Search results for "Wittig reaction"
showing 10 items of 42 documents
Asymmetric Organocatalytic Wittig [2,3]-Rearrangement of Oxindoles
2016
A highly enantioselective organocatalytic [2,3]-rearrangement of oxindole derivatives is presented. The reaction was catalyzed by squaramide, and this provides access to 3-hydroxy 3-substituted oxindoles in high enantiomeric purities.
Designing Silylatedl-Amino Acids using a Wittig Strategy: Synthesis of Peptide Derivatives and18F-Labelling
2017
An efficient semisynthesis of silylated l-amino acids by reaction of silylated benzaldehydes with a phosphonium l-amino acid used as a Wittig reagent is described. The efficiency of the silylated l-amino acids in peptide synthesis was investigated by coupling both the carboxylic acid and the amino moiety with l-alanine and phenylalanine derivatives, respectively. The silylated derivatives were treated with KF or tetrabutylammonium fluoride to give the corresponding fluorosilyl derivatives without racemization. The hydrolysis of the fluorosilylated derivatives in phosphate buffer at pH 7.2 was checked. Finally, the 18F-labelling of di-tert-butylsilylated saturated and unsaturated dipeptides …
A Close Look to the Oxaphosphetane Formation along the Wittig Reaction: A [2+2] Cycloaddition?
2020
The Wittig reaction between triphenylphosphine methylide and benzaldehyde has been studied both from conceptual and computational approaches. The supernucleophilic character of ylide accounts for the feasibility of the initial nucleophilic attack. The nature of bonding driving the formation of the first oxaphosphetane (OPA) intermediate in such a domino reaction is examined within a topological-based bonding evolution theory perspective. The sequence of the electronic flow associated to the changes in electron density supports a rationalization via two main electronic stages characterizing the single kinetic step: first, the C-C bond formation, which takes place via donation of electron den…
ChemInform Abstract: Synthesis of (E)- and (Z)-29-Methylidyne-2,3-oxidosqualene Derivatives as Inhibitors of Liver and Yeast Oxidosqualene Cyclase.
2010
The synthesis of (E)- and (Z)-29-methylidyne-2,3-oxidosqualene derivatives is described starting from the C22 and C17 squalene aldehyde monobromohydrins. The conversion was achieved by means of a Wittig reaction, followed by desilylation of the terminal acetylene. For trisubstituted 1,3-enynes, preliminary alkylation with a suitable allyl bromide was performed. A new procedure for the synthesis of squalene aldehyde C27, C22 and C17 monobromohydrins is also described. Some of the new compounds behaved as inhibitors of pig liver and yeast oxidosqualene cyclase and were time-dependent inhibitors of the animal enzyme.
Synthesis of (E)- and (Z)-29-methylidyne-2,3-oxidosqualene derivatives as inhibitors of liver and yeast oxidosqualene cyclase
2002
The synthesis of (E)- and (Z)-29-methylidyne-2,3-oxidosqualene derivatives is described starting from the C22 and C17 squalene aldehyde monobromohydrins. The conversion was achieved by means of a Wittig reaction, followed by desilylation of the terminal acetylene. For trisubstituted 1,3-enynes, preliminary alkylation with a suitable allyl bromide was performed. A new procedure for the synthesis of squalene aldehyde C27, C22 and C17 monobromohydrins is also described. Some of the new compounds behaved as inhibitors of pig liver and yeast oxidosqualene cyclase and were time-dependent inhibitors of the animal enzyme.
Modular Hemisyntheses of Boronato- and Trifluoroborato-SubstitutedL-NHBoc Amino Acid and Peptide Derivatives
2013
Modular hemisyntheses of boronato- and trifluoroborato-substituted amino acid and peptide derivatives by using Wittig and C–H iridium-catalyzed borylation as key reactions, are described. Amino ester precursors bearing an aromatic moiety on a lateral chain were prepared by reaction of a new L-NHBoc-amino acid Wittig reagent with the corresponding aromatic aldehydes. After esterification and hydrogenation, the borylation of amino esters was achieved with yields up to 82 % by using the catalysed reaction of bis(pinacolato) diborane reagent (B2Pin2) in the presence of an iridium complex. Interestingly, this iridium-catalyzed borylation was also performed with a dipeptide in 78 % yield. Finally…
Synthesis of novel functionalized cispentacins through C–C oxidative cleavage of diendo-norbornene β-amino acid
2013
Difunctionalized cispentacin derivatives with two new stereogenic centres have been synthesized from a diendo-norbornene β-amino acid in a stereocontrolled route, involving C–C double bond functionalization by dihydroxylation, followed by oxidative ring cleavage and transformation of the dialdehyde intermediates through a Wittig reaction.
4-Alkenyl-1,2,3-thiadiazole
1986
Die Titelverbindungen 5 werden aus entsprechenden Alkylderivaten durch Bromierung/Dehydrobromierung (Weg A) oder durch Wittig-Reaktion (Weg B) dargestellt. Mit 4-Phenyl-4H-1,2,4-triazol-3,5-dion entstehen unter Erhaltung des Thiadiazolrings die Monoaddukte 12. 4-Alkenyl-1,2,3-thiadiazoles The title compounds 5 are prepared from the corresponding alkyl derivatives by bromination/dehydrobromination (route A) or by Wittig reaction (route B). 4-Phenyl-4H-1,2,4-triazole-3,5-dione yields the monoadducts 12 by maintenance of the thiadiazole ring.
Preparation of 9a-Fluorinated Sesquiterpenic Drimanes and Evaluation of Their Antifeedant Activities
2010
19 pages, figures, and tables statistics.
Stereoselective synthesis of unsaturated and functionalized L-NHBoc amino acids, using Wittig reaction under mild phase-transfer conditions.
2012
The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the γ-iodo NHBoc-amino ester, derived from L-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid-liquid phase-transfer conditions in chlorobenzene and in the presence of K(3)PO(4) as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with subs…