Step- and atom-economical synthesis of 2-aryl benzimidazoles via the sulfur-mediated redox condensation between o-nitroanilines and aryl methanols

Abstract

The synthesis of benzimidazoles usually requires use of expensive and sensivitve substrates such as phenylenediamine and aldehyde or metal catalysts. In this work, 2-nitroanilines and benzyl alcohols were alternatively applied for the condensation towards 2-phenyl benzimidazoles in the presence of elemental sulfur and an amine. Mechanistic results proved a dual role of sulfur as both oxidizing and reducing agents in this synthetic pathway. The study was expanded to the synthesis of benzimidazoles containing a variety of functionalities including halogens, methyl, trifluoromethyl, methoxy, cyano, and heterocycles groups in moderate-to-good yields. The utilization of more stable and available substrates in the absence of transition metals and other solvents offers a rapid and green synthesis of benzimidazoles.