Under nitrogen atmosphere at -78° C., 4.29 ml of 1.5 M n-butyl lithium (hexane solution) was added, while stirring, to 0.98 ml of diisopropylamine dissolved in 13 ml of anhydous tetrahydrofuran. The stirring was conducted for 15 minutes. To the resultant was added, taking 5 minutes, 1.18 g of dimethyl 2-oxoglutarate dimethyl acetal dissolved in 7 ml of anhydrous tetrahydrofuran, followed by stirring for 15 minutes. To the mixture was added, taking 5 minutes, a solution of 0.76 ml of benzyl bromide and 0.28 ml of hexamethylphosphoramide in 7 ml of anhydrous tetrahydrofuran. The mixture was stirred for 30 minutes at -78° C. The temperature of the reaction solution was raised up to -20° C. under stirring taking 2 hours, followed by addition of saturated aqueous solution of ammonium chloride, which was subjected to extraction with ethyl acetate. The extract solution was washed with water, dried (MgSO4), followed by evaporating off the solvent. The residue was subjected to a silicagel column chromalography, followed by elution with hexane-ethyl acetate (5:1→2:1) to give 1.64 g of dimethyl 4-benzyl-2-oxoglutarate dimethyl acetal as a pale yellow oily product.
