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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 745-749 
    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.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1517-1520 
    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.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1919-1922 
    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.
    Type of Medium: Electronic Resource
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  • 4
    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.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1145-1152 
    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.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1163-1168 
    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.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 305-310 
    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.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1615-1623 
    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.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1997-2001 
    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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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 843-849 
    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-.
    Type of Medium: Electronic Resource
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 847-851 
    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.
    Type of Medium: Electronic Resource
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  • 12
    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.
    Type of Medium: Electronic Resource
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  • 13
    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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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1353-1360 
    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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  • 15
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2775-2784 
    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.
    Type of Medium: Electronic Resource
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  • 16
    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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  • 17
    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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  • 18
    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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  • 19
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1391-1395 
    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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  • 20
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 593-594 
    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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  • 21
    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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  • 22
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1471-1477 
    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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  • 23
    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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  • 24
    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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