An efficient solvent-free synthesis of isoxazolyl-1,4-dihydropyridines on solid support SiO₂ under microwave irradiation

An efficient synthesis of 1,4-dihydropyridines was developed. 1,4-Dihydropyridines were synthesized starting from various 3-substituted isoxazolyl-5-carbaldehydes, ethyl acetoacetate, and ammonium acetate under microwave irradiation and solvent-free conditions (86–96 %), and were characterized by HRMS, FT-IR, ¹H NMR, and ¹³C NMR spectroscopy. Solid support SiO₂ was found to possess favorable catalysis and dispersancy for the condensation reaction. The merits of the method included the environmental friendly reaction conditions, simple operation, extensive substrates, good yields and reuse of the SiO₂. Moreover, the crystal structure of compound diethyl 4-[3-(2-methoxyphenyl)isoxazol-5-yl]-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate in orthorhombic Pbca space group was presented. Graphical abstract: [Figure not available: see fulltext.]