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  • 2020-2022
  • 1995-1999  (33)
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  • Synthetic methods
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 751-756 
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Streptenol A ; Synthetic methods ; Natural products ; SAMP/RAMP hydrazones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The asymmetric synthesis of (+)-streptenol A was carried out in ten steps and with high enantioselectivity (ee ≥ 96%). The key steps are the α-alkylation of 2,2-dimethyl-1,3-dioxan-5-one RAMP hydrazone A (1), subsequent deoxygenation and elaboration of the side chain via aldehyde B to furnish (+)-streptenol A in 23% overall yield. In analogy, the enantiomer (-)-streptenol A was synthesized using the corresponding SAMP hydrazone in 18% overall yield.
    Type of Medium: Electronic Resource
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  • 2
    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.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-193X
    Keywords: Homogenous catalysis ; Iron ; Imidation ; Sulfur ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The imidation of sulfides and sulfoxides to the corresponding sulfimides and sulfoximides was carried out with N-tert-butyloxycarbonyl azide (BocN3) in the presence of FeCl2. Sulfoxides 1 reacted at room temperature in CH2Cl2 to give the corresponding sulfoximides 3 in 40-95% yield. The imidation of the sterically congested substrate tert-butyl methyl sulfoxide (1f) proceeded sluggishly (10% yield). The sterospecificity of the reaction was demonstrated with the enantiomerically enriched substrates (R)-(+)-1b and (S)-(-)-1d which yielded the sulfoximides (R)-(+)-3b and (S)-(-)-3d with retention of configuration. Mechanistically, an intermediate (nitrene)FeIV complex is postulated as the reactive nitrene transfer reagent which is formed from FeCl2 and BocN3. The more nucleophilic sulfides 2 reacted more readily in the imidation than sulfoxides. Their conversion to the corresponding sulfimides 4 was conducted with BocN3 and a substoichiometric amount of FeCl2 (0.25 equiv.). Yields ranged between 44 and 92%. In an alternative reaction mode, BocN3 was utilized at 0°C in the presence of FeCl2 and acetyl acetone. The sulfimidation, which did not otherwise occur at this temperature, was accelerated by the ligand (36-90% yield).
    Additional Material: 4 Tab.
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  • 4
    ISSN: 1434-193X
    Keywords: Organocerium reagents ; Phosphane oxides ; Phosphonates ; Electrophiles ; Synthetic methods ; Electrophilic Additions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of organocerium reagents 2a-g to phosphinoyl chloride 1a or chlorophosphates 1b leads to the synthesis of phosphane oxides 3aa-ag and phosphonates 3bb, be in good to high yield. The reaction can be extended to cerium enolates 4 (of ketones) and 6 (of nitriles) except when a benzyl group bound to the carbonyl moiety should be metallated. The latter reaction is the first reported synthesis of β-oxophosphane oxides by a simple reaction between enolates and a phosphorus(V) halide.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2315-2321 
    ISSN: 1434-193X
    Keywords: Asymmetric catalysis ; Transfer hydrogenations ; Ruthenium ; Coordination chemistry ; Nitrogen heterocycles ; Synthetic methods ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral 1,2,3,4-tetrahydroisoquinoline intermediates in the Rice and Beyerman routes to morphine, (+)-(R)-1-(3-hydroxy-4-methoxybenzyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline (6) and (+)-(R)-1-(3,5-dibenzyloxy-4-methoxybenzyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline (5), were prepared in high ee by ruthenium-catalyzed asymmetric transfer hydrogenation of the corresponding imine precursors (Noyori method). The yield of the key raw material in the Beyerman route, 3,5-dibenzyloxy-4-methoxyphenylacetic acid (1), starting from gallic acid methyl ester (7) was improved by a factor of 5 over previously described syntheses. Key steps in the new procedure are the selective formation of methyl 3,5-dihydroxy-4-methoxybenzoate (9) via the 3,5-diacetate and an improved benzylation of the hydroxyl groups in 9.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2769-2773 
    ISSN: 1434-193X
    Keywords: Rubicenes ; Cyclization ; Polycyclic aromatic hydrocarbons ; Arenes ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of novel disubstituted rubicenes 1a-k is described. Starting from 1,5-dichloroanthraquinone and aryllithium reagents 3, the diol adducts 4 are reduced and the resulting diarylanthracenes 5 are cyclized to afford the title compounds in fair to good overall yield.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1434-193X
    Keywords: Thia-aza heterocycles ; Bis(azolyl)alkanes ; 1-(Haloalkyl)pyridinium halides ; Synthetic methods ; Cyclization reactions ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel 5/6/5 heterocycles, 1,3,4-thiadiazolo[3,2-a]-1,3,4-thiadiazolo[3,2-d]-1,3,5-triazinium halides 7, have been synthesized by the reaction of 2-amino-1,3,4-thiadiazoles 6 with either 1-(haloalkyl)pyridinium halides 4 or N,N′-methylenebis(pyridinium) dibromides 5. The tricyclic compounds 7 are generated in the course of several successive reaction steps in which specific proton migrations, bond-breaking and bond-forming processes occur. The structures 7 have been verified by spectral data (1H and 13C NMR, MS), X-ray analysis and ab initio calculations. The latter show that both sp2-C atoms C(10) and C(12) of 7 are significantly positively charged and, therefore, exhibit electrophilic properties towards the primary amino group of the amino-thiadiazoles 6. In the course of a multi-step reaction cascade of the 6/7 mixture, novel multi-aza/thia heterocycles 8 are formed. The structures of the latter compounds have been confirmed by X-ray analysis as well as by detailed experimental and theoretical NMR-spectroscopic studies.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1434-193X
    Keywords: Epoxides ; Regioselectivity ; Nucleophilic additions ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regiochemical outcome of the ring-opening of epoxides bearing remote polar functionalities has been established in the case of carbocyclic (1 and 2) and the corresponding furanosidic (3 and 4) title epoxides. Under standard conditions, the regioisomeric C-1 products are the sole (from trans epoxides 2 and 4) or predominant (from cis epoxides 1 and 3) ring-opening products. However, under chelating conditions, and only in the case of the cis epoxides 1 and 3, a consistent increase in C-2 selectivity is unexpectedly observed.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1434-193X
    Keywords: Sulfur heterocycles ; Synthetic methods ; Conducting materials ; Desulfurization ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two types of naphtho-fused 1,3-dithiole-2-thiones (2a-f and 4a-d) were obtained by the reaction of 3,4,7,8-tetrachloro-naphtho[1,8-cd:5,6-c′d′]bis(1,2-dithiole) (1) and sodium trithiocarbonate. The dechalcogenization of the thiones, using mercury acetate, leads to the corresponding naphtho-1,3-dithiol-2-ones (3a-d and 5a-d). The structures of 3a and 4a were confirmed by X-ray investigation. The tetrathiafulvalenes (TTFs) 6 and 7 were synthesized from 2d and 3c by coupling of the starting compounds with the help of triethyl phosphite. Using 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) the TTFs were converted into semiconducting charge-transfer complexes.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1434-193X
    Keywords: Synthetic methods ; Vinyloxiranes ; Chloroallylation ; Thioallylation ; DIBAL-H ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A practical and straightforward procedure is described for the diastereoselective synthesis of functionalized cis- and trans-vinyloxiranes. Readily available esters and lactones were sequentially treated in a one-pot procedure with DIBAL-H and (Z)-γ-chloroallyl-BBN or (E)-phenylthioallyltitanium reagents to give syn-β-chlorohydrins or anti-β-hydroxy thioethers in good yields with high regio- and diastereoselectivities. The β-hydroxy intermediates were stereoselectively converted into the corresponding cis- or trans-vinyloxiranes upon treatment with DBU (for halohydrins) or by alkylation/elimination (for β-hydroxy thioethers). The protocol tolerates several functional groups and promises to be of general applicability.
    Type of Medium: Electronic Resource
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 885-887 
    ISSN: 1434-1948
    Keywords: Chirality ; P ligands ; Synthetic methods ; Triphosgene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of (1S,2S)-C5H8(PH2)2 (1) with OC(OCCl3)2 gave (1S,2S)-C5H8(PCl2)2 (2) as the first example of an optically active bis(phosphonous dichloride). 2 was converted to (1S,2S)-C5H8(PX2)2 [PX2 = P(OMe)2 (3), P(OPh)2 (4), P[OCH-(Me)Et-(S)]2 (5), P[2-OC10H6C10H6O-2′-(R)] (6), P(NC4H8O-cyclo)2 (7), P(C6H11-cyclo)2 (8)] by reactions with oxygen, nitrogen, and carbon nucleophiles.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2839-2849 
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Hydrazones ; Synthetic methods ; Alkylations ; Deoxygenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient asymmetric synthesis of protected anti-1,3-diols 5 (de ≥ 98%, ee = 92-98%) from 2,2-dimethyl-1,3-dioxan-5-one SAMP hydrazone 1 is described. The key steps are the diastereo- and enantioselective α,α′-bisalkylation followed by reduction of the ketones 2 and a variant of the Barton-McCombie deoxygenation. The new method allows the synthesis of acetonide-protected anti-1,3-diols with a broad range of substituents in good overall yields (31-69%).
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1645-1652 
    ISSN: 1434-193X
    Keywords: Azomethine ylides ; Nitrogen heterocycles ; Ring expansion ; Small ring systems ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mechanistic investigations by means of proton spectroscopy detected intermediates and uncovered the course of reactions in acetate-buffered [D4]methanol of primary cyclopropanediamines cis- and trans-2a with benzaldehyde (3a) or 2,2-dimethylpropanal (3b), of secondary cyclopropanediamines cis- and trans-2b with 3b, and of the ring-methylated cyclopropanediamine trans-14a and the aromatic aldehydes 3a and c. This study provided the basis of an expedient synthesis of pyrroles which takes place under exceptionally mild conditions. Irrespective of the configuration, primary (2a·2HBr) and secondary cyclopropanediammonium dibromides 2b and c·2HBr that are devoid of ring substituents react with aromatic aldehydes 3a, e-h, cinnamic aldehyde (3i), and 3b to afford 2-substituted (8a, b) and 1,2-disubstituted pyrroles (8c-i), respectively. The 3-substituted secondary trans-cyclopropanediammonium dibromides 24·2HBr furnish 1,2,4-trisubstituted pyrroles 25. While the primary 1-methylcyclopropanediammonium dibromide trans-14a·2HBr reacts regioselectively with 3a and c to produce only 2,3-substituted pyrroles 19a, c, the corresponding secondary dibromide trans-14c·2HBr gives rise to the formation of mixtures of 1,2,3- (22) and 1,2,5-trisubstituted pyrroles 23. The key step of pyrrole formation from 1,2-cyclopropanediamines and aldehydes is the ring expansion of intermediate monoiminium ions of type 5 via azomethine ylides (E, Z)-6 to yield dihydropyrrolium ions 7.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 623-635 
    ISSN: 0947-3440
    Keywords: High-pressure chemistry ; Nucleophilic aromatic substitution ; Cycloadditions ; Synthetic methods ; Synthesis under neutral, mild conditions ; Supramolecular chemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The most recent successes achieved in organic synthesis by use of high-pressure technique are reviewed.
    Type of Medium: Electronic Resource
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  • 15
    ISSN: 0947-3440
    Keywords: C-C coupling ; Dienediynes ; Enol triflates ; McMurry reaction ; Neocarzinostatin ; Synthetic methods ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel synthetic strategy leading to bicyclic dienediyne models of the chromophore 1 of the anti-tumor antibiotic neocarzinostatin is described. Its key step is a ring-closing McMurry reaction of the dienediyne keto aldehydes 17 or 23. It leads to dienediynediols (compounds 19 and 24, respectively) or to trienediynes (compounds 18 and 25, respectively). Low temperatures favor the formation of dienediynediols while high temperatures favor the formation of trienediynes, so that the McMurry reactions of keto aldehyde 23 show an almost perfect temperature-dependent chemoselectivity (Scheme 6). The trienediyne 25 contains a ketal group which was removed by acid-catalyzed methanolysis (Scheme 8). The resulting diol 31 was mono-tert-butylsilylated to provide the allyl alcohol 36 (Scheme 10). It was epoxidized regio- and stereoselectively with Sharpless' asymmetric epoxidation reagent. The resulting epoxide 37 was converted into the dienediyne epoxycarbonate syn-33 in the final step of a sequence totaling seven steps and 5% yield starting from the bistriflate 3b; 3b itself is accessible from 2-formylcyclohexa none in two steps and 47% overall yield. The dienediyne epoxycarbonate syn-33 is the first synthetic congener of the neocarzinostatin chromophore furnished both with the - correctly configured - epoxide and carbonate rings.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 16
    ISSN: 0947-3440
    Keywords: Photochemistry ; Synthetic methods ; Oxetanes ; Diols ; Amino alcohols ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of 3-heteroatom-substituted oxetanes by the Paternò-Büchi reaction, and their application in synthesis are reviewed. 3-Oxetanols and 3-aminooxetanes are the two most important oxetanes in this respect. By tuning the electronic properties of the enol and enamine substrates, a successful photocycloaddition to carbonyl compounds, with high yield, is possible. Since the oxetane formation proceeds stereoselectively, diastereomerically pure products are readily accessible, which can then be used in further transformations. To this end, regioselective ring-opening reactions have been developed, some of which will be discussed in this account.
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  • 17
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 961-965 
    ISSN: 0947-3440
    Keywords: C—C coupling ; Dienediynes ; McMurry reaction ; Neocarzinostatin ; Synthetic methods ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The monocyclo-diendiyne → bicyclo-trienediyne strategy for obtaining dienediyne models of the antitumor antibiotic neocarzinostatin chromophore (1) was extended from generating 6-/11-membered bicyclotrienediynes (e.g. 2 → 4) to generating the 6-/10-membered bicyclotrienediyne 5. In the preparatory steps (Scheme 2), the bistriflate 10 was successively coupled with alkynes 9 and 11. Via the dienediynediol and its subsequent oxidation with the Dess-Martin periodinane, we obtained the monocyclic dienediyne keto aldehyde 13. Cyclization of 13 with low-valent titanium afforded the bicyclotrienediyne 5 in 42% yield (Scheme 3). Compound 5 was converted in five steps - namely ketal cleavage, monosilylation of the resulting diol 14, asymmetric Sharpless epoxidation, desilylation and carbonate formation - into the dienediyne epoxycarbonate 3. The structure of the latter is more closely related to the neocarzinostatin chromophore than our earlier analogues.
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  • 18
    ISSN: 0947-3440
    Keywords: Cholesterol ; Steroid side chain construction ; Alkylations ; Synthetic methods ; Steroids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 21-(3-hydroxy-3-methylbutyl)- and 21-(2-hydroxy-2-methylpropoxy)cholestane derivatives 3 and 5, formally double chain hybrid (20R)- and (20S)-cholesterol analogues, were synthesized. The C-22 to C-27 section of the 25-hydroxycholestane side chain was established by stereoselective alkylation with 5-bromo-2-methyl-2-(triethylsilyl)oxypentane of the pregnanoic ester 8, derived from 3β-acetoxyandrost-5-en-17-one (7). Reduction of the ester 9 to the 21-alcohol 10 permitted elaboration of a second hydroxylated side chain, either via the tosylate 11 by alkynation/hydrogenation (yielding intermediate 13) or by alkylation of 10 with bromoacetate (yielding 14) followed by reaction with methyl magnesium bromide.
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  • 19
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2581-2585 
    ISSN: 0947-3440
    Keywords: Ozonides, functionalized ; Substitutions ; Alcohols ; Aldehydes ; Synthetic methods ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substitution of 3-chloro-3,5-bis(chloromethyl)-5-methyl-1,2,4-trioxolane (3) with allyl alcohol gave the corresponding diastereomeric allyloxy-substituted ozonides 4, which were converted into diozonides 7 by ozone treatment. Substitutions of 3 with ethanediol or with 1,3-propanediol gave the corresponding hydroxyalkoxy-substituted ozonides 8, 14, which were oxidized to the corresponding aldehydes 10, 16. Reaction of 3,5-dichloro-3,5-bis(chloromethyl)-1,2,4-trioxolane (1a) with ethanediol gave the corresponding bis(hydroxy)-substituted ozonide 19 as well as a bicyclic ozonide 18 by reaction of 1a with ethanediol in a ratio of 1:1.
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  • 20
    ISSN: 0009-2940
    Keywords: Bis(tetramethylipiperidino)aluminum halides ; Alkoxy((tetramethylpiperidino)aluminum halides ; 27Al-NMR spectra ; Aluminum ; Amides ; Synthetic methods ; Bridging ligands ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Lithio-2,2,6,6-tetramethylpiperidine [Li(tmp)] reacts with AlX3 (X = Cl, Br) in diethyl ether/ n-hexane solution to generate the products of substitution and ether cleavage, [tmpAl(X)(μ-OEt)], (la, X = Cl; 1b, X = Br). However, when the reaction is allowed to proceed in n-hexane alone, an almost quantitative yield of compounds tmp2AlX (2a, X = Cl; 2b, X = Br; 2c, X = I) is obtained. According to 27AI-NMR spectroscopy, mass spectroscopy, cryoscopy, and X-ray crystal structure determinations, these compounds are monomeric in the solid state, in solution, and in the gas phase. 2b reacts with AgBF4 yielding the fluoride-bridged dimer (tmp2AlF), 2d, as shown by X-ray crystal structure determination.
    Additional Material: 3 Tab.
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  • 21
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 1164-1170 
    ISSN: 0570-0833
    Keywords: carbenes ; carbenoids ; cyclizations ; rearrangements ; synthetic methods ; Carbenes ; Carbenoids ; Cyclization ; Rearrangement ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkenylidenes R2C=C: (= alkylidene carbenes) undergo regio- and stereoselective intramolecular C—H insertion reactions that are excellently suited for the synthesis of cyclopentenes. The 1, 2-shifts occurring with R=H and R=Ar are useful for the preparation of alkynes. Alkenylidenes are efficiently generated from carbonyl compounds by diazomethylation, from vinyl halides by α-elimination, from alkynyliodonium salts by addition of nucleophiles, and from alkynes by retro-1, 2-shifts. Specific applications of the various methods, particularly in the synthesis of natural products, are discussed.
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  • 22
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 186-204 
    ISSN: 0570-0833
    Keywords: chirality ; catalysis ; copper ; reagents ; synthetic methods ; Homogeneous catalysis ; Chirality ; Copper ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Of all of the organometallic reagents currently used to form carbon-carbon bonds, organocopper reagents rank amongst the most important. Interest in these reagents centers not only on their regioselectivity, but also increasingly on their application in stereoselective transformations (principally Michael additions and SN2′ reactions); the use of suitable substrates or chirally modified cuprates can lead to highly diastereo- and enantioselective reactions. Simultaneously, extensions of methods for the preparation and application of these reagents (for example functionalized organocopper species and Lewis acid catalysis, respectively) have opened up new horizons for organocopper reagents. Mechanistically, the reactions are well-documented and understood, but this aspect of the subject has not kept pace with the many rapid developments in preparative chemistry. Organocopper ragents have proved to be indispensable in the synthesis of complex natural products and pharmaceuticals, chiral auxiliaries, and molecules with interesting structural features. In this review we will discuss some of the more recent important developments in this area; the organization will follow the type of selectivity (regio-, diastereo-, and enantioselectivity).
    Additional Material: 1 Tab.
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  • 23
    ISSN: 0570-0833
    Keywords: carbonyl complexes ; cations ; superacidic systems ; synthetic methods ; transition metals ; Carbonyl ligands ; Cations ; Superacidic systems ; Synthetic methods ; Transition metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homoleptic carbonyl cations of the electron-rich metals in Groups 8 through 12 are the newest members of the large family of transition metal carbonyls. They can be distinguished from typical metal carbonyl complexes in several respects. Their synthesis entails carbonylation of metal salts in such superacids as fluorosulfuric acid and “magic acid” HSO3F—SbF5. Thermally stable salts with [Sb2F11]- as counterion are obtained with antimony pentafluoride as reaction medium. Both the [Sb2F11]- anion and superacid reaction media have previously found little application in the organometallic chemistry of d-block elements. Also unprecedented in metal carbonyl chemistry are the coordination geometries with coordination numbers 4 (square-planar coordination) and 2 (linear coordination) for the cation. Formal oxidation states of the metals, and the charges of the complex cations, extend from + 1 to +3: thus CO is largely σ-bonded to the metal, and the CO bond is strongly polarized. Minimal metal → CO π-backbonding and a positive partial charge on carbon are manifested in long M—C bonds, short C—O bonds, high frequencies for C—O stretching vibrations (up to 2300 cm-1), and small 13C NMR chemical shifts (up to δc, = 121). Prominent examples of these unusual homoleptic carbonyl cations, which were recently the subject of a Highlight in this journal, include the first carbonyl cation of a p-block metal [Hg(CO)2]2+, the first trivalent carbonyl cation [Ir(CO)6]3+, and the first multiply charged carbonyl cation of a 3d metal [Fe(CO)6]2+. In this overview we propose to (a) outline the historical origins of cationic metal carbonyls and their methods of synthesis; (b) present a summary of the general field of carbonyl cations, which has developed over a yery short period of time; (c) discuss the structural and spectroscopic characteritics of metal-CO bonding; (d) discuss the special significance associated with reaction media and the [Sb2F11]- anion; and (e) point to the most recent results and anticipated future developments.
    Additional Material: 8 Ill.
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  • 24
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 1050-1066 
    ISSN: 0570-0833
    Keywords: carbon-carbon coupling ; carbon monoxide ; carbonylation ; radicals ; synthetic methods ; C-C coupling ; Carbonylation ; Radicals ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Although known since the 1950s, free-radical carbonylation has not received much attention until only recently. In the last few years the application of modern free-radical techniques has revealed the high synthetic potential of this reaction as a tool for introducing CO into organic molecules. Clearly now is the time for a renaissance of this chemistry. Under standard conditions (tributyltin hydride/CO) primary, secondary, as well as tertiary alkyl bromides and iodides can be efficiently converted into the corresponding aldehydes. Aromatic and α,β-unsaturated aldehydes can also be prepared from the parent aromatic and vinylic iodides. If the reaction is carried out in the presence of alkenes containing an electron-withdrawing substituent, the initially formed acyl radical subsequently adds to the alkene, leading to a general method for the synthesis of unsymmetrical ketones. This three-component coupling reaction can be extended successfully to allyltin-mediated reactions. Thus, β,γ-enones can be prepared from organic halides, CO, and allyltributylstannanes. In a remarkable one-pot procedure alkyl halides can be treated with a mixture of alkene, allyltributylstannane, and carbon monoxide in a four-component coupling reaction that provides β-functionalized δ,∊-unsaturated ketones by the formation of three new C—C bonds. The reaction of 4-pentenyl radicals with CO leads to acyl radical cyclization, which provides a useful method for the synthesis of cyclopentanones. Certain useful one-electron oxidations can be combined efficiently with free-radical carbonylations. These findings and others discussed in this article clearly demonstrate that free-radical carbonylation can now be considered a practical alternative to transition metal mediated carbonylation.
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  • 25
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 2056-2083 
    ISSN: 0570-0833
    Keywords: protecting groups ; retrosynthetic analyses ; synthetic methods ; total syntheses ; Protecting groups ; Retro reactions ; Synthetic methods ; Total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The choice of protecting groups is one of the decisive factors in the successful realization of a complex, demanding synthetic project. The protecting groups used influence the length and efficiency of the synthesis and are often responsible for its success or failure. A wide range of blocking groups are currently available for the different functional groups; however, an overall strategy combining these different masking techniques in an advantageous and reliable manner has never been proposed or at best only for individual cases. This review attempts to make a contribution to filling this gap. First a very short overview of the most commonly used protecting groups will be given, in which they are classified according to their lability and not according to the functional group they protect. This classification clarifies coherent concepts for the development of blocking strategies. On the basis of this brief summary reliable strategies will then be illustrated and developed with selected examples from the recent literature by which protecting groups may be combined successfully and advantageously in synthetic projects of differing degrees of complexity and difficulty.
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  • 26
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 1380-1419 
    ISSN: 0570-0833
    Keywords: glycals ; glycoconjugates ; glycosylations ; oligosaccharides ; synthetic methods ; Glycals ; Glycoconjugates ; Glycosylation ; Oligosaccharides ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This review provides a personal account of the explorations of a research group in oligosaccharide and glycoconjugate construction. The journey began twenty years ago with the study of Diels-Alder reactions of complex dienes. By extending this methodology to aldehydo-type heterodienophile equivalents, access to unnatural glycals was gained (LACDAC reaction). From this point a broad-ranging investigation of the use of glycals in the synthesis of oligosaccharides and other glycoconjugates was begun. Mobilization of glycals both as glycosyl donors and glycosyl acceptors led to the strategy of glycal assembly. Several new glycosylation techniques were developed to provide practical underpinning for this logic of glycal assembly. Glycal-based paradigms have been shown to be nicely adaptable to solid phase supported synthesis. Moreover, glycal assembly - both in solution and on solid phases - has been used to gain relatively concise and efficient entry to a variety of biologically interesting and potentially valuable constructs. Some of these syntheses, particularly in the field of tumor antigens, have led to novel compounds which are in the final stages of preclinical assessment. This review presents an account of the chemical reasoning at the center of the program.
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  • 27
    ISSN: 0570-0833
    Keywords: computer chemistry ; synthesis planning ; WODCA ; Synthetic methods ; Computer chemistry ; Synthesis design ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The planning of syntheses in organic chemistry has continuously been given more solid foundations during the last decades. Widely applicable rules have been formulated. Nearly parallel with the systematization of this field the potential for the automation of synthesis planning by the use of computers has been promulgated. However, after more than two decades of continuing efforts by a number of groups, computer-assisted synthesis planning, which relies on large libraries of synthons and transforms, has failed to establish itself firmly. This is in marked contrast to the acceptance of reaction databases. Their use has become routine with a surprisingly short time. Apparently the classical approaches to computer-assisted synthesis planning do not satisfy the needs of the preparative chemist. However, this lack of success does not yet mean the complete demise of the whole field. The conceptual shortcomings and problems of the first generation of programs are both of technical and psychological nature and need to be critically analyzed. Meanwhile, work has begun on systems of the second generation, which try to support the chemist in the synthesis laboratory with new methods in novel ways. Care is taken to mimic and support the typical planning style of the human chemist, who often on the spur of the moment switches direction in planning as well as his (sub) goals and methods. New tools that correspond better to the thinking patterns and working habits of chemists empower the user to plan syntheses of organic molecules in an interactive and innovative fashion. We feel that this field is far from dead and continue our research activities. In this article we introduce a system with a number of novel concepts and demonstrate its capabilities with some practical examples.
    Additional Material: 19 Ill.
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  • 28
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    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 241-270 
    ISSN: 0570-0833
    Keywords: alkenes ; asymmetric syntheses ; Horner-Wittig reactions ; phosphane oxides ; synthetic methods ; Alkenes ; Asymmetric synthesis ; Horner-Wittig reaction ; Phosphane oxides ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In 1959, Horner showed that metalated alkyldiphenylphosphane oxides react with aldehydes or ketones to give alkenes. With this reaction, the diphenylphosphoryl (Ph2PO) group made its entrance into synthetic organic chemistry. In the thirty-six years since that date, extensive research has shown that this olefination, the Horner-Wittig reaction, has unique properties that make it much more than simply the phosphane oxide cousin of the more famous phosphorus-based olefinations - the Wittig reaction (based on phosphonium salts) and the Wadsworth-Emmons reaction (based on phosphonate esters). Early work on the Horner-Wittig reaction concentrated on the reactivity of phosphane oxides and the regioselectivity of their reactions, but more recently the power of the Ph2PO group to control the stereochemistry of alkenes, and to produce “on demand” either stereoisomer in high stereochemical purity, has emerged. From the study of these stereocontrolled Horner-Wittig reactions arose the realization that the Ph2PO group is useful not only for the control of the two-dimensional stereochemistry of alkenes, but also of three-dimensional stereochemistry in general.After a brief introduction to phosphane oxide chemistry, this review will examine the Horner-Wittig reaction, in both its original and “stereocontrolled” varieties. From there, we will move on to an account of the stereoselective construction of molecules containing the Ph2PO group, concentrating on the stereochemical directing effects of the Ph2PO group and on the role of its unique combination of attributes - steric bulk, electronegativity, and Lewis basicity - in controlling these reactions. Finally, we will present what is intended as a practical guide to this chemistry, covering the type of functionalized alkenes that have been made with the help of the Ph2PO group and giving guidelines that we hope will help the organic chemist to make the most of the chemistry the Ph2PO group has to offer.
    Additional Material: 11 Tab.
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  • 29
    ISSN: 0570-0833
    Keywords: carbohydrates ; enzymes ; organic synthesis ; Synthetic methods ; Enzymes ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbohydrates on cell surfaces are information molecules. Although only seven or eight monosaccharides are commonly used as building blocks in mammalian systems, the multifunctionality of these monomers can lead to the assembly of an immense variety of complex structures. Millions of different tetrasaccharide structures, for example, can be constructed from this small number of building blocks, if branching, the stereochemistry of glycosidic linkages, and the modification of hydroxyl and amino groups are taken into consideration. Oligosaccharides therefore represent an effective class of biomolecules that code for a vast amount of information required in various biological recognition processes, such as intercellular communication, signal transduction, cell adhesion, infection, cell differentiation, development and metastasis. The pace of development of pharmaceuticals based on carbohydrates has, however, been slower than that based on other classes of biomolecules. Part of the reason is the lack of technologies for the study of complex carbohydrates. There is no method to amplify oligosaccharides for sequence analysis. There is no machine available for automated synthesis of oligosaccharides. In addition, the possibly poor bioavailability and difficulties in the large-scale synthesis of carbohydrates have undoubtedly contributed to this slow pace. The enzymatic and chemoenzymatic methods, especially those based on aldolases and glycosyltransferases, described here appear to be useful for the synthesis of mono- and oligosaccaharides and related molecules. Further advances in glycobiology will probably lead to the development of new technologies for the study of carbohydrate recognition and for the synthesis of bioactive carbohydrates and mimetics to control the recognition processes.
    Additional Material: 4 Tab.
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  • 30
    ISSN: 0570-0833
    Keywords: carbohydrates ; enzymes ; organic synthesis ; Synthetic methods ; Enzymes ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recognition of carbohydrates by proteins and nucleic acids is highly specific, but the dissociation constants are relatively high (generally in the mM to high μM range) because of the lack of hydrophobic groups in the carbohydrates. The high specificity of this weak binding often comes from many hydrogen bonds and the coordination of metal ions as bridge between sugars and receptors. Though weak hydrophobic interactions between sugars and proteins have also been identified, the unique shape of a complex carbohydrate under the influence of anomeric and exo anomeric effects (the glycosidic torsion angles are therefore often not flexible but are typically somewhat restricted) and the topographic orientation of the hydroxyl and charged groups contribute most significantly to the recognition process. Studies on the structure-function relationship of a complex carbohydrate therefore require deliberate manipulation of its shape and functional groups, and synthesis of oligosaccharide analogs from modified monosaccharides is often useful to address the problem. The availability of various monosaccharides and their analogs for the synthesis of complex carbohydrates together with the information resulting from structural studies (such a NMR or X-ray studies on sugar-protein complexes) will certainly provide a basic understanding of complex carbohydrate recognition. An ultimate goal is to develop simple and easy-to-make non-carbohydrate molecules that resemble the active structure involved in carbohydrate-receptor interaction or the transition-state of an enzyme-catalyzed transformation (for example, glycosidase or glycosyltransferase reactions) and have the approprite bioavailability to be used to control the carbohydrate function in a specific manner. In part one of this review we described various enzymatic approaches to the synthesis of monosaccharides, analogs, and related structures. We describe in this part enzymatic and chemoenzymatic approaches to the synthesis of oligosaccarides and analogs, including those involved in E-selectin recognition, and strategies to inhibit glycosidases and glycosyltransferases.
    Additional Material: 1 Tab.
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  • 31
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    Angewandte Chemie International Edition in English 33 (1995), S. 2379-2411 
    ISSN: 0570-0833
    Keywords: C-C coupling ; Synthetic methods ; Heck reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The palladium-catalyzed coupling of haloarenes and haloalkenes with alkenes, which was discovered by Richard F. Heck in the late sixties, has been a topic of fluctuating interest; however, in the last six years activity in this area has flourished. Careful choice of substrates and skillful tailoring of reaction conditions lead to impressive sequences consisting of even different reaction types that occur not only in a consecutive mode, but also in a single operation. The wellestablished Heck reaction, together with other mechanistically related palladiumcatalyzed transformations with arene, alkene, and alkyne derivatives, opens the door to a tremendous variety of elegant and highly convergent routes to structurally complex molecules. The reaction is not disturbed by heteroatoms such as oxygen and nitrogen (nor by sulfur and phosphorus with some limitations). The spectrum of recent achievements starts with a range of chemoselective and regioselective monocouplings of highly functionalized substrates with unsymmetrical and multisubstituted reaction partners. Other advances include cascade reactions in which three, four, five, and even eight new C—C bonds are formed to yield oligofunctional and oligocyclic products with impressive molecular complexity. Even the enantioselective construction of complex natural products with quaternary stereocenters has been achieved with Heck reactions in key steps, as exemplified by the synthesis of crinan, picrotoxinin, and morphine. Today, the Heck reaction is indispensible in the arsenal of synthetic methods available to organic chemists. Certainly it is only a matter of time before the Heck reaction is applied in industrial syntheses.
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  • 32
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    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 34 (1995), S. 259-281 
    ISSN: 0570-0833
    Keywords: carbon-carbon coupling ; catalysis ; cycloadditions ; synthetic methods ; C-C coupling ; Atom economy ; Homogeneous catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enhancing the efficiency of the synthesis of complex organic products constitutes one of the most exciting challenges to the synthetic chemist. Increasing the catalogue of reactions that are simple additions or that minimize waste production is the necessary first step. Transition metal complexes, which can be tunable both electronically and sterically by varying the metal and/or ligands, are a focal point for such invention. Except for catalytic hydrogenation, such methods have been rare in complex synthesis and virtually unknown for C—C bond formation until the advent of cross-coupling reactions. These complexes may orchestrate a variety of C—C bond-forming processes, important for creation of the basic skeleton of the organic structure. Their ability to insert into C—H bonds primes a number of different types of additions to relatively nonpolar π-electron systems. Besides imparting selectivity, they make feasible reactions that uncatalyzed were previously unknown. The ability of these complexes to preorganize π-electron systems serves as the basis both of simple additions usually accompanied by subsequent hydrogen shifts and of cycloadditions. The ability to generate “reactive” intermediates under mild conditions also provides prospects for new types of C—C bond-forming reactions. While the examples reveal a diverse array of successes, the opportunities for new invention are vast and largely untapped.
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  • 33
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    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 34 (1995), S. 2443-2465 
    ISSN: 0570-0833
    Keywords: catalysis ; oxidations ; synthetic methods ; Amines ; Homogeneous catalysis ; Oxidation ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The metabolism of amines is governed by a variety of enzymes such as amine oxidase, flavoenzyme, and cytochrome P-450. A wide variety of compounds are produced such as ammonia and alkaloids in selective and clean oxidation reactions that proceed under mild reaction conditions. Simulation of the functions of these enzymes with simple transition metal complex catalysts may lead to the discovery of biomimetic, catalytic oxidations of amines and related compounds. Indeed, metal complex catalyzed oxidations have been found to proceed with high efficiency. The first section of this review discusses the dehydrogenative oxidations of amines with transition metal catalysts by transition metal catalysts that simulate amine oxidase. The second section highlights the catalytic oxidation of secondary amines to nitrones by simulation of flavoenzymes. The third section describes the simulation of the function of cytochrome P-450 with lowvalent ruthenium complexes and peroxides. Biomimetic ruthenium-catalyzed oxidations of tertiary amines, secondary amines, and other substrates such as amides, β-lactams, nitriles, alcohols, alkenes, ketones, and even nonactivated hydrocarbons can be performed selectively under mild conditions. These three general approaches provide highly useful strategies for synthesis of fine chemicals and biologically active compounds such as alkaloids, amino acids, and β-lactams.
    Additional Material: 8 Tab.
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  • 34
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    Angewandte Chemie International Edition in English 33 (1994), S. 2009-2023 
    ISSN: 0570-0833
    Keywords: Photochemistry ; Synthetic methods ; Fine chemicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The light of the sun can be used directly for changing chemical structures photochemically. Any industrial application must conform to the limitations imposed by the spectral distribution of the photons from the sun, the interruptions to the radiation due to the day/night rhythm, and the weather. In this review, we describe the photochemical potential of the sun, give a fundamental treatment of the concept of photoreactors driven by sunlight (abbreviated to solar photoreactors), and give an account of the realization of this concept in the first pilot plant on the “Plataforma Solar de Almeria” in southern Spain and in other activities in this field. Based on experimental data from photochemical investigations on the pilot plant scale, possibilities, limitations, and the potential growth of solar photochemistry are described. Solar photochemistry, in our opinion, is a technique which could make a contribution to the chemistry of the future because of its photochemical synthesis potential, the avoidance of waste products, and the direct utilization of the sun, not only as a primary energy source, but also as a reaction partner.
    Additional Material: 21 Ill.
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  • 35
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    Angewandte Chemie International Edition in English 32 (1993), S. 336-358 
    ISSN: 0570-0833
    Keywords: Carbohydrates ; Chiral auxiliaries ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbohydrates are inexpensive natural products in which numerous functional groups and stereogenic centers are combined in one molecule. By directed regio-and stereoselective formation of derivatives they can be converted into efficient chiral auxiliaries for controlling asymmetric syntheses. Stereoelectronic effects and pre-orientation of the reactive and shielding groups through formation of complexes can often be used for effective diastereofacial differentiation. In aldol reactions and alkylations on carbohydrate ester enolates intramolecular complexation promotes simultaneous elimination with formation of ketene. The steric, stereoelectronic, and coordinating properties of carbohydrate templates can also be used selectively to attain high levels of asymmetric induction in processes such as Diels-Alder reactions, hetero-Diels-Alder reactions, [2 + 2] cycloadditions, cyclopropanations, and Michael additions. It was possible with bicyclic, strongly stereodifferentiating carbohydrate auxiliaries to achieve a diastereoselective synthesis of carboxylic acid derivatives branched in the β position by a new 1,4-addition of alkylaluminum halides to α,β-unsaturated N-acylurethanes, in which methylaluminum halides and higher alkyl- or arylaluminum compounds behave mechanistically in a strikingly different manners. As complex ligands in chiral reagents and promoters, carbohydrates allow highly stereoselective reductions and aldol reactions that lead, amongst others, to chiral alcohols and β-hydroxy-α-amino acids in excellent enantiomeric excesses. Glycosylamines offer the possibility of versatile stereoselective applications: in the presence of Lewis acids the corresponding aldimines permit high-yielding syntheses of enantiomerically pure α-amino acids by Strecker and Ugi reactions, controlled by steric and stereoelectronic effects and by complex formation. They can be used with equal efficiency for asymmetric syntheses of chiral homoallylamines and for asymmetric Mannich syntheses of β-amino acids and chiral heterocycles, for example alkaloids.
    Additional Material: 15 Tab.
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  • 36
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    Angewandte Chemie International Edition in English 32 (1993), S. 164-189 
    ISSN: 0570-0833
    Keywords: Metals ; Reactivity ; Activation ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Today, the synthetic chemist has a large repertoire of metal activation methods at his disposal. After a first breakthrough was made at the beginning of the seventies with the introduction of the Rieke metals, a series of further, in part more efficient methods were describes, based on which not only classical metal-induced reactions could be substantially improved but also completely new reactions could be discovered. In this article the individual activation methods are discussed and compared as far as is possible using the currently available data. Especially noteworthy are the metal-graphite combinations because of their unsurpassed reactivity and concomitant easy preparation and manipulation. As shown by numerous applications of these reagents on polyfunctional substrates, particularly natural products, high reactivity of the metal and excellent selectivity are by no means precluded. Besides the purely preparative aspects also insights gained so far into the general principles and limits of metal activation are outlined, and attempts at determining the morphology of highly dispersed systems are reported.
    Additional Material: 5 Ill.
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  • 37
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    Angewandte Chemie International Edition in English 32 (1993), S. 1010-1022 
    ISSN: 0570-0833
    Keywords: Natural products ; Polycycles ; Michael addition ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The one-pot intramolecular double Michael reaction of compounds having two different α, β-unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first the substrate is treated with lithium hexamethyldisilazide, in the second with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third with tert-butyldimethylsilyl trifluoromethanesulfonate and triethylamine. The reaction proceeds with complete regioselectivity and high stereoselectivity following a stepwise mechanism. Spiro-fused bicyclo[2.2.2]octane derivatives can be constructed with high stereoselectivity by the intromolecular double Michael reaction by using the first method. Enantiomerically pure atisine and the enantiomer of atisirene were synthesized stereoselectively by application of this methodology. The syntheses of steroids and angular triquinane-type sesquiterpenoids were possible with the second method. Heterocyclic compounds with a bridgehead nitrogen atom were obtained by the reaction of α, β-unsaturated amides following the second and third methods. The asymmetric synthesis of tylophorine with diastereofacial control was achieved by the intramolecular reaction according to the third method. The sulfur-mediated intramolecular double Michael reaction utilizing the third method produced trans-hydroindane derivatives. Furthermore, the intramolecular Michael-aldol reaction can be employed in synthesizing polycyclic systems with cyclobutane units by treatment with tert-butyldimethylsilyl trifluoromethanesulfonate in the presence of triethylamine. The intermolecular double Michael reaction and related reactions will also be described.
    Additional Material: 28 Ill.
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  • 38
    ISSN: 0570-0833
    Keywords: Alkaloids ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oriental plant Yuzuriha (Daphniphyllum macropodum) elaborates a fascinating family of polycyclic, squalene-derived alkaloids that provide a test for state-of-the-art methods of organic synthesis. The intriguing structures of these natural products have inspired us to design and explore two rather different approaches for their laboratory synthesis. This article recounts and contrasts these two different syntheses. The first approach was based on a method of synthetic design that emphasizes efficient construction of the polycyclic skeleton of the molecule (Corey's “network analysis”). A strategic bond was identified and the synthesis planned around the late formation of this bond. The synthesis that was designed by this approach proceeded smoothly until the point where it was necessary to remove functional groups that had been incorporated solely for the purpose of forming the strategic bond. Although the problems were eventually overcome, the resulting synthesis was too long and did not control the configuration of one of the stereocenters. The second approach was based on a possible biosynthesis of one of the alkaloids and provided surprisingly easy access to the simpler members of the family. The success of this synthesis led to a concrete proposal about the biosynthesis of the alkaloids and to the discovery of the astonishing transformation depicted in Scheme 27. In this marvelous reaction, an acyclic squalene derivative is converted by successive treatment with ordinary commodity chemicals into a pentacyclic alkaloid. The transformation involves the formation of four carbon-carbon bonds, two carbon-nitrogen bonds, and one carbon-hydrogen bond!
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  • 39
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    Angewandte Chemie International Edition in English 30 (1991), S. 238-264 
    ISSN: 0570-0833
    Keywords: 3-Amino-2H-azirines ; Azirines ; Amino acids ; Peptides ; Heterocycles ; Synthetic methods ; 2-Aminoisobutyric acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recent upswing in peptide chemistry has been accompanied by an increasing interest in nonproteinogenic amino acids. These include the α,α-disubstituted glycines, the best known of which is Aib (2-aminoisobutyric acid, 2-methylalanine). These α-amino acids occur in natural oligopeptides such as the peptaibols, a class of membrane-active ionophores that has been isolated from fungal cultures. The twofold substitution at the α-C atom of the amino acids severely restricts the conformational freedom of the peptides and causes particular secondary structures to be favored; thus, α, α-disubstituted α-amino acids induce the formation of β turns or helices. 3-Amino-2H-azirines are ideal synthons for the construction of oligopeptides, cyclic peptides and depsipeptides (peptolides) containing such α,α-disubstituted α-amino acids. The presence of the ring strain in these molecules means that they can be used in peptide coupling without the need for additional activating reagents. Using 3-amino-2H-azirines a large array of heterocycles containing α, α-disubstituted α-amino acids as structural elements within their skeleton can be synthesized. The driving force in these reactions is the release of the strain on the three-membered ring, which usually takes place in a ring-expansion reaction. The mechanistic elucidation of these reactions, which can be quite complex, contains some surprises.
    Additional Material: 7 Ill.
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  • 40
    ISSN: 0570-0833
    Keywords: Rearrangement ; Synthetic methods ; Cyanides ; Isocyanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Until recently the isocyanide-cyanide rearrangement was of interest almost solely as an example of a unimolecular gas-phase reaction, and kinetic studies had been carried out in only a few simple cases. Kinetic measurements in solution were made possible only by the discovery and suppression of a parallel free-radical chain process which leads to the same products. The rate of the isomerization is almost independent of the structure of the starting material and of the substituents present. An exception is provided by extreme steric hindrance in three dimensions which, as in tris-α-substituted triptycyl isocyanides, leads to a considerable increase in the activation energy. The results can be interpreted in terms of a purely sigmatropic mechanism, as predicted by ab initio calculations. The preparative application of this rearrangement reaction requires the suppression of side reactions and can best be carried out by flash pyrolysis; yields are then almost quantitative. Allyl isocyanides react without allyl isomerization, optically active isocyanides with complete retention of configuration. New, economically interesting syntheses for the known nonsteroidal anti-inflammatory drugs ibuprofen and (S)-naproxene are described. The application of the useful synthetic building blocks, the optically active β-acyloxy cyanides, which are formed from optically active α-amino acids, will be demonstrated.
    Additional Material: 2 Ill.
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  • 41
    ISSN: 0570-0833
    Keywords: Chirality transfer ; Carbonyl compounds ; Addition ; Enantioselectivity ; Synthetic methods ; Alcohols ; Reaction mechanisms ; Catalysis ; Alkylation ; Organometallic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic addition of organometallic reagents to carbonyl substrates constitutes one of the most fundamental operations in organic synthesis. Modification of the organometallic compounds by chiral, nonracemic auxiliaries offers a general opportunity to create optically active alcohols, and the catalytic version in particular provides maximum synthetic efficiency. The use of organozinc chemistry, unlike conventional organolithium or -magnesium chemistry, has realized an ideal catalytic enantioselective alkylation of aldehydes leading to a diverse array of secondary alcohols of high optical purity. A combination of dialkylzinc compounds and certain sterically constrained β-dialkylamino alcohols, such as (-)-3-exo-dimethylaminoiso- borneol [(-)-DAIB], as chiral inducers affords the best result (up to 99% ee). The alkyl transfer reaction occurs via a dinuclear Zn complex containing a chiral amino alkoxide, an aldehyde ligand, and three alkyl groups. The chiral multiplication method exhibits enormous chiral amplification: a high level of enantioselection (up to 98%) is attainable by use of DAIB in 14% ee. This unusual nonlinear effect is a result of a marked difference in chemical properties of the diastereomeric (homochiral and heterochiral) dinuclear complexes formed from the dialkylzinc and the DAIB auxiliary. This phenomenon may be the beginning of a new generation of enantioselective organic reactions.
    Additional Material: 19 Ill.
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  • 42
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 1531-1546 
    ISSN: 0570-0833
    Keywords: Amino acids ; Asymmetric synthesis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: α-Amino acids protected at nitrogen in quite different ways can be transformed without racemization into the corresponding α-amino aldehydes. Provided one chooses the right protecting groups (e.g., two benzyl residues on nitrogen) it is possible for the first time to carry out Grignard-like, aldol, and Me3SiCN additions, and hetero-Diels-Alder reactions with a high degree of nonchelation control. If the reactions of classical carbanions turn out to be nonselective, transmetalation, for example into organotitanium reagents, constitutes an important tool in controlling stereoselectivity. Diastereoselectivity can be reversed by specific variation of the protecting group and reagent. “Protecting-group tuning”, “metal tuning”, and “ligand tuning” are very useful in reactions of α-amino aldimines as well. The α-amino aldehydes can also be converted by Wittig reactions into electron-poor γ-amino olefins, which in turn undergo stereoselective cuprate, Michael, and cycloadditions.
    Additional Material: 3 Ill.
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  • 43
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Retro reactions ; Computer chemistry ; Nobel lecture ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 44
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 1387-1416 
    ISSN: 0570-0833
    Keywords: Calicheamicins ; Synthetic methods ; Antitumor agents ; Antibiotics ; Enediynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel, biologically active substances from nature often provide excitement, stimulation, challenges, and opportunities for the scientific and medical communities. Experience and wisdom dictate investigation of their chemistry and pursuit of their chemical synthesis for more often than not, the rewards for both chemistry and medicine are great. The enediyne anticancer antibiotics are a rapidly emerging class of such compounds derived from bacterial sources. Combining unprecedented and highly unusual molecular architecture, phenomenal biological activities and fascinating modes of action, these DNA cleaving compounds burst onto the scene in the latter half of the 1980s when their structures became known, and they rapidly moved to center stage. Today the enediyne family includes the neocarzinostatin chromophore, the calicheamicins, the esperamicins, and the dynemicins, and soon the number of family members is certain to increase. These molecules elicited extensive research activities in chemical, biological, and biomedical circles and inspired the design of a number of novel molecular assemblies to probe and mimic their chemical and biological actions. A new body of synthetic technology and several novel synthetic strategies have already been devised to address the challenges posed by these molecules, and several new DNA cleaving agents have been designed and synthesized. This article summarizes the chemistry and biology of the enediynes and discusses mechanistic, synthetic, molecular design, and DNA cleavage aspects associated with the field.
    Additional Material: 19 Ill.
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  • 45
    ISSN: 0570-0833
    Keywords: Arene ligands ; Intermediates ; Cocondensation ; Sandwich complexes ; Synthetic methods ; Iron ; Metal atoms ; Cobalt ; Nickel ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In 1969, P. L. Timms reported the first preparative cocondensation reactions of metal vapors with organic and inorganic substrates. The use of this technique in preparative chemistry soon spread rapidly, but in recent years there has been less activity in this sector. If metal atom reactions are not utilized primarily for the formation of new products, but for the synthesis of highly reactive intermediates, a new synthetic strategy may be developed. Our aims are reaction sequences which, based on an effective cocondensation reaction, lead gradually and selectively to new substance classes. This principle can be illustrated by the example of the cocondensation products of arenes and iron, cobalt, or nickel vapor, which decompose between -70 and -50°C. The classes of products accessible by this method extend from clusters, through π-complexes, organophosphorus and organoboron cage compounds to pure organic cycloaddition products.
    Additional Material: 13 Ill.
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  • 46
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 609-626 
    ISSN: 0570-0833
    Keywords: Oxy-Cope rearrangement ; Ring expansion ; Cope rearrangement ; Diastereoselectivity ; Rearrangement ; Ketones ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Convergency is a highly serviceable aspect of organic synthesis, particularly when its application is accompanied by high levels of chirality transfer and regiocontrol. A reaction that is notably well suited to these objectives is the oxy-Cope rearrangement. In addition, the benefits that can accrue from suitable condensation of β γ-unsaturated ketones with a vinyl organometallic and subsequent [3,3] sigmatropic shift are substantive enhancement in structural complexity and the ability to generate a myriad of polycyclic frameworks. Another profitable feature is the complementary regeneration of the carbonyl group in a new structural context. In view of the pivotal role played by the carbonyl functionality in synthetic transformations, reacquisition of such a reaction site translates into heightened chemical versatility. The trajectories followed by vinyl organometallics as they engage in 1,2 addition to ketones are gradually being understood. Proper diastereoselective control of this bond-making process, when coupled with full awareness of the chair or boat topography adopted during the ensuing oxy-Cope electronic reorganization, provides for exciting new strategy-level dimensions not often available in other contexts. The use of this two-step sequence as a prelude to a third chemical event clearly serves to expand the possibilities for molecular construction still more. While a considerable amount of the work to date has focused on the preparation of rather elaborate carbocyclic molecules, principally with a view to gaining access to complex natural products, the possibilities for heterocyclic synthesis are currently being accorded increased attention.
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  • 47
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 1320-1367 
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Future of chemistry ; Chemistry today ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This review article is an attempt to sketch the important developments in organic synthesis during the past 25 years, and to project them into the future. - The primary motivations that once induced chemists to undertake natural product syntheses no longer exist. Instead of target structures themselves, molecular function and activity now occupy center stage. Thus, inhibitors with an affinity for all the important natural enzymes and receptors have moved to the fore as potential synthetic targets. - New synthetic methods are most likely to be encountered in the fields of biological and organometallic chemistry. Enzymes, whole organisms, and cell cultures for enan-tioselective synthesis of specific substances have already been incorporated into the synthetic arsenals of both research laboratories and industry. In addition, designing appropriate analogues to transition states and intermediates should soon make it possible, with the aid of the mammalian immune system and gene technology, to prepare catalytically active monoclonal antibodies for almost any reaction; perhaps, more important, such processes will increasingly come to be applied on an industrial scale.-The discovery of truly new reactions is likely to be limited to the realm of transition-metal organic chemistry, which will almost certainly provide us with additional “miracle reagents” in the years to come. As regards main group elements (“organoelemental chemistry”), we can surely anticipate further stepwise improvements in experimental procedures and the broader application of special techniques, leading to undreamed of efficiency and selectivity with respect to known procedures. The primary center of attention for all synthetic methods will continue to shift toward catalytic and enantioselective variants; indeed, it will not be long before such modifications will be available with every standard reaction for converting achiral educts into chiral products. Analysis, spectroscopy, structure determination, theory, and electronic data processing have all become indispensable in organic synthesis. Only with the aid of these “tools” will the methods of organic chemistry permit selective syntheses of ever larger and more complex systems on both the molecular and supramolecular levels. - Examples have been introduced throughout this discourse to illustrate its many themes, and a very comprehensive bibliography should help the interested reader become more familiar with important keywords and authors.[The list of references is also available upon request in the form of a Microsoft Word© file on diskette.] - This article will have served its intended purpose if it changes the minds of some of those who claim organic chemistry is a mature science, and if it causes students to discover the vitality and forcefulness with which organic synthesis is meeting new challenges and attempting to fulfill old dreams.Er zeigt uns so in seinem wissenschaftlichen Leben, daß die Chemie nicht von einer Theorie, nicht von einer Methode aus zu erschöpfen ist, und daß Erkenntnis und Nutzen in ihr untrennbar verwoben sind.“He showed us through his scientific life that chemistry cannot be exploited fully with the aid of a single theory or a single methodology, and that it is a field in which knowledge and application are inextricably linked.” G. Bugge: Das Buch der großen Chemiker, Vol. 2, 4th reprint, Verlag Chemie, Weinheim 1974.R. Koch, writing about Louis Pasteur
    Additional Material: 14 Ill.
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  • 48
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 977-991 
    ISSN: 0570-0833
    Keywords: Biaryls ; Arenes ; Synthetic methods ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and utilization of specific biaryl systems, particularly those which suffer hindered rotation, is a demanding goal not only in the synthesis of natural products and Pharmaceuticals, but also for example in the discovery of new reagents for asymmetric synthesis. This article will attempt to provide a topical review of modern, efficient processes for the specific preparation of biaryls. This appears to be of particular urgency, since, under the pressure of continually increasing demand, a wealth of new or modified synthetic approaches to the ever more important biaryl systems has been realized in recent years. The high standard which has been reached in this field is impressively demonstrated by regio- and stereoselective syntheses of important biaryl natural products such as steganone, ancistrocladine, ancistrocladisine, and dioncophylline A. Besides the utilization of asymmetric induction in the actual coupling step, the thermodynamically or kinetically controlled torsion of biaryl axes belongs to the most important concepts discussed.
    Additional Material: 2 Ill.
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  • 49
    ISSN: 0570-0833
    Keywords: Cyclization ; Dialdehydes ; Nitromethane ; Carbohydrates ; Polyalcohols ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Condensation of nitromethane with suitable diadehydes in alkaline medium provides a general method of cyclization, in which the methyl group of the nitromethane is incorporated into the ring. This method leads to 5-, 6-, and 7-membered rings and is equally applicable to aliphatic, aromatic, and sugar dialdehydes. For example, glyoxal is converted into 1,4-dideoxy-1,4-dinitro-neo-inositol, and glutaraldehyde into trans-2-nitrocyclohexane-1,3-diol, while the corresponding cyclization of xylo-trihydroxyglutaraldehyde leads to deoxy-nitroinositols having the scyllo, myo-1, and muco-3 configurations.-In the case of aromatic dialdehydes, the cyclization is accompanied by elimination of water. Thus, phthalaldehyde, naphthalene-2,3-dicarboxaldehyde, and homophthalaldehyde yield, respectively, 2-nitroindenol, 2-nitrobenzindenol, and 2-nitronaphthalene. -Application of the method to sugar dialdehydes (aldehydic diglycol derivatives of monosaccharides formed by periodate oxidation) constitutes an excellent synthesis of 3-amino sugars, since 3-deoxy-3-nitropyranoses are formed smoothly on cyclization, and the corresponding 3-amino derivatives are obtained by hydrogenation. Thus, the reaction sequence: periodate oxidation → cyclization with nitromethane → hydrogenation, leads in the case of α-and β-D-pentosides to 3-amino-3-deoxy-D-and-L-pentosides, respectively, with ribo, xylo, and arabino configurations. α-D-hexosides give derivatives with gluco, manno, and galacto configurations. 3-Amino-3,6-dideoxyglucosides of the D-and L-series are obtained from 6-deoxy-D-or-L-hexosides, respectively, and 3-aminohexosans with gulo, ido, and altro configurations are obtained from 1,6-anhydro sugars. Cyclization of the dialdehydes obtained from sedoheptulose and methyl 4,6-O-ethylidene-α-D-glucoside by periodate oxidation, leads to 3-nitro and, after hydrogenation, to 3-amino derivatives of 3-deoxyheptopyranoses.
    Type of Medium: Electronic Resource
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  • 50
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 250-260 
    ISSN: 0570-0833
    Keywords: Unsaturated fatty acids ; Fatty acids ; Carbonyl olefination ; Synthetic methods ; Wittig reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that carbonyl olefination, i.e. the reaction of carbonyl compounds with alkylidene phosphoranes, can be sterically controlled. In some cases cis-olefins can be obtained by proper choice of the reaction conditions; trans-olefins are formed only in the presence of suitable structural factors. These cis-and trans-olefination reactions have opened new, stereo-specific routes to unsaturated and polyunsaturated fatty acids with differing positions and sequences of cis- and trans-double bonds and to ω-hydroxy and branched chain fatty acids.
    Additional Material: 2 Tab.
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  • 51
    ISSN: 0570-0833
    Keywords: Quinones ; Quinones ; Michael addition ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: If catechol or other hydroquinones are dehydrogenated in the presence of a nucleophilic reagent, the latter reacts, usually by Michael addition, with the quinone formed in situ. The wide range of possible variations offered by this synthetic method is comprehensively described in the present paper. procedures are given for carrying out typical reactions.
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  • 52
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 24-29 
    ISSN: 0570-0833
    Keywords: 3-Aminoquinazol-4-one ; 3-Aminobenzotriazin-4-one ; Quinazolones ; Benzotriazinones ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Among the derivatives of 3-aminoquinazol-4-one and 3-aminobenzotriazin-4-one are compounds with narcotic, sedative, analgetic, and muscle-relaxant properties. Of special interest are compounds with one or several urethane groups and those substituted in the 3-position by a morpholine moiety.
    Additional Material: 4 Tab.
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  • 53
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 225-238 
    ISSN: 0570-0833
    Keywords: Pyridinium salts ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This review discusses syntheses leading to a new type of N-vinylpyridinium salts, to novel anionocyanines, to aminophenazines and alloxazines, as well as to (aza-) dehydroquinolizinium, acridizinium, and morphanthridizinium salts. In addition, Mannich reactions and aminoalkylations at active methylene groups of cycloimmonium salts, and their reactions with amines are treated. The possibilities offered by the “Ortoleva-King” reaction are demonstrated using numerous examples, such as a new route leading to the yohimbine skeleton.
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  • 54
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 309-323 
    ISSN: 0570-0833
    Keywords: s-Triazines ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and properties of s-triazine are discussed. Nucleophilic reagents (even water) readily attack s-triazine. Thus, open-chain and heterocyclic compounds, e.g. formamidines, aminomethylene compounds, and triazole, pyridine, and pyrimidine deravatives are accessible from s-triazine. With amidines and imido ethers substituted triazines are obtained (by trans-triazination).The latter are formed via open-chain intermediates.
    Additional Material: 11 Tab.
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  • 55
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 380-393 
    ISSN: 0570-0833
    Keywords: Pyridinium salts ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cleavage of N-phenylpyridinium or N-vinylpyridinium salts with secondary aliphatic amines leads to aromatic amino compounds or enamines which are often unobtainable by other routes. The other fragment, glutacondialdehyde or its monoanil, gives azulenes, as shown by Ziegler and Hafner, as well as König; these compounds can also be prepared from alkylpyridinium salts with cyclopentadienylsodium (Hafner). Syntheses of labile aldehydes which are otherwise difficult to obtain and of α-ketocarboxylic acids, starting from pyridinium salts and proceeding via nitrones or α-cyanoanils, are illustrated by many new examples. Benzimidazoles, benzothiazoles, and amidines are accessible from pyridinium salts via nitrones or α-cyanoanils; cyanoanils can be transformed into quinoxalines (including xanthopterine), perimidines, etc. Furthermore, nitrosonaphthols and nitrosonaphthylamines react with pyridinium salts containing an active methylene group on the nitrogen, leading to new ring systems. Further synthetic possibilities arise from nucleophilic displacements of the pyridine in pyridinium salts by SN 2 reactions. Combination of the route via nitrones with the methods of Arndt-Eistert, Ortoleva-King, or with chloromethylation constitutes a significant enlargement of its range of application. The formation of α-cyanoanils from diazoketones permits synthesis of α-keto-β-amino acids from α-amino acids, or of phenylglyoxylic acids from benzoic acids by chain extension.
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  • 56
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 1 (1962), S. 8-21 
    ISSN: 0570-0833
    Keywords: Addition ; Immonium ions ; Isocyanides ; Amino acids ; Synthetic methods ; Alkylidene ammonium ions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The α-addition of immonium ions and anions (OH-, SeH-, S2O3 2-, N3- NCO- NCS-, R—CO2 -, RO—CO2-) to isonitriles, accompanied by secondary reactions provides a means for the one-stage synthesis of organic nitrogen compounds starting with two to five different components. Thus, by the condensations of amines (ammonia, primary, and secondary aliphatic and aromatic amines, hydrazines) and aldehydes or ketones with isonitriles and acids, a number of α-aminocarboxylic acid amides, thioamides, selenoamides, 1,5-disubstituted retrazoles, hydantoin imides, thiohydantoin imides, α-acylamino carboxylic acid amides, oligopeptide derivatives, β-lactams, derivatives of penicillanic acid, urethanes, diacylimides, and various hydrazine derivatives, can be prepared. The reactions are easily carried out and take place under mild conditions. Yields of more than 90% are frequently encountered.
    Additional Material: 4 Tab.
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  • 57
    ISSN: 0570-0833
    Keywords: Amides ; Azolides ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 58
    ISSN: 0570-0833
    Keywords: Michael addition ; Pyridinium salts ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By Michael addition of the active methylene groups in pyridinium salts onto suitable acceptor compounds, α-pyridones, substituted pyridines, particularly pyridinecarboxylic acids and pyridylpyridines, including the minor alkaloid of tobacco nicotelline and annelized pyridines, can be prepared by a simple procedure and generally in good yields. From the Michael adducts, polycyclic aromatic hydrocarbons, e.g. substituted fluoranthenes and “bisfluoranthenes” can be prepared; internal Michael addition leads to pyrrolinopyrdinium salts. For example, Michael addition of pyridinium salts onto quinones gives phenacyl substituted quinones, from which benzofurans and cinnolines can be readily obtained.
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