To a 1,2-dichloroethane (15 mL) solution of 4-(2-{[tert-butyl(dimethyl)silyl]-oxy}ethyl)benzaldehyde (0.70 g) and tert-butyl piperazine-1-carboxylate (0.52 g) was added NaBH(OAc)3 (0.83 g) at 0° C. The resultant mixture was stirred at room temperature for 66 hours. To the reaction mixture was added saturated aqueous NaHCO3, and extracted with CH2Cl2. The organic layer was washed with saturated aqueous NaCl, dried over anhydrous MgSO4, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (n-hexane/AcOEt=9/1 to 2/1) to afford tert-butyl 4-[4-(2-{[tert-butyl(dimethyl)silyl]oxy}ethyl)benzyl]piperazine-1-carboxylate (0.96 g) as a colorless oil.
