Reaction Steps
To 24 (1.15 g, 1.49 mmol, 1.0 equiv) in THF (20 mL) in a high density polyethylene vial was added hydrogen fluoride-pyridine (1 mL) once an hour for 4 hours (4 mL total), after which time saturated aqueous ammonium chloride was added and the THF was removed under reduced pressure. The remaining solution was extracted with CH2Cl2. The organics were combined, washed with brine, dried over Na2SO4, and concentrated. Purification by flash chromatography (20→60% EtOAc/hexane) afforded 25 (0.86 g, 94%) as a colorless oil. Rf=0.23 (50% EtOAc/hexane); [α]28D=−29.24° (c=1, CH2Cl2); FTIR (neat, cm−1) 3447, 2932, 1761, 1695, 1588, 1435, 1421, 1242; 1H NMR (400 MHz, DMSO, 80° C.) δ7.18-7.12 (m, 2H), 7.10-7.04 (m, 2H), 6.63 (s, 2H), 6.07-5.94 (m, 3H), 5.90-5.78 (m, 1H), 5.42 (dd, J=15.2, 2.0 Hz, 2H), 5.39 (dd, J=14.0, 1.6 Hz, 1H), 5.30 (dd, J=10.4, 1.6 Hz, 1H), 5.25 (dd, J=10.6, 1.8 Hz, 2H) 5.18 (d, J=16.8 Hz, 1H), 5.13 (d, J=10.4 Hz), 4.73-4.71 (m, 2H), 4.55-4.54 (m, 4H), 4.72 (d, J=4.0 Hz, 2H), 4.36 (d, J=16.0 Hz, 1H), 4.24 (d, J=16.4 Hz, 1H), 4.21-4.12 (m, 1H), 3.62-3.57 (m, 1H), 3.53-3.49 (m, 1H), 2.90-2.77 (m, 2H); 13C NMR (100 MHz, DMSO, 80° C.) δ155.3, 155.1, 152.2, 148.8, 140.1, 136.3, 132.9, 132.8, 131.5, 129.3, 120.1, 116.8, 116.6, 116.3, 105.8, 105.6, 99.1, 69.2, 69.0, 68.1, 64.7, 61.3, 60.5, 48.1, 34.3; HRMS (ES+) calculated for C30H34BrNO8 (M+H)+: 616.1468, found: 616.1570.
