Facile Access to 1H-Indazoles through Iodobenzene-Catalyzed C-H Amination under Mild, Transition-Metal-Free Conditions

The transition-metal- and halogen-free synthesis of N-arylsubstituted 1H-indazole and derivatives was accomplished on the basis of the iodobenzene-catalyzed intramolecular C-H amination of hydrazones under mild conditions. Reactions of hydrazones derived from ketones and hydrazines with a catalytic amount of iodobenzene in the presence of Oxone as an oxidant in trifluoroacetic acid took place to afford 1H-indazoles in moderate to good yields. A plausible reaction mechanism was described on the basis of the control experiments.