Enantio- and Diastereoselective, Lewis Base Catalyzed, Cascade Sulfenoacetalization of Alkenyl Aldehydes.

A catalytic, enantio-, and diastereoselective formation of sulfenyl acetals bearing multiple stereogenic centers is reported. Alkenyl aldehydes undergo a chiral thiiranium ion initiated cascade starting with intramolecular capture by a formyl group and termination by capture with HFIP solvent. This method provides a one-pot synthesis of dihydropyran and 1,3-disubstituted isochroman acetals in good to excellent yield and with high levels of diastereo- (up to >99:1 dr) and enantiocontrol (up to 99:1 er).