Asymmetric Synthesis of Hydroindoles via Desymmetrizing [3+2] Annulation of p-Quinamines and Arylalkylketenes.

The asymmetric desymmetrizing [3+2] annulation reaction of p-quinamines and arylalkylketenes to synthesize hydroindoles was realized. Catalyzed by chiral bisguanidinium hemisalt via multiple hydrogen bond interactions, enantiomerically enriched products with reversal of diastereoselectivity in comparison with the racemic version were afforded in good yields under mild reaction conditions. Diaryl-substituted hydroindoles could also perform the Friedel-Crafts type of addition to give more complicated multicycles. Density functional theory calculations revealed that the enantio- and diastereoselectivity stem from varied hydrogen-bonding manners.