To a solution of 1-[2-(4,4-dimethylcyclohex-1-enyl)-5-methoxyphenyl]piperazine (90 mg, 0.29 mmol) prepared in Example (1e) in tetrahydrofuran (10 mL) were added valeraldehyde (31 mg, 0.36 mmol), sodium triacetoxyborohydride (95 mg, 0.59 mmol) and acetic acid (35 mg, 0.59 mmol) in that order, and the mixture was stirred for 3 hours. Saturated aqueous sodium hydrogencarbonate was added to the reaction mixture and the mixture was extracted with ethyl acetate. The organic layer was dried over anhydrous magnesium sulfate, the desiccant was filtered off and then the filtrate was concentrated under reduced pressure. The resultant residue was purified by NH silica gel column chromatography (ethyl acetate/hexane) to give 110 mg of 1-[2-(4,4-dimethylcyclohex-1-enyl)-5-methoxyphenyl]-4-pentylpiperazine as a light yellow oil.
