To a mixture of 1-[2-(3,3,5,5-tetramethylcyclohexyl)phenyl]piperazine (300 mg, 1 mmol) produced in Example (8b), the crude product of 2-methyl-1-cyclopropanecarbaldehyde produced in Example (96a) (365 mg) and tetrahydrofuran (10 mL) were added sodium triacetoxyborohydride (424 mg, 2 mmol) and acetic acid (0.057 mL, 1 mmol) in that order, followed by stirring for 15 hours and 30 minutes at room temperature. Ethyl acetate, saturated aqueous solution of sodium hydrogencarbonate and water were 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 NH silica gel column chromatography (ethyl acetate/heptane), to give 163 mg of 1-(2-methylcyclopropylmethyl)-4-[2-(3,3,5,5-tetramethylcyclohexyl)phenyl]piperazine as a colorless oil, as a mixture of cis/trans at the position of cyclopropane ring.
