Reaktionsschritte
To a flask 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 (1.22 g, 2.187 mmol) was added phosphoric acid, potassium salt (1.393 g, 6.56 mmol), ethyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)cyclohex-3-enecarboxylate (0.613 g, 2.187 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxy-1,1′-biphenyl (S-phos) (0.067 g, 0.164 mmol), and palladium(II)acetate (0.025 g, 0.109 mmol). The mixture was diluted with 1,4-dioxane (10 mL) and water (1 mL), was flushed with nitrogen, then was sealed and heated to 75° C. After 15 h of heating, the mixture was cooled to rt and was concentrated under reduced pressure. The residue was diluted with water (40 mL) and was extracted with ethyl acetate (3×50 mL). The organic layers were washed with brine, dried over magnesium sulfate, filtered, and concentrated under reduced pressure. The residue was purified by flash chromatography using a 10-70% EtOAc in hexanes gradient and an 80 g silica gel column. The fractions containing the expected product were combined and concentrated under reduced pressure to give ethyl 4-((1R,3aS,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 (806 mg, 1.434 mmol, 65.6% yield) as an off-white solid. LCMS: m/e 562.7 (M+H)+, 2.17 min (method 1).
