The synthesis of 1,1-difluoro-1-alkenes was achieved by the treatment dithioesters and thioketones with trimethylsilyl 2-fluorosulfonyl-2,2-difluoroacetate in presence a proton sponge catalyst, namely, 1,8-bis(dimethylamino)naphthalene. generated electrophilic difluorocarbene (:CF2) reacted thiocarbonyl functionalities to form 2,2-difluorothiirane intermediates, desulfurization which afforded p...

A route to unsymmetrical polyene dialdehydes is described. The utility of these intermediates is illustrated by a synthesis of okenone. The stereochemistry assigned to methyl natural bixin has been confirmed by preparation of the cis-4 isomer. Support has been obtained for the cis-6 formulation of natural cis-crocetin. Oxidation of astacene with manganese dioxide yields violaxanthin. The synthe...

The regiodivergent ring contraction of diastereomeric 2-silyl-5,6-dihydro-6-aryl-(2H)-pyrans via [1,2]- and [1,4]-Wittig rearrangements to the corresponding α-silylcyclopentenols or (α-cyclopropyl)acylsilanes favor the [1,4]-pathway by ortho and para directing groups in the aromatic appendage and/or by sterically demanding silyl groups. The [1,2]-pathway is dominant with meta directing or elect...

α,β-Unsaturated esters are versatile building blocks for organic synthesis and of significant importance for industrial applications. A great variety of synthetic methods have been developed, and quite a number of them use aldehydes as precursors. Herein we report a chemo-enzymatic chain elongation approach to access α,β-unsaturated esters by combining an enzymatic carboxylic acid reduction and...

Combretastatin A-4 (CA4) is a potent anti-mitotic and vascular disrupting agent. Organic chemists have been working to optimize the synthesis of CA4 for past 3 decades, with methods requiring hazardous solvents harsh reaction conditions. Here, we report variety stilbenes in an aqueous Wittig system. Potassium carbonate or lithium hydroxide were used as base this give excellent yields mixtures E...