An Insight into the Recent Synthetic Approaches of Benzimidazole Motifs Based on Divergent Substrate Scope

Simple heterocyclic moieties are quite famous in synthetic organic chemistry due to their bioavailability, ease of laboratory synthesis, and variety of applications in multidisciplinary fields. Benzimidazole is an N-containing benzo-fused chemical compound with the formula C7H6N2 and belongs to the family of heterocyclic aromatic organic compounds. It is a potent bioactive molecule with prominent therapeutic activities and has been found to have prior importance in medicinal chemistry. Several advanced investigations also proved benzimidazole and its derivatives have significant antimicrobial, antiparasitic, antifungal, and anti-carcinogenic activities. It has also gained popularity in material science as well. Because of its versatile applications, numerous research groups paid considerable attention to synthesizing benzimidazoles. o-Phenylenediamine (OPD) is considered the traditional substrate for benzimidazole synthesis. This review discussed the synthetic approaches of benzimidazoles from OPD as a primary reactant with diverse substrates like aldehydes, alcohols, carboxylic acids/ esters, etc. We have also briefed up reactions using primary substrates such as o-nitroanilines and o-dinitrobenzenes. This review report covers research findings published since 2016 and describes numerous practical and greener synthesis methods. It also narrates innovative biocatalysts, photocatalysts, and nanocatalysts, which are used for the synthesis of benzimidazoles.