Dithioacetals vinylsilane terminated cyclizations

Trost has reported the use of dithioacetals as initiators in vinylsilane-terminated cyclizations (Scheme 11). Reaction of the dimethyl thioketal (26) with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) led to the formation of the allylic sulfide (28) via a 2,3-sigmatropic rearrangement of the initially formed sulfonium salt (27a), which may have been catalyzed by complexation with excess DMTSF. 

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