P-phenylbenzaldehyde (1 mmol), 5,5-dimethyl-1,3-cyclohexanedione (0.14 g, 1 mmol), ethyl acetoacetate (0.13 g, 1 mmol), ammonium acetate (0.115 g, 1.5 mmol), and Fe2O3 (catalytic amount) loaded on hydroxyapatite (HAP, catalytic amount) were used as raw materials and melamine (0.15 g) was added as an additive, and the reaction was heated at 80 °C. The reaction process was monitored by thin layer chromatography (TLC, unfolding agent was hexane/ethyl acetate, 10:3, v/v). Upon completion of the reaction, the reaction mixture was cooled to room temperature, washed with hot ethyl acetate and the catalyst was removed by magnetic separation. The solid residue was separated and purified by recrystallization in hot ethanol to afford the target product ethyl 4-([1,1'-biphenyl]-4-yl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate.
