Asymmetric [3 + 3] cycloaddition of cinnamaldehyde-derived N -aryl nitrones with 2-indolemethanols enabled by chiral phosphoric acid.

We described a chiral phosphoric acid (CPA) catalyzed asymmetric [3 + 3] cycloaddition of cinnamaldehyde-derived N -aryl nitrones with 2-indolylmethanols to prepare various indole-fused 1,2-oxazines in high yields (up to 96%) with excellent enantioselectivity (>99% ee). Control experiments indicate that hydrogen bonding plays important roles in controlling the enantioselectivity of products. This strategy provides an efficient pathway to construct enantioenriched indole-fused 1,2-oxazines from N -aryl nitrones with 2-indolylmethanols.