A rapid and efficient solvent-free microwave-assisted synthesis of pyrazolone derivatives containing substituted isoxazole ring

An efficient synthesis of 4-substituted pyrazolone derivatives was developed. 4-Substituted pyrazolone derivatives were synthesized in 78–97% yields starting from various 3-substituted isoxazole-5-carbaldehydes, ethyl acetoacetate and hydrazine under microwave irradiation and solvent-free conditions, and were characterized by HRMS , FTIR, 1 H NMR and 13 C NMR spectroscopy. SiO 2 was found to possess favorable catalytic activity and dispersancy for the condensation reaction . The merits of this method include the environmentally friendly reaction conditions, simple operation, broad substrate, satisfied yields and the reuse of the silica. Moreover, the crystal structure of the compound 2-(4-chlorophenyl)-4-((1-(4-chlorophenyl)-5-hydroxy-3-methyl-1 H -pyrazol-4-yl)(3-phenylisoxazol-5-yl)methyl)-5-methyl-1 H -pyrazol-3(2 H )-one ( 5a ) in the monoclinic space group C2/c was presented.