characterized by the presence of a methylthio substituent at C-2 of the tricyclic system. We describe here the total synthesis of these natural compounds following the synthetic strategy that we have used previously for the synthesis of damirones A and B, batzelline C, isobatzelline C, discorhabdin C, and makaluvamines A, B, C, and D. The introduction of the methylthio group by electrophilic substitution of a pyrrolo[4,3,2-de]quinoline, appropriately substituted and in a suitable oxidation state, is the key step in the success of these syntheses.
    Additional Material: 2 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Intramolecular Copper- and Rhodium-Mediated Carbenoid Reactions of α-(Propargyloxy)silyl-α-diazoacetates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1213-1221 
    Details
    ISSN: 1434-193X
    Keywords: Diazo compounds ; Carbenes ; Carbenoids ; Silicon ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Copper(I) triflate catalyzes the transformation of α-[(2-alkynyl)oxy]silyl-α-diazoacetates 1a-g into 1,2-bis(2,5-dihydro-1,2-oxasilol-4-yl)ethenes 2 and/or 2H-1,2-oxasilines 3. With rhodium(II) perfluorobutyrate as catalyst, 1a-e furnish only 3 but no 2. Bicyclic 2-methoxyfurans 6 are formed when 1a,c,e (containing terminal alkyne functions) are treated with catalytic amounts of copper(I) chloride. The experimental observations are explained in terms of metal-mediated intramolecular cyclopropenation and subsequent metal-assisted ring-opening of the strained bicyclic cyclopropene leading to vinylcarbene-metal complexes. An unusual autoxidation of 2H-1,2-oxasilines 3a,c,e is also described.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    The Preparation of 2,3,5-Tri- and 2,3-Disubstituted Furans by Regioselective Palladium(0)-Catalyzed Coupling Reactions: Application to the Syntheses of Rosefuran and the F5 Furan Fatty Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2045-2057 
    Details
    ISSN: 1434-193X
    Keywords: Homogenous catalysis ; Palladium ; Cross-coupling ; Heterocycles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5-acceptor-substituted 2,3-dibromofurans 1 and 2 underwent a regioselective Pd0-catalyzed coupling reaction at the C-2 carbon atom. With alkynes the corresponding 2-alkynylfurans 4 and 5 were accessible (49-97% yield). Alkyl-, aryl-, and alkenylzinc reagents gave the 2-substituted furans 8 starting from compound 2 (66-84% yield). The 2-allylfurans 8e and 8f were obtained by a regioselective Stille coupling in 79% and 73% yield. The latter reaction was also applied to the parent 2,3-dibromofuran (27) and yielded the substitution product 28 (60% yield). Subsequent Pd0-catalyzed reactions to introduce a methyl group in 3-position by a methyldebromination were successfully conducted for 2-alkynyl-3-bromofurans with MeZnCl and PdCl2(PPh3)2 as the catalyst in THF (reflux) to yield compounds 13-16 and 24 (67-76%) and with SnMe4 and PdCl2[P(o-Tol)3]2 as the catalyst in DMA (90 °C) for the 2-allyl-3-bromofuran 8e to yield 18 (70%). The more facile reaction of the 2-alkynylfurans relative to those of furans bearing an sp3-carbon atom at C-2 appears to be due to steric reasons. Studies on the 2-alkyl-3-bromofuran 20 supported this notion. With the regioselective coupling methodology the terpene rosefuran (22) was prepared in four steps starting from furan 2 (35% yield overall). The F5 furan fatty acid (26) was synthesized from furan 1 in five steps (29% yield overall).
    Additional Material: 4 Tab.
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of (-)-Cytoxazone, a Novel Cytokine Modulator Isolated from Streptomyces sp. (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2965-2967 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohol ; Asymmetric synthesis ; Cell signaling ; Dihydroxylations ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cytoxazone [(4R,5R)-(-)-5-hydroxymethyl-4-(4-methoxyphenyl)-2-oxazolidinone, 1], a new immunosuppressant, was synthesized by starting from p-methoxycinnamyl alcohol (2) employing the Sharpless asymmetric dihydroxylation as the key reaction in 26% overall yield (7 steps).
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  • 5
    Electronic Resource
    Electronic Resource
    Borane Insertion into Group-4 Metal-to-Carbon Bonds: The Reaction of HB(C6F5)2 with (η2-Formaldehyde)zirconocene Dimer and with (Butadiene)zirconocene (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2243-2247 
    Details
    ISSN: 1434-1948
    Keywords: Metallaoxirane ; HBR2 addition ; (Formaldehyde)zirconocene ; (Butadiene)zirconocene ; Heterocycles ; Boron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (η2-Formaldehyde)zirconocene dimer (8) cleanly adds one or two molar equivalents of the borane HB(C6F5)2 by insertion of the H-[B] unit into the zirconium-carbon bond of the metallaoxirane moieties to form the mono- and bis-insertion products 16 and 17, respectively. These systems contain five-membered heterocyclic rings that are built up by connecting five different elements, namely H, B, C, O, and Zr. The bis(borane) insertion product 17 was characterized by an X-ray crystal structure analysis. (Butadiene)zirconocene reacts with HB(C6F5)2 in a similar way by insertion of the H-[B] unit into the (butadiene)C4-Zr linkage to form the metallacycle 18.
    Additional Material: 1 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Insights into the Staudinger Reaction: Experimental and Theoretical Studies on the Stabilization of cis-Phosphazides (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1659-1664 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus ; Iminophosphorane ; Staudinger reaction ; Heterocycles ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Staudinger-model reaction H3P (1) + HN3 (2) → H3P=NH (5) + N2 (6) has been investigated at the CCSD(T)/6-31G**//MP2(Full)/6-31G* level. Primary products formed in this reaction are the phosphazides H3P=N-N=NH (3) which exist as trans and cis isomers. In contrast to some previous assumptions, cis -3is 8.2 kcal mol-1 more stable than trans -3 but decomposes rather easily into the expected products H3P=NH and N2. This decomposition can be effectively hampered by intramolecular donor-acceptor interactions as shown by calculations on model compounds as well as by experiments. Thus the reaction of a methylene-σ3,λ3-phosphanyl-σ5,λ5-phosphorane with PhN3 led to a new four-membered heterocycle containing a thermally remarkable stable cis-phosphazide moiety.
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New Inorganic Metallacycles and the First Six-Membered Covalent “True” Heterocycle - Oxidation of RC(E)NHPPh2 (E = O or S; R = H2N, Ph, or Py) with O, S, or Se to Give RC(E)NHP(E′)Ph2 (E′ = O, S, Se) and Their Coordination Chemistry (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1445-1452 
    Details
    ISSN: 1434-1948
    Keywords: Metallacycles ; Solid-state structures ; Heterocycles ; Oxidations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct oxidation of PhC(O)NHPPh2, H2NC(S)NHPPh2, (C5H4N)C(S)NHPPh2 with O2, S8, or Se gives [PhC(O)NHP(O)Ph2] (1), [H2NC(S)NHP(S)Ph2] (2), [H2NC(O)NHP-(S)Ph2] (3), [PhC(O)NHP(S)Ph2] (4), [(C5H4N)C(S)NHP(S)Ph2] (5), and [H2NC(S)NHP(Se)Ph2] (6). Deprotonation of 1, 2, 4-6 with potassium tert-butoxide gives K[PhC(O)NP(O)Ph2] (7), K[H2NC(S)NP(S)Ph2] (8), K[PhC(O)NP(S)Ph2] (9), K[(C5H4N)C(S)NP(S)Ph2] (10), and K[H2NC(S)NP(Se)Ph2] (11). Reaction of 4with KOBu and [Cu(Ph3P)2][NO3] gives [Cu(Ph3P)(PhC(O)NP(S)Ph2)] (12) which is the first crystallographically characterised example of a non-ionic six-membered “true” heterocycle (i.e. a ring in which every heterocatom is different). 9 and 10 were treated with [PdCl2(COD)] to give [Pd{PhC(O)NP(S)Ph2}2] (13) and [Pd{(C5H4N)C(O)NP(S)Ph2}2] (14), respectively The anion of 8 coordinates to zinc forming [Zn{H2NC(S)NP(S)Ph2}2] (15). Treatment of 2 or 8 with [PtCl2(COD)] gives [Pt{H2NC(S)NP(S)Ph2}{H2NC(S)NHP(S)Ph2}]+Cl- (16) and [Pt{H2NC(S)NP(S)Ph2}2] (17), respectively. The X-ray structures of 12, 15-17are reported.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Syntheses, Structures, and Coordination of Diborylbipyridines and Bipyridinediborates (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 393-398 
    Details
    ISSN: 1434-1948
    Keywords: Boranes ; Bipyridine ; Crystal structures ; Donor-acceptor interaction ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6,6′-Bis(diethylboryl)-2,2′-bipyridine (1a) was obtained in low yield by in situ deprotonation of 2,2′-bipyridine in the presence of diethyl(methoxy)borane. 6,6′-Dilithio-2,2′-bipyridine reacts with various alkoxyboranes leading to bipyridinediborates 2 in good yields. The derivatives 2b and 2c allow the formation of the free diborylbipyridines 1b and 1c. The coordination properties of the diboryl-bipyridines as tetrafunctional donor-acceptor compounds have been used for the formation of the copper complex 4 and of the adduct 5 which is built from diborylbipyridine and a dihydroxydiboroxan derivative. The composition of the products follows from spectroscopic data and from X-ray structure analyses for 2f, 4, and 5.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis and Structure of 2-Hydro-, 2-Alkyl-, 2-Alkynyl-, and 2-Stannyl-2,3-dihydro-1H-1,3,2-diazaboroles (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 491-497 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Diazaboroles ; Hydrides ; Tin ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (4a) and 1,3-bis(2,6-dimethylphenyl)-2,3-dihydro-1H-1,3,2-diazaborole (4b) were formed by the reaction of the corresponding 2-bromo or 2-iodo derivatives 1a and 2b with LiAlH4. Treatment of 1a with n-butyllithium afforded 2-n-butyl-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (5a), whereas 1,3-di-tert-butyl-2-cyano-2,3-dihydro-1H-1,3,2-diazaborole (3a) was converted into the 2-tert-butyl derivative 6a or the 2-ethynyl-1,3,2-diazaborole 7a by means of tert-butyllithium or by the ethylenediamine adduct of lithium acetylide. Similarly, 1,3-di-tert-butyl-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8a) and 1,3-bis(2,6-dimethylphenyl)-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8b) were accessible from 1a or 2b and trimethylstannyllithium. In the complex 9a the compound 3a serves as an η1 ligand towards the [Cr(CO)5] unit via the cyano group. These novel compounds were characterized by 1H-, 11B-, 13C-, and 119Sn-NMR spectroscopy, as well as by X-ray structure analyses of 4b, 8a, and 9a.
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Reactions of 1,8-Diheterocyclotetradeca-4,11-diynes with (η4-Cycloocta-1,5-diene)(η5-cyclopentadienyl)cobalt (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 499-504 
    Details
    ISSN: 1434-1948
    Keywords: Alkynes ; Heterocycles ; Cyclizations ; Cobalt ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following monocyclic and bicyclic 14-membered diynes were treated with [CpCo(cod)]: 1-oxacyclotetradeca-4,11-diyne (2), 1,8-dioxacyclotetradeca-4,11-diyne (3), cyclotetradeca-4,11-diynone (4), cyclotetradeca-4,11-diyne-1,8-dione (5), 1,1,8,8-tetramethyl-1,8-disilacyclotetradeca-4,11-diyne (6), 1-allyl-1-azacyclotetradeca-4,11diyne (7), 1,8-dipropyl-1,8-diazacyclotetradeca-1,11-diyne (8), 1,8-diallyl-1,8-diazacyclotetradeca-4,11-diyne (9), 1,8-diazabicyclo[6.6.4]octadeca-4,11-diyne (10), 1,8-diazabicyclo[6.6.6]eicosa-4,11-diyne (11), 1,10-diazabicyclo[8.6.6]docosa-13,19-diyne (12) and 1,12-diazabicyclo[10.6.6]tetracosa-15,21-diyne (13). In all cases we obtained an intramolecular cyclobutadiene complex stabilized with a CpCo fragment (15-26). For 3 we could isolate, besides the cyclobutadiene complex 16, the trimerization product 28. In the cases of 15, 16, 18, 20, 23, 25, and 26 the structure of the cylobutadiene complexes could be confirmed by X-ray studies. Common to all structures is a boat-like conformation of the tricyclic unit containing the cyclobutadiene ring. The two cycloheptene units adopt a chair conformation in which the heteroatom is removed from the metal center.
    Additional Material: 1 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    Synthesis, X-ray Crystal Structures and Reactivity Towards Alkynes of Gold(I)-Phosphinine Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2233-2241 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus ; Heterocycles ; Phosphinines ; Gold ; Cycloadditions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coordination behaviour of 2,6-disilyl-substituted phosphinines towards gold(I) has been examined. The reaction of the bis(trimethylsilyl)phosphinine 1 with [AuCl(SMe2)] gives the corresponding AuCl derivative 2. X-ray crystal structure analysis reveals that the aromaticity of the phosphinine ring is slightly reduced as a result of the poor π-back bonding ability of the AuCl fragment. The same phenomenon is observed in the cationic complex [Au(1)2][GaCl4] (3) which was readily prepared by reaction of two equivalents of 1 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. Reaction of 2,6-bis(phenylethynyldimethylsilyl)phosphinine (4) with the same precursor leads similarly to the complex [AuCl(4)] (5). Interestingly, this complex dimerizes upon crystallization to give the bis(phosphabarrelene) complex 6, also structurally characterized. The formation of 6 results from a [4 + 2] cycloaddition between one alkynyl group of each phosphinine with the other phosphinine subunit. The formation of the cationic complex [Au(4)][GaCl4] (8) occurs under classical conditions but it disproportionates to give the cationic complex [Au(4)2][GaCl4] (9) and colloidal gold deposition. The formation of 9 has been ascertained by treating 8 with one equivalent of ligand 4. Additionally, 9 can also be obtained in a straightforward fashion by treating two equivalents of 4 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. The structure of 9 has been elucidated. Despite a particular arrangement of the alkyne groups which encapsulate the gold coordination sphere, no gold-alkyne interactions are visible.
    Additional Material: 5 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    Intramolecular Donor-Assisted Cyclization of Organotin Compounds (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 887-898 
    Details
    ISSN: 1434-1948
    Keywords: Tin ; Phosphorus ; Intramolecular coordination ; O ligands ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New intramolecularly coordinated organotin compounds containing the monoanionic O,C,O-coordinating ligand {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}- have been synthesized by substitution reactions starting from organotin halides. In view of the enhanced reactivity of the intramolecularly coordinated compounds {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}SnR2R′ (2, R = Ph, R′ = CH2SiMe3; 3, R = R′ = Ph; 6, R = R′ = Cl), cationic tin species are suggested to occur as intermediates in the formation of the heterocyclic compounds [1(Sn),3(P)-Ph2SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)2]C6H2 (8), [1(Sn), 3(P)-Ph(Me3SiCH2)SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)2]C6H2 (15), and {[1(Sn),3(P)-Cl2SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)]C6H2}2 (16). The latter compounds are formed by intramolecular cyclizations of pentacoordinate cationic tin species under elimination of ethyl halide. Furthermore, the synthesis of [1(Sn),3(P)-Ph2SnOP(O)(OH)-5-tert-Bu-7-P(O)(OH)2]C6H2 (13) is described. Reaction of 8 with an excess of Me3SiBr leads to the unexpected formation of {2-[P(O)(OEt)(OSiMe3)]-4-tert-Bu-6-[P(O)(OEt)2]C6H2}SnPhBr2 (9) as a result of an O-Sn bond cleavage initiated by Me3SiBr and subsequent reaction of the intermediate with further Me3SiBr under Sn-C bond cleavage. The high donor capacity and the rigidity of the new ligand {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}- are demonstrated by X-ray diffraction analyses of the tetraorganotin compound 2 and the monoorganotin trichloride 6. Furthermore, the molecular structures of the 2,3,1-oxaphosphastannoles 8 and 16 are discussed.
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  • 13
    Electronic Resource
    Electronic Resource
    Cyclic Ketiminoboranes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 7-9 
    Details
    ISSN: 1434-1948
    Keywords: Boranes ; Diazaboroles ; Heterocycles ; Ketiminoboranes ; Crystal Structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cyclocondensation reaction of benzil-bis(trimethylsilylimin) (3) and Cl2B-NiPr2 via silicon-boron exchangeresults in the solvent-dependent formation of the 1,3,2-diazaborole 1a or the 1,3,6,8,2,7-tetraazadiborecin 2a. Using the more rigid 9,10-bis(trimethylsilylimino)phenanthrene instead of 3 only the five-membered heterocycle 4,5-biphenylene-2-diisopropylamino-1,3,2-diazaborole (1b) is formed. The cyclic ketiminoboranes are characterized by NMR and X-ray diffraction data. The 1,3,2-diazaborole ring is almost planar, while the conformation of the 1,3,6,8,2,7-tetraazadiborecin has the shape of a figure-eight loop.
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  • 14
    Electronic Resource
    Electronic Resource
    Synthesis and 1H-, 15N-, 31P-, 183W-Multinuclear Magnetic Resonance Study of the Cyclotriphosphazenes [N3P3(dobp)2(OC5H4N-4)2] and [N3P3(dobp)(OC5H4N-4)4] and Their W(CO)5 Complexes (dobp = 2,2′-dioxybiphenyl) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1015-1020 
    Details
    ISSN: 1434-1948
    Keywords: Cyclotriphosphazenes ; Oxypyridine ; Carbonyltungsten compounds ; NMR spectroscopy ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of [N3P3(dobp)2Cl2] and [N3P3(dobp)Cl4] with a mixture of HOC5H4N-4 and K2CO3 in acetone give the cyclotriphosphazenes [N3P3(dobp)2(OC5H4N-4)2] and [N3P3(dobp)(OC5H4N-4)4], respectively. These compounds react with [W(MeOH)(CO)5] in methanol to give mixtures of the polymetallic complexes [N3P3(dobp)2(OC5H4N-4)2{W(CO)5}x] (x = 1, 2) and [N3P3(dobp)(OC5H4N-4)4{W(CO)5}x] (x = 1-4), which are unstable in solution, slowly undergoing loss of the pentacarbonyl moiety. A complete characterization by multinuclear 1H, 15N, 31P, 183W magnetic resonance has revealed that the complexation of the N atom of one 4-oxypyridine ligand by the W(CO)5 fragment has a measurable effect on other parts of the phosphazene molecule very far away from the coordination site. The changes observed in δ183W have been used to identify the components in mixtures of compounds incorporating different numbers of tungsten atoms in the molecule. The characterization of less sensitive nuclei has been accomplished by means of indirect detection methods.
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  • 15
    Electronic Resource
    Electronic Resource
    Novel Condensed Thionated Bis(phosphonic) Acid Salts with a Rigid Naphthalene-1,8-diyl Backbone (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2327-2333 
    Details
    ISSN: 1434-1948
    Keywords: Heterocycles ; Organo-phosphorus compounds ; Dithiadiphosphetane disulfides ; Phosphonates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New salts of thionated (naphthalene-1,8-diyl)bis(phosphonic) acid monoanhydrides [PPh4+]2[C10H6PS2(μ-S)PS22-] (2) and [K+]2[C10H6PS2(μ-S)POS2-]·H2O (3) both containing the C3P2S ring, were prepared in high yields by the reaction of 2,4-(naphthalene-1,8-diyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (1) with NaHS and PPh4Cl, or KOH, respectively, in water. The derivative 3, containing a P=O terminal bond as well as P-S-P bridge, undergoes, in acid conditions, a rearrangement reaction leading to the O,S-symmetrically substituted derivative [K+]2[C10H6PS2(μ-O)PS22-] (4) containing a C3P2O heterocycle. Dipotassium salt 4 was converted into the bis(tetraphenylphosphonium) salt 5 by the treating with PPh4Cl. Hydrolysis of [PyH+][C10H6P(S)(NHMe)(μ-S)PS22-] (15) led to [CH3NH3+][PyH+][C10H6POS(μ-O)POS2-]·1.5 Py (6). New compounds were characterised by 31P{1H}-, 1H- and 13C{1H}-NMR, FT-IR, ES-MS and in the cases 2-6 by X-ray structure determination. The 31P{1H}-NMR spectra of these mixed O,S-derivatives are briefly discussed.
    Additional Material: 5 Ill.
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  • 16
    Electronic Resource
    Electronic Resource
    Synthesis, Structure and Reactivity of 3,4-Dihydro-2H-1,2,4,3-triazaboroles (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1193-1198 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Triazaboroles ; Heterocycles ; Halogens ; Cyanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,4-Dihydro-2,4-diphenyl-2H-1,2,4,3-triazaboroles 3a, 3b, and 4 were synthesized by cyclocondensation of N1,N3-diphenylformamidrazone (1) with dibromophenylborane, dibromomethylborane, and boron trichloride. 3-Chloro-3,4-dihydro-2,4-diphenyl-2H-1,2,4,3-triazaborole (4) was converted into 3,4-dihydro-2,4-diphenyl-2H-1,2,4,3-triazaborole (5) by treatment with LiAlH4. The corresponding 3-cyanato and 3-cyano derivatives 6 and 7 resulted from the reaction of 4 with AgOCN and AgCN, respectively. Compound 7 was transformed into the bis(1,2,4,3-triazaborolyl)oxane 8 by silver oxide. Compounds 1-8 were characterized by elemental analyses and spectroscopic methods (1H, 11B, and 13C NMR; IR; MS). The molecular structure of 8 was established by single-crystal X-ray diffraction analysis.
    Additional Material: 2 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    The Synthesis of Novel Cyclic β-Amino Acids as Intermediates for the Preparation of Bicyclic β-Lactams (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2433-2441 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Lactams ; Schiff bases ; Nitrogen heterocycles ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several derivatives of homopipecolic acid are prepared by α-amino alkylation of malonic acid with cyclic imines 6 and 7. These are prepared on a large scale and with different substitution patterns. The β-amino acids 8 and 9 were formed in high yield and with remarkable diastereoselectivity if chiral imines are used as starting materials. The diastereoselectivity of the amino alkylation leading to homopipecolic acid analogues is compared to those of thiazolidineacetic acids by epimerisation experiments. A method for resolution of the obtained racemic β-amino acids by diastereomeric salt formation is described. The β-amino acids 9 and 15 were converted into their corresponding carbacepham analogues 14 and isopenam 16. The isopenam endo-16 was selectively epimerised by mild basic treatment of the N/S-acetal to give an exo-configured precursor of isopenicillin G.
    Additional Material: 2 Tab.
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  • 18
    Electronic Resource
    Electronic Resource
    Pd-Catalyzed Asymmetric Allylic Alkylation of 3-Acetoxy-N-(tert-butyloxycarbonyl)-1,2,3,6-tetrahydropyridine - Preparation of Key Intermediates for Natural Product Synthesis (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2515-2521 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Heterocycles ; Palladium ; Alkylations ; Allyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A convenient synthesis of racemic tetrahydropyridine 1 was developed. Pd-catalyzed allylic alkylation of 1 with malonate and dimethylacetoxymalonate as nucleophiles with the phosphanylcarboxylic acid L1 and the dihydrooxazol L2 as ligands, were carried out and gave enantiomeric excesses of up to 98%. Absolute configurations were determined for all compounds described. From the alkylation products (+)- and (-)-2a, and (+)- and (-)-2b a variety of versatile, nonracemic chiral intermediates were prepared.
    Additional Material: 1 Tab.
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  • 19
    Electronic Resource
    Electronic Resource
    Nucleophilic Substitution Reactions with the 3-Borane-1,4,5-trimethylimidazol-2-ylidene Anion. - Unexpected Formation of an Imidazabole Isomer (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 789-793 
    Details
    ISSN: 1434-1948
    Keywords: Boranes ; Carbenes ; Heterocycles ; Imidazoles ; X-ray structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nucleophilic carbene 3-borane-1,4,5-trimethylimidazol-2-ylidene anion (1-) reacts with the electrophiles CH3I, (CH3)3SiCl, (CH3)3SnCl, and the bromodiazaboroline 7 to form the 2-substituted imidazoles 4, 5, 6, and 8. With triethylborane, the anionic carbene borane adduct 9- is obtained. An unexpected result was achieved when chlorodimethoxyborane and HBCl2 · S(CH3)2 were used as electrophiles. In both cases only the imidazabole 14a could be isolated. Imidazole 5, the imidazole borane adduct 3a and the imidazabole 14a were characterized by X-ray structure analyses.
    Additional Material: 3 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    Carbon=Carbon Hydrogenation of Silicon-Functionalized Silaheterocycles (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1095-1102 
    Details
    ISSN: 1434-1948
    Keywords: Silanorbornenes ; Silanorbornanes ; Silicon-functionalized olefins ; Silacyclobutanes ; Hydrogenations ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Catalytic hydrogenation of olefins containing functionalized silicon groups affords the saturated products in good yields. Chloro and alkoxy substituents at the silicon atom remain unaffected and, in the case of heterocyclic compounds, the cyclic or bicyclic moieties remain intact. The 2-silanorbornanes 4, 5, and 6 were synthesized from the corresponding 2-silanorbornenes 1, 2, and 3, and organosilanes 13 and 14 possessing the cyclopentyl group, were prepared from the cyclopentenyl-substituted precursors 10 and 12. The 3-vinyl-substituted silacyclobutanes 15, 17, and 18 were also hydrogenated in a simple apparatus with diethyl ether or THF as solvent, and Pd/C as a recoverable catalyst system. A basic organosilicon compound, trichloro(vinyl)silane, is hydrogenated in a nearly quantitative yield to form the saturated trichloro(ethyl)silane; this emphasizes the general applicability of this method.
    Additional Material: 2 Ill.
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  • 21
    Electronic Resource
    Electronic Resource
    Synthesis of N-Acetylglucosaminyl and Diacetylchitobiosyl Amides of Heterocyclic Carboxylic Acids as Potential Chitinase Inhibitors (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2293-2297 
    Details
    ISSN: 1434-193X
    Keywords: Carboxylic acid amides ; Chitinase ; Chitobiose ; Heterocycles ; Enzyme inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-(Dimethylamino)oxazoline-4-carboxylic acids 5 were prepared by condensation of binucleophilic amino acids 4and O-ethyl-N,N-dimethylisourea 3. New heterocyclic N-acetylglucosaminyl amides and chitobiosyl amides 8 were obtained by the coupling of tetraacetylglucosamine 6a or heptaacetylchitobiosylamine 6b with acid chlorides of heterocyclic carboxylic acids 2 or 5a and subsequent deacetylation. Based on their substitution patterns, compounds 8were expected to have inhibitory activity towards chitinases. Enzyme assays showed that glycosyl amides 8 indeed were moderate inhibitors of chitinases, the diacetylchitobiosyl amides 8d-f generally having higher inhibitory activities than the N-acetylglucosaminyl amide derivatives 8a-c. Inhibitory activities depended on the chitinase tested.
    Additional Material: 2 Tab.
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  • 22
    Electronic Resource
    Electronic Resource
    2-Substituted 5-Acetyl-4-Thiazolyl Triflates as Useful Building Blocks for the Preparation of Functionalized Thiazoles (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3117-3126 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Thiazoles ; Pyrido[3,4-c]thiazoles ; Triflates ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The readily available 2-substituted 5-acetyl-4-thiazolyl triflates 2are useful building blocks for the preparation of functionalised thiazoles by means of palladium-catalysed cross-coupling reactions with organometallic reagents and alkoxycarbonylation and deoxygenation reactions. The combination of palladium-catalysed coupling of 2 together with 1-alkynes/6-endo-dig annulation reactions in the presence of ammonia leads to functionalised pyrido[3,4-c]thiazoles in satisfactory yields. The utilisation of uncatalysed displacement reactions of the triflate group represents a very simple method for the synthesis of 4-N-,4-O-, and 4-S-substituted thiazoles.
    Additional Material: 2 Tab.
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  • 23
    Electronic Resource
    Electronic Resource
    Silicon-Oxygen Heterocycles from Thermal, Photochemical, and Transition-Metal-Catalyzed Decomposition of α-(Alkoxysilyl and Alkenyloxysilyl)-α-diazoacetates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1939-1946 
    Details
    ISSN: 1434-193X
    Keywords: Diazo compounds ; Carbenes ; Carbenoids ; Silicon ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photolysis of (ethoxy)silyl-, (propyloxy)silyl-, and (isopro-pyloxy)silyl-substituted diazoacetates 1a-c leads to tetrahydro-1,2-oxasiloles 2a-c by intramolecular C-H insertion of a carbene intermediate. Photochemical or catalytic decomposition of (allyloxysilyl)diazoacetates 3a-e results in intramolecular cyclopropanation which provides 3-oxa-2-silabicyclo[3.1.0]hexane systems 5a-e. In contrast, the thermal reaction of 3b-d gives rise to 2,5-dihydro-1,2-oxasiloles 4b-d, which are likely to be formed on a pyrazoline rather than a carbene route. For (3-butenyloxysilyl)diazoacetate 3f, all modes of decomposition generate the 3-oxa-2-silabicyclo[4.1.0]heptane system 7. Fluoride-induced cleavage of the bicyclic systems 5b-d provides trans-2-hydroxyalkyl-1-cyclopropanecarboxylates 9 diastereospecifically.
    Additional Material: 1 Tab.
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  • 24
    Electronic Resource
    Electronic Resource
    An Easy Access to 1-Azaspiropentane-2-carboxamides - The First Derivatives of a New Type of Amino Acids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2017-2024 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Azaspiropentanes ; Heterocycles ; Peptides ; Strained molecules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azaspiropentanecarboxamides 10 and 12 are formed with remarkable ease in two steps in a one-pot operation from methyl 2-chloro-2-cyclopropylideneacetate (4) by addition of a primary amine in tetrahydrofuran and subsequent treatment with sodium hydride/triethylamine in the presence of another equivalent of a primary amine or ammonia. Achievable yields of the amides 10, 12 were moderate to good (27-59%, 12-48%), while the corresponding esters 9 could only be obtained in poor yields (4-14%). The new α-amino acid amides are surprisingly stable, and they can be incorporated into small peptides as demonstrated with the preparation of the glycine 13e and the spirocyclopro-paneoxazoline derivative 14e.
    Additional Material: 2 Ill.
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  • 25
    Electronic Resource
    Electronic Resource
    New Heterocycles from the Reaction between Some Natural α-Amino Acid Hydrazides and Formaldehyde (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2943-2948 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; α-Amino acid phenylhydrazides ; Heterocycles ; Cyclization reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring forming condensation between some natural α-amino acid phenylhydrazides (1) and aqueous formaldehyde (2) has opened a novel synthetic route to hexahydro-1,2,4-triazin-6-one derivatives (3). Polycyclic systems were obtained from the same reaction carried out with L-aspartic acid 1,4-bis(2-phenylhydrazide) (1d), L-histidine phenylhydrazide (1e) and L-tryptophan phenylhydrazide (1f) which gave perhydro-4,6-dioxo-2,8-diphenyl[1,2,4]triazino[4,5-d][1,2,4]triazepine (5) perhydro-1-oxo-3-phenylimidazo[5,4-d][1,2,4]triazino[4,5-a]pyridine (7) and 1,2,3-H-3-(2-phenylcarbazoyl)-β-carboline (8), respectively. Substrates 1 were conveniently obtained by direct reaction of phenylhydrazine with L-α-amino acid esters retaining the original chirality.
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  • 26
    Electronic Resource
    Electronic Resource
    Synthesis Mediated by Ring-Closing Metathesis - Applications in the Synthesis of Azasugars and Alkaloids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 959-968 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Alkaloids ; Castanospermine ; Metathesis ; Azasugars ; Manzamine A ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The application of the ring-closing metathesis (RCM) reaction to the construction of a wide variety of nitrogen-containing ring systems is described. The examples include pyrrolizidine, indolizidine, and quinolizidine derivatives related to azasugars. A formal total synthesis of castanospermine (5) is presented. The utilisation of two RCM steps in the synthetic sequence leading to the multicyclic ABCDE nucleus 7 of the complex alkaloid manzamine A (6) is discussed.
    Additional Material: 3 Ill.
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  • 27
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    Electronic Resource
    A New Strategy for the Asymmetric Synthesis of 1,3-Oxathiolane-Based Nucleoside Analogues (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1455-1458 
    Details
    ISSN: 1434-193X
    Keywords: Nucleoside analogues ; 1,3-Oxathiolanes ; Chiral sulfoxides ; Heterocycles ; Antiviral agents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A ready asymmetric synthesis of 3′-oxathionucleosides has been accomplished in three main steps from benzoyloxyethanal. The synthesis is characterized by high overall yield and considerable enantiomeric excesses. It represents a general synthetic path to prepare a wide range of heterosubstituted sulfur-containing nucleoside analogues.
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  • 28
    Electronic Resource
    Electronic Resource
    Novel Stereoelectronic Behavior of Bicyclic Glycosyl Donors: Application to the Synthesis of Both 2-Deoxy-α- and -β-Glycosides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1869-1874 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Heterocycles ; Electrostatic interactions ; Glycosylation ; Glycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two pairs of novel stereoisomeric, cyclic glycosyl donors exhibit different behaviors in glycosylation processes. In the pair of α-gluco (1) and β-manno (2), the former exhibits reversability with its glycoside product whereas the latter does not. In the α-gluco (3) and β-manno (4) set, the former undergoes glycosyl transfer via an isolable intermediate whereas the latter does not. The differing anomeric effects exerted in the ground states are proposed as the force which explains the differences in behavior.
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  • 29
    Electronic Resource
    Electronic Resource
    Synthesis of the Enantiomers of 2-sec-Butyl-4,5-dihydrothiazole and (1R,5S,7R)-3,4-Dehydro-exo-brevicomin, Pheromone Components of the Male Mouse, Mus musculus (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2167-2173 
    Details
    ISSN: 1434-193X
    Keywords: Acetals ; Heterocycles ; Mouse ; Mus musculus/ Pheromones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two components [2-sec-butyl-4,5-dihydrothiazole (1) and 3,4-dehydro-exo-brevicomin (2)] of a male-produced pheromone of the mouse Musmusculus have been synthesized in optically active forms. The enantiomers of 1 were obtained with an enantiomeric purity of ca. 92% ee and were found to be readily racemizable. Asymmetric dihydroxylation was employed as the key reaction (15→16) allowing the preparation of (1R,5S,7R)-2 with ca. 94% ee.
    Additional Material: 1 Tab.
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  • 30
    Electronic Resource
    Electronic Resource
    Umpolung of Reactivity of Lithium Trimethylsilyldiazomethane at the C-5 Position of 6-Substituted Uracil Derivatives (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2751-2755 
    Details
    ISSN: 1434-193X
    Keywords: Lithium ; Lithium trimethylsilyldiazomethane ; Heterocycles ; Uracil derivatives ; Pyrazolo[4,3-d]pyrimidindiones ; Pyrazolo[4,3-d]pyrimidindiones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nucleophilic addition of TMSC(Li)N2 at the low reactive C-5 position of the uracil ring of C-6 substituted uracil derivatives is reported. The ratio of C-5 versus C-6 nucleophilic addition of TMSC(Li)N2 dramatically depends on the stereoelectronic properties of the C-6 substituent. In particular, substituents characterized both by sterically bulky and/or electron-withdrawing (EWG) effects appear to direct the nucleophile mainly (methyl, chloromethyl or halogen) or completely (isopropyl) toward the C-5 position. The fine-tuned substituent selectivity found in the nucleophilic addition of TMSC(Li)N2 to C-6 substituted uracils plays a leading role in the synthesis of new trimethylsilyl-1H-[4,3-d]pyrimidin-5,7-dione derivatives, which can in turn be easily modified through known silicon chemistry.
    Additional Material: 1 Ill.
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  • 31
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    Electronic Resource
    Synthesis and Structure of Gallium/Silicon Heterocycles with a Ga2Si2 and a Ga3Si Framework⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 745-749 
    Details
    ISSN: 1434-1948
    Keywords: Gallium ; Silicon ; Heterocycles ; Main group elements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Ga2X4· 2 dioxane with four equivalents of (Me3Si)3SiLi(thf)3 (= hypersilyllithium) affords for X = Br a 1,3,2,4-disiladigalletane together with tetrahedral hypersilylgallium(I). For X = Cl an anionic 1,2,3,4-silatrigalletanate, a four-membered heterocycle with a Ga3 unit, is isolated. These primary examples of gallium/group-14 heterocycles have been investigated by NMR spectroscopy as well as by X-ray single-crystal structure analysis. In addition, the synthesis and structure of bis(hypersilyl)gallium chloride is described. This monomeric molecule has a nearly T-shaped Si2GaCl framework.
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  • 32
    Electronic Resource
    Electronic Resource
    2,3-Dihydroimidazol-2-ylidene (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1517-1520 
    Details
    ISSN: 1434-193X
    Keywords: Nucleophilic carbenes ; Heterocycles ; Decarboxylation ; Photochemistry ; Matrix isolation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation of imidazole-2-carboxylic acid (3) - matrix-isolated in argon at 10 K - with a wavelength of 254 nm leads to decarboxylation and the formation of a complex between 2,3-dihydroimidazol-2-ylidene and carbon dioxide (1·CO2). Upon irradiation of 2,3-dihydroimidazol-2-ylidene (1) with λ = 254, 193, and 185 nm no imidazole can be detected. On the other hand flash vacuum pyrolysis of imidazole-2-carboxylic acid (3) produces imidazole and carbon dioxide. 2,3-Dihydroimidazol-2-ylidene (1) - the possible intermediate - cannot be trapped under these conditions.
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  • 33
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    Electronic Resource
    Kinetics of the [2+ + 4]-Cycloaddition Reactions of 1,3-Dithian-2-ylium Ions with 1,3-Dienes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1919-1922 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Carbocations ; Dienes ; Cycloadditions ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the [2+ + 4] cycloadditions of 1,3-dithian-2-ylium ions (1) with 1,3-dienes was investigated photometrically in dichloromethane. The second-order rate constants determined for the reactions of 1 with 2,3-dimethyl-1,3-butadiene (2a) and isoprene (2b) were identical to those calculated for the first step of a stepwise cycloaddition pathway by the correlation lg k = s (E + N). Though a concerted cycloaddition pathway is not excluded by this finding, it is obvious that the transition states of these reactions are not noticeably stabilized by the simultaneous formation of two new σ bonds.
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  • 34
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    Electronic Resource
    A General Route to the Monomeric Subunits of the Macrotetrolides - A Short Synthesis of Methyl Nonactate (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2073-2078 
    Details
    ISSN: 1434-193X
    Keywords: Sultones ; Intramolecular Diels-Alder reaction ; Desulfurization ; Heterocycles ; Actic acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A highly stereoselective and flexible sultone route to actic acids, the monomeric subunits of the macrotetrolides, has been developed and exemplified for nonactic acid (2a). Due to the extensive application of tandem transformations, only six steps were needed to secure methyl nonactate (20) from furan.
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  • 35
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    Preparation, Structure and Reactivity of 2-Chloro-, 2-Fluoro- and 2-Iodo-2,3-dihydro-1H-1,3,2-diazaboroles (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1145-1152 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Diazaboroles ; Halogens ; Isocyanides ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of differently substituted 2-chloro-, 2-fluoro- and 2-iodo-2,3-dihydro-1H-1,3,2-diazaboroles have been prepared by various methods. 1,3-Di-tert-butyl-2-fluoro-2,3-dihydro-1H-1,3,2-diazaborole (3a), 1,3-di-tert-butyl-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (5a), 1,3-bis(2,6-dimethyl-phenyl)-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (5b), 2-chloro-4,5-dimethyl-1,3-dineopentyl-2,3-dihydro-1H-1,3,2-diazaborole (5c), and 1,3-di-tert-butyl-2-iodo-2,3-dihydro-1H-1,3,2-diazaborole (6a) were formed from the corresponding lithiated Z-1,2-diaminoethenes, by treatment with BF3·OEt2, BCl3, or BI3 in n-hexane. Compounds 3a, 5a, and 5b are also available by sodium amalgam reduction of the adduct (tBu)(BF3)N=CH-CH=N(BF3)(tBu) (2a), and the borolium salts [RNa=CH-CH=Nb(R)BCl2]X (Na-B) (4a: R = tBu, X = BCl4 and 4b: R = 2,6-Me2C6H2, X = Cl) respectively. The iodo derivative (2,6-Me2C6H2)-Na-CH=CH-Nb(2,6-Me2C6H2)BI (Na-B) (6b) was synthesized in a redox reaction between the 1,4-diazabutadiene 1b and BI3. The novel compounds were characterized by 1H-, 11B- and 13C-NMR spectroscopy, as well as by an X-ray structure analysis of 6b.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1998/98047_s.pdf or from the author.
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  • 36
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    Electronic Resource
    New P,N-Chelate Ligands Based on Pyridyl-Substituted Phosphaferrocenes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1163-1168 
    Details
    ISSN: 1434-1948
    Keywords: Chelates ; P,N ligands ; Phosphaferrocene ; Catalysis ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new pyridyl-substituted phosphaferrocene ligands 3 and 6 are prepared by addition of lithiated pyridine or α-picoline to 2-formyl-3,4-dimethylphosphaferrocene (1). The ligands 3 and 6 react with [Cp*RuCl]4 in THF to give the P,N-chelate complexes [Cp*RuCl·3] (9) and [Cp*RuCl·6] (10) with high diastereoselectivity. Addition of monodentate ligands like CO or PPh3 to the complexes leads by displacement of the Ru-bound pyridyl group to the respective carbonyl or phosphane complexes with monodentate P-coordinated phospha-ferrocene ligands. Reaction of the ligand 6 with [(C3H5)PdCl]2 and NH4PF6 gives the seven-membered chelate complex [(C3H5)Pd·6]PF6 (13) which was characterized by X-ray diffraction. The ligands 3 and 6 were tested in the palladium-catalyzed asymmetric alkylation of 1,3-diphenylallyl acetate.
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  • 37
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    Electronic Resource
    Isoelectronic Arduengo-Type Carbene Analogues with the Group IIIa Elements Boron, Aluminum, Gallium, and Indium (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 305-310 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Carbene homologues ; Boron ; Isoelectronic analogues ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: While Arduengo-type carbenes are now well established for the Group IVa elements carbon, silicon and germanium, they are experimentally unknown for the isoelectronic anions with the Group IIIa elements boron, aluminum, gallium, and indium. In the present quantum chemical investigations, the bonding features of this class of compounds are explored. As a result, they are predicted to be stable species with sizeable singlet-triplet energy separations and electron affinities. Hence, they may be considered as valid targets for experimental investigations. An analysis of the electron density distribution in the case of boron and aluminum reveals a strongly polar B-N bond for the former, and a half Al-N bond with positive charge at the aluminum, emphasizing the donor-acceptor formulation for the latter.
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  • 38
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    Electronic Resource
    On the Homoconjugation of Two Acceptor Groups (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1615-1623 
    Details
    ISSN: 1434-193X
    Keywords: Homoconjugation ; Cyclovoltammetry ; ESR spectroscopy ; Diketones ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclovoltammetric investigations have been carried out on 3,3,6,6-tetramethylcyclohexane-1,2,4,5-tetrone (4), bicyclo-[3.2.2]nonane-6,7,8,9-tetrone (5), and several of their congeners, such as 6,13-dihydro-6,6,13,13-tetramethylquin-oxalino[2.3-b]phenazine (13), 5,10-dihydro-5,5,10,10-tetra-methylpyrazino[2,3-g]quinoxaline (17), and 6,13-dihydro-6,13-propanoquinoxalino[2,3-b]phenazine (20). For 5 and 20 a large difference (ΔE° ≥400 mV) between the first and second reduction potentials was found. The ESR results of the radical anion 20•- are in support of a strong homoconjugation. ESR studies of 4•-, 13•-, and 17•- also reveal a symmetrical displacement of the unpaired electron over both acceptor groups on the ESR time scale which, however, based on the small potential difference ΔE° ≤ 200 mV can be most likely described to a fast electron exchange.
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  • 39
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    Electronic Resource
    2-(Het)aryl-Substituted 7-Azabicyclo[2.2.1]heptane Systems (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1997-2001 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Acetylcholine receptor ; Palladium ; C-C coupling ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Epibatidine (1) is a recently discovered trace alkaloid found in the skin of a Latin-American poisonous frog. Its remarkably high analgetic activity is accompanied by high toxicity. Therefore, in order to tune its biological activity, a convergent and efficient synthetic pathway was sought to synthesize epibatidine derivatives with different (het)aryl substituents. The hydro(het)arylation of the key intermediate 7-azabicycloheptene (10) represents such an approach. The synthesis of 10 by a Diels-Alder reaction of an N-activated pyrrole (7) with ethynyl p-tolyl sulfone (6) and subsequent steps has been optimized. The crucial last step, the reductive cleavage of the vinyl sulfone 9, has been replaced by a high-yield fluoride-induced degradation of the β-silylated sulfone 12 to give 10. A number of structurally different racemic epibatidine analogs (16b-e) can be prepared by palladium-catalyzed hydro(het)arylation of 10 with iodo(het)arenes 15b-e in good yields.
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  • 40
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    Electronic Resource
    Borane-Substituted Imidazol-2-ylidenes: Syntheses, Structures, and Reactivity⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 843-849 
    Details
    ISSN: 1434-1948
    Keywords: Boranes ; Carbenes ; Carbene complexes ; Heterocycles ; Imidazoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of the Lewis acids BH3 and BEt3 with trimethylimidazole (1) lead to the borane adducts 2a and 2b. Deprotonation of 2a with n-butyllithium results in the formation of the novel N-borane-substituted imidazol-2-ylidene anion 3a- whereas deprotonated 2b rearranges unexpectedly to the anionic compound 3b-. This can be transformed into the carbene-borane adduct 4 by methylation. The reaction of 3a- with [Mn(CO)5Br] yields the carbene complex 5. Surprisingly, 3a- attacks Fe(CO)5 at a carbon atom which leads to the iron acyl complex anion 6-. The compositions of the products follow from spectroscopic and analytical data and from X-ray structure analyses for Li(thp)+3a-, Li(thf)2+3b- and Li(thp)3+6-.
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  • 41
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    Electronic Resource
    The Synthesis of Perylenebisimide Monocarboxylic Acids (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 847-851 
    Details
    ISSN: 1434-193X
    Keywords: Fluorescent dyes ; Perylenes ; Heterocycles ; Carboxylic acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and properties of perylene-bisimides 4 with one carboxylic acid anchor group are described. The properties of 4 are strongly influenced by the spacer between the carboxylic acid group and the imide moeity. Dyes with aliphatic (4d-4g) and aromatic (4a-4c) spacers have been prepared.
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  • 42
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    Electronic Resource
    Alkoxycarbonylcarbene Transfer to Semicyclic Enaminones - A Route to Cyclopenta[b]pyrrole and Indole Ring Systems (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1177-1187 
    Details
    ISSN: 1434-193X
    Keywords: Diazo compounds ; Carbenes ; Heterocycles ; Enaminones ; Indoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper-catalyzed decomposition of alkyl diazoacetates in the presence of semicyclic enaminones 1a-o leads primarily to enamino esters 2 which constitute formal products of C-C insertion of the carbene unit. In the case of N-methyl (1a-e) and N-benzyl (1f-i) enaminones, 2a-i are accompanied by 2,3,5,6-tetrahydroindoles 3a-i, in which two carbene moieties are incorporated. At 250 °C, compounds 2b-e, which could not be isolated in pure form, undergo cyclocondensation to form 1,2,3,5-tetrahydrocyclopenta-[b]pyrroles 4b-e. In contrast, 2f-i can be isolated as Z,E mixtures and are transformed thermally into 4f-i only in the presence of silica gel. Carbene transfer to N-phenyl enaminones 1j-m and N-methyl enamino esters 1n,o leads only to the 1:1 adducts, enamino esters 2j-o, which do not undergo the cyclocondensation reaction under the previous conditions. Dehydrogenation of tetrahydroindoles 3c-e with tetrachloro-p-benzoquinone can be controlled to give either 1,2-dihydroindole-6,7-dicarboxylates 5 or indole-6,7-dicarboxylates 6.
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  • 43
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    Electronic Resource
    Generation of 6,7-Dihydro-5H-1,3,4-thiadiazolo[3,2-a]pyridines  -  Unexpected Products in the Reaction of 5-Ethylthio-1,3,4-thiadiazole-2-amine and 3-(Dimethylamino)propiophenones (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1201-1203 
    Details
    ISSN: 1434-193X
    Keywords: 1,3,4-Thiadiazoles ; Pyridines ; Cyclizations ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of 6,8-diaroyl-6,7-dihydro-5H-1,3,4-thiadiazolo[3,2-a]pyridines 4a-e was prepared by the reaction of 5-ethylthio-1,3,4-thiadiazole-2-amine (1) and p-substituted 3-(dimethylamino)propiophenones 2a-e in pyridine. The unexpected cyclization process was established by NMR and X-ray diffraction measurements.
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  • 44
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    Electronic Resource
    Synthesis of Hetaryl Glycosides and Their Glycosyl Donor Properties (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1353-1360 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Substitution ; Carbohydrates ; Anomeric O-hetarylation ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Anomeric O-hetarylation of tetra-O-benzyl- and tetra-O-acetylglucose (1a, b) can be directly performed with electron-deficient heteroaromatic/heterocyclic systems 2-14, which contain imide halide moieties. The reactions were carried out in the presence of a base and led, through an exchange of the halide by the glucopyranosyloxy moiety, to the products 2a-14a, 7b-14b. Predominantly or exclusively β-products were obtained. Systems bearing more than one imide halide moiety, such as cyanuric fluoride (15) or 5-chloro-2,4,6-trifluoropyrimidine (16), can be employed for successive anomeric O-hetarylations. Investigation of the glycosyl donor properties of O-glucosyl heteroaromatic imidates with 6-O- and 4-O-unprotected glucose derivatives 18 and 19 as acceptors and comparison of the results obtained with data for the corresponding β-trichloroacetimidates 17aβ and 17bβ, reveals that 2,3,5,6-tetrafluoropyridin-4-yl glucopyranosides 14aβ and 14bβ exhibit similar properties. For specific tasks, for instance α-glucopyranoside formation, 14aβ may even be advantageous.
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  • 45
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    Electronic Resource
    2-Chloro-1,4-benzodithiin 1,1,4,4-Tetraoxide - A Conjunctive Dienophile for the Preparation of Tetrasubstituted Polycyclic Olefins (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2775-2784 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Cycloadditions ; Diatomic carbon ; Sulfones ; Alkenes ; Polycycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Chloro-1,4-benzodithiin 1,1,4,4-tetraoxide 11 is a reactive dienophile that forms Diels-Alder adducts with a number of dienes. Adducts 17a-j undergo facile dehydrochlorination to give 2,3-substituted 1,4-benzodithiin tetraoxides 18a-j, which react further with another molecule of diene (the same or a different one) affording the “double” adducts 19-23. Upon reductive desulfonylation with sodium amalgam, the latter are transformed to tetrasubstituted polycyclic olefins 24-27. These olefins correspond to the cycloadducts that would theoretically have been formed by the cycloaddition of diatomic carbon with two molecules of diene, reacting in a Diels-Alder fashion.
    Additional Material: 4 Ill.
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  • 46
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    Electronic Resource
    Isoquinolinium N-Arylimides and Some Cycloadditions to Heterocumulenes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 379-385 
    Details
    ISSN: 1434-193X
    Keywords: Isoquinolinium N-arylimides ; Azomethine imines ; Cycloadditions ; Heterocycles ; 1,3-Dipoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The red isoquinolinium N-arylimides 19-23 are azomethine imines of which the C=N bond is part of an aromatic ring. The N-(4-nitrophenyl)imide 22 and the N-(2-pyridyl)imide 23 were obtained crystalline; in solution the latter equilibrates with the hexahydrotetrazine 24 as its dimer. The N-phenylimide 19 is not stable; an isolated solid appears to be a tetramer. Generated by deprotonation of 11-13, the N-arylimides 19-21 undergo in situ cycloadditions to carbon disulfide, phenyl isocyanate, phenyl isothiocyanate, and diphenylketene. The storable CS2 adduct 29 offers a neutral source of theN-phenylimide 19, since a cycloreversion equilibrium is established in solution.
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  • 47
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    Electronic Resource
    Cycloaddition-Elimination Reactions of 5-Imino-1,2,4-thiadiazolidin-3-ones and 5-Imino-1,2,4-dithiazolidin-3-ones with Electron-Rich Double Bonds (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 515-520 
    Details
    ISSN: 1434-193X
    Keywords: Cycloaddition ; Elimination ; Heterocycles ; 1,2,4-Thiadiazolidines ; 1,2,4-Dithiazolidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5-Imino-1,2,4-thiadiazolidin-3-ones 1 react with compounds containing electron-rich double bonds such as enamines and ester enolates to afford the 2-iminothiazolidines 3, 4, and 10 in cycloaddition-elimination reactions. The less reactive 5-imino-1,2,4-dithiazolidin-3-ones 2 only give the 2-iminothiazolidines 3 or 4 with enamines; with ester enolates the 5-alkylidene-1,2,4-dithiazolidines 12 are formed. The reaction products with enamines undergo hydrolysis and elimination to form the corresponding hydroxy compounds 5, 6 or the unsaturated compounds 7, 8, depending on the size of the fused ring.
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  • 48
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    Electronic Resource
    Synthesis of Stegobiol and Its Oxidation to Stegobinone, the Components of the Female-Produced Sex Pheromone of the Drugstore Beetle (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1135-1141 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Lipases ; Oxidations ; Pheromones ; Stegobinone ; Stegobium paniceum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crystalline (-)-stegobinone [(2S,3R,1′R)]-2,3-dihydro-2,3,5-trimethyl-6-(1′-methyl-2′-oxobutyl)-4H-pyran-4-one (1)], the major component of the female-produced sex pheromone of the drugstore beetle (Stegobium paniceum L.), was synthesized by oxidation of crystalline and the minor component (-)-stegobiol [(2S,3R,1′S,2′S)-2,3-dihydro-2,3,5-trimethyl-6-(2′-hydroxy-1′-methylbutyl)-4H-pyran-4-one (2)] under the appropriate conditions using Jones's chromic acid, Dess-Martin's periodinane or Ley's ruthenium reagent. The latter (2) was synthesized by employing lipase and the Sharpless epoxidation for the introduction of the proper chiral centers. The streostructure of 1 was comfirmed by X-ray analysis.
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  • 49
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    Thermal Isomerization of 1,3-Dipolar Cycloadducts of 3,4-Dihydro-β-carboline 2-Oxide (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1391-1395 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Nitrones ; 1,3-Dipolar cycloadditions ; β-Carbolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal isomerization of the 1,3-dipolar cycloadducts of 3,4-dihydro-β-carboline 2-oxide is studied using 1H-NMR spectroscopy. Stereoisomerizations of the cis or syn cycloadducts with dipolarophiles such as methyl crotonate, methyl cinnamate, and methyl methacrylate into the trans or anti cycloadducts are observed. On the other hand, regioisomerization of the 1-substituted cycloadduct with nitroethylene into the 2-substituted cycloadduct is also observed.
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  • 50
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    Electronic Resource
    Selective Bromination of 4,5-Dimethylthiazole with N-Bromosuccinimide (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 593-594 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; NBS bromination ; Selective bromination ; Polybrominated thiazole ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical bromination of 4,5-dimethylthiazole (1) was carried out using different stoichiometries of N-bromosuccinimide in the presence of 2,2′-azobisisobutyronitrile. Mono-, tri- and tetrabromo compounds 2, 5, and 6 were obtained in good yields with regioselectivity while the dibromo derivatives 3 and 4 were formed without any selectivity. Substitution at the thiazole ring occurred in the presence of silica gel or in the perfluoro ether FC-77 (C8F16O), affording the 2-bromothiazole 7. The order of reactivity observed was 5-Me 〉 4-Me 〉 C-2. Structural assignment of compounds 2-7 was made by chemical correlations and NMR spectroscopy.
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  • 51
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    Reaction of Ambident Dianions with Oxalic Acid Dielectrophiles - Effect of the Heteroatoms of the Dinucleophile on the Regiochemistry of Cyclization (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1467-1470 
    Details
    ISSN: 1434-193X
    Keywords: Ambident dianions ; Regioselectivity ; Heterocycles ; C-C coupling ; Oxalyl dielectrophiles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Y-Shaped ambident dianions 1-6 were reacted with dielectrophilic oxalic acid-bis(imidoyl)dichlorides 7 providing a convenient access to novel N-heterocycles 8-13 containing a heteroanalogous oxalic acid unit. The cyclization reactions generally proceeded with good regioselectivity which is controlled by the heteroatoms of the dianion reagents.
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  • 52
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    The First 1,10-Diaza[2.2]metacyclophanes - Strained Medium Membered Heterocycles⋆ (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1471-1477 
    Details
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Dilution principle ; Heterocycles ; Medium membered rings ; Ring strain ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The N-protected 1,10-diaza[2.2]metacyclo- and 1,10-diaza-[2]metacyclo[2](2,6)-pyridinophanes 4 and 5 have been synthesized for the first time using high dilution conditions. The free secondary diamine 7 was obtained from 4 by alkaline hydrolysis. - Quantum chemical calculations support the hypothesis that 7 is one of the most strained anti-hetera[2.2]metacyclophanes known. This is also evident from the 1H-NMR spectrum of 7, which shows one of the strongest high field shifts for the intraannular protons in comparison to other anti-[2.2]metacyclophanes.
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  • 53
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    Unprecedented 1,3-Dipolar Cycloaddition of Azomethine Ylides Derived from Difluorocarbene and Imines to Carbonyl Compounds. - Synthesis of Oxazolidine Derivatives (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 133-137 
    Details
    ISSN: 1434-193X
    Keywords: Azomethine ylides ; Difluorocarbene ; Cycloadditions ; Heterocycles ; Oxazolidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Iminiodifluoromethanides generated by the reaction of difluorocarbene with benzaldehyde and benzophenone imines undergo regioselective 1,3-dipolar cycloaddition to aldehydes to give oxazolidine derivatives.
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  • 54
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    Total Synthesis of TAN-1057 A/B, a New Dipeptide Antibiotic from Flexibacter sp. PK-74 (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 777-783 
    Details
    ISSN: 1434-193X
    Keywords: Antibiotics ; Dipeptides ; Heterocycles ; β-Amino acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: TAN-1057 (1a, b) - a new natural dipeptide antibiotic active against methicillin resistant strains of Staphylococcus aureus - was synthesized starting from Nα, Nδ, Nω-tri-Z-L-arginine 20b via the corresponding diazoketone 21b. This upon photolysis rearranged to the ketene which was trapped by (±)-2,4,5,6-tetrahydro-5-methylamino-2-ureidopyrimidin-4-one (3) to yield the fully protected dipeptide 23 (30%). The latter was deprotected by hydrogenolysis to give the final compound as a mixture of two epimers - TAN-1057A, B - isolated previously from a strain of Flexibacter sp. PK-74. The intermediate 3 was prepared from 3-amino-2-(N-Z-N-methylamino)propionic acid methyl ester hydrochloride (16) and 2-methyl-2-thiopseudobiuret hydroiodide (18) in one step in 35% yield.
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    Reaction of 1,3-Dialkyl-4,5-dimethylimidazol-2-ylidenes with 2-Bromo-2,3-dihydro-1H-1,3,2-diazaboroles (Alkyl=iPr and tBu)Dedicated to professor Adolf Zschunke on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 705-710 
    Details
    ISSN: 0009-2940
    Keywords: Boron ; Diazaboroles ; Carbenes ; Heterocycles ; Imidazoles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Bromo-2,3-dihydro-1H-1,3,2-diazaboroles (3a-c) were synthesized by cyclocondensation of dilithiated 1,4-diazabutadienes (5a-c) with boron tribromide in hexane. 3a was also obtained by sodium amalgam reduction was conducted in ether solvents, diboroxane (2) resulted as the main product. Compound 3a and 1,3-dialkyl-4,5-dimethylimidazol2-ylidenes (6a, b) underwent halide displacement to afford the borolylimidazolium salts 7a, b. Compounds 2, 3a-c, and 7a, b were characterized by elemental analyses and spectroscopic methods (1H, 11B, 13C NMR; Ir; MS). The molecular structures of 2 and 7a were established by single-crystal X-ray diffraction analyses.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300606
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    Phosphanyl-Substituted Phosphaferrocenes as p,p-Chelate Ligands (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1771-1776 
    Details
    ISSN: 0009-2940
    Keywords: Chelates ; P ligands ; Phosphaferrocene ; Carbonyl complexes ; Heterocycles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dicyclohexyl-acid diphenylphosphanyl-substituted phosphaferrocenes 2 and 3 were synthesized by substitution of the amino group in 2-dimethylaminomethyl-3,4,-dimethylphosphaferrocene 1 · Homologization of 2-formyl-3,4-dimethylphosphaferrocene 4 by one CH2 unit via Wittig olefination provided access to the phosphanylethyl derivative 9. Ligands 2, 3 and 9 formed P, P-chelate complexes with tetracarbonyl metal fragments in good yield. X-ray crystal structure determinations were carried out for the five-ring chelate complex 2. Mo(CO)4 (≡ l0), and the six-ring chelate complex 9 . Mo(CO)4, (≡ 13).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971301211
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    Palladium  -  Catalyzed Reactions, 1 Palladium-Catalyzed Enantioselective Hydrophenylation and Hydrohetarylation of Bicyclo[2.2.1]Hept-2-ene: Influence of the Chiral Ligand, the Leaving Group, and the Solvent (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1327-1331 
    Details
    ISSN: 0009-2940
    Keywords: Asymmetric catalysis ; Hydroarylation ; Palladium ; P-N ligands ; Heterocycles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of optically active biaryl bisphosphanes 10-12, a diphenylphosphanylphenyloxazoline 8, and a (β-N-sulfonyl-aminomethyl)bisdiphenylphosphane 7 as ligands in the Pd-catalyzed Heck-type hydroarylation of norbornene (1) with phenyl 2 and various hetaryl derivaties 3-5 leads exclusively to the formation of exo-2(het)arylnorbornanes 6 with asymmetric inductions of up to 86.4% ee. In addition to an investigation into the effects of different chiral ligands, a systematic study has been made of the influence of various (het)aryl compounds, leaving groups, and solvents on the chemical and optical yields of this reductive arylation.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300924
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    Diastereoselective Synthesis of Tricarbonyl(thiophene)chromium Complexes (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 659-662 
    Details
    ISSN: 0009-2940
    Keywords: Thiophene derivatives ; Complexation, diastereoselective ; Chromium ; Heterocycles ; Steric hindrance ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,3-Disubstituted 2-hydroxyalkylthiophenes 9 and 10 were synthesized in a five-step sequence and their diastereoselective complexation with the Cr(CO)3 fragment leading to the corresponding tricarbonyl(thiophene)chromium complexes 11 and 12 was investigated. The diastereoselectivity achieved in the complexation reaction was up to 85% d. e. and depends primarily on the bulkiness of the substituent in the 3-position of the thiophene. The relative configuration of the stereogenic center and the planar element of chirality of complex 11a was determined by X-ray diffraction analysis.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300518
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    Iminoacylcobalt Compounds as Starting Materials for the Synthesis of Alkynylcobalt Halfsandwiches and CobaltaheterocyclesDedicated to Professor Günter Schmid on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 565-570 
    Details
    ISSN: 0009-2940
    Keywords: Cobalt ; Cycloadditions ; Heterocycles ; Alkynyl complexes ; Cyclopentadienyl complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iminoacylcobalt compound [C5H5Co(C(CH3)=NCH3)(PMe2Ph)] (3) reacts with propargylic acid ester HC=CCO2R (R = Me, Et) to give the alkynylcobalt halfsandwich-type complexes [C5H5Co(C(CH3)=NHCH3)(C=CCO2R)-(PMe2Ph)]I (5, 6). With HC=CCO2Me as the substrate, besides 6 (R = Me) the five-membered cobaltaheterocycle [C5H5Co{K2(N, C)-N(CH3)C(CH3)CHC(CO2Me)}(PMe2Ph)]I (7) is also obtained. The reactions of 3 and the analogous benzyl derivative 4 with terminal alkynes HC=CR' (R' = CH2OH, CMe2OH, [CH2]2OH, CH2OMe, H, Me, nBu, Ph) afford exclusively the heterocyclic complexes [C5H5Co(K2(N,C)-N(R)C(CH3CHCR')(PMe2Ph)]I (R = CH3, CH2Ph) (8-18) in 60-70% yield. The molecular structures of 5 (R = Et) and 16 (R = Me, R' = Ph) have been determined by X-ray crystallography.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300506
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  • 60
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    Organo-Substituted 1,2-Dihydro-1,2,5-Disilaborepines (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1349-1352 
    Details
    ISSN: 0009-2940
    Keywords: Heterocycles ; 1,1-Organoboration ; Disilanes ; 1- Alkynylsilanes ; NMR spectroscopy ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,2-Di-1-propynyl-tetramethyldisilan (1) reacts with triorganoboranes R3B [R = Et (2a), CH2Ph (2c), 2-thienyl (2d)], 9-ethyl-9-borabicyclo[3.3.1]nonane (3), and diethyl(N-pyrrolyl)borane (4) by twofold 1,1-organoboration to give selectively the respective organo-substituted 1,2-dihydro-1,2,5-disilaborepines 5a-d,6, and 7 in high yields. The compounds 5-7 were characterized by 1H-, 11B-, 13C-, and 29Si-NMR spectroscopy in solution. The molecular structures of the distance 1 and of the heterocycle 5c were determined by X-ray structure analysis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300928
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    Concave Reagents,22. Cyclopropanation of Alkenes with Ethyl Diazoacetate: Copper(I) Complexes of Concave 1,10-Phenanthrolines as Diastereoselective Catalysts (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 231-234 
    Details
    ISSN: 0009-2940
    Keywords: Diasteroselective cyclopropanation ; Copper compounds ; Homogeneous catalysis ; Molecular recognition ; Bimacrocycles ; Alkenes ; Macrocyclic ligands ; Heterocycles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Concave 1,10-phenanthrolines 1a-c have been used as ligands in the copper(I)-catalyzed cyclopropanation of alkenes 2 with ethyl diazoacetate. The complexes proved to be efficient cyclopropanation catalysts and exhibited an enhanced diastereoselectivity, particularly in the reactions of cyclic alkenes 2b-d. The preferred formation of exo-cyclopropanes 3b-d can be explained by the concave shape of these catalysts.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300215
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    Mono- and Bicyclic Organometallic Ring Systems with Exocyclic C=C and C=S BondsDedicated to Professor Joachim Strähle on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 871-877 
    Details
    ISSN: 0009-2940
    Keywords: Cobalt ; Cyclopentadienyl complexes ; Heterocycles ; Electrophilic addition ; Insertion reaction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cobaltaheterocycles [C5H5Co{κ2(C,S)-C(=CH2)-N(R)C(=S)S](PMe2Ph)] (5-7), which contain both an exocyclic C=C and C=S bond, were prepared from the iminoacylcobalt compounds [C5H5Co(C(CH3)=NCH} (PMe2Ph)]I (2-4) on treatment with either CS2/NaOCH3 or K[S2CNMe2], respectively. While protonation of 5 (R = CH3) and 7 (R = CH2Ph) with HBF4 occurs at the exocyclic C=CH2 bond to give cations containing a CoC(CH3)N(R)C(=S)S ring, the methylation of 5 and 7 with [OMe3]BF4 takes place at the exocyclic C=S bond and generates five-membered heterocycles heterocycles with an SCH4 substituent. The reaction of 5-7 with S8 leads to the elimination of the phosphane ligand and affords the bicyclic dithiolenecobalt complexes 14 - 16 in moderate to good yields. On treatment of 5-7 with C2(CO2R′)2 (R′ = Me,Et), an insertion of the alkyne into the C=CH2 bond occurs and five-membered ring systems 19-22 with an unsaturated exocyclic =C(CO2R′)-C(CO2R′)=CH2 group are formed. As in the case of 5 and 7, protonation and methylation reactions of 19 also take place at different sites leading to cations with either a delocalized CoCN or NCS unit.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19971300710
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    2,4-Diphosphoranediyl-1,3-diphosphetanes (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1519-1527 
    Details
    ISSN: 0009-2940
    Keywords: Phosphorus ; Heterocycles ; Phosphorus ylides ; Phosphoranediyl ; Phosphonio substituents ; P-Cl bond dissociation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1,3-dichloro- and 1,3-dibromo-substituted title compounds 5b, c result from the condensation of triphenylphosphonium-bis(trimethylsily1)methylide 1 with PC13 and PBr3. The chloro derivative 5b undergoes a variety of single and double substitution reactions, of which some have merely been tested and others have been made preparative use of. The substitution of one chloride by an ylidyl, amino, phosphino, or metal carbonyl group is accompanied by the spontaneous dissociation of the other P-CI bond to yield the, 1,3-diphosphetenium chlorides 14/15, 19, 31 and 36, respectively. In other cases (9, 27, 32) dissociation can be achieved by means of a Lewis acid. Protonation of 5b occurs at the carbon ring members; methylation and formation of transition metal complexes occurs at a phosphorus ring member. PCl3 degrades the four-membered ring of5b or enlarges the ring to yield 3,5-diphosphoranediyl-l,2,4-triphospholane derivatives 39, 40, 42.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971301027
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    Balanced Decarboxylation of Aromatic Polyacids - A One-Step Synthesis of Perylene-3,4-dicarboxylic Anhydride (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 467-468 
    Details
    ISSN: 0947-3440
    Keywords: Decarboxylation ; Carboxylic acids ; Fluorescence spectroscopy ; Perylenes ; Heterocycles ; Dyes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Perylene-3,4-dicarboxylic anhydride (3) is prepared from technical grade perylene-3,4:9,10-tetracarboxylic anhydride (1) in 25% yield by a partial decarboxylation reaction using noncondensing amines. Perylene-3-carboxylic acid (4) and perylene-3,4-dicarboxylic imide (5) are prepared in the same way in yields of 24% and 76%, respectively, by a variation of the reaction conditions.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970305
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    Stereoselective Synthesis of Alcohols, LPart L: See ref.[1]; also Part VI of studies on “Flexible Molecules with Defined Shape”, for part V see ref.[2].. Synthesis and Conformational Studies of 1,5-Dioxa-cis-decalin (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1143-1150 
    Details
    ISSN: 0947-3440
    Keywords: Intramolecular allylboration ; 1,5-dioxa-cis-decalins ; Preferred conformation ; Conformation analysis ; Heterocycles ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: cis-2-Vinyltetrahydropyran-3-ol (6) is accessible by a selective intramolecular allylboration reaction. Compound 6 was converted into 1,4-dioxa-cis-decaline (4) and cis-syn-cis-perhydrotrioxaanthracene 32; heterocycles with fused tetrahydropyran rings. These ring systems populate predominantly the conformation in which the oxygen atoms are in a gauche arrangement. The tricycle 31 is a rigid derivative of 14-crown-3 and, as in the case of 12-crown-3, it forms complexes with lithium ions in acetonitrile.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970614
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    Synthese und Konformation von Hexahydro-isochino[1,2-b][3]benzazepinen (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 447-457 
    Details
    ISSN: 0947-3440
    Keywords: Isoquino[1,2-b][3]benzazepines ; Iso-C-homoberbines ; Conformation analysis ; Bischler-Napieralski reaction ; Methyl ∊-hydroxycarboxylates ; Heterocycles ; Alkaloids ; Drug research ; Medicinal chemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Conformation of Hexahydro-isoquino[1.2.-b][3]benzazepinesThe synthesis of the six hexahydro-isoquino[1,2-b][3]benzazepines 13a-f is described; their conformation is investigated by NMR spectroscopic methods, X-ray analysis and dehydrogenation with mercury(II) acetate.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970225
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    Regiospecific Synthesis of 3,4-Disubstituted Furans and ThiophenesDedicated to Professor Xi-Kui Jiang, Shanghai Institute of Organic Chemistry, on the occasion of his 70th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 459-466 
    Details
    ISSN: 0947-3440
    Keywords: Furans ; Thiophens ; Palladium catalysis ; Coupling reactions ; Heterocycles ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regiospecific synthesis of 3,4-disubstituted furans and thiophenes is reviewed. Our initial approach used 3,4-bis(tri-n-butylstannyl)furan as a building block, which led to many structurally diverse 3,4-disubstituted furans. Another avenue was explored by using 3,4-bis(trimethylsilyl)furan and 3,4-bis(trimethylsilyl)thiophene as precursors. A variety of unsymmetrically 3,4-disubstituted furans and thiophenes were prepared in this way. The advantages of our strategy lie in its stepwise manner as well as its prospect of yielding 3,4-disubstituted furans and thiophenes with rather different substitution pattern.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970304
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    Demethyl(trifluoromethyl)actinomycins, IIPart I: Ref.[1].. Bis(trifluoromethylated) 4-(2′-Benzoxazolyl)actinocin Derivatives (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 999-1003 
    Details
    ISSN: 0947-3440
    Keywords: Antibiotics ; Actinomycins ; Trifluoromethyl actinocins ; Heterocycles ; NMR spectroscopy ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a previous study, performed in connection with the total synthesis of trifluoromethylated actinocinyl peptides 2a, the oxidative condensation of the corresponding o-aminophenol precursor 1 furnished a novel trimerisation product, which had been tentatively assigned to the triphenedioxazine structure 3[1]. Now, an improved synthesis of the trimer and extensive 1- and 2D-NMR studies have resulted in a new, quite unexpected structure: the 4-(2′-benzoxazolyl)actinocin derivative 8a, which replaces 3. Apparently, the quinone-sided CF3 group of an actinocin intermediate is unusually activated and reacts with a third o-aminophenol unit. The modifications to the synthesis increase the overall yield of demethyl-(trifluoromethyl)actinomycins by a factor of five.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970531
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    Metallated 2-Alkenyl Sulfoximines in Asymmetric Synthesis: Regio- and Stereoselective Synthesis of Highly Substituted Tetrahydrofurans (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1881-1886 
    Details
    ISSN: 0947-3440
    Keywords: Asymmetric synthesis ; Sulfoximines ; Homoallylic alcohols ; Heterocycles ; Tetrahydrofurans ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from the enantiopure 2-alkenyl sulfoximines 4/5 and epi-4/5, a one-pot procedure has been developed for the synthesis of tri- and tetrasubstituted tetrahydrofuran derivatives with excellent control of all relevant aspects of their structural description. The cyclization of the intermediate γ-hydroxyvinyl sulfoximines is strictly regioselective due to the electronic properties of the double bond involved. The absolute configuration at C-2 can be selected at will by a proper choice of the corresponding lactaldehydes 14 or ent-14 respectively. The absolute configuration at the 3- and 4-positions of the THF derivatives is under control of the sulfoximine moiety during aldehyde uptake, whereas their relative configuration is fixed due to the 1k relative topicity of attack of the reactands involved in their generation. The configuration at position 5 is determined mainly by the release of 1,3-allylic strain and is therefore the only stereogenic centre under substrate control. This becomes obvious in two cases (17a and 18a) where stereocontrol at this position is diminished. Here, the absence of a 3-methyl group as a control element reduces the energetic difference between the Re- and the Si-side attack.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/jlac.199719970912
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    Synthetic Microbial Chemistry, XXXPart XXIX: A. Yajima, K. Mori, Liebigs Ann. 1996. 1091-1093.. Synthesis of Acetophthalidin, a Fungal Metabolite which Inhibits the Progression of the Mammalian Cell Cycle (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 721-723 
    Details
    ISSN: 0947-3440
    Keywords: Acetophthalidin ; Fungal metabolite ; Isocoumarin ; Mammalian cell cycle ; Phthalide ; Natural products ; Heterocycles ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acetophthalidin [(±)-3-acetyl-5,7-dihydroxyphthalide (1)] was synthesized from 6,8-diacetoxy-3-methylisocoumarin (8) by its epoxidation followed by hydrolysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970412
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    Methylchalcogen Derivatives of 1,4,5,8-TetrathiatetralinThis paper is dedicated to Professor Klaus Hafner. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 729-732 
    Details
    ISSN: 0947-3440
    Keywords: Organic donor ; Tetrathiatetralin ; Tetrathiafulvalene ; Solvent effects ; Heterocycles ; Sulfur ; Selenium ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrakis(methylthio)- and tetrakis(methylseleno)-1,4,5,8-tetrathiatetralin 3 and 4 were prepared by the reaction of tetrathiatetralin 2 with LDA (lithium diisopropylamide) and MeS-SMe or MeSeSeMe in diethyl ether. A remarkable solvent effect was observed in that the similar reaction in tetrahydrofuran gave tetrakis(methylthio)tetrathiafulvalene 5 through a novel rearrangement. The iodine complex of 3 was prepared to be a rare example of complex formation in the tetrathiatetralin series.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/jlac.199719970414
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    Intramolecular Heck Reaction for the Synthesis of Isochromanes under Ambient and High pressure (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 887-891 
    Details
    ISSN: 0947-3440
    Keywords: Heck reaction, intramolecular ; Isochromane ; Palladium ; Heterocycles ; High-pressure chemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iodoarenes 9 and 10, bearing (E)- and (Z)-alkene moieties, respectively, easily prepared by alkylation of the corresponding alcohols 7a-c and 8a-c with 2 iodobenzyl iodide, undergo intramolecular Heck reactions to give the isochromanes 12-15a-c in good yields. The selectivity of the reaction depends on the size of the substituent R in 9 and 10; increasing bulkiness of R leads to a decrease in diastereoselectivity and an increase in regioselectivity. High-pressure experiments confirm the proposed mechanism and show that bromoarenes such as 11, which tend to be unreactive at ambient pressure, give good results when the cyclisation is performed under high pressure.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970516
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    Chiral Bifluorophoric Perylene Dyes with Unusually High CD Effects - a Simple Model for the Photosynthesis Reaction Center (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1151-1153 
    Details
    ISSN: 0947-3440
    Keywords: Fluorescent dyes ; Perylenes ; Heterocycles ; Photosynthesis reaction center ; CD effects ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a bifluorophoric perylene dye (4a) is described, in which the two chromophores are linked by a chiral binaphthyl unit. A strong exciton coupling of the two chromophores, a bathochromically shifted fluorescence and strong CD effects are observed. The structure of 4 is compared to the photosynthesis reaction center.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970615
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  • 74
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    Cycloaddition Reactions of 2H-Benzo[b]thiete and Thiocarbonyl Compounds (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1603-1605 
    Details
    ISSN: 0947-3440
    Keywords: 4H-1,3-Benzodithianes ; Heterodienes ; Heterodienophiles ; Spiro compounds ; Heterocycles ; Cycloaddition ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2H-Benzo[b]thiete (1) reacts in the o-quinoid form 1′ with the cyclic trithiocarbonates 4 and 6a, b and with the thioketones 8, 10 and 12 in [8π + 2π] cycloaddition reactions to the spiro compounds 5, 7a, b, 9, 11a, b. Irrespective of the presence of C=C double bonds, chemoselective and regioselective addition processes at the C=S double bonds take place that lead to 4H-1,3-benzodithianes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970743
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  • 75
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    Rearrangement Reactions, 6.Part 5: Ref. New Functionalized Allenes: Synthesis Using Sigmatropic Rearrangements and Unusual ReactivityIn memoriam of Professor Gerrit L'abbé. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2005-2018 
    Details
    ISSN: 0947-3440
    Keywords: Allenes ; Sigmatropic rearrangements ; Heterocumulenes ; Cyclizations ; Metastable compounds ; Heterocycles ; 1,3-Butadienes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present article summarizes the synthesis of allenes, which bear a functional group with at least two heteroatoms, by [2,3] or [3,3] sigmatropic rearrangements of appropriate propargyl precursors. Recently, this method has been extended to prepare new types of functionalized allenes such as isocyanates, isothiocyanates, isoselenocyanates, azides, thiocarbonates, and azo compounds. The title compounds are very reactive as shown by rapid intra- and intermolecular consecutive reactions. This reactivity can be used to synthesize heterocycles and doubly functionalized 1,3-butadienes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971003
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  • 76
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    Preparation of 1-Azacyclododeca-3,8-diynes and 1,6-Diazacyclododeca-3,8-diynes (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2113-2118 
    Details
    ISSN: 0947-3440
    Keywords: Medium-sized rings ; Cyclizations ; Alkynes ; Heterocycles ; Multicomponent reactions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of N,N′-dialkyl- and N,N′-diaryl-1,6-diazacyclodeca-3,8-diynes was achieved by reaction of alkyl- or arylamines with 1,4-dihalobut-2-yne under dilution conditions in yields of 5-15%. The compounds synthesized by this procedure were the N,N′-dimethyl (2b), N,N′-diethyl (2c), N,N′-diisopropyl (2d), N,N′-di-tert-butyl (2e), N,N′-dicyclohexyl (2f), N,N′-diphenyl (2g), and N,N′-di-p-tolyl (2h) derivatives. The parent compound 2a was obtained in ca. 40% yield by heating 2d with α-chloroethylchloroformate (20). Using 1,9-dibromonona-2,7-diyne (10) and methylamine or isopropylamine, respectively, the corresponding N-alkyl-1-azacyclodeca-3,8-diynes 4b and 4d were synthesized under dilution conditions. By heating 4d with 20 we obtained 1-azacyclodeca-3,8-diyne (4a). As side products of the cyclization reactions the trimers 18 and tetramers 12 and 19 were isolated and characterized. N-methyl-1-azacycloundeca-3,9-diyne (14b) was prepared by reaction of 1,10-dibromodeca-3,8-diyne (13) with methylamine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971013
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  • 77
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    Reactions of Uracils, 22.Part 21: Ref. Synthesis of Pyrimido[5,4-c]quinolizines (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1619-1625 
    Details
    ISSN: 0947-3440
    Keywords: Heterocycles ; Anellation ; Pyrimido[5,4-c]quinolizines ; 6-tert-Aminouracil-5-ylmethylenemalonodinitriles ; Pyrido[2,3-d]pyrimidine ; [1,4]Oxazino[3,4-a]pyrido[2,3-d]pyrimidone ; Aza-Wittig reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several heterocyclization reactions of uracil derivatives are described. 1,3-Dimethyl-6-(triphenylphosphoranylideneamino)uracil-5-acrylic ester (1) undergoes aza-Wittig cyclization to give pyrido[2,3-d]pyrimidine 2. In a special application of the tert-amino effect, 6-tert-amino-substituted uracil-5-ylmethylenemalodinitriles 8a-f are cyclized with ZnCl2/toluene to afford pyrimido[5,4-c]quinolizines 10b, d-f, and 1,4-oxazino[3,4-a]pyrido[2,3-d]pyrimidine 10c, while the corresponding diesters 12a, b and 13 could not be cyclized. Alternative reaction mechanisms involving 1,6- and 1,5-H shifts are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970746
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  • 78
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    Application of Vicarious Nucleophilic Substitution in Organic SynthesisDedicated to Professor Waldemar Adam on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1805-1816 
    Details
    ISSN: 0947-3440
    Keywords: Nucleophilic aromatic substitution ; σ-Adducts ; Aromatic nitro compounds ; Heterocycles ; Carbanions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Vicarious Nucleophilic Substitution (VNS) provides the possibility of the replacement of hydrogen atoms in electrophilic arenes with α-functionalized alkyl substituents. This review focuses on the transformations of products obtained by VNS, particularly into heterocyclic compounds. In addition, some characteristic features of the VNS mechanism are briefly described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970903
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  • 79
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    An Intramolecular 1,3-Dipolar Cycloaddition Involving One Alkyne and Two Nitrone Groups (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 469-471 
    Details
    ISSN: 0947-3440
    Keywords: Cycloadditions ; Asymmetric Synthesis ; Heterocycles ; Alkynes ; Reductions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral nonracemic compound 4 was prepared from ethyl (S)-(-)-lactate and 1,4-dibromo-2-butyne. Reduction with DIBAH at -72°C and subsequent treatment of the resulting dialdehyde with N-methylhydroxylamine yielded the dinitrone 5, which underwent two consecutive intramolecular cycloadditions to give the chiral nonracemic compound 7. The structure of 7 was confirmed by an X-ray analysis. Reductive ring opening afforded compound 8.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970306
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  • 80
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    Photochemical Formation of Heteromethylenecyclopropanes, 27Part 26: Ref.[1].. Annulated Tetrazolium Salts (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 671-683 
    Details
    ISSN: 0947-3440
    Keywords: Alkylations ; Annulation ; Azides ; Cations ; Cyclizations ; Cycloadditions ; Heterocycles ; Lithiation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lithiation of the annulated tetrazoles 6a, c with butyllithium yields the N-lithiotetrazoles 7a, c which are allowed to react with alkyl halides. Alkylation at the α-carbon atom is observed in the reaction with methyl iodide (→ 6b, d), 1-bromo-2-chloroethane (7c→14a), and 1,3-dibromopropane (→ 16, 17), while 1,2-dichloro- and 1,2-dibromoethane give other products, viz. 11-13. Quaternisation of 6 with dimethyl sulphate affords mixtures of 1-methyl- (1) and 2-methyltetrazolium salts (8) (3:1-4:1) from which the hexafluorophosphates 1 PF6 are obtained by crystallisation. Methyl triflate converts the ω-azidonitriles 9 into the N-methylnitrilium triflates 10 which immediately undergo an intramolecular 1,3-dipolar cycloaddition to afford the 1-methyltetrazolium triflates 1 F3CSO3. Cyclisation of 16 by intramolecular N-alkylation furnishes the bisannulated tetrazolium bromide 3a · Br. Attempts to obtain the lower homologue 15, either from 14a or from 17, met with failure. Instead, 17 rearranges via 15b into 14b. The α-branched tetrazole 24 is synthesised from ethyl cyanoacetate and the bromide 18. Double cyclisation of 24 affords the bisannulated tetrazolium chloride 3b · Cl. The analogous scheme, envisaged for the synthesis of the lower homologue 32, failed in the last step owing to the high strain of this system.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970408
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  • 81
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    Diastereo- and Regioselective Intramolecular Heck Reaction of α-Amino Alcohol Derivatives for the Synthesis of Enantiomerically Pure Isoquinolines and Benzazepines at Ambient and High Pressure (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1407-1413 
    Details
    ISSN: 0947-3440
    Keywords: Heck reaction, intramolecular ; α-Amino acids ; Isoquinolines ; Palladium ; Heterocycles ; Synthesis, enantioselective ; High pressure ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkylation and acylation of the alkenes 9b, c and 10a, b, which are easily prepared from the corresponding α-amino alcohols, with 2-halobenzyl and 2-halobenzoyl halides respectively, gives 11-15. These compounds cyclize with excellent diastereo- and regioselectivity to the enantiomerically pure N-heterocycles 18-20 in an intramolecular Heck reaction using 5 mol-% of Pd(OAc)2 in the presence of PPh3, TPAB and KOAc. Under the same conditions substrate 17 leads to the enantiomerically pure benzazepine 24. The reaction of the bromoarene derivatives 14-15 must be performed under high pressure to give good results.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970718
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  • 82
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    The Reaction of Hexachloroacetone with Diamines (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 925-929 
    Details
    ISSN: 0947-3440
    Keywords: Amides ; Heterocycles ; Bisimidazolidine ; Tetrahydrobenzimidazolidinene ; Bisbenzimidazol ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of hexachloroacetone (HCA) with various diamines led either to the corresponding diamides or to cyclic ureas, depending on the molar ratio of the reactants. In the cases of ethylenediamine, 1,2-diaminocyclohexane and o-phenylenediamine, the reaction with HCA also formed bisimidazole derivatives. These latter unexpected products were also formed when the diamine reacted with trichloroacetate esters or with carbon dioxide.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970521
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  • 83
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    A DFT Study on the Vinylcyclopropanecarbaldehyde-to-2,5-Dihydrooxepin Hetero-Cope-type Rearrangement and on Related ReactionsDedicated to Prof. Dr. Klaus Hafner on the occasion of his 70th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2443-2449 
    Details
    ISSN: 0947-3440
    Keywords: Pericyclic reactions ; Hetero-Cope-type rearrangement ; Cyclopropanes ; Heterocycles ; Substituent effects ; Transition structures ; Density functional calculations ; Ab initio calculations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The prototypical 1,2-cis-vinylcyclopropanecarbaldehyde-to-2,5-dihydrooxepin hetero-Cope-type rearrangement was studied by “exact” first-principle methods. The reaction pathway was examined. The reaction, as well activation energies, was calculated for the unimolecular transformation of vinylcyclopropanecarbaldehyde and various derivatives. The derivatives differ from vinylcyclopropanecarbaldehyde by replacement of the formyl (CH=O) by the thioformyl (CH=S) or formiminyl (CH=NH) group and, in part, by replacement of hydrogen atoms at the substituted carbon atoms of the cyclopropane ring by hydroxyl or formyl substituents. The experimental reaction parameters of vinylcyclopropanecarbaldehyde are surprisingly well reproduced by B3LYP/6-31G* density functional and MP2/6-31G* ab initio quantum theoretical calculations. Reactant and product are nearly isoenergetic, while the activation energy amounts to about 25 kcal/mol. In the case of the nitrogen and sulfur containing compounds the isomeric seven-membered ring structures are considerably favoured over the cyclopropanes. Due to a low calculated activation energy a rapid formation of the 2,5-dihydrothiepin is expected. Substitution of the hydrogen at the substituted ring carbon atoms in vinylcyclopropanecarbaldehyde by OH and CH=O also lowers the barrier and increases, in general, the exothermicity of the reaction. As shown by the reaction energies of isodesmic reactions both reactants and products are stabilized by substitution. However, the seven-memberd ring compounds are more strongly stabilized than the cyclopropanes. The OH group exerts a different effect depending on whether the linkage is geminal or vicinal to the C=X group. The difference is caused by hydrogen bond formation in geminal arrangements. The substituent effects in the cyclopropane series parallel those for the prototypical Cope-type and Claisen-type series. The particular feature of the cyclopropane series is the lower stability of the cyclopropanes relative to the corresponding open chain congeners. This is obviously due to the ring strain which over-compensates for attractive interactions between cyclopropane and the substituents. In consequence, the formation of seven-membered ring compounds proceeds more easily than the formation of the corresponding compounds in related Cope-type rearrangements.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971207
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  • 84
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    N-Heterocyclic CarbenesEssays on Organometallic Chemistry, Part 9. Part 8: W. A. Herrmann, B. Cornils, Angew. Chem. 1997, 109, 1074; Angew. Chem. Int. Ed. Engl. 1997, 36, 1047.Dedicated to Professor Heribert Offermanns on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 2162-2187 
    Details
    ISSN: 0570-0833
    Keywords: carbenes ; heterocycles ; homogeneous catalysis ; metal complexes ; Carbenes ; Heterocycles ; Homogeneous catalysis ; Metal complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemistry of N-heterocyclic carbenes has long been limited to metal coordination compounds derived from azolium precursors, a development that was started by Öfele and Wanzlick in 1968. Since free carbenes are now available through the work of Arduengo (1991), a renaissance in this little-recognized area of chemistry has occurred. A leading motive is the advantages of N-heterocyclic carbenes as ligands in organometallic catalysts, where they extend the scope of application reached by phosphanes (functionalized, chiral, water-soluble, and immobilized derivatives). The present review summarizes the state of the art with regard to synthesis, structure, bonding theory, metal coordination chemistry, and catalysis. Chelating, functionalized, chiral, and immobilized ligands can be generated and attached to metal centers in straightforward procedures under mild conditions. A wealth of new chemistry is thus opened. It is also shown how carbenes derived from imidazoles and triazoles behave as ligands in catalysis. It is reasonable to assume that N-heterocyclic carbenes surpass the ubiquitous phosphanes as ligands in a number of organometallic catalytic reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199721621
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  • 85
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    Pyrrolo- and Thiophenoperylenedicarboximides - Highly Fluorescent Heterocycles (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1587-1591 
    Details
    ISSN: 0947-3440
    Keywords: Perylenes ; Heterocycles ; Fluorescent dyes ; Fluorescent labelling ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrrolo- and thiophenoperylenedicarboximides 4 and 7 were prepared by reductive cyclization of 1-nitroperylenedicarboximides 3 and 5 with phosphorous acid esters and sulfur, respectively. The imides 4 and 7 are highly fluorescent and are easily monofunctionalized by nucleophilic substitution reactions which makes them useful for fluorescent labeling.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961014
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    New Developments in the Chemistry of Low-Valent TitaniumDedicated to Professor Henri B. Kagan on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 2442-2469 
    Details
    ISSN: 0570-0833
    Keywords: alkenes ; carbonyl compounds ; heterocycles ; McMurry reactions ; titanium compounds ; Alkenes ; Carbonyl compounds ; Heterocycles ; McMurry reaction ; Titanium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Among the applications of low-valent titanium in organic synthesis, the reductive coupling of carbonyl compounds to produce alkenes (the McMurry reaction) is particularly prominent. Discovered at the beginning of the 1970s, it has been developed and tested repeatedly, for example in numerous syntheses of natural products. This alkene synthesis has become a standard reaction in the repertoire of preparative chemists. However, the possibilities of low-valent titanium are by no means limited to this process: the last few years have brought some spectacular applications of the conventional McMurry reaction (for example the synthesis of taxol) along with a considerable extension of the scope of reductive carbonyl couplings. Thus, diverse heterocycles are now accessible following novel and efficient pathways based on intramolecular cross-coupling of functional groups - some of which were hitherto considered to be inert to titanium. The use of this method for the synthesis of indole and pyrrole alkaloids illustrates the new possibilities. At the same time, considerably simplified methods for conducting McMurrytype reactions have been developed. Examples include the particularly convenient “instant” method, the first ketone-amide coupling reactions requiring only catalytic amounts of titanium salts, and the first application of commercially available titanium powder as a coupling agent. Last but not least, the detailed investigation of diverse classical McMurry reagents has afforded a deeper understanding of the nature and mode of action of low-valent titanium. Revision of some of the current conceptions of the process of reductive carbonyl coupling is thus indispensable.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199624421
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  • 87
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    [1,3]Dioxolo[5,6][1]benzothieno[2,3-c]-quinolin-6(5H)-ones (1995)
    Springer
    Monatshefte für Chemie 126 (1995), S. 1253-1256 
    Details
    ISSN: 1434-4475
    Keywords: Heterocycles ; 1H NMR ; Synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Reaktion von 3,4-Methylendioxyzimtsäure (1) mit Thionylchlorid ergab 7-Chlorothieno[2,3-f]-1,3-benzodioxol-6-carbonsärechlorid (2) und Zimtsäurechlorid (3). Darauffolgende Umsetzung von2 mit substituierten Anilinen führte zur Bildung von 7-Chloro-N-(p-X-phenyl)-thieno[2,3-f]-1,3-benzodioxol-6-carboxamiden (4a–c), welche mittels Photocyclisierung in akzeptablen Ausbeuten zu 2-substituierten [1,3]Dioxolo[5,6][1]benzothieno[2,3-c]chinolin-6(5H)-onen (5a–c) hoher Reinheit umgesetzt wurden. Die Strukturen wurden durch spektroskopische (IR,1H-NMR) und analytische Methoden bestätigt.
    Notes: Summary The reaction of 3,4-methylenedioxycinnamic acid (1) with thionyl chloride resulted in the formation of 7-chlorothieno[2,3-f]-1,3-benzodioxole-6-carbonyl chloride (2) and cinnamoyl chloride (3). Subsequent reaction of the former withp-substituted anilines led to the formation of 7-chloro-N-(p-substituted phenyl)-thieno[2,3-f]-1,3-benzodioxole-6-carboxamides (4a–c) which on photocyclization afforded 2-substituted [1,3]dioxolo[5,6][1]benzothieno[2,3-c]quinolin-6(5H)-ones (5a–c) in fairly good yields and high purity. The structures have been confirmed by IR,1H NMR, and analytical methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00824304
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  • 88
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    Stereo- and regioselective intramolecular heck reaction of α-amino acid derivatives for the synthesis of enantiopure 3,4-dihydroisoquinolinones (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1153-1157 
    Details
    ISSN: 0947-3440
    Keywords: Heck reaction, intramolecular ; α-Amino acids ; Isoquinolinones ; Palladium catalyst ; Heterocycles ; CNS agents ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acylation of the alkenes 1a-d and 3, easily prepared from the corresponding α-amino acids, with 2-iodobenzoyl chloride gives 2a-d and 4 which cyclize to the enantiopure dihydroisoquinolinones 5a-d and 9, resp., in an intramolecular Heck reaction using 5 mol- % of Pd(OAc)2 in the presence of PPh3, TPAB, and KOAc with excellent diastereoselectivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507156
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  • 89
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    The Diels-Alder route to trifluoromethyl-substituted carbo- and heterocyclesThis work is dedicated to Prof. R. Neidlein, Heidelberg, on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1587-1589 
    Details
    ISSN: 0947-3440
    Keywords: Trifluoromethyl substituents ; Carbocycles ; Heterocycles ; Diels-Alder reactions ; Electron-rich/electron-poor diene ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting with 1,1,1-trifluoroacetone, 3-(trifluoromethyl)-1-(trimethylsilyloxy)-1,3-butadiene (2) has been prepared as a mixture of (Z) and (E) isomers. The diene undergoes [4 + 2] cycloaddition reactions with a variety of dienophiles affording trifluoromethyl-substituted carbocyclic and heterocyclic compounds 7-11 in yields ranging from moderate to good.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199509221
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  • 90
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    Three-Membered Rings Containing Two Hetero-Atoms (1964)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 333-341 
    Details
    ISSN: 0570-0833
    Keywords: Strained molecules ; Heterocycles ; Diaziridines ; Diazirines ; Oxaziranes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Since their discovery five years ago, the diaziridines have become an extensive and easily accessible class of compounds. Hydrolysis of these compounds effects a simple synthesis of hydrazine, alkylhydrazines, and N,N′-dialkylhydrazines. They are also powerful oxidizing agents. The rigidity of the three-membered ring gives rise to a few stereoelectronic peculiarities. Investigations on the mechanism of formation of the three-membered rings led to a new synthesis of oxaziranes and to discovery of the isomeric oximes with a three-membered ring structure. The latter decompose readily to form diimide. Diazirines are cyclic isomers of the aliphatic diazo compounds and are surprisingly easy to obtain by dehydrogenation of suitable diaziridines; they are chemically much more stable than the linear isomers. Grignard reagents add onto the N=N double bond without destruction of the three-membered ring. Thermal decomposition yields carbenes.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196403331
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  • 91
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    Kinetics and Mechanism of 1,3-Dipolr CycloadditionsExtended version of a lecture given at the Annual Meeting of the Dechema in Frankfurt/Main on June 14th, 1962, and of the Max Tishler Lecture at Harvard University on December 10th, 1962. (1963)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 633-645 
    Details
    ISSN: 0570-0833
    Keywords: Kinetics ; Dipolar cycloaddition ; Cycloaddition ; Heterocycles ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Criteria for the mechanism of 1,3-dipolar cycloadditions which lead to 5-membered rings are provided by the stereoselectivity observed with cis-trans isomeric dipolarophiles, by the effect of solvent and substituents on the rate constants, by the activation parameters, and by orientation phenomena. A concerted addition, which can also be described in terms of molecular orbitals and in which the two new σ-bonds are formed simultaneously, although not necessarily at equal rates, offers the best explanation of the experimental facts.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196306331
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  • 92
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    Electronic Resource
    Syntheses of Heterocyclic Compounds from Aminoguanidine (1963)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 459-476 
    Details
    ISSN: 0570-0833
    Keywords: Aminoguanidine ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Due to its unique structure, aminoguanidine is capable of reacting as a derivative of hydrazine, guanidine or formamidine. Addition and condensation reactions yield products which can be cyclized to heterocyclic compounds. Frequently, heterocyclics are directly accessible from aminoguanidine in one stage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196304591
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  • 93
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    Electronic Resource
    1,3-Dipolar Cycloadditions. Past and FutureExtended version of lectures given at the Chemists' Meeting in Vienna (Austria) October 1961, and at the Gordon Research Conference, New Hampton (U.S.A.), 1961. (1963)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 565-598 
    Details
    ISSN: 0570-0833
    Keywords: Dipolar cycloaddition ; Cycloaddition ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In contrast to the very large number of special methods applicable to syntheses in the heterocyclic series, relatively few general methods are available. The 1,3-dipolar addition offers a remarkably wide range of utility in the synthesis of five-membered heterocycles. Here the “1,3-dipole”, which can only be represented by zwitterionic octet resonance structures, combines in a cycloaddition with a multiple bond system - the “dipolarophile” - to form an uncharged five-membered ring. Although numerous individual examples of this reaction were known, some even back in the nineteenth century, fruitful development of this synthetic principle has been achieved only in recent years.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196305651
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