Synthesis of 1H-Indazoles and 1H-Pyrazoles via FeBr3/O2 Mediated Intramolecular C-H Amination

A new synthesis of substituted 1H-indazoles and 1H-pyrazoles from arylhydrazones via FeBr3/O-2 mediated C-H activation/C-N bond formation reactions is reported. The corresponding 1,3-diaryl-substituted indazoles and trisubstituted pyrazoles were obtained in moderate to excellent yields under mild conditions.