CeO2/ZrO2 as green catalyst for one-pot synthesis of new pyrano[2,3-c]-pyrazoles

Abstract

Ceria-doped zirconia (CeO2/ZrO2)-catalyzed synthesis of pyrano[2,3-c]-pyrazoles via four-component reaction of malononitrile, hydrazine hydrate, ethyl acetoacetate, and substituted aldehydes is described. The catalytic material CeO2/ZrO2 was prepared and characterized by different techniques including powder X-ray diffraction (P-XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) analysis. Twelve new pyrano[2,3-c]-pyrazole derivatives (5a–k) were synthesized in good to excellent yield (89–98%) and their structures established and confirmed by different spectroscopic methods, viz. 1H, 13C, and 15N nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). The environmental benefits of the process include excellent yield, short reaction time, simple work-up, elimination of toxic solvents, and avoidance of chromatographic separation. The CeO2/ZrO2 catalyst enables a facile synthesis procedure, is inexpensive, and has good reusability (at least six times).