Novel iron doped calcium oxalates as promising heterogeneous catalysts for one-pot multi-component synthesis of pyranopyrazoles

Abstract

The co-precipitation method using a surface modifier, glutamic acid was employed in the design of iron doped calcium oxalates (Fe-CaOx). Fe-CaOx with diverse iron loading (0.5–3.0 mmol) were prepared and their phase purity and surface features were examined by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), electron microscopy (SEM, TEM), energy dispersive X-ray (EDX), Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), N₂-sorption, thermal and fluorescent analysis. The Fe-CaOx materials proved excellent as catalysts in the one-pot syntheses of eight 2,4-dihydro pyrano[2,3-c]pyrazole derivatives via four component condensation of aromatic aldehydes, malononitrile, hydrazine hydrate and dimethyl acetylenedicarboxylate in ethanol with impressive yields (92–98%) in short reaction times (<20 min). The 2.0 mmol loaded iron in Fe-CaOx showed the finest catalytic performance with 98% yield in 10 min compared to other loadings. The stability, ease of separation, and reusability for up to six cycles of Fe-CaOx make it an environmentally friendly and cost-effective viable choice for the value-added organic transformations.