| Summary: | We investigated the catalytic efficacy of supported gold nanoparticles (AuNPs) towards the selective reaction between <i>o</i>-phenylenediamine and aldehydes that yields 2-substituted benzimidazoles. Among several supported gold nanoparticle platforms, the Au/TiO<sub>2</sub> provides a series of 2-aryl and 2-alkyl substituted benzimidazoles at ambient conditions, in the absence of additives and in high yields, using the mixture CHCl<sub>3</sub>:MeOH in ratio 3:1 as the reaction solvent. Among the AuNPs catalysts used herein, the Au/TiO<sub>2</sub> containing small-size nanoparticles is found to be the most active towards the present catalytic methodology. The Au/TiO<sub>2</sub> can be recovered and reused at least five times without a significant loss of its catalytic efficacy. The present catalytic synthetic protocol applies to a broad substrate scope and represents an efficient method for the formation of a C–N bond under mild reaction conditions. Notably, this catalytic methodology provides the regio-isomer of the anthelmintic drug, Thiabendazole, in a lab-scale showing its applicability in the efficient synthesis of such <i>N</i>-heterocyclic molecules at industrial levels.
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