α-Amidino Rhodium Carbenes: Key Intermediates for the Preparation of (E)-2-Aminomethylene-3-oxoindoles and Pyranoindoles

Rhodium-catalyzed reactions of 3-diazoindolin-2-imines with aromatic aldehydes and α,β-unsaturated aldehydes respectively furnished (E)-2-aminomethylene-3-oxoindoles and pyranoindoles in moderate to excellent yields with nice functional group tolerance. The reaction proceeds in a cascade involving α-amidino rhodium carbene as the key intermediate.