Synthesis of 1H-indazoles by an electrochemical radical Csp2–H/N–H cyclization of arylhydrazones

The development of efficient and sustainable C–N bond-forming reactions to N-heterocyclic frameworks has been a long-standing interest in organic synthesis. In this work, we develop an electrochemical radical Csp2–H/N–H cyclization of arylhydrazones to 1H-indazoles. The electrochemical anodic oxidation approach was adopted to synthesize a variety of 1H-indazole derivatives in moderate to good yields. HFIP was not only employed as a solvent or the proton donor, but also can promote the formation of N free radicals. This synthetic methodology is operationally simple, and less expensive electrodes would be suitable for this chemistry.