After adding 313 mg of cesium carbonate and 0.257 ml of (3-bromopropoxy)-t-butyldimethylsilane to a solution of 339 mg of [2-(2-fluoro-3-hydroxy-5-methoxyphenyl)-2-[4-(5-methyl-[1,2,4]oxadiazol-3-yl)phenylimino]-1-methylsulfanylethylidene]carbamic acid methyl ester (Example (3d)) in 8 ml of DMF, the mixture was stirred at room temperature for 15 hours. Next, 100 ml of water was added to the reaction mixture and extraction was performed with 300 ml of ethyl acetate. The organic layer was washed with 50 ml of water and 50 ml of saturated brine in that order and then dried over anhydrous magnesium sulfate. The desiccating agent was filtered off and the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate-heptane) to give the title compound (413 mg).
