Boron trifluoride etherate (7.80 μL, 0.062 mmol) was added to 23e (80.0 mg, 0.21 mmol) and (3aR,4S,7R,7aR)-7-methoxy-6,6-dimethyl-2-oxo-tetrahydro-3aH-[1.3]dioxolo[4,5-c]pyran-4-yl 2,2,2-trichloroacetimidate (299 mg, 0.83 mmol) in anhydrous CH2Cl2 (5.20 mL). After stirring at room temperature for 48 hours, triethylamine (150 μL) was added and the solvent was concentrated. The residue was purified via column chromatography (SiO2, 40:1 CH2Cl2:Acetone) to give 25e as a colorless foam (47.0 mg, 39%): 1H NMR (CDCl3, 500 MHz) δ 8.22 (s, 1H), 7.46 (s, 1H), 7.35-7.27 (m, 5H), 7.17-7.06 (m, 5H), 6.86 (d, J=10 Hz, 1H), 6.01 (d, J=10 Hz, 1H), 5.65 (d, J=1.6 Hz, 1H), 5.23 (s, 2H), 5.16 (s, 2H), 4.77-4.70 (m, 1H), 4.10 (s, 1H), 3.50 (s, 3H), 3.28 (s, 1H), 3.16 (d, J=7.4 Hz, 1H), 1.25 (s, 3H), 1.18 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 155.1, 153.2 (2C), 153.1, 148.6 (2C), 139.6 (2C), 128.7, 128.6 (2C), 128.4 (2C), 128.3 (2C), 128.3 (2C), 126.5, 126.2, 123.1, 122.4, 121.7, 117.6, 114.9, 111.5, 94.7, 82.8, 67.6, 60.6 (2C), 29.7, 27.6, 21.9; IR (film) νmax 2926, 2854, 2359, 2341, 1811, 1709, 1607, 1522, 1456, 1381, 1366, 1259, 1209, 1171, 1078, 1049, 968, 766, 700 cm−1; HRMS (ESI+) m/z: [M+H]+ calcd for C33H31NO10, 602.2026. found, 602.2053.
