Cobalt-Promoted Para C─H Amination of 3-Acetyl Substituted Nitroarenes with Arylhydrazines

Abstract

We report a method to furnish substituted 1H-indazoles via a coupling of 3-acetyl substituted nitroarenes and arylhydrazines. Reactions progressed in the presence of cobalt(II) acetylacetonate catalyst, TEMPO oxidant, and Cs₂CO₃ base. Functional groups including bromo, chloro, nitro, and trifluoromethoxy groups were compatible with reaction conditions. The proposed mechanism was based on a nucleophilic substitution of hydrogen para to nitro group. Our method feature a convenient pathway to directly obtain substituted 1H-indazoles which avoid the use of pre-functionalized starting materials. Indazole could play a role as the directing group for a palladium-catalyzed C(sp²)─H arylation with iodobenzene.