Synthesis of 2,4,5-trisubstituted imidazoles, quinoxalines and 1,5-benzodiazepines over an eco-friendly and highly efficient ZrO2–Al2O3 catalyst

Abstract

ZrO₂–Al₂O₃ containing 80 mol% of ZrO₂ was prepared by solution combustion, impregnation and precipitation methods. All the prepared catalytic materials were characterized by PXRD, NH₃-TPD, N₂ adsorption isotherms, FTIR, TEM, SEM, EDAX and ICP-OES techniques. These catalytic materials were used in a rapid, simple, versatile and efficient synthesis of 2,4,5-trisubstituted imidazoles under solvent-free conditions at moderate temperature in shorter reaction time (20 min). This is achieved by three-component cyclo-condensation of benzil, aldehydes and ammonium acetate in excellent yields. The derivatives of quinoxalines and 1,5-benzodiazepines were synthesized effectively by cyclo-condensation of 1,2-diamine with α-diketones and carbonyl compound with O-phenylenediamines respectively over ZrO₂–Al₂O₃ at moderate temperature (80 °C) for the reaction time of 20–40 min in presence of ethanol as a solvent. The present method is experimentally simple, non-toxic and involves inexpensive reagents, clean reaction pathways and an eco-friendly catalyst. The catalytic materials used can be easily separated from the reaction mixture and reused for several reaction cycles without much loss of catalytic activity.