To a solution of 4-[(1S,4R)-(4-acetoxycyclopent-2-en-1-yl)oxy]-2-(1-piperazinyl)quinazoline (2.07 g) in dry methylene chloride (15 ml) is added triethylamine (1.63 ml) with stirring under ice-cooling, and thereto is further added dropwise a solution of benzyl chlorocarbonate (0.92 ml) in dry methylene chloride (5 ml). The mixture is stirred under ice-cooling for 2 hours, and the reaction mixture is diluted with chloroform, washed with water, and dried over anhydrous magnesium sulfate. The solution is evaporated to dryness under reduced pressure, and the residue is purified by medium pressure liquid column chromatography (eluent, chloroform) to give 4-[(1S,4R)-(4-acetoxycyclopent-2-en-1-yl)oxy]-2-[4-(benzyloxycarbonyl)piperazin-1-yl]quinazoline (2.36 g) as crystals.
