2-Phenylthio-3-bromopropene, A Valuable Synthon, Easily Prepared by a Simple Rearrangement

Treatment of allyl phenyl sulfide with bromine, followed by aqueous sodium hydroxide, provides a good yield of 2-phenylthio-3-bromopropene 2 via a mechanism that is elucidated by isolation of the 1,3-dibromo-2-(phenylthio)propene intermediate 7. Three uses of 2 as an annulating agent for cycloheptanone are illustrated, demonstrating that this reagent is a synthetic equivalent of acetonyl halide and an α-halo vinyllithium. It is also readily converted to the useful synthons 2,3-bis(phenylthio)propene 16 and 2-phenylthio-3-(phenylsulfonyl)propene 17.