To a stirred suspension of crude (2R,3R,4S)-2,3,4,6-tetrakis(benzyloxy)-5-oxohexanal 3 (20 g, 37.13 mmol) in MeOH (400 mL) were added 3-chloro propylamine (47 g, 743 mmol) at 0° C. and activated molecular sieves (100 g) and the reaction mixture was stirred at room temperature for 20 min. Then the reaction mixture was cooled to 0° C. and solid NaBH3CN (9.33 g, 148.5 mmol) was added to the reaction mixture and stirred at same temperature for 1 h. Then the reaction mixture was stirred at room temperature for 20 h. After removal of the molecular sieves through celite pad, the filtrate was concentrated under reduced pressure. The crude mass was dissolved in ethyl acetate (250 mL) and organic part was washed with saturated solution of NaHCO3 (100 mL), dried over Na2SO4 and concentrated under reduced pressure to get crude which was purified by column chromatography using 100-200 mesh silica gel and eluting with 8% EtOAc/hexane to afford (2R,3R,4R,5S)-3,4,5-tris(benzyloxy)-2-[(benzyloxy)methyl]-1-(3-chloropropyl)piperidine 4 (8.0 g, 36%) as white solid.
