Substituent-Promoted Thio-Belluš–Claisen Rearrangement with Difluoroketene

The thio-Belluš-Claisen rearrangement with difluoroketene is reported herein. By resorting to fluoride-initiated desilylative β-elimination of difluorobromoacetylsilane, a new protocol that enables controlled release of the unstable difluoroketene and its efficient capture by allyl thioether for the ensuing rearrangement is successfully developed. The presence of an electron-withdrawing group on the internal alkene site of allyl thioether is proven to be vital for this reaction by promoting the rearrangement through charge stabilization in the transition state.