Diisopropylethylamine → tert-butyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-((3-tert-butoxy-N-(2-(dimethylamino)ethyl)-3-oxopropanamido)methyl)-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)benzoate

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Reaction Steps

To a solution of tert-butyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-((2-(dimethylamino)ethylamino)methyl)-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)benzoate (27 mg, 0.040 mmol) in DCE (2 ml) was added Hunig's base (0.021 ml, 0.121 mmol), DMAP (1 mg, 8.19 μmol), Mono-tert-butyl malonate (0.012 ml, 0.080 mmol), and O-benzotriazol-1-yl-N,N,N′,N′-tetramethyluronium tetrafluoroborate (19.38 mg, 0.060 mmol). The mixture was stirred at rt. After 5 h of stirring, the mixture was loaded directly onto a silica gel column and was purified using a 0-5% MeOH in dichloromethane gradient to afford tert-butyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-((3-tert-butoxy-N-(2-(dimethylamino)ethyl)-3-oxopropanamido)methyl)-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)benzoate as a white foam (31.8 mg, 0.039 mmol, 97% yield). LCMS: m/e 813.4 (M−H)−, 3.46 min (method 6).

Provenance & Evidence