The above crude product tert-butyl (S)-1-hydroxy-3-((R)-tetrahydro-2H-pyran-3-yl)propan-2-ylcarbamate was dissolved in anhydrous DCM (22 mL). To this solution was added pyridine (2 mL) and TsCl (1.230 g, 6.45 mmol). After stirred at rt for 4 hr, another batch of pyridine (3 mL) and TsCl (0.700 g, 3.67 mmol) was added and stirred for another 12 hr. The reaction mixture was diluted with EtOAc (80 mL), washed with 1N HCl (75 mL), followed by H2O (2×30 mL), saturated aq. NaHCO3, brine, and dried over anhydrous Na2SO4, and filtered, and concentrated under reduced pressure. The resulted slurry was purified through flash chromatography on silica gel (eluted with gradient system: 0-35% EtOAc in hexane) to afford (S)-2-(tert-butoxycarbonylamino)-3-((R)-tetrahydro-2H-pyran-3-yl)propyl 4-methylbenzenesulfonate, 670 mg, yield 75% for two steps. MS ESI+ve m/z 436 (M+Na).
