Reaction Steps
To a solution of tert-butyl ((3S,7S,8R,9S)-7-benzyl-8-(3-hydroxybutoxy)-9-methyl-2-oxo-1,5-dioxonan-3-yl)carbamate (82 mg, 0.18 mmol, 1.00 equiv) in CH2Cl2 (1.8 mL) were added proton sponge (156 mg, 0.726 mmol, 4.00 equiv) and trimethyloxonium tetrafluoroborate (54 mg, 0.36 mmol, 2.0 equiv). The resulting suspension was stirred at room temperature for 1 h, poured into ½ sat'd NaHCO3 solution (20 mL), and extracted with CH2Cl2 (3×20 mL). The combined organic extracts were dried over Na2SO4, filtered, and concentrated to provide a yellow oil. Purification by automated silica gel column chromatography (1-6% acetone in CH2Cl2) provided tert-butyl ((3S,7S,8R,9S)-7-benzyl-8-(3-methoxybutoxy)-9-methyl-2-oxo-1,5-dioxonan-3-yl)carbamate (71 mg, 84%) as a sticky oil: 1H NMR (400 MHz, CDCl3) δ 7.32-7.23 (m, 2H), 7.23-7.13 (m, 3H), 5.18 (d, J=6.9 Hz, 1H), 5.02-4.86 (m, 1H), 4.60 (q, J=7.2 Hz, 1H), 3.94-3.75 (m, 2H), 3.75-3.62 (m, 1H), 3.62-3.41 (m, 3H), 3.36 (dd, J=10.5, 6.5 Hz, 1H), 3.33-3.22 (m, 4H), 3.21-3.04 (m, 2H), 2.29 (t, J=12.5 Hz, 1H), 2.00-1.81 (m, 1H), 1.81-1.68 (m, 2H), 1.48 (s, 3H), 1.41 (s, 9H), 1.15 (d, J=6.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 172.21, 154.98, 139.93, 139.88, 129.13, 128.42, 126.10, 85.02, 80.03, 75.51, 75.45, 73.41, 73.39, 72.91, 72.58, 69.09, 68.84, 55.94, 55.89, 53.01, 47.27, 47.14, 37.41, 37.35, 35.14, 35.03, 28.27, 19.09, 18.73.
