A solution containing 22 (4.49 g, 9.42 mmol) in anhydrous THF (50 mL) was cooled to 0° C. Tetra-n-butylammonium fluoride (1 M in THF, 14 mL, 14 mmol) was added via syringe. After 1 h, reaction complete by TLC analysis [3:1 hexane/EtOAc, Rf(22)=0.7; Rf(23)=0.1] therefore diluted with EtOAc. The EtOAc solution was washed twice with 1 M HCl, water, brine, dried over anhydrous Na2SO4, filtered, and concentrated to afford 3.9 g of 23 (>100%; contaminated with some TBS-containing impurities) as a tan-colored oil which was used without further purification. 1H NMR (CDCl3, 300 MHz) δ7.59 (br s, 1H), 7.01-6.85 (m, 3H), 4.19-4.10 (m, 3H), 3.90 (br s, 2H), 3.38-3.31 (m, 2H), 3.15 (dd, J=1.4, 4.6 Hz, 1H), 2.68 (m, 1H), 1.79-1.72 (m, 4H), 1.47 (d, J=10.9 Hz, 9H) ppm.
