Reaction Steps
To a solution of (1R,3aS,5aR,5bR,7aR,11aR,11bR,13aR,13bR)-benzyl 5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-9-(((trifluoromethyl)sulfonyl)oxy)-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 (3.0 g, 4.43 mmol) in THF (100 mL) was added 1,4-benzenediboronic acid (1.469 g, 8.86 mmol) and tetrakis(triphenylphosphine)palladium(0) (0.259 g, 0.222 mmol). The resulting yellow mixture was purged with N2. Then, a solution of sodium carbonate (2.82 g, 26.6 mmol) in H2O (25.00 mL) was added and the reaction mixture was heated to reflux at 90° C. After 6 h, the reaction mixture was cooled to rt, diluted with EtOAc (50 mL) and washed with H2O (50 mL). The aqueous layer was extracted with EtOAc (2×50 mL). The combined organic layer was filtered through celite pad, washed with brine, dried over MgSO4, filtered and concentrated to afford a light brown solid. The crude material was absorbed onto silica gel (20 g), loaded onto a silica gel column and eluted with 3:1 hexanes:EtOAc to give (4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-((benzyloxy)carbonyl)-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]chrysen-9-yl)phenyl)boronic acid (983 mg, 34.2%) as white solid. 1H NMR (500 MHz, CHLOROFORM-d) δ 8.18-8.14 (m, 2H), 7.43-7.38 (m, 4H), 7.38-7.35 (m, 1H), 7.31-7.29 (m, 1H), 5.37-5.34 (m, 1H), 5.17 (t, J=1.0 Hz, 2H), 4.77 (d, J=1.5 Hz, 1H), 4.64 (s, 1H), 3.08 (td, J=10.8, 4.7 Hz, 1H), 2.35-2.30 (m, 1H), 2.30-2.25 (m, 1H), 2.15 (dd, J=17.1, 6.1 Hz, 1H), 1.98-1.89 (m, 2H), 1.73 (s, 3H), 1.69 (d, J=3.7 Hz, 1H), 1.67-1.64 (m, 1H), 1.56-1.37 (m, 10H), 1.37-1.23 (m, 3H), 1.19 (d, J=13.1 Hz, 1H), 1.07 (dd, J=13.1, 4.3 Hz, 1H), 1.02 (s, 6H), 0.99 (br. s., 3H), 0.99 (br. s., 3H), 0.96-0.93 (m, 1H), 0.87 (s, 3H). 13C NMR (126 MHz, CHLOROFORM-d) δ 175.8, 150.6, 148.41-148.39 (m, 1C), 148.3, 146.8, 136.5, 134.6, 129.7, 128.5, 128.2, 128.1, 123.7, 109.6, 65.7, 56.6, 52.9, 49.6, 49.4, 46.9, 42.4, 41.8, 40.5, 38.4, 37.5, 37.0, 36.3, 33.6, 32.1, 30.6, 29.6, 29.5, 25.7, 21.3, 21.1, 19.8, 19.4, 16.5, 15.6, 14.7. Step 2: A −78° C. solution of (4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-((benzyloxy)carbonyl)-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]chrysen-9-yl)phenyl)boronic acid (0.200 g, 0.308 mmol) in DCM (3 mL) was purged with N2(g). Boron tribromide (1M solution in DCM) (1.079 mL, 1.079 mmol) was added dropwise. The resulting yellow reaction mixture was stirred at −78° C. for 1 h. The cold bath was removed and H2O (5 mL) was added to quench the reaction. The resulting white paste was filtered and washed with H2O. The crude material was dissolved in THF and DCM loaded onto a silica gel column and eluted with 1:1 hexanes:EtOAc. The fractions containing the desired product were reunited and concentrated in vacuo. The residue was further purified by reverse phase HPLC to give (1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-9-(4-boronophenyl)-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-carboxylic acid (45.2 mg, 24.15%) as a white solid. 1H NMR (500 MHz, DMSO-d6) δ 12.09 (br. s., 1H), 7.97 (br. s., 2H), 7.68 (d, J=7.9 Hz, 2H), 7.04 (d, J=7.9 Hz, 2H), 5.18 (d, J=4.6 Hz, 1H), 4.70 (s, 1H), 4.57 (s, 1H), 3.02-2.90 (m, 1H), 2.33-2.23 (m, 1H), 2.12 (d, J=6.4 Hz, 1H), 2.05 (dd, J=17.2, 6.3 Hz, 1H), 1.80 (d, J=7.3 Hz, 2H), 1.69-1.66 (m, 1H), 1.65 (s, 3H), 1.56 (t, J=11.3 Hz, 1H), 1.50 (br. s., 1H), 1.45-1.36 (m, 8H), 1.33-1.28 (m, 1H), 1.23 (br. s., 1H), 1.21-1.12 (m, 3H), 1.02-0.98 (m, 1H), 0.97 (s, 3H), 0.93 (s, 6H), 0.87 (s, 3H), 0.86 (s, 3H). Preparation of Compounds of Formula III.
