To 5 ml of a tetrahydrofuran solution containing 600 mg of dimethyl 3-methoxycarbonylmethylglutarate, 1.36 ml of a 1.5M lithium diisopropylamide cyclohexane solution and 0.54 ml of hexamethylphosphoramide were dropwise added at -78° C. under a nitrogen atmosphere, followed by stirring at the same temperature for 1.5 hours. Then, a tetrahydrofuran solution containing 620 mg of benzyl bromoacetate was added thereto, followed by further stirring for one hour. The reaction solution was warmed to room temperature over a period of one hour and then stirred at the same temperature for 2 hours. A saturated ammonium chloride aqueous solution was added to the reaction solution, and the mixture was extracted with ethyl ether. Then, the organic layer was washed with a saturated sodium chloride aqueous solution and dried over anhydrous magnesium sulfate. The drying agent was filtered off, and then, the solvent was distilled off under reduced pressure. The residue was purified by medium pressure liquid column chromatography (hexane/ethyl acetate=3/1) to obtain 555 mg of the above-identified compound as colorless oily substance.
