Rhodium(III)-Catalyzed Indazole Synthesis by C–H Bond Functionalization and Cyclative Capture

An efficient, one-step, and highly functional group-compatible synthesis of substituted <i>N</i>-aryl-2<i>H</i>-indazoles is reported via the rhodium­(III)-catalyzed C–H bond addition of azobenzenes to aldehydes. The regioselective coupling of unsymmetrical azobenzenes was further demonstrated and led to the development of a new removable aryl group that allows for the preparation of indazoles without <i>N</i>-substitution. The 2-aryl-2<i>H</i>-indazole products also represent a new class of readily prepared fluorophores for which initial spectroscopic characterization has been performed