Sulfuric Acid → Dipyranyl ethylmalonate

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To 130 ml of benzene, were added 12.9 g (97.7 mmol) of ethylmalonic acid, 20.2 g (240.5 mmol) of 3,4-dihydropyran and 2 droplets of concentrated sulfuric acid. They were reacted for 1 hour under ice cooling, whereby dipyranyl ethylmalonate was prepared. The reaction mixture was added with 4.7 g (117.5 mmol) of 60% sodium hydride, followed by heating under stirring at 50° C. for 5 hours. A solution of 15.0 g (79.4 mmol) of 3-phenylisoxazole-5-carboxylic acid chloride, which had been synthesized above in the procedure (3), in 70 ml of tetrahydrofuran was added under ice cooling to the above-prepared reaction mixture. The mixture thus obtained was then subjected to a reaction at room temperature for 12 hours. The reaction mixture was added with 20 ml of acetic acid and then heated under reflux for 8 hours. The reaction mixture so obtained was poured into water and then extracted with benzene. The organic layer was washed successively with water, an aqueous solution of sodium hydrogen-carbonate and saturated saline, and was then dried over anhydrous sodium sulfate. After the benzene was distilled off, hexane was added into the residue. Crystals precipitated was collected by filtration, so that 3-phenyl-5-butyrylisoxazole was obtained.

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