To a solution of benzyl((2R,3R)-3-(tert-butoxy)-1-hydroxybutan-2-yl)carbamate (5.88 g, 19.9 mmol) in 100 mL DMF was added NaH (60% in mineral oil, 1.62 g, 40.6 mmol) at 0° C. The reaction mixture was stirred for 30 min at 0° C. To the reaction mixture were added 4-methoxybenzyl chloride (4.07 mL, 29.9 mmol) and tetrabutylammonium iodide (0.74 g, 1.99 mmol) and the resulting mixture was warmed to room temperature and stirred for 15.5 h. The reaction mixture was poured into ice water (200 mL) forming a white suspension. EtOAc (100 mL) was added and the resulting mixture was stirred for 5 min to form a clear two layer solution. After separation, the aqueous phase was extracted with EtOAc (100 mL×3). The combined organic solution was washed with brine (80 mL), dried over Na2SO4, filtered and concentrated. Flash column chromatography (EtOAc/Heptane 0 to 70%) gave 5.90 g of (R)-4-((R)-1-(tert-butoxy)ethyl)-3-(4-methoxybenzyl)oxazolidin-2-one with minor impurities. Major product 1H NMR (400 MHz, MeOD) δ 7.38-7.29 (m, 2H), 6.99-6.93 (m, 2H), 4.68-4.58 (m, 1H), 4.33 (dd, J=9.3, 4.5 Hz, 1H), 4.27-4.17 (m, 2H), 3.89 (dd, J=6.4, 4.8 Hz, 1H), 3.81 (s, 3H), 3.65 (dd, J=9.0, 4.6 Hz, 1H), 1.09 (s, 9H), 1.02 (d, J=6.3 Hz, 3H). MS m/z 308.2 (M+H).
