Synthesis of Indazoles and Azaindazoles by Intramolecular Aerobic Oxidative C-N Coupling under Transition-Metal-Free Conditions

A transition-metal-free oxidative CN coupling method has been developed for the synthesis of 1H-azaindazoles and 1H-indazoles from easily accessible hydrazones. The procedure uses TEMPO, a basic additive, and dioxygen gas as the terminal oxidant. This reaction demonstrates better reactivity, functional group tolerance, and broader scope than comparable metal catalyzed reactions.