Polarized ketene dithioacetals. 28. A new general highly stereoselective and regiospecific method for homologation of ketones to .alpha.,.beta.-unsaturated esters via .alpha.-oxoketene dithioacetals
A new silyl ketene dithioacetal, 1, 1-bis(methylthio)-2-trimethylsilylethene, was synthesized by the reaction of the enolate of methyl trimethylsilylmethyldithiocarboxylate, which was prepared by treating trimethylsilylmethylmagnesium chloride with carbon disulfide followed by successive treatment with methyl iodide and then lithium diisopropylamide in ether combined with methyl iodide. The silyl ketene dithioacetal, which can be viewed as a vinylsilane, reacted with substituted benzaldehydes in the presence of a Lewis acid to give the corresponding allylic alcohols.