Reaction Steps
To a cold solution (0° C.) of 21 (40 mg, 50.3 μmol) in dry CH2Cl2 (10 mL) were added 4 Å molecular sieves (0.40 g) and BF3.OEt2 (0.18 g, 1.27 mmol) with vigorous stirring. The mixture was stirred at 0° C., and the reaction was monitored by TLC (hexanes/EtOAc 2:1). On the disappearance of 21 (˜5 h), the reaction was quenched by adding saturated aqueous NaHCO3 solution (10 mL). After the mixture was stirred for 30 min, CH2Cl2 (30 mL) was added. The organic layer was separated and washed with saturated aqueous NaHCO3 solution (20 mL), water (2×20 mL), and brine (2×20 mL). The solution was dried (Na2SO4) and concentrated under vacuum. The residue was purified by chromatography (CH2Cl2/MeOH 9:1) to give 3 (20.1 mg, 61%). 1HNMR δ 7.96 (d, 2H, J=8.4 Hz), 7.84 (s, 1H), 7.34 (d, 2H, J=8.4 Hz), 7.11-7.01 (m, 4H), 5.98 (s, 2H), 4.39 (t, 2H, J=7.2 Hz), 3.85-3.57 (m, 4H), 3.56-3.01 (br s, 4H), 2.61-2.51 (m, 4H), 2.55 (s, 6H), 2.00-1.92 (m, 2H), 1.70-1.56 (m, 2H), 1.43 (s, 6H), 1.46-1.05 (m, 4H); 13C NMR δ 155.6, 147.0, 143.0, 141.2, 139.8, 138.6, 134.7, 131.4, 128.6, 128.5, 128.3, 126.3, 122.5, 121.3, 119.9, 50.4, 35.1, 30.8, 30.3, 29.7, 29.4, 26.0, 14.6, 14.1; 19F NMR δ-146.1 (m). HRMS m/z: calcd for C37H46BF2N6O2 (MH+), 655.3737; found, 655.3746.
