Reaktionsschritte
To a solution of (1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-benzyl 9-(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 (3.82 g, 5.76 mmol) in dichloroethane (100 mL) was added triethylamine (1.285 mL, 9.22 mmol), tert-butyldimethylsilane (1.912 mL, 11.52 mmol), and palladium(II) acetate (0.647 g, 2.88 mmol). The mixture was flushed with N2 and heated to 60° C. After 2 h, the reaction was cooled to rt, filtered through a pad of celite and silica gel to remove the solids which were washed with 25% EtOAc in hexanes. The filtrate was concentrated under reduced pressure and treated with acetic acid (25 mL), THF (10 mL) and water (3 mL). After stirring for 1 h the solids formed were collected by filtration and washed with water to give the title compound (3.62 g, 5.27 mmol, 91% yield) as a white solid. 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 7.94 (d, J=8.28 Hz, 2H), 7.21 (d, J=8.28 Hz, 2H), 5.30 (dd, J=6.15, 1.63 Hz, 1H), 4.75 (d, J=1.76 Hz, 1H), 4.62 (s, 1H), 3.92 (s, 4H), 3.08 (td, J=10.92, 4.27 Hz, 1H), 2.35-2.22 (m, 2H), 2.17-2.06 (m, 1H), 2.02-1.84 (m, 2H), 1.71 (s, 3H), 1.01 (s, 6H), 0.99 (br. s., 3H), 0.98 (s, 9H), 0.94 (s, 6H), 1.78-0.90 (m, 16H), 0.32-0.28 (m, 6H).
