Catalytic, Enantioselective, Intramolecular Carbosulfenylation of Olefins. Preparative and Stereochemical Aspects

The first catalytic, enantio­selective, intra­molecular carbo­sulfenylation of isolated alkenes with aromatic nucleophiles is described. The combination of N-phenyl­sulfenyl­phthalimide, a chiral seleno­phosphoramide derived from BINAM, and ethane­sulfonic acid as a cocatalytic Brønsted acid induced an efficient and selective cyclo­functionalization of various alkenes (aliphatic and aromatic) tethered to a 3,4-methylene­di­oxy­phenyl ring. Under these conditions, 6-phenyl­thio-5,6,­7,8-tetra­hydro­naphthalenes are formed diastereo­specifically in good yields (50–92%) and high enantio­selectivities (71:29–97:3 er). E-Alkenes reacted much more rapidly and with much higher selectivity than Z-alkenes, whereas electron-rich alkenes reacted more rapidly but with comparable selectivity to electron-neutral alkenes and electron-deficient alkenes. The Brønsted acid played a critical role in effecting reproducible enantioselectivity. A model for the origin of enantioselectivity and the dependence of rate and selectivity on alkene structure is proposed along with a rationale for the site selectivity in reactions with mono­activated arene nucleophiles.