Dichloromethane → (2R)-Methyl 2-((tert-butoxycarbonyl)amino)-3-((tetrahydro-2H-pyran-2-yl)oxy)propanoate

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To a 2 L three neck flask fitted with a magnetic stirbar, under argon, was added CH2Cl2 (500 mL), PPTs (pyridinium-p-toluene sulfonate) (2 g, 0.008 mol). After dissolving the PPTs by stirring, N-(tert-butoxycarbonyl)-D-serine methyl ester 1 (97.9 g, 0.446 mol) was added to give a clear yellow solution. DHP (3,4-dihydro-2H-pyran) (105 mL, 1.16 mol) was added in one portion. The clear yellow solution was stirred at room temperature over 60 hr to give a slightly cloudy yellow mixture. The mixture was evaporated to give an off-white solid. Ethyl acetate (650 mL) was added to the residue and stirred for 20 minutes to dissolve. The solution was washed with 1.2M HCl (1×500 mL) to pH 4, sat. NaHCO3 (1×600 mL plus 1λ300 mL) to pH 7, brine (1×500 mL), dried over MgSO4 (20 g), filtered and concentrated under reduced pressure to give 129 g (96%) of product 2 as a waxy white solid. 1H NMR (60 MHz, CDCl3) δ 5.2-5.7 (br m, 1H), 3.4-4.8 (m, 9H), 1.4-1.8 (m, 15H).

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