Boron trifluoride etherate (14.6 μL, 0.12 mmol) was added to 23f (155 mg, 0.39 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 (560 mg, 1.55 mmol) in anhydrous CH2Cl2 (9.70 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, 100:1→40:1 CH2Cl2:Acetone) to give 25f as a colorless foam (225 mg, 99%): 1H NMR (CD2Cl2, 400 MHz) δ 8.37 (s, 1H), 7.75-7.73 (m, 2H), 7.60-7.36 (m, 10H), 7.32 (d, J=8.8 Hz, 1H), 5.77 (d, J=1.7 Hz, 1H), 5.26 (s, 2H), 4.76-4.68 (m, 1H), 4.36-4.28 (m, 1H), 3.56 (s, 3H), 3.28 (d, J=7.2 Hz, 1H), 1.37 (s, 3H), 1.31 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 157.2, 153.0 (2C), 152.1 (2C), 152.1, 134.4, 129.9, 129.8, 129.4, 127.7 (2C), 127.5, 127.2 (2C), 127.1 (2C), 127.0, 126.3, 121.5 (2C), 120.3, 111.2 (2C), 93.9, 81.9, 66.5, 59.4 (3C), 20.9 (2C); IR (film) νmax 3400, 2959, 2926, 2853, 2359, 2341, 1819, 1715, 1601, 1522, 1381, 1366, 1261, 1215, 1173, 1111, 1059, 970, 800, 700 cm−1; HRMS (ESI+) m/z: [M+H]+ calcd for C32H29NO10, 588.1870. found, 588.1846.
