A solution of 10.99 g of isoamyl nitrite in 10 ml of acetonitrile was added to a mixture of 15.46 g of 3-{2-amino-4-fluoro-5-[3-methyl-2,6-dioxo-4-(trifluoromethyl)-1,2,3,6-tetrahydropyrimidin-1-yl]phenoxy}-2-(ethoxycarbonyl)methoxypyridine, 6.19 g of copper(I) chloride, 12.61 g of copper(II) chloride and 120 ml of acetonitrile dropwise at room temperature, and the mixture was stirred for 3 hours. This reaction solution was poured into a mixture of ice and hydrochloric acid, and extracted with ethyl acetate. The organic layer was washed with saturated saline, dried over anhydrous magnesium sulfate, and concentrated. The residue was subjected to silica gel column chromatography to obtain 13.16 g of 3-{2-chloro-4-fluoro-5-[3-methyl-2,6-dioxo-4-(trifluoromethyl)-1,2,3,6-tetrahydropyrimidin-1-yl]phenoxy)-2-(ethoxycarbonyl)methoxypyridine [present compound 7-8].
