Synthesis of 3-Silylated 3-Sulfolenes from Propargylsilanes and their Reductive Desulfitation

Protonation of propargylsilanes induces 1,2-silyl group shift and provides 2-silylated dienes. If this reaction is performed in liquid SO2, the diene formation is followed by instant cheletropic SO2 addition, and 3-silylated 3-sulfolenes are obtained. Liquid SO2 as polar and Lewis acidic reaction medium makes it possible to use relatively weak Bronsted acid catalysts such as H2O and benzoic acid. Depending on the starting material, reductive desulfitation of 3-silylated 3-sulfolenes provides vinyl, allyl, or aliphatic silanes.