To a solution of 1-(2-bromophenyl)-4-cyclopropylmethylpiperazine (700 mg, 2.37 mmol) produced in Example (108a) in anhydrous tetrahydrofuran (7 mL) was added dropwise n-butyllithium (1.60 M solution in hexane, 1.63 mL, 2.61 mmol) over a period of 3 minutes at an external temperature of −70° C. After stirring for 45 minutes under the same conditions, 3,3,5,5-tetramethylcyclohexanone (0.49 mL, 2.85 mmol) was added dropwise to the reaction mixture over a period of 4 minutes at an external temperature of −70° C. Stirring was continued for 15 minutes under the same conditions, and then for 18 hours and 30 minutes while warming until the external temperature reached room temperature. Water was added to the reaction mixture and extraction was performed with ethyl acetate. The separated organic layer was washed with brine and then dried over anhydrous sodium sulfate. The desiccant was filtered off and the filtrate was concentrated under reduced pressure. The resultant residue was purified by silica gel column chromatography (ethyl acetate/heptane) to give 765 mg of the title compound as a light yellow oil.
