Reaction Steps
A solution of 14 (500 mg, 1.65 mmol) in freshly distilled t-BuOH (165 mL) was treated with Et3N (0.276 mL, 1.98 mmol, 1.2 equiv) and 5 g of activated 4 Å molecular sieves. Diphenylphosphoryl azide (0.426 mL, 1.98 mmol, 1.2 equiv) was added and the reaction mixture was warmed at reflux for 14 h. The mixture was cooled to 25° C. and the solvent was removed under vacuum. The residue was dissolved in EtOAc and the organic phase was washed with 10% aqueous HCl, dried (Na2SO4), and concentrated in vacuo. Chromatography (SiO2, 3×20 cm, 20% EtOAc-hexane) afforded 15 (534 mg, 618 mg theoretical, 87%) as a white crystalline solid: mp 145° C. (white needles, 10% EtOAc-hexane); 1H NMR (CDCl3, 250 MHz) δ8.26 (d, 1H, J=8.7 Hz), 8.01 (s, 1H), 7.45 (m, 7H), 7.23 (s, 1H), 6.84 (s, 1H), 5.21 (s, 2H), 1.57 (s, 9H); 13C NMR (CDCl3, 62.5 MHz) δ154.9, 152.5, 138.1, 136.1, 133.6, 132.6, 128.6, 128.2, 127.4, 124.1, 123.6, 123.5, 119.3, 110.5, 106.5, 101.7, 81.1, 70.4, 28.3; IR (KBr) vmax 3327, 2980, 2223, 1701, 1586, 1545, 1420, 1369, 1341, 1251, 1160, 1107, 1064, 1002, 910, 820, 744, 694 cm-1 ; FABHRMS (NBA) m/z 374.1641 (M+, C23H22N2O3 requires 374.1630).
