To a solution prepared by dissolving 8.26 g (36.0 mM) of 2-(1-tert-butoxycarbonylpiperidin-4-yl)ethanol and 10.0 ml (72.0 mM) of triethylamine in 50 ml of ether was added 3.34 ml (43.2 mM) of methanesulfonyl chloride dropwise at 0° C. After completion of dropwise addition, the reaction mixture was stirred at room temperature for 30 minutes. After completion of the reaction, the reaction mixture was poured in 100 ml of iced water and the mixture was extracted with 100 ml of ethyl acetate. The organic layer was washed with 100 ml of saturated aqueous NaCl solution and dried over anhydrous magnesium sulfate (MgSO4) and the solvent was distilled off under reduced pressure to recover the mesylate as solid. To a solution prepared by dissolving this mesylate and 10.37 g (36.0 mM) of 1,2-dihydro-1,4,7b-triazacyclopent[cd]inden-2-one.2NaCl in 25 ml of DMF was added 6.46 ml (43.2 mM) of DBU and the mixture was heated at 80° C. for 2 hours. After completion of the reaction, the reaction mixture was poured in iced water and the mixture was extracted with 200 ml of ethyl acetate. The organic layer was washed with 200 ml of purified water 3 times and further with 200 ml of saturated aqueous NaCl solution and dried over MgSO4. The solvent was then distilled off under reduced pressure and the residue was purified by silica gel column chromatography (eluent: ethyl acetate) to provide 9.10 g (yield 68.2%) of the title compound as light-yellow solid.
