P2O5/SiO2 as an efficient heterogeneous catalyst for the synthesis of heterocyclic alkene derivatives under thermal solvent-free conditions

A highly efficient methodology is developed for the synthesis of a series of heterocyclic alkene derivatives 3a-k from 5-chloro-3-methyl-1-phenylpyrazole-4-carboxaldehyde 1 and active methylene compounds 2a-k, in the presence of P2O5/SiO2, under thermal solvent-free conditions, in high yields, within a short reaction time. The catalyst is characterized for the first time by using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX) and transmission electron microscopy (TEM). The stability of the catalyst is evaluated by thermogravimetric analysis/differential thermal analysis (TG/DTA) and differential scanning calorimetry (DSC) techniques. The molecular structure of alkene 3a is confirmed by single crystal X-ray diffraction. The advantages of the present methodology are excellent yields of products, recyclability of the catalyst and an easy operational procedure.