Reaction Steps
tert-butyl 3-hydroxy-1-(methoxy(methyl)amino)-1-oxopropan-2-ylcarbamate (21a) (4.4 g, 17.5 mmol, 1.0 equiv.) was added to a 100 mL RBF followed by DMF (35 mL) and cooled to 0° C. via an ice bath. Next, TBDMSCl (2.90 g, 19.3 mmol, 1.1 equiv.) and imidazole (2.40 g, 35.1 mmol, 2.0 equiv.) were added to the reaction flask. The solution was stirred at 0° C. for 1 h and then allowed to warm to rt, stirring an additional 2 h. The reaction solution was transferred to a 500 mL separatory funnel with EtOAc (150 mL). The mixture was washed with 1% HCl (3×40 mL), sat. NaHCO3 (1×40 mL), and sat. NaCl (2×40 mL). The organic layer was separated and dried over Na2SO4. The solution was concentrated on a rotary evaporator and dried under vacuum to give 5.9 g (93%) of 22a as an oil which crystallized to a white solid upon standing. Rf=0.54 (50% EtOAc/hexanes); mp=71-72° C.; IR (film) 3437, 3324, 2953, 2929, 2884, 2856, 1715, 1666, 1496, 1471, 1365, 1253, 1171, 1114 cm−1; 1H NMR (500 MHz, CDCl3) δ 5.34 (br d, J=8.5 Hz, 1H, carbamate-NH), 4.73 (br s, 1H, Boc-NH—CH), 3.83 (m, 1H, CH—CH2), 3.77 (m, 1H, CH—CH2), 3.73 (s, 3H, N—OCH3), 3.19 (s, 3H, N—CH3), 1.41 (s, 9H, Boc-t-butyl-CH3), 0.84 (s, 9H, Si-t-butyl-CH3), 0.00 (s, 6H, Si—(CH3)2); 13C NMR (125 MHz, CDCl3) δ 170.9, 155.5, 79.7, 63.6, 61.6, 52.6, 32.3, 28.5, 25.9, 18.4, −5.4; LRMS (ESI-MS m/z): Mass calcd for C16H34N2O5Si [M]+, 362.54. Found 363.
