Reaction Steps
Boron trifluoride etherate (5.30 μL, 0.042 mmol) was added to 23a (50.0 mg, 0.14 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 (171 mg, 0.47 mmol) in anhydrous CH2Cl2 (3.00 mL). After stirring at room temperature for 14 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 25a as a colorless foam (74.0 mg, 95%): 1H NMR (CD2Cl2, 400 MHz) 8.29 (s, 1H), 7.64 (s, 1H), 7.47-7.39 (m, 5H), 6.91 (s, 1H), 5.52 (d, J=3.4 Hz, 1H), 5.26 (s, 2H), 5.23 (dd, J=8.4, 3.5 Hz, 1H), 4.95 (t, J=8.2 Hz, 1H), 3.92 (s, 3H), 3.60 (s, 3H), 3.33 (d, J=8.0 Hz, 1H), 2.42 (s, 3H), 1.38 (s, 3H), 1.33 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 157.6, 152.7, 152.1, 148.1, 144.8, 141.8, 134.5, 127.8, 127.7, 127.5, 127.3, 122.3, 120.2, 119.8, 115.1. 109.6, 105.2, 98.3, 82.0, 77.1, 66.5, 65.5, 59.4, 57.4, 55.1, 26.0, 20.9, 8.9; IR (film) νmax 2957, 2928, 2854, 2359, 2341, 1817, 1709, 1522, 1464, 1389, 1371, 1205, 1174, 1111, 1072, 1034, 957, 800 cm−1; HRMS (ESI+) m/z: [M+H]+ calcd for C28H29NO11, 556.1819. found, 556.1822.
