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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 437-439 
    ISSN: 0947-3440
    Keywords: Tinospora sinensis ; Menispermaceae ; Tinosineside A and B ; Dinorditerpene glucosides ; Terpenes ; Glucosides ; Carbohydrates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new dinorditerpene glucosides, tinosineside A (1) and B (2-O-acetyltinosineside A, 2), were isolated from the fresh stems of Tinospora sinensis Merr. (Menispermaceae). Their structures were established on the basis of chemical and spectroscopic findings.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 509-514 
    ISSN: 0947-3440
    Keywords: Pyrroles ; Polypyrrol ; p-Chloranil ; p-Bromanil ; p-Fluoranil ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the reaction of pyrroles with tetrahalo-1,4-benzoquinones two different processes occur: the oxidation of pyrrole and the coupling reaction to 3,5,6-trihalo-2-(pyrrol-2-yl)-1,4-benzoquinones. Excess of pyrrole results in doped polypyrrole as the principal reaction product. Excess of tetrahalobenzoquinone and dilution, provides the title compounds. The UV/Vis spectra and the electrochemical behaviour show that the title compounds have the HOMO localized at the pyrrole and the LUMO at the quinone ring.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 537-543 
    ISSN: 0947-3440
    Keywords: Pyrrole-2,3-diones ; Nucleophilic addition ; Substituent effects ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 1H-pyrrole-2,3-diones 2a-i with N- and O-nucleophiles proceed by initial attack at C-2 or/and C-5. Consequently, earlier results suggesting structures of type A (attack at C-3) have to be revised (5, 13, 17, 18b). In general, electron-withdrawing substituents at C-4 favor attack at C-5 with formation of 2-pyrrolones 5, 6, 10, 13, 17, and 20. Alternatively, attack at C-2 leads to α-oxobutenoic acid derivatives 3, 7, 11, 12, 15, and 18. IR and 13C-NMR spectroscopic techniques were employed to differentiate between the possible isomeric addition products formed. The structure of methyl α-oxobutenoate 15 was established by an X-ray crystallo-graphic analysis.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 551-558 
    ISSN: 0947-3440
    Keywords: Apionucleosides ; Nucleosides ; Antiviral agents ; Tris(trimethylsilyl)silane ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Convenient Route to D-Apio-β-D-furanosyl- and 2′-Deoxyapio-β-D-furanosyl Nucleosides2,3-O-Isopropylidene-D-apio-β-D-furanose (1), available in 40% overall yield by modified literature procedures, is acylated regioselectively to the new 3′-O-benzoyl-derivative 2. This is converted to the anomeric triacetates 4 (β-4; α-4 = 1.8:1) by cleavage of the isopropylidene protecting group from 2 followed by peracetylation. Reaction of compounds 4 with silylated nucleobases and subsequent deprotection gives the D-apio-β-D-furanosyl nucleosides 8-10 in good yields. Regioselective hydrazinolysis of the protected nucleosides 5 and 6 affords the 2′-hydroxy-derivatives 11 and 12, respectively, which are converted to the 2′-deoxyapio-β-D-furanosyl nucleosides 17 and 18, respectively, via deoxygenation of the corresponding thionocarbonates 13 and 14 with tris(trimethylsilyl)silane and subsequent deprotection. The 2′-deoxyapio-β-D-furanosyl cytosine 20 is prepared from the 2′-deoxyapio-β-D-furanosyl uracil derivative 16.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 583-586 
    ISSN: 0947-3440
    Keywords: tert-Trifluoromethyl carbinols ; Trifluoromethyl oxiranes ; Phase transfer catalysis ; Ruthenium tetraoxide oxidation ; Hydroxy acids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the novel β-hydroxy acid 3 in six steps is described, starting from the commercially available trifluoromethyl ketone 6.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 19-27 
    ISSN: 0947-3440
    Keywords: Photochemistry ; Epoxides ; Carbonyl ylides ; Cycloaddition, intramolecular ; Spiro ketals ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photocyclization reactions of δ-hydroxybutyl α,β-unsaturated γ,δ-epoxy nitriles 4a, b at 254 nm lead to spiro ketals 5a, b and 6a, b arising from the carbonyl ylide intermediate A. The spiro ketal 6b containing an endocyclic double bond is transformed to spiro ether 16 by an acid-catalyzed 1,3-sigmatropic rearrangement. The ratio of spiro ketals 5 and 6 has been shown to depend on solvent polarity and acidity of additives. Application to the synthesis of pheromones is presented. X-ray crystal structure analyses are performed on dispiro compound 18 and spiro ester 25.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 29-40 
    ISSN: 0947-3440
    Keywords: Vinyl anions ; Umpolung ; Bromine-lithium exchange ; Retro-1,4-Brook rearrangement ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Non-chelate control is found to be the favored stereochemical outcome in the addition of the 1-bromo-1-lithio-1-alkenes 2b and (S)-5b to O-protected lactaldehydes (S)-1. Thus diastereoselectivities of 84 to 96% d.e. are reached in the formation of alcohols 3 and 6, which are converted into the O-protected 2,3-dihydroxyaldehyde 31 or O-protected 1,2,3-triols 24 and 27. In an analogous way, a non-chelate-controlled addition of (R)-5b to (R)-3-(benzyloxy)butyraldehyde (14a) leads to the predominant formation of the diastereomer 15a (92% d.e. after enrichment by chromatography) which yields the alcohol 42a upon debromination, O-protection, and ozonolysis. Thus, the carbenoids 2b and 5b enable the introduction of the synthons -CH2OH and -CHO into enantiomerically pure aldehydes (S)-1 and (R)-14 in a highly stereoselective manner. Relatively low diastereoselectivities are reached in the „mismatched“ combination of (R)-5b with (S)-1 as well as (S)-5b with (R)-14. The dilithium compound 20b, generated at -78°C, reacts in a retro-1,4-Brook rearrangement at -20°C to give vinylsilane 44b after protonation.
    Additional Material: 1 Tab.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 53-66 
    ISSN: 0947-3440
    Keywords: Carbohydrates ; Saccharides ; Glycosyltransferases ; Trichloroacetimidates ; Transferases ; Enzymes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Building Units of Oligosaccharides, CIX.  -  Synthesis of Modified Oligosaccharides of N-Glycoproteins for Substrate Specificity Studies of N-Acetylglucosaminyltransferase IA series of modified derivatives of the trisaccharide octyl α-D-Man(1→3)-[α-D-Man(1→6)]-β-D-Man were synthesized for substrate specificity studies of N-acetylglucosaminyltransferase I (GlcNAc-T I). The hydroxyl groups at C-3, C-4 and C-6 of the α(1→3)-linked Mannose were replaced by hydrogen and methoxy groups. At the α(1→6)-linked mannose the hydroxyl group at C-2 was deoxygenated and the hydroxyl groups at C-3, C-4 and C-6 were replaced by methoxy groups. The syntheses of the ten trisaccharides were carried out by the interchangeable combination of modified building blocks. The trichloroacetimidate method was favourable for all glycosylation steps.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 41-51 
    ISSN: 0947-3440
    Keywords: Enthalpies of formation ; Geminal substituents, energetic interaction of ; Bond cleavage, C—C, kinetics of ; Radicals, stability of ; Increments, thermochemical ; Bond strength, substituent effects on ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituent Effects on the CC Bond Strength, 16.  -  Thermal Stability and Enthalpies of Formation of β-Dicarbonyl Compounds.  -  Stabilisation Enthalpies of α,α′-Diketoalkyl RadicalsThe geminal interactions of the two carbonyl groups in seven β-diketones of the type 8-9 and 11-13 were estimated from their enthalpies of formation, which were deduced from their heats of combustion and enthalpies of vaporization. The radical stabilisation enthalpies RSE of the α,α′-diketoalkyl radicals 9-13 were obtained from the enthalpies of activation ΔH≠ of thermal CC bond cleavage of eight model compounds of the type 9-13 by their comparison with ΔH≠ of comparable hydrocarbons of similar strain. For non-cyclic α,α′-diacyl-alkyl radicals and six-membered cyclic ones RSE = 54.8 ± 1.3 kJ mol-1 was determined, which indicates an additive stabilisation by two carbonyl groups.
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 637-644 
    ISSN: 0947-3440
    Keywords: Ethynylbenzene ; pyrolysis of ; Scavenging of radicals ; PAH formation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pyrolysis of ethynylbenzene (1) in helium was studied in a tubular flow reactor at 10.7 mbar/1030°C and reaction times ranging from 5 to 30 ms. Reactive intermediates such as radicals and carbenes were scavenged with dimethyl disulfide (DMDS), Qualitative and quantitative analysis of the scavenging products and of the stable pyrolysis products were carried out by GC-MS analysis. - The radicals phenyl (2a), o-, m-, and p-ethynylphenyl (1c, d, e), 2- and 1-phenyl-vinyl (1a, b) 1- and 2-naphthyl (3a, b), methyl, hydrogen atoms, and radicals resulting from the addition of phenyl and ethynylphenyl radicals to the triple bond of ethynylbenzene were detected. Carbenes, such as phenylvinylidene, occur only in small traces and obviously play no role in the overall pyrolysis. Concentration profiles of the radicals and of some important pyrolysis products are presented and discussed. Based on the detected radicals, a reaction scheme for the pyrolysis of ethynylbenzene is proposed. Results of pyrolyses of mixtures of ethynylbenzene and ethyne show that naphthalene (3), acenaphthylene (12), and other compounds are produced by a sequence of ethyne addition and cyclization reactions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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