The desilylation reaction of γ-silylated allylic sulfones was found to proceed through γ- silylated (E)-vinylic sulfones to afford the corresponding allylic sulfones by treatment with DBU and H 2 O. The Z/E ratio of the resulting allylic sulfones varied according to the γ- substituents of the γ-silylated sulfones. This stereochemical outcome was rationalized by “syn-effect.”