Reaction Steps
To a solution of 21 (10 g, 87% purity, 24.3 mmol) in THF (70 ml) was added tert-BuOLi (2.5 g, 31.2 mmol) at 5° C. in one portion. The solution was cooled to between 0 and 5° C. and trifluoroethyl trifluoromethanesulfonate (10.0 g, 43 mmol) was added in one portion. DMPU (7 mL) was added slowly over 15 min while maintaining the reaction temperature below 5° C. After the mixture was stirred at 0° C. for 3 h, additional tert-BuOLi (0.9 g, 11.2 mmol) was added. The mixture was aged for an additional 90 min. The mixture was quenched with 0.2 N HCl (70 ml), followed by addition of heptane (80 ml). The organic layer was separated and aqueous layer extracted with heptane (30 ml). The combined organic layers were washed with 15% aqueous citric acid (50 mL) and 5% aqueous NaHCO3 (50 mL). The solution was concentrated under vacuum at 40° C. and the resulting oil was dissolved in iPAc (30 mL). The solution was used directly in the next step without further purification. The HPLC analysis indicated that the solution contained 22 (9.8 g, 92% as cis and trans mixture in a ratio of 6.5 to 1) along with 4% of starting material 21 and 8% of a N,N′-alkylated compound. Analytically pure 22 (cis isomer) was isolated by chromatography on silica gel with ethyl acetate and heptane as an eluant. 1H NMR (CDCl3, 500 MHz): δ 7.15 (m, 1H), 6.85 (m, 1H), 5.45 (broad, s, 1H), 4.90 (m, H), 4.20 (m, 1H), 3.92 (m, 2H), 3.28 (m, 1H), 2.70 (m, 2H), 1.48 (s, 9H), 1.20 (d, J=5.9 Hz, 3H); 13C NMR (CDCl3, 100 MHz): δ 170.2, 156.9 (ddd, J=245, 6.3, 2.7 Hz), 156.0, 149.6 (ddd, J=251, 14.8, 8.8 Hz), 147.6 (ddd, J=246, 13.9, 3.6 Hz), 124.5 (q, J=281 Hz), 117.6 (dd, J=19.2, 3.7 Hz), 116.4 (dd, J=19.1, 10.4 Hz), 111.4 (ddd, J=25.8, 6.4, 4.1 Hz), 56.6, 52.8, 45.3 (q, J=34.2 Hz), 35.2, 28.7, 28.3 (br t, J=4 Hz), 14.6; HRMS: m/z calcd for C19H22F6N2O3 (M+H): 441.1607. found 441.1617.
