Tosyl Hydrazine‐Promoted Tandem Condensation and Cyclization of Acyl Azobenzenes Enabling Access to 2H‐Indazoles under Metal‐Free Aerobic Conditions

Tosyl hydrazine‐promoted tandem condensation and cyclization of 2‐acyl azobenzenes under metal‐free aerobic conditions was demonstrated to give 2‐aryl‐2H‐indazoles having alkyl‐ or aryl groups at the 3‐position in quantitative yields through the release of water, molecular nitrogen, and sulfinic acid. All of the examples produced the corresponding 2H‐indazoles in quantitative yields. The present reaction was determined to have a wide substrate scope and good functional group tolerance.