Asymmetric (4 + 2) Cyclization of γ-Substituted Propargyl Carboxylates with o-Quinone Methides Catalyzed by Chiral Tertiary Phosphine

An enantioselective (4 + 2) cycloaddition reaction of γ-aryl-substituted alkynyl carboxylates with ortho-quinone methides (o-QMs) was developed for the first time in the catalysis of (R,R)-DIPAMP. A series of chiral 4H-chromenes derivatives were available in good yields (62%-89% yield) and excellent enantioselectivities (up to 96% enantiomeric excess). Those obtained products could be further transformed to other derivatives.