In 50 ml of benzene, 2.6 g (57.5 mmol) of 60% sodium hydride were added to dipyranyl ethylmalonate which had been prepared from 5.7 g (43.2 mmol) of ethylmalonic acid, 9.0 g (107.1 mmol) of 3,4-dihydropyran and 1 droplet of concentrated sulfuric acid. At 40°-50° C., the ethylmalonate was converted to sodium dipyranyl malonate, to which a tetrahydrofuran solution of 3-(4-methylphenyl)isoxazole-5-carboxylic acid chloride synthesized above in the procedure (3) was added dropwise at room temperature. They were reacted for 3 hours. The reaction mixture was added with 10 ml of acetic acid and then heated under reflux for 6 hours. The mixture thus obtained was added into water and then extracted with benzene. The benzene extract was washed successively with an aqueous solution of sodium hydrogencarbonate and water. The organic layer was dried over anhydrous sodium sulfate and the solvent was distilled off. Hexane was added to the residue, and 3-(4-methylphenyl)-5-butyrylisoxazole precipitated as crystals was collected by filtration.
