Mechanistic Investigation of a Synthetic Route to Biaryls by the Sigmatropic Rearrangement of Arylsulfonium Species

A comprehensive mechanistic investigation was conducted on the coupling reaction of aryl sulfoxides with phenols by means of trif luoroacetic anhydride to yield biaryls. NMR experiments revealed that our previously proposed mechanism, which consists of a cascade of an interrupted Pummerer reaction and a rate-determining [3, 3] sigmatropic rearrangement, is reasonable. The electronic ef fects of the substrates have also been evaluated to elucidate the nature of the rearrangement step. Based on experimental observations and theoretical calculations, w e conclude that the rearrangement is highly asynchronous and stepwise rather than concerted when electron-rich phenols are employed for the reaction.