Chlorosulfonic Acid Supported Piperidine-4-carboxylic acid Functionalized Fe3O4 Nanoparticles: A Green Catalyst for the Synthesis of 2- Arylbenzimidazoles under Solvent Free Conditions

Benzimidazoles are an important class of heterocycles that are frequently used in drug andagrochemical discovery programs. Recent medicinal chemistry applications of benzimidazoleanalogs include antibacterial and antifungal agents, anthelmintic agents, HIV-1-induced cytopathicinhibitor, and receptor agonists or antagonists [1]. Therefore, the construction of theseheterocycles has always been of great interest to organic and medicinal chemists and has consequentlyreceived much attention. The classical and most common methods to assemble benzimidazolesinvolve the condensation of benzene-1,2-diamines with aldehydes, carboxylicacids, or their derivatives under strong acid/high temperature conditions or using a stoichiometricoxidant [2–4]. Although these transformations are widely used owing to their inherentsimplicity, this method is restricted to the available starting materials and involves harsh reactionconditions. In this study, we report a highly versatile and efficient synthesis of 2-arylbenzimidazoles3from o-phenylenediamine, aldehyde and catalytic amounts of the catalyst(Fe3O4-PCA) under solvent-free conditions in high yields (Fig. 1). (***) The main advantages of the presented protocol are mild, clean and environmentally benignreaction conditions, as well as the high yields, simple work-up, ease of separation, and recyclabilityof the magnetic catalyst.