Reaction of a,&unsaturated sulphoxides with trtfluoroacetic anhydri& gives a,j+bis(trifhwroacetoxy)thioethers in near-quantitative yields. Subsequent basic methanolysis gives monomeric and dimeric a-hydroxyaldehydes or ahydroxyketones, &pending on the nature of the 8-R group. The former undergo Wittig olefination with methoxycar~ny!methyle~~ip~~lp~sphorane to give rhy&oxy-a&unsaturated esters in high overall yiekis.
The electron-withdrawing nature of the sulphinyl group in a&unsaturated sulphoxides confers electrophilic character on the g-position of the adjacent carbon-carbon double bond. This reactivity has been exploited in both Michael' and Diels-Alder2 reactions of these readily available synthetic intermediates. In contrast, the sulphinyl oxygen atom in these systems is nucleophilic. Reaction at oxygen with an electmphile gives a highly reactive intermediate in which the g-position is activated by the positively-charged sulphur atom. g-Addition of a nucleophile then causes cleavage of the S-O bond to yield a sulphenium intermediate. Attack at the u-carbon by a second nucleophiles gives an a$-disubstituted thioether, the product of formal addition of two negativelycharged nucleophiles to a thioether a$-dication in an 'additive Pummerer reaction'.4 As part of a pqramme involving the development of new carbon-carbon and carbon-heteroatom bond-forming reactions of nucleophiles with electrophile-activated vinylic sulphoxides. we have looked at the interaction of simple, disubstituted vinylic sulphoxides with trifluoroacetic anhydride ('PAA). This Letter presents the results of these studies, and details some synthetically useful transformations of the intermediates accessible via these additive Pummerer reactions.