[CH2:1]([O:3][C:4]([C@@H:6]1[CH2:10][CH2:9][CH:8](OC)[N:7]1[C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14])=[O:5])[CH3:2].[CH2:20]([Si](C)(C)C)[CH:21]=[CH2:22].B(F)(F)F.CCOCC.C([O-])(O)=O.[Na+]>C(Cl)Cl.O>[CH2:1]([O:3][C:4]([C@@H:6]1[CH2:10][CH2:9][CH:8]([CH2:22][CH:21]=[CH2:20])[N:7]1[C:13]([O:15][C:16]([CH3:17])([CH3:18])[CH3:19])=[O:14])=[O:5])[CH3:2]
A solution of 9.25 g of α-methoxycarbamate 168 (33.8 mmol) in 100 ml of anhydrous CH2Cl2 was cooled to −78° C., added initially with 13.50 ml of allyltrimethylsilane (84.6 mmol, 2.5 eq.), followed by dropwise addition of 8.58 ml of BF3.OEt2 (67.7 mmol, 2 eq.) and stirring for one hour. Thereafter, 10 ml of H2O and 30 ml of saturated NaHCO3 solution were added at low temperature, the batch was allowed to come to 0° C., stirred for 30 min and thawed to RT. After separating the phases, the aqueous phase was extracted with 3×50 ml of CH2Cl2, the combined organic phases were washed with 30 ml of saturated NaCl solution and dried over MgSO4. After removing the solvent, the residue was purified using silica gel column chromatography (EE/CH 1:6) to obtain 6.83 g of allyl substitution product 169 (24.1 mmol, 71%) as a colorless oil (mixture of epimers, cis/trans 4:1).
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