Reaction Steps
To a solution of (1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-benzyl 9-(3-fluoro-4-(methoxycarbonyl)phenyl)-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-2,3,3a,4,5,5a,5b,6,7,7a,8,11,11a,11b,12,13,13a,13b-octadecahydro-1H-cyclopenta[a]chrysene-3a-carboxylate (3.59 g, 5.27 mmol) in DCE (25 mL) was added TEA (1.176 mL, 8.44 mmol), t-butyldimethylsilane (1.749 mL, 10.54 mmol), and palladium(II) acetate (0.118 g, 0.527 mmol). The mixture was flushed with N2 and heated to 60° C. for 1 h. The mixture was cooled to rt and was filtered through a plug of celite and silica gel (washed with 25% EtOAc in hexanes). The filtrate was concentrated under reduced pressure. The residue was diluted with 25 mL of dioxane and TBAF (75% in water) (2.76 g, 7.91 mmol) was added. The mixture was stirred for 30 minutes at rt then was diluted with 50 mL of 1N HCl. The solids that formed were collected by filtration and were washed with water to give the title compound (2.95 g, 4.99 mmol, 95% yield) as a white solid. 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 7.83 (1H, t, J=7.9 Hz), 6.90-7.00 (2H, m), 5.34 (1H, dd, J=6.1, 1.6 Hz), 4.77 (1H, d, J=2.0 Hz), 4.64 (1H, s), 3.94 (3H, s), 3.04 (1H, td, J=10.7, 4.8 Hz), 2.24-2.34 (2H, m), 2.13 (1H, dd, J=17.3, 6.3 Hz), 1.96-2.06 (2H, m), 1.72 (3H, s), 1.03 (3H, s), 1.02 (3H, s), 0.98 (3H, s), 0.93-0.96 (6H, m), 0.91-1.80 (17H, m).
