New green perspective to dihydropyridines synthesis utilizing modified heteropoly acid catalysts

The classical Hantzsch reaction is a simple and utmost efficient protocol for the synthesis of biologically and pharmacologically important 1,4-dihydropyridine derivatives. The present study deals with the utilization of modified heteropoly acid (HPA) catalysts (5 wt% WOx-FeP and 5 wt% MoOx-FeP) in the synthesis of novel Hantzsch 1,4-dihydropyridines, which contains diphenylsulfone moiety via one-pot synthesis strategy under ultrasound irradiation. The developed protocol is simple and green procedure for the synthesis of 1,4-dihydropyridines and is applicable to synthesize different 1,4-dihydropyridine derivatives. The synthesized HPA catalysts offered a sustainable methodology to produce excellent products yields (88–92%) of 1,4-dihydropyridine derivatives. The catalysts were characterized by XRD, Raman, FT-IR, DRUV-vis, XPS, H2-TPR, N2-physisorption and acidity measurements. The HPA supported iron phosphate nanotubes (FeP) catalysts offered enhanced the catalytic performance through the improved Lewis acid site density, redox properties and surface area, compared to the parent phosphomolybdic and phosphotungstic acids. Moreover, the synthesized catalysts can be easily separated from reaction system and reused for six times efficiently without significant loss of activity.