To a solution of 4′-{[6-ethyl-3-[2-(4-methoxyphenyl)-2-oxoethyl]-2,4-dioxo-3,4-dihydrothieno[2,3-d]pyrimidin-1(2H)-yl]methyl}biphenyl-2-carbonitrile (1.0 g), (diethoxyphosphoryl)ethyl acetate (0.56 ml) in THF (20 ml) was added NaH (0.1 g) under ice-cooling, and the mixture was stirred at room temperature for 1 hr. The reaction mixture was poured into water and the mixture was extracted with ethyl acetate and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography to give ethyl (2E)-4-[1-[(2′-cyanobiphenyl-4-yl)methyl]-6-ethyl-2,4-dioxo-1,4-dihydrothieno[2,3-d]pyrimidin-3(2H)-yl]-3-(4-methoxyphenyl)but-2-enoate (1.0 g, 88%). This was dissolved in dimethyl sulfoxide (5 mL), and the mixture was added to a mixture of hydroxylammonium chloride (1.15 g), sodium hydrogencarbonate (1.40 g) and dimethyl sulfoxide (20 mL), which had been stirred at 40° C. for 30 min in advance. The reaction mixture was stirred at 90° C. for 16 hr, diluted with chloroform, washed successively with water and saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography, dissolved in tetrahydrofuran (20 mL), N,N′-carbonyldiimidazole (0.32 g) and then 1,8-diazabicyclo[5.4.0]undec-7-ene (0.30 mL) were added, and the mixture was stirred at room temperature for 2 hr. The reaction mixture was diluted with ethyl acetate, washed successively with saturated aqueous potassium hydrogensulfate solution and saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography to give the title compound as a stereoisomer mixture (0.078 g, 13%).
