Search results for "Wittig reaction"
showing 10 items of 42 documents
4,4′‐Distyrylazobenzol als Chromophor
1992
4,4′-Distyrylazobenzene as Chromophore 4,4′-Distyrylazobenzenes are prepared from 4,4′-dimethylazobenzene. Whereas the Siegrist method furnishes stereoselectively the (E,E,E) configuration, a Wittig olefination leads to a mixture of (Z,E,Z), (Z,E,E) and (E,E,E) isomers which can be easily separated. Irradiation of the intense absorption at λ ≈ 400 nm causes a selective (E) (Z) isomerization of the N = N bond of all three isomers. The reverse reaction takes part in the photochemical equilibration, moreover, it is a thermal process with a relatively low activation barrier.
Synthesis of (Z)-5-Decenol and (Z)-5-Decenyl Acetate, Components of the Sex Pheromones of a Variety of Lepidoptera.
2003
Two simple Wittig procedures for the synthesis of (Z)-5-decenol and (Z)-5-decenyl acetate based on the monoacetylation or monobromination of 1,5-pentanediol were followed.
Synthesis of (Z)-5-Decenol and (Z)-5-Decenyl Acetate, Components of the Sex Pheromones of a Variety of Lepidoptera
2003
Two simple Wittig procedures for the synthesis of (Z)-5-decenol and (Z)-5-decenyl acetate based on the monoacetylation or monobromination of 1,5-pentanediol were followed.
Synthesis of (±)-(E)-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid and the corresponding amide (“acacialactam”)
1994
Abstract The total synthesis of the title compounds in racemic form is described. Linalool was used as the starting material and transformed into the target molecules in 6 steps. The synthetic amide displays spectral properties identical to those reported for the natural compound acacialactam, indicating that the structure proposed for the latter compound is not correct.
Synthesis and Biological Evaluation of Combretastatin A-4 and Three Combretastatin-Based Hybrids
2012
The syntheses of combretastatin A-4 from gallic acid and of three combretastatin-based hybrids are described. Starting from commercial gallic acid, the phosphonium salt (3,4,5-trimethoxybenzylphosphonium bromide) is synthesized and coupled, through a Wittig reaction, with several aldehydes, including methoxymethyl-protected isovanillin, the aldehyde γ-bicyclohomofarnesal having a labdane skeleton, 3-(3-pyridyl) propanal, and furfural. The biological properties of the cis-coupled compounds as cytotoxic, antiviral and antifungal agents are also reported. In addition, pyrogallol, gallic and 3,4,5-trimethoxybenzoic acids have been studied biologically.
Synthesis of natural polyhydroxystilbenes
1986
Synthese en particulier de pinosylvine, isorhapontigenine, piceatannol et du methoxy-4 stilbenetetraol-3,3',5,5'
Hydrophobic Encapsulated Phosphonium Salts-Synthesis of Weakly Coordinating Cations and their Application in Wittig Reactions
2015
Large and rigid tetraarylphosphonium tetrafluoroborate salts have been synthesized representing weakly coordinating cations with diameters of several nanometers. Divergent dendritic growth by means of thermal Diels-Alder cycloaddition was employed for the construction of the hydrophobic polyphenylene framework up to the third generation. X-ray crystal structure analysis of first-generation phosphonium tetrafluoroborate supported the rigidity of the non-collapsible shell around the phosphorus center and gave insight into solid-state packing and cation-anion distances. Copper(I)-catalyzed azide-alkyne ligation served as reliable method for the preparation of a first-generation triazolylphenyl…
Introducing a 1,1-diphenylethylene analogue for vinylpyridine: anionic copolymerisation of 3-(1-phenylvinyl)pyridine (m-PyPE)
2021
3-(1-Phenylvinyl)pyridine (m-PyPE), prepared by Wittig reaction from the readily available 3-benzoylpyridine, represents a structural analog of 1,1-diphenylethylene (DPE), one phenyl group being replaced by pyridine. The suitability of m-PyPE for the copolymerisation with vinylpyridine is reflected by the 13C NMR shifts of the β-carbon of 2-vinylpyridine (2-VP; 118.32 ppm) and m-PyPE (115.83 ppm, measured in CDCl3), which possess predictive character for carbanionic copolymerisation. In analogy to DPE and its manifold reported derivatives, carbanionic homopolymerisation of m-PyPE was not possible, due to its steric bulk. Copolymers of 2-VP and m-PyPE with varied composition have been synthe…
Tris[oligo(1,4-phenylenevinylene)]methylium Dyes
2009
The tris[oligo(1,4-phenylenevinylene)]carbinols 2a–f (n =1–4) and the tris(4-styrylphenyl)methanes 7a,b have been prepared by Wittig–Horner (3 + 4a–f 2a–f) and Siegristreactions (5 + 6a,b 7a,b). The Wittig–Horner reactions in these examples are accompanied by an autoxidation, whereas a reduction occurs in the Siegrist reactions. Compound 2a, the lowest member (n = 1) of the series 2a–d with terminal dialkylamino groups, generates first, on treatment with acids, the methylium dye 2′a, which absorbs far into the NIR region (λmax = 1100 nm). The higher members 2b,c (n = 2,3) of the carbinol series yield by acidic treatment only N-protonated methylium dyes 2″′b,c. The different behavior is due …
Synthesis of Tetrastilbenylmethanes by Wittig−Horner Reactions
2004
The all-(E)-configured tetrastilbenylmethanes 3a−e and 5a,b can be obtained by fourfold Wittig−Horner reactions. The tetrahedral arrangement of these compounds guarantees independent stilbenoid chromophores with a high chromophore density. Apart from (E)/(Z) isomerization reactions, irradiation leads to a three-dimensional network with isolated unchanged stilbene units. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)