Into a mixture of 1.0 g of 3-[2-chloro-4-fluoro-5-(3-methyl-2,6-dioxo-4-trifluoromethyl-1,2,3,6-tetrahydropyrimidin-1-yl)phenoxy]-1H-pyridin-2-one, 121 mg of tin tetrachloride and 40 ml of 1,2-dichloroethane, 0.4 ml of ethyl diazoacetate (purity: 90%) is dropped at room temperature over 2 hours. After dropping, the reaction mixture is further stirred for 2 hours, and subjected to silica gel column chromatography (eluent; hexane/ethyl acetate=2/1) to give 3-[2-chloro-4-fluoro-5-(3-methyl-2,6-dioxo-4-trifluoromethyl-1,2,3,6-tetrahydropyrimidin-1-yl)phenoxy]-2-(ethoxycarbonylmethoxy)pyridine.
