6-Bromo-2-naphthoic acid (1.51 g) was dissolved in dry THF (50 ml), and cooled to −100° C. in a liquid nitrogen/diethyl ether bath. Under stirring a solution (1.6M; 7.88 ml) of n-butyllithium in hexane was added dropwise at −95° C. or below over 5 min. After stirring at −100° C. for 30 min and at −80° C. for 10 min, the mixture was cooled to −100° C. again. A solution of 5,6-dihydro-7H-pyrrolo[1,2-c]imidazol-7-one (0.61 g) in dry THF (11 ml) was added dropwise at −90° C. or below over 5 min. After stirring at the same temperature for 30 min, the temperature was raised to −70° C. over 30 min, and saturated aqueous ammonium chloride solution (25 ml) was added to quench the reaction. After stirring for 10 min, ethyl acetate (50 ml) was added to partition the solution. The organic layer was removed and the aqueous layer was concentrated to dryness. The obtained residue was purified by flash column chromatography, and the object fraction was dissolved in methanol. This solution was concentrated, ether was added to the precipitated powder and the powder was collected by filtration and dried. The title compound (180 mg) was obtained as a colorless powder. The mother liquor was concentrated to give a residue (449 mg) containing the title compound.
