The desilylation reaction of gamma-silylated allylic sulfones was found to proceed through gamma-silylated (E)-vinylic sulfones to afford the corresponding allylic sulfones by treatment with DBU and H2O. The Z/E ratio of the resulting allylic sulfories varied according to the gamma-substituents of the gamma-silylated sulfones. This stereochemical outcome was rationalized by "syn-effect".