Reaction Steps
To a solution of alcohol 6 (6.5 g, 13.2 mmol) in anhydrous CH2Cl2, (diethylamino)sulfur trifluoride (DAST, 1.84 mL, 13.9 mmol) was added slowly at room temperature. The reaction mixture was quenched with iced H2O after 20 min. The organic layer was collected and the aqueous phase was extracted with dichloromethane. The organic layer was then combined, dried over magnesium sulfate, filtered and concentrated in vacuo. The crude residue was used immediately for the next deprotection step. The analytic sample of 8 was obtained by the purification using column chromatography on a silica gel (EtOAc:Hexanes=1:100 to 1:20).[α]24D −104.08° (c 0.51, CHCl3); 1H NMR (500 MHz, CDCl3) δ 7.39-7.26 (m, 5H), 5.36 (t, J=2.5 Hz, 1H), 5.20 (dd, J=2.5 and 5.0 Hz, 1H), 4.92 (ddd, J=6.0, 7.5 and 55.0 Hz, 1H), 4.78 (d, J=11.5 Hz, 1H), 4.65 (d, J=11.5 Hz, 1H), 4.31-4.26 (m, 1H), 4.23-4.16 (m, 1H), 4.01-3.92 (m, 1H), 1.08-0.94 (m, 27H); 13C NMR (100 MHz, CDCl3) δ 142.6 (d, J=9.2 Hz), 137.9, 128.4, 127.8, 127.7, 112.7, 103.4 (d, J=189.0 Hz), 80.4 (d, J=21.3 Hz), 73.8 (d, J=19.8 Hz), 71.3, 61.6, 48.8 (d, J=5.3 Hz), 17.5, 17.4, 17.1, 17.0, 16.9, 16.8, 13.4, 13.3, 12.7, 12.5. HR-MS Calcd. for (C26H43FO4Si2+H)+ 495.2762, found 495.2769.
