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.