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).