Microwave-Assisted Synthesis of Benzimidazoles from Resin-Bound Esters

Abstract

Solid-phase synthesis of benzimidazoles via microwave-assisted condensation of resin-bound esters with 1,2-phenylenediamine is described. Thus, the resin-bound esters 2a-d were prepared from the corresponding acid chloride (RCOCl) with Wang resin. Microwave-assisted condensation of 2a with 1,2-phenylenediamine was carried out in the presence of polyphosphoric acid (PPA) in NMP at 150 ˚C for 10 min and then at 230 ˚C for 30 min to give 2-phenylbenzimidazole 3aa in 94% yield. The condensation reactions of esters 2a-d and diamine 4 took place with the aid of microwave irradiation to give the corresponding imidazoles 3 in 47-96% yield.