t‐BuONa‐Mediated Redox Condensation between o‐Nitroanilines and Benzyl Alcohols towards 2‐Phenyl Benzimidazoles under Transition‐Metal‐Free Conditions

Abstract

AbstractA novel and environmentally benign method was developed for the direct synthesis of 2‐substituted benzimidazoles via a transition metal‐free redox tandem annulation of benzyl alcohols and ortho‐nitroanilines in the presence of a strong base, e.g. alkaline alkoxides or hydroxides. A good tolerance of functional groups was observed, affording an array of 2‐aryl benzimidazole derivatives in high yields. Early mechanistic studies showed that sodium tert‐butoxide could initiate the hydrogen transfer from benzyl alcohol to the nitro group in ortho‐nitroaniline followed by imine condensation, cyclization, and oxidation. This protocol features a convenient tactic that does not require any external oxidants or solvents for the synthesis of bioactive benzimidazole‐involving compounds.