Direct Indazole Synthesis via Ruthenium(II)-Catalyzed Acceptorless Dehydrogenative Annulation of Alcohols and Arylhydrazines.

Indazole serves as an important organic synthetic intermediate with significant pharmaceutical activity. Herein, we report the first example of efficiently constructing the indazole framework through an acceptorless dehydrogenative annulation reaction using alcohols and hydrazines as starting materials. This strategy, which employs an N-heterocyclic carbene (NHC)-imine-phosphine (CNP) pincer ruthenium catalyst, operates under mild conditions with high efficiency, offering a new pathway to simplify indazole synthesis.