12.3 g (0.0251 mol) of the product of Step (3) was added and dissolved in dimethylformamide (125 ml). Then, dried tetrahydrofuran (250 ml), 4.1 g (0.0251 mol) of N-hydroxyphthalimide and 9.9 g (0.0376 mol) of triphenylphosphine were added thereto. Further, 5.8 ml (0.0377 mol) of diethyl diazodicarboxylate was dropwise added under cooling with ice. The mixture was stirred at the same temperature for 10 minutes, and then ethyl acetate (500 ml) and water (1,500 ml) were added thereto. The ethyl acetate layer was washed with water and a saturated sodium chloride solution, and then dried over anhydrous magnesium sulfate, and then concentrated to dryness. The residue was subjected to silica gel column chromatography and eluted by benzene/ethyl acetate (4/1) to obtain 8.0 g of the above identified compound (yield: 50.2%)
