Example 36 Synthesis of N-tert-butoxycarbonyl-O-benzyl-L-serine 39: Boc-L-serine (15 g, 73.09 mmol) was dissolved in DMF (300 mL) at 0 °C, NaH (6.43 g, 160.80 mmol, 60% mineral oil dispersion) was slowly added, and the reaction temperature was maintained at 0 °C and stirred for 1.5 hours. Subsequently, benzyl bromide (13.75 g, 80.40 mmol) was added, and the reaction mixture was gradually warmed to room temperature and continued to stir overnight. Upon completion of the reaction, DMF was removed by evaporation under reduced pressure and the residue was dissolved in H2O. The crude product was partitioned between water and Et2O. The aqueous phase was acidified with 3N HCl to pH < 4 and then extracted three times with EtOAc. The EtOAc extracts were combined, washed with H2O, dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure to give N-tert-butoxycarbonyl-O-benzyl-L-serine (17.27 g, 80% yield).
