Selective Electrosynthesis of Benzimidazole N-Oxides and Benzimidazoles from o-Nitroanilides Using Metal-Free Electrodes

The electrochemical synthesis of benzimidazole N-oxides was achieved by tuning the pH and current density during the reduction of o-nitroanilides. By using boron-doped diamond cathodes and glassy carbon anodes in undivided cells, a collection of various aryl-, acyl-, and nitrogen-substituted benzimidazoles and their N-oxide derivatives was obtained in up to very good yields. The simple setup and purification steps render this methodology a powerful tool for synthesizing valuable heterocyclic motifs on up to a gram scale in a sustainable way. Additionally, our methodology allows for the electrochemical access to benzimidazole-containing active pharmaceutical ingredients, including clemizole, thiabendazole, and, in an unprecedented way, chlormidazole N-oxide as well as precursors of bendamustine N-oxide derivatives.