Davis-Beirut Reaction: A Photochemical Brønsted Acid Catalyzed Route to N-Aryl 2H-Indazoles.

The Davis-Beirut reaction provides access to 2H-indazoles from aromatic nitro compounds. However, N-aryl targets have been traditionally challenging to access due to competitive alternate reaction pathways. Previously, the key nitroso imine intermediate was generated under alkaline conditions, but as reported here, the photochemistry of o-nitrobenzyl alcohols empowered Brønsted acid catalyzed conditions for accessing N-aryl targets. Anilines and alkyl amines give different outcomes under optimized conditions; the proposed mechanism was studied using quantum chemical calculations.