Palladium-Catalyzed Enantioselective Hydrosulfonylation of Vinylarenes

Transition-metal-catalyzed hydrofunctionalization of vinylarenes via a hydrometalation-nucleophilic trapping pathway is a particularly attractive yet challenging transformation in asymmetric catalysis. Herein we report a Pd-catalyzed enantioselective hydrosulfonylation of vinylarenes with sodium sulfinates in the presence of a Bro?nsted acid, providing rapid access to chiral benzylic sulfones. The reaction is initiated by stereoselective migratory insertion of Pd-H into the vinylarene, followed by isomerization from a s-benzylic-Pd species to an ?3-benzylic-Pd species, which then undergoes a pseudo-allylic substitution reaction with the nucleophilic sulfinate anion with stereoinversion to produce the chiral benzylic sulfone product. This mechanism was confirmed by experimental and computational studies, and the origin of the enantioselectivity was elucidated.