Reaction Steps
To a round bottom flask containing a solution of (1R,3aS,5aR,5bR,7aR,11aR,11bR,13bR)-benzyl 5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-9-(trifluoromethylsulfonyloxy)-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 (6.21 g, 9.18 mmol) in dioxane (25 mL) was added 2-propanol (25 mL) and water (15 mL) followed by sodium carbonate monohydrate (3.42 g, 27.5 mmol), 4-methoxycarbonylphenylboronic acid (2.478 g, 13.77 mmol), and tetrakis(triphenylphosphine)palladium(0) (0.318 g, 0.275 mmol). The flask was attached to a reflux condenser, was flushed with N2, and was heated to reflux overnight. After heating the mixture for 14.5 h, it was cooled to rt and was diluted with water (75 mL). The mixture was extracted with ethyl acetate (3×75 mL) and washed with brine. The combined organic layers were dried with MgSO4, filtered, and concentrated under reduced pressure. The residue was adsorbed to silica gel and was purified by flash chromatography using a 0-20% ethyl acetate in hexanes gradient. The fractions containing the expected product were combined and concentrated under reduced pressure to give the title compound, (1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR13bR)-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 (4.16 g, 68.4% yield), as a white foam. 1H NMR (500 MHz, CHLOROFORM-d) δ ppm 7.92 (d, J=8.24 Hz, 2H), 7.40-7.29 (m, 5H), 7.19 (d, J=8.24 Hz, 2H), 5.28 (dd, J=6.10, 1.83 Hz, 1H), 5.19-5.07 (m, 2H), 4.73 (d, J=1.83 Hz, 1H), 4.60 (s, 1H), 3.90 (s, 3H), 3.04 (td, J=10.91, 4.73 Hz, 1H), 2.20-2.32 (m, 2H), 2.09 (dd, J=17.24, 6.26 Hz, 1H), 1.95-1.82 (m, 2H), 1.69 (s, 3H), 0.97 (s, 3H), 0.95 (s, 3H), 0.92 (s, 3H), 0.91 (s, 3H), 1.75-0.87 (m, 17H), 0.82 (s, 3H).
