Catalytic Enantioselective Synthesis of 3,4-Unsubstituted Thiochromenes through Sulfa-Michael/Julia–Kocienski Olefination Cascade Reaction

A highly enantioselective cascade sulfa-Michael/Julia–Kocienski olefination reaction between 2-mercaptobenzaldehydes and β-substituted vinyl PT-sulfones has been realized for the synthesis of 3,4-unsubstituted 2H-thiochromenes. This reaction, catalyzed by diphenylprolinol TMS ether, proceeds through an aromatic iminium intermediate and furnishes a wide range of 2-substiuted 2H-thiochromenes with excellent enantioselectivities (up to 99:1 er).