2-Benzylpiperazine and 200 mL of a buffer solution consisting of sodium carbonate and sodium bicarbonate were added to a three-necked flask equipped with a stirrer. The mixture was placed in an ice bath, and tert-butyl dicarbonate was added dropwise using a dropping funnel. The reaction mixture was stirred in a water bath at 30°C for 22 hours. The reactants were extracted with diethyl ether (100 mL × 2) to remove unreacted tert-butyl dicarbonate. The resulting aqueous phase was adjusted to pH 2-3 with 3 mol/L hydrochloric acid solution, then extracted with ethyl acetate (100 mL × 4), dried over anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation to obtain a colorless oily liquid (S)-1-Boc-2-benzylpiperazine.
