(2S,3R,4S,5R,6R)-2-(3-(4-(2-(allyloxy)ethyl)benzyl)-4-chlorophenyl)-3,4,5-tris(benzyloxy)-6-(benzyloxymethyl)-2-methoxytetrahydro-2H-pyran (intermediate BJ) (55 mg, 0.065 mmol) was taken up in 1 mL anhydrous DCM kept under argon, and triethylsilane (31.4 μL, 0.197 mmol) was added. The mixture was brought to −20° C. and borontrifluoride diethyletherate (20.1 μL, 0.164 mmol) was added. The mixture was allowed to warm and stirred at −5° C. to 0° C. for 3 h. Water (0.5 mL) was added to quench the reaction and the organic layer was separated. The aqueous layer was extracted with DCM (1 mL), and the combined organic solution was washed with brine (1 mL), dried (Na2SO4), filtered and evaporated. Preparative TLC using 10:1 hexane:EtOAc gave intermediate BK (39.5 mg, yield 60%). 1H NMR (300 MHz, CDCl3): δ 7.30-7.03 (m, 27H), 5.90 (m, 1H), 5.22 (m, 2H), 4.88-4.70 (m, 3H), 4.65-4.38 (m, 5H), 4.16-4.08 (m, 3H), 4.05-3.88 (m, 4H), 3.82-3.72 (m, 5H), 3.60-3.52 (m, 3H); LC-ESI-MS (m/z): 808 (M+H).
