Reaction Steps
A solution of 17 (180 mg, 0.345 mmol) in 22 mL (0.016 M) of 20% CH3OH--CH2Cl2 was cooled to -78° C. A stream of 3% O3 /O2 (160 L/min) was bubbled through the solution for 72 s. The reaction was immediately quenched with the addition of 0.81 mL of dimethyl sulfide and the mixture was allowed to stir at -78° C. for 5 min before being allowed to warm to 25° C. and stirred for 5 h. The solvent was removed in vacuo. Chromatography (SiO2, 2×20 cm, 30% EtOAc-hexane) afforded 18 (155 mg, 171 mg theoretical, 91%) as a white foamy solid: 1H NMR (CDCl3, 400 MHz) δ9.76 and 9.73 (two s), 8.63 and 8.61 (two s, 1H), 8.41 and 8.36 (two d, 1H, J=8.7 Hz), 7.64 and 7.60 (two dd, 1H, J=1.4, 8.7 Hz), 7.50-7.34 (m, 5H), 7.17 and 7.14 (two s, 1H), 5.26, 5.29 and 5.17 (one s and two d, 2H, J=11.4 Hz), 4.76 and 4.65 (two d, 1H, J=18.8 Hz), 4.01 and 3.95 (two d, 1H, J=18.8 Hz), 1.31 and 1.52 (two s, 9H); 13C NMR (CDCl3, 100 MHz, major rotamer) δ197.3, 154.1, 140.8, 135.6, 133.4, 132.0, 128.8, 128.7, 128.5, 127.9, 127.6, 127.1, 124.2, 118.7, 113.8, 112.0, 110.5, 81.8, 70.9, 58.9, 28.1; IR (film) vmax 2976, 2229, 1706, 1596, 1415, 1369, 1335, 1259, 1225, 1152, 1096, 848 cm-1 ; FABHRMS (NBA) m/z 495.0922 (M+ +H, C25H23BrN2O4 requires 495.0919).
