Catalytic Asymmetric [4+2] Cyclization of para‐Quinone Methide Derivatives with 3‐Alkyl‐2‐vinylindoles

A catalytic asymmetric [4+2] cyclization of para‐quinone methide (p‐QM) derivatives with 3‐alkyl‐2‐vinylindoles in the presence of a chiral phosphoric acid has been established, and this method provides chiral chroman frameworks in good yields (up to 98%) with high diastereoselectivities (up to >95:5 dr) and excellent enantioselectivities (up to 96% ee). This reaction represents the first catalytic asymmetric [4+2] cyclization of p‐QM derivatives with electron‐rich alkenes, which will enrich the field of catalytic asymmetric reactions of p‐QM derivatives. In addition, this catalytic asymmetric cyclization was successfully applied to 3‐alkyl‐2‐vinylindoles. More importantly, this reaction will offer a useful method for the construction of enantioenriched chroman frameworks.