Compound 31 (6.41 g, 18.8 mmol) was dissolved in 500 mL anhydrous Et2O and cooled to −25° C. n-BuLi (2.5 M in hexane, 9.8 mL, 24.4 mmol) was added dropwise over 45 min. Lithiation was determined to be complete by TLC after the addition of approximately 7 mL. The lithiated species precipitated from solution. Octafluorocyclopentene (5.18 mL, 37.6 mmol) was added and the reaction mixture stirred at −70° C. for 1.5 hours before warming slowly to −20° C. over 30 min, to 0° C. for 30 minutes then to room temperature for 1 hour. The reaction mixture was quenched with water and extracted with EtOAc (3×100 mL). The combined organic fractions were washed with brine, dried over MgSO4 and concentrated under vacuum. Purification by column chromatography afforded 32 (5.73 g, 67% yield). 1H NMR (600 MHz, CDCl3) δ 7.59 (d, J=8.3, 2H), 7.46 (d, J=8.2, 2H), 7.45-7.35 (m, 6H), 6.74 (dd, J=17.6, 10.9, 1H), 5.81 (d, J=17.6, 1H), 5.31 (d, J=10.9, 1H).
