Reaction Steps
Boron trifluoride etherate (16.7 μL, 0.13 mmol) was added to 23b (170 mg, 0.44 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 (643 mg, 1.77 mmol) in anhydrous CH2Cl2 (11.1 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 25b as a colorless foam (246 mg, 95%): 1H NMR (CDCl3, 500 MHz) 8.17 (s, 1H), 7.35-7.27 (m, 5H), 6.84 (s, 1H), 5.96 (s, 1H), 5.15 (s, 2H), 4.99 (d, J=7.5 Hz, 1H), 4.59 (d, J=9.7 Hz, 1H), 4.23 (d, J=9.6 Hz, 1H), 3.97 (t, J=6.6 Hz, 1H), 3.82-3.75 (m, 2H), 3.37 (s, 3H), 1.84-1.79 (m, 2H), 1.51 (s, 3H), 1.41 (s, 3H), 1.18 (s, 3H), 1.00 (t, J=7.5 Hz, 3H); 13C NMR (CDCl3, 125 MHz) δ 157.8, 154.3, 152.2, 151.8, 146.7, 144.2, 142.9, 134.6, 127.8, 127.6, 127.5, 127.5, 127.2, 121.0, 120.9, 111.1, 105.3, 101.7, 91.6, 85.7, 82.8, 80.0, 69.8, 58.1, 54.8, 28.3, 28.2, 22.4, 21.3, 9.4; IR (film) νmax 2961, 2939, 2906, 2359, 2341, 1811, 1757, 1726, 1522, 1445, 1371, 1267, 1175, 1113, 1086, 825, 768 cm−1; HRMS (ESI+) m/z: [M+Na]+ calcd for C30H33NO11, 606.1952. found, 606.1950.
