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.