Metal-free selective synthesis of 2-substituted benzimidazoles catalyzed by Bronsted acidic ionic liquid: Convenient access to one-pot synthesis of N-alkylated 1,2-disubstituted benzimidazoles

A novel efficient method for the selective synthesis of 2-substituted benzimidazoles is described through condensation reaction of o-phenylenediamines with a wide rang of aliphatic, aromatic and heteroaromatic aldehyde substrates using Bronsted acidic ionic liquid as a reusable catalyst under metal-free conditions at ambient temperature. Notably, Dodecylimidazolium hydrogen sulfate ([Dodeclm][HSO4]) is the most efficient catalyst for good to excellent yields of the corresponding products (up to 98%). Subsequently, this protocol was successfully applied for the preparation of N-alkylated 1,2-disubstituted benzimidazoles in high to excellent yields via sequential one-pot reaction. In addition, catalysts are recycled at least four times without significant loss in activity. (C) 2019 Elsevier Ltd. All rights reserved.