Reaction Steps
A solution of 15 (137 mg, 0.366 mmol) in freshly distilled THF (7.3 mL) and cooled to -78° C. under Ar was treated with 10 μL of a 1 μL/mL solution of H2SO4 in THF and the solution was stirred for 20 min before the addition of NBS (78 mg, 439 mmol, 1.2 equiv). The reaction mixture was allowed to warm to -60° C. and was stirred for 4 h at which time the reaction was complete by TLC. Et2O (7.3 mL) was added and the resulting organic phase was washed with 5% aqueous NaHCO3 (1×10 mL), saturated aqueous NaCl (1×10 mL), dried (MgSO4), and concentrated in vacuo. Chromatography (SiO2, 2×20 cm, 10% EtOAc-hexane) afforded 16 (145 mg, 166 mg theoretical, 87%) as a white crystalline solid: mp 179° C. dec (white needles, 10% EtOAc-hexane); 1H NMR (CDCl3, 250 MHz) δ8.40 (s, 1H, C8-H), 8.26 (d, 1H, J=8.5 Hz), 8.23 (s 1H, C3-H), 7.5-7.3 (m, 6H), 5.23 (s, 2H), 1.58 (s, 9H); 13C NMR (CDCl3, 75 MHz) δ154.4, 152.4, 137.0, 136.0, 132.2, 132.0, 128.7, 128.6, 128.4, 128.0, 124.9, 124.8, 124.2, 119.1, 111.9, 102.0, 81.9, 70.8, 28.3; IR (KBr) vmax 3416, 2978, 2230, 1738, 1623, 1603, 1570, 1498, 1405, 1364, 1335, 1229, 1158, 990, 970, 878, 850, 823, 758, 696 cm-1 ; FABHRMS (NBA-CsI) m/z 584.9793 (M+ +Cs, C23H21BrN2O3 requires 584.9790).
