Chloroacetaldehyde → 2-[Benzyl-(2-chloro-ethyl)-amino]-propionic acid ethyl ester

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To a solution of 2-benzylamino-propionic acid ethyl ester (24.72 g, 1 eq.) in 114 mL of dry DCM under nitrogen was added MgSO4 (10.80 g, 0.75 eq.). The reaction was cooled to 0° C. then acetic acid (6.82 mL, 1 eq) and the above solution of chloroacetaldehyde in dry DCM (solution I) were added. Sodium triacetoxyborohydride (38 g, 1.5 eq.) was added portionwise. The reaction was stirred for 2 h at 0° C. The crude was carefully quenched with 160 mL of a saturated aqueous solution of NaHCO3. Then 75 mL of an aqueous solution of NaOH (2N) was added. The aqueous layer was extracted twice with 120 mL of DCM. The combined organic layers were washed twice with 120 mL of a saturated aqueous solution of NaHCO3, then dried over MgSO4, filtered and concentrated under reduced pressure. The crude was purified by chromatography on silica gel (elution with heptane/EtOAc: 100/0 to 93/7) to afford 2-[benzyl-(2-chloro-ethyl)-amino]-propionic acid ethyl ester (27.40 g, yield=85%).

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