Reaction Steps
To a vial containing (1R,3aS,5aR,5bR,7aR,11aR,11bR,13aR,13bR)-3a-amino-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 trifluoromethanesulfonate (0.05 g, 0.090 mmol) was added phosphoric acid, potassium salt (0.057 g, 0.269 mmol), (S)-benzyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)cyclohex-3-enecarboxylate (0.062 g, 0.181 mmol) (enantiomer 2 prepared above), 2-dicyclohexylphosphino-2′,6′-dimethoxy-1,1′-biphenyl (S-phos) (5.52 mg, 0.013 mmol), and palladium(II) acetate (2.013 mg, 8.96 mmol). The mixture was diluted with 1,4-dioxane (1 mL) and water (0.1 mL), was flushed with nitrogen, then was sealed and heated to 75° C. After 6 h of heating, the mixture was cooled to rt, was diluted with dichloromethane, and was dried with sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure. The residue was purified by flash chromatography using a 10-60% ethyl acetate in hexanes gradient and a 12 g silica gel column. The fractions containing the expected product were combined and concentrated under reduced pressure to give (S)-benzyl 4-((1R,3 aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-amino-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)cyclohex-3-enecarboxylate (0.042 g, 0.067 mmol, 75% yield) as an off-white solid. 1H NMR (500 MHz, chloroform-d) δ=7.42-7.31 (m, 5H), 5.37 (br. s., 1H), 5.21-5.17 (m, 1H), 5.16 (s, 2H), 4.75 (d, J=1.9 Hz, 1H), 4.62 (s, 1H), 2.65-2.52 (m, 2H), 2.39-2.32 (m, 2H), 2.22-2.15 (m, 2H), 2.10-1.96 (m, 3H), 1.71 (s, 3H), 1.09 (s, 3H), 0.98 (s, 6H), 0.91 (s, 3H), 0.88 (s, 3H), 1.82-0.83 (m, 23H).
