Stereospecific formation of a vinyl sulphide via a sulphonium ylide–salt coupling reaction

Abstract

The identification of tetramethyl 1 -(methylthio)hexa-1,5-diene-2,3,4,5-tetracarboxylate (X), formed in low yield during attempted oxidation of dimethyl α-(bromomethyl)fumarate (IV) by dimethyl sulphoxide in the presence of a weak base, is described. It is shown that the production of the vinyl sulphide (X) under these conditions takes place via the intermediate (2,3-bismethoxycarbonylprop-2-enyl)dimethylsulphonium bromide (XIV), which undergoes a stereospecific Michael addition reaction with the derived sulphonium ylide (XX).