Synthesis of Tri- and Tetrasubstituted Pyrazoles via Ru(II) Catalysis: Intramolecular Aerobic Oxidative C-N Coupling

An unprecedented ruthenium(II)-catalyzed intramolecular oxidative C-N coupling method has been developed for the facile synthesis of a variety of synthetically challenging tri- and tetrasubstituted pyrazoles. Dioxygen gas is employed as the oxidant in this transformation. The reaction demonstrates excellent reactivity, functional group tolerance, and high yields.