One-pot solvent-free synthesis of 1,3,5-trisubstituted 1H-pyrazoles catalyzed by H3[PW12O40]/SiO2 under microwave irradiation

An efficient synthesis of 1,3,5-trisubstituted 1H-pyrazoles was developed. 1,3,5-Trisubstituted-1H-pyrazoles were synthesized starting from alpha,beta-unsaturated aldehydes/ketones and hydrazine using catalyst H-3[PW12O40]/SiO2 under microwave irradiation and solvent-free conditions (74-90%) and were characterized by HR-MS, FT-IR, H-1 NMR, and C-13 NMR spectroscopy. It was found that silica had a good loading and dispersing effect on phosphotungstic acid and could effectively absorb microwave energy to promote the condensation reaction. The merits of the method included the environmental friendly reaction conditions, simple operation, extensive substrates, good yields, and reuse of the H-3[PW12O40]/SiO2. Moreover, the crystal structure of compound 1-(4-chlorophenyl)-5-(2-methoxyphenyl)-3-(4-nitrophenyl)-1H-pyrazole in triclinic P-1 space group was presented. [GRAPHICS] .