Pivaloyl chloride (0.22 ml) was added dropwise to a mixture of acetylsarcosine (264 mg), N-methylmorpholine (0.22 ml) and N-methylpyrrolidone (30 ml) under a dry ice-tetrachloromethane bath cooling. This mixture was stirred for 10 minutes under ice-cooling, and 8-[3-amino-2,6-dichlorobenzyloxy]-2-methylimidazo[1,2-a]pyridine (500 mg) was added thereto under a dry ice-tetrachloromethane bath cooling. The mixture was stirred for 22 hours at ambient temperature. The mixture was partitioned between ethyl acetate and a saturated aqueous sodium bicarbonate solution, and the aqueous layer was extracted with ethyl acetate twice. The combined organic layer was dried over magnesium sulfate and concentrated in vacuo, and the residue was purified by flash column chromatography (methylene chloride:methanol=50:1, V/V) to give 8-[3-(acetylsarcosylamino)-2,6-dichlorobenzyloxy]-2-methylimidazo[1,2-a]pyridine (260 mg).
