Ce(III) immobilized on aminated poly(vinyl chloride): high-performance synergistic bifunctional acid-base catalyst for one-pot synthesis of 1,4-dihydropyrano [2,3-c]pyrazoles

A bifunctional acid-base catalyst of Ce-III immobilized on ethylenedi-amine (EDA)-grafted poly(vinyl chloride) (PVC) has been prepared by a simple approach. First, PVC was treated with EDA to afford aminated poly(vinyl chloride) (PVC-EDA). Thereafter, the PVC-EDA were used in the mobilization of CeCl3 to obtain a bifunctional catalyst (PVC-EDA-Ce-III) in which a harmonious coexistence of Lewis acid (Ce3+) sites and Lewis base (amine) moieties on PVC was achieved. The obtained PVC-EDA-Ce-III complex was characterized by EA, ICP-AES, FTIR, SEM, EDS, TGA, and DTG techniques. The as-prepared catalyst can efficiently catalyze the one-pot four-component reactions of aromatic aldehydes, malononitrile, ethyl acetoacetate, and hydrazine in ethanol under mild conditions to afford polyfunctionalized 1,4-dihydropyrano[2,3-c]pyrazoles with excellent yields. The high catalytic performance of the PVC-EDA-Ce-III bifunctional catalyst is attributed to a synergistic effect of Lewis acid sites (Ce-III) and Lewis base sites (amino moieties). The significant features of the present protocol are environmentally benign, simple operation, short reaction time, high yields, and without chromatographic separation. Moreover, the catalyst can easily be separated by simple filtration and reused for five runs without obvious decline or losing its catalytic activity.