Microwave-Assisted Expedite Synthesis of 2-Phenylimidazo[1,2-a]pyridylquinoxalin-2(1H)-ones

Abstract

An efficient methodology has been developed for the synthesis of quinoxalin-2(1H)-one derivatives of 2-phenylimidazo[1,2-a]pyridines by microwave-irradiated Hinsberg heterocyclization between 2-phenylimidazo[1,2-a]pyridine-3-glyoxalates and o-phenylenediamine using either montmorillonite K-10 or Yb(OTf)3 as catalysts. Montmorillonite K-10 was proven to be an efficient catalyst for the heterocyclization reaction between sterically hindered glyoxalate and o-phenylenediamine only under microwave conditions. The use of Yb(OTf)3/tetrahydrofuran was also found to be an effective catalyst for the above chemical transformation among a series of Lewis acids screened under microwave conditions; however, comparatively lesser yields were obtained as compared with the use of montmorillonite K-10.