Reaction Steps
To a sealable 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 (0.25 g, 0.448 mmol) was added diethyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)cyclohex-3-ene-1,1-dicarboxylate (0.374 g, 0.531 mmol), sodium carbonate hydrate (0.167 g, 1.345 mmol), and palladium tetrakis (0.016 g, 0.013 mmol). The mixture was diluted with 1,4-dioxane (4 mL) and water (1 mL) then was flushed with nitrogen and was sealed and heated to 85° C. in an oil bath. After 5 h of heating, the mixture was cooled to rt, was diluted with water (20 mL), and was extracted with ethyl acetate (3×20 mL). The combined 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 10-50% ethyl acetate in hexanes gradient. diethyl 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-ene-1,1-dicarboxylate, a white solid, was recovered as the minor isolate (0.032 g, 0.05 mmol, 11.3% yield). LCMS: m/e 634.6 (M+H)+, 2.10 min (method 1).
