A mixture of 1-[2-(3,3,5,5-tetramethylcyclohexyl)phenyl]piperazine (30 mg, 0.1 mmol) produced in Example (8b), 1-bromo-2-fluoroethane (16.2 mg, 0.125 mmol), sodium iodide (1.5 mg, 0.01 mmol), potassium carbonate (20.8 mg, 0.15 mmol) and dimethylformamide (1 mL) was stirred for 2 hours at an external temperature of 80° C. Saturated aqueous solution of sodium hydrogencarbonate was added to the reaction mixture and extraction was performed with diethyl ether. The solvent was distilled off by nitrogen stream to the separated organic layer. The resultant residue was purified by NH silica gel column chromatography (ethyl acetate/heptane) to give 1-(2-fluoroethyl)-4-[2-(3,3,5,5-tetramethylcyclohexyl)phenyl]piperazine.
