Catalytic Asymmetric Addition of Aldehydes to Oxocarbenium Ions: A Dual Catalytic System for the Synthesis of Chromenes

A synergistic catalytic system for the first asymmetric addition of aldehydes to in situ generated prochiral oxocarbenium ions has been developed. The dual catalytic protocol allows the simultaneous activation of both electrophile and nucleophile and provides access to a variety of valuable chiral 2H-chromenes with excellent enantioselectivities.