Reaction Steps
A DCM (2.3 mL) solution of 25 (47.7 mg, 0.12 mmol, 1 equiv.) and pyridine (57 μL, 0.70 mmol, 6 equiv.) was cooled to −40° C. in a 10-mL recovery flask, and trifluoromethanesulfonic anhydride (99 μL, 0.59 mmol, 5 equiv.) was added dropwise. The yellow slurry was allowed to slowly warm to 0° C. over 45 min, whereupon it was quenched at 0° C. with saturated aqueous NaHCO3. The mixture was extracted thrice with EtOAc. The combined organic extracts were washed with H2O and brine, dried over Na2SO4, filtered, and concentrated in vacuo to a brown oil, which was used without further purification due to its propensity to decompose upon standing. A THF (1 mL) solution of this brown oil was cooled to −78° C. in a 10-mL test tube, and a freshly prepared THF solution of lithium diethylamide (0.50 M, 1.2 mL, 0.59 mmol, 5 equiv.) was added. The resulting brown-orange solution was allowed to slowly warm to 0° C. over 40 min and stirred at 0° C. for 10 min. At this time, chlorotrimethylsilane (150 μL, 1.2 mmol, 10 equiv.) was added. The red solution subsequently turned bright orange and was stirred at 0° C. for 15 min. The solution was then quenched at 0° C. with saturated aqueous NaHCO3 and extracted thrice with EtOAc. The organic extracts were combined, washed with H2O and brine, dried over Na2SO4, filtered, and concentrated in vacuo to a brown oil. Flash column chromatography (30 mL SiO2, 9:1 to 8:2 hexane:EtOAc) afforded 16.5 mg (42 μmol, 35% yield over 2 steps) of 26 as a yellow oil. TLC Rf 0.39 (8:2 hexane:EtOAc). TLC Rf 0.39 (8:2 hexane:EtOAc). 1H NMR (500 MHz; C6D6): δ 5.58 (t, J=6.9 Hz, 1H), 5.50 (t, J=7.2 Hz, 1H), 5.45 (s, 1H), 3.05 (s, 3H), 3.02 (s, 3H), 3.01 (s, 3H), 2.87-2.79 (m, 2H), 2.37 (m, 2H), 1.99 (dd, J=13.4, 6.6 Hz, 1H), 1.87 (td, J=12.3, 5.2 Hz, 1H), 1.79 (s, 3H), 1.77-1.73 (m, 2H), 1.70 (s, 6H), 1.60 (s, 3H), 1.56 (s, 3H), 0.89 (t, J=7.0 Hz, 1H).
