Reaction Steps
A solution of 20 (25 mg, 0.095 mmol) in pyridine (2 mL) was cooled to 0° C. To this solution was added acetic anhydride (1.0 mL, 11 mmol) and a catalytic amount of DMAP. The reaction mixture was stirred overnight and allowed to warm to rt. The resulting light yellow solution was diluted with CH2Cl2 (100 mL) and washed with 1 N HCl (3×50 mL), sat. NaHCO3 (1×50 mL), water (1×50 mL) and sat. NaCl (1×50 mL). The combined aqueous layers were back extracted with 50 mL of CH2Cl2. The combined organic layers were dried over Na2SO4 and concentrated. The crude product was purified by silica gel chromatography eluting with a gradient of 1:10 to 1:2 EtOAc/hexanes to afford 39 mg (95%) of a light yellow oil. IR (thin film): 3317, 2106, 1744, 1677, 1529 cm−1. 1H NMR (500 MHz, CDCl3): δ 2.05 (app s, 6H), 2.10 (s, 3H), 2.12 (s, 3H), 3.82 (ddd, 1H, J=2.4, 4.5, 9.6), 3.93 (s, 2H), 4.13 (dd, 1H, J=2.4, 12.6), 4.29 (dd, 1H, J=4.5, 12.6), 5.15 (app t, 1H, J=9.6), 5.21 (app t, 1H, J=5.7), 5.78 (app t, 1H, J=4.5), 6.37 (d, 1H, J=5.7). 13C NMR (125 MHz, CDCl3): δ 20.5, 20.5, 20.6, 20.6, 20.6, 20.8, 20.8, 51.2, 52.4, 52.5, 53.2, 61.4, 61.5, 67.4, 67.6, 69.8, 70.3, 72.0, 72.1, 72.9, 90.2, 92.1, 166.9, 168.6, 169.1, 169.2, 170.6, 170.8, 171.5. HRMS (FAB) m/z 437.1496 (MLi+ C16H22LiN4O10 requires 437.1496).
