Reaction Steps
To a sealable flask containing methyl 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)-2-fluorobenzoate (50 mg, 0.089 mmol) was added potassium iodide (39.9 mg, 0.240 mmol) and phosphoric acid, potassium salt (83 mg, 0.392 mmol). The mixture was diluted with acetonitrile (1 mL) and 3-(2-oxopyrrolidin-1-yl)propyl trifluoromethanesulfonate (the crude solution prepared above) (1.0 mL, 0.384 mmol) was added. The mixture was flushed with N2, then the vial was sealed and heated to 120° C. After 15.5 h of heating, the mixture was cooled to rt. An additional 0.5 mL of the above crude solution containing the triflate was added and the mixture was again heated to 120° C. After heating the mixture for an additional 70.25 h, the mixture was cooled to rt. The mixture was adsorbed to silica gel and was purified by flash chromatography using a 0-5% MeOH in DCM gradient and a Thomson 12 g silica gel column. The fractions containing the expected product were combined and concentrated under reduced pressure to give methyl 2-fluoro-4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-5a,5b,8,8,11a-pentamethyl-3a-(3-(2-oxopyrrolidin-1-yl)propylamino)-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)benzoate (16 mg, 0.023 mmol, 26.2% yield) as a yellow film. LCMS: m/e 687.5 (M+H)+, 2.04 min (method 2).
