Synthetic Approaches Towards Benzimidazoles by the Reaction of o-Phenylenediamine with Aldehydes Using a Variety of Catalysts: A Review

The benzimidazole moiety is a privileged heterocyclic nucleus which has been used broadly in medicinal chemistry. Benzimidazole derivatives are useful building blocks for the development of important compounds of biological and therapeutic interest. The developments of facile synthetic routes to achieve access to these molecules are of prime interest, therefore synthetic organic chemists focused to invent an efficient method for the synthesis of benzimidazole derivatives. In recent years, several reports have been evident forthe synthesis of these heterocyclic compounds in the presence of various conditions; like solvent free, reactant immobilized on solid support, microwave irradiation condition, using various solvents and using different catalysts. Therefore in the present review, we tried to represent a systematic survey on various synthetic strategies leading to the synthesis of compounds bearing benzimidazole moiety by the direct condensation reaction carried out between o-phenylenediamine and aromatic aldehydes using differentcatalytic reagents during last 10 years. This review is a brief account of some frequently used methods to synthesize benzimidazole derivatives using different type of catalysts in various conditions.