Divergent Synthesis of 1H-Indazoles and 1H-Pyrazoles from Hydrazones via Iodine-Mediated Intramolecular Aryl and sp3 C-H Amination

A divergent intramolecular C-H amination of hydrazones has been developed employing molecular iodine (I-2) as the sole oxidant. The required hydrazone substrates were readily obtained by condensation of hydrazines with the corresponding ketones. In the presence of potassium iodide, I-2-mediated oxidative cyclization of diaryl and tert-butyl aryl ketone hydrazones produced 1H-indazoles via direct aryl C-H amination. Under similar reaction conditions, primary and secondary alkyl ketone hydrazones were transformed into 1H-pyrazole products in a reaction involving sp(3) C-H amination. This synthetic methodology does not involve transition metals, and is operationally simple, providing a facile access to indazole and pyrazole derivatives in an efficient and scalable fashion.