Reaktionsschritte
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 to give 93 mg crude material which 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).
