Rh(III)-catalyzed annulation of azobenzenes and α-Cl ketones toward 3-acyl-2H-indazoles

Rhodium(III)-catalyzed [4 + 1] cyclization of azobenzenes with α-Cl ketones has been developed. 3-Acyl-2H-indazoles could be easily obtained in up to 97% yields for more than 30 examples. Easily available azobenzenes and α-Cl ketones allow the reaction to proceed smoothly under the mild reaction conditions with excellent yields and large functional groups tolerance.