Electrochemically driven reductive cyclization of <i>o</i> -nitroanilines: synthesis of 1,2-fused benzimidazoles and benzo[ <i>d</i> ]imidazoles

The electrochemical synthesis of 1,2-fused benzimidazoles and benzo[<i>d</i>]imidazoles from <i>o</i>-nitroanilines in an undivided cell under constant current conditions was developed. The electrosynthesis proceeded through a tandem process involving nitro reduction/C(sp³)-H amination/condensation. The method can accommodate a broad range of <i>o</i>-nitroanilines and results in the desired products in yields of up to 99%. A plausible reaction mechanism was proposed on the basis of controlled experiments and cyclic voltammetry (CV) analysis. The benefits of the developed method include one-pot synthesis, open-air conditions, gram-scale synthesis and no requirement for a strong reductant.