Spiro[isobenzofuran-1(3H),4′-piperidine]-3-one hydrochloride (515 mg) and phenyl N-(5-phenyl-2-pyrazinyl)carbamate (583 mg) were dissolved into dimethyl sulfoxide (2.6 mL), followed by dropwise addition of dimethylbenzylamine (0.33 mL). The temperature of the resultant mixture was raised up to 50° C., and the mixture was stirred for one hour. The reaction mixture was cooled to room temperature, and acetonitrile/water (1:2) mixture solution (7.8 mL) was dropwise added. At the time when 0.2 mL of the mixture solution was added, seed crystal was added. The resultant mixture was stirred at room temperature for 6 hours. The yielded colorless crystals were collected by filtration, washed with acetonitrile/water (1:1) and dried in vacuum at room temperature for 15 hours to obtain the above-identified compound (793 mg) as crude colorless crystals. Crude crystals (26 g) prepared by the repetition of the above procedure were suspended in water-saturated isopropyl acetate (143 mL). The mixture was seeded with seed crystal and stirred at room temperature for 18 hours. The yielded crystals were collected by filtration, washed with isopropyl acetate (20 mL) and dried in vacuum at 30° C. for 15 hours to obtain the above-identified compound in the crystal form D (25.2 g) as colorless crystals (melting point; 206° C. measured without correction by the use of Melting Point B-545 distributed by Buchi Company).
