A hexane solution of n-butyl lithium (1.68 M, 11.3 ml, 19.0 mmols) was dropwise added to a THF (100 ml) solution of ethyl 2-(4-benzyloxyphenyl)-3-(6-bromo-2,3,4,5-tetramethoxyphenyl)-2-ethoxycarbonylpropionate (10.0 g, 15.8 mmols), under a nitrogen stream at −90° C or lower. The reaction mixture was stirred for 30 minutes, and a THF (10 ml) solution of acetic acid (1.86 g, 31.6 mmols) was dropwise added thereto still at −90° C. or lower. The reaction mixture was allowed to warm to room temperature, and diluted with diethyl ether. The organic layer was washed with a saturated aqueous sodium bicarbonate solution, water and a saturated aqueous sodium chloride solution, and then dried. The solvent was evaporated out in vacuo, and the resulting crude product was purified by silica gel column chromatography (hexane:ethyl acetate=10:1 to 5:1) to obtain the entitled compound (3.78 g) as an oil.
