Reaction Steps
To a solution of alcohol 25 (5.1 g, 10.7 mmol) in anhydrous CH2Cl2, (diethylamino) sulfur trifluoride (DAST) (9.3 ml, 70.5 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 Na2SO4 and the volatiles removed under reduced pressure. The crude residue was purified by flash silica gel column chromatography (1% EtOAc/Hexane) to give 26 (2.5 g, 49%). [α]24D −98.08° (c 0.51, CHCl3); 1H NMR (500 MHz, CDCl3) δ 7.39-7.26 (m, 5H), 4.92 (ddd, J=6.0, 7.5 & 5.5 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, 2H), 2.70 (m, 1H) 1.08-0.94 (m, 28H), 0.72 (m, 1H), 0.68-0.43 (m, 2H), 0.28 (m, 1H); 13C NMR (125 MHz, CDCl3) δ142.6 (d, J=9.2 Hz), 141.8, 137.9, 128.4, 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), 29.4, 24.5, 17.5, 17.4, 17.3, 17.2, 17.1, 17.0, 16.9, 16.8, 13.4, 13.3, 12.7, 12.5, 7.9; HR-MS Calcd. For (C27H45FO4Si2+H)+ 509.2840, found 509.2923.
