To a THF (40 mL) solution of tert-butyl 4-[4-(2-hydroxyethyl)benzyl]piperazine-1-carboxylate (4.74 g) and p-cresol (1.76 g) were added triphenylphosphine (4.27 g) and 2.2 M solution of DEAD in toluene (7.40 mL) at 0° C. After stirring at room temperature for 85 hours, the solvent was removed under reduced pressure. The residue was purified by silica gel column chromatography (n-hexane/AcOEt=3/1 to 1/2), then the concentrated eluate was diluted with CH2Cl2, and washed with 5 M NaOH and saturated aqueous NaCl, dried over anhydrous MgSO4, and concentrated under reduced pressure to give tert-butyl 4-{4-[2-(4-methylphenoxy)ethyl]benzyl}piperazine-1-carboxylate as a yellow solid (3.87 g).
