Reaction Steps
Trifluoromethanesulfonic acid (120 μl, 204 mg, 1.36 mmol) was added to 32 (184 mg, 0.30 mmol) in 1:1 CH2Cl2:TFA (1.36 mL) and the solution was stirred at room temperature for two hours. The resulting solution was diluted with CH2Cl2 (100 mL), washed with saturated aqueous NaHCO3 (3×50 mL), saturated aqueous NaCl solution (2×50 mL), dried (Na2SO4), filtered, and concentrated. The residue was purified via column chromatography (SiO2, 100:1 EtOAc:MeOH to 4:1 EtOAc:MeOH) to give 34 as a yellow oil (51 mg, 43%): 1H NMR (CD3OD, 500 MHz) δ 9.01 (bs, 1H), 8.61 (bs, 1H), 8.02 (dd, J=8.5, 1.7 Hz, 1H), 7.97 (d, J=1.9 Hz, 1H), 7.74 (d, J=8.9 Hz, 1H), 7.30 (t, J=8.2 Hz, 1H), 7.27 (d, J=1.9 Hz, 1H), 7.19 (dd, J=8.9, 2.1 Hz, 1H), 7.17 (d, J=8.8 Hz, 1H), 7.11-7.08 (m, 2H), 6.89 (m, 1H), 3.88 (s, 3H), 3.81 (s, 3H); 13C NMR (CD3OD, 125 MHz) δ 168.7, 161.2, 160.9, 160.2, 147.1, 146.2, 140.5, 132.0, 132.0, 131.5, 130.4, 130.2, 130.1, 128.5, 127.6, 124.2, 123.2, 121.5, 116.5, 113.8, 112.4, 109.7, 56.5, 55.9; IR (film) νmax 3281, 3203, 2930, 2835, 1605, 1545, 1499, 1371, 1252, 1036, 764, 735 cm−1; HRMS (ESI+) m/z: [M+H]+ calcd for C24H20N2O4, 401.1501. found, 401.1481.
