Au catalyzed synthesis of benzimidazoles from 2-nitroanilines and CO2/H-2

The gold-catalyzed synthesis of benzimidazoles from 2-nitroanilines and CO2 in the presence of H-2 was reported, and a series of benzimidazoles were obtained under relatively mild conditions. Several supported Au catalysts including Au/TiO2, Au/Al2O3, Au/ZnO, Au/polyurea and Au/hydrotalcite were examined for the synthesis of benzimidazole from the reaction of 2-nitroaniline with CO2 and H-2, among which Au/TiO2 displayed the best performance. The reaction mechanism was investigated, and it was found that the production of benzimidazole underwent the formation of o-phenylenediamine via the hydrogenation of 2-nitroaniline, followed by the cyclization of o-phenylenediamine with CO2 and H-2. This work provides a CO2-involved route for the synthesis of benzimidazoles, which may widen the applications of CO2 in the chemical synthesis.