Reaction Steps
To 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, flushed with N2 and heated to reflux overnight. The mixture was then cooled to rt and diluted with water (75 mL). The mixture was extracted with ethyl acetate (3×75 mL) and washed with brine (75 mL). The combined organic layers were dried with MgSO4, filtered, and concentrated under reduced pressure. The residue was adsorbed to silica gel and purified by silica gel 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 (4.16 g, 6.28 mmol, 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).
