Reaction Steps
To the solution of methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-((hydroxyimino)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 (800 mg, 1.399 mmol), in ethanol (40 ml) was added excess of ammonium acetate (1078 mg, 13.99 mmol) and sodium cyanoborohydride (879 mg, 13.99 mmol). The mixture was stirred in an ice bath until cold. To this suspension was added an aqueous solution of titanium(III) chloride (Aldrich Chemicals, 20% solution used as supplied, 10 ml, 1.963 mmol). The resulting mixture was blanketed with nitrogen, ice bath was removed and stirring continued at rt for an hour. LCMS showed the reaction was complete. At this point, the mixture was dark greenish-blue. A solution of sodium hydroxide, (3 ml, 10N) in 25 ml water was added into the reaction mixture, along with 30 ml of methylene chloride. The mixture was stirred vigorously until the dark blue phase was floating on top of the organic phase. The mixture was filtered through a plug of paper cellulose, the filtrate was clear. The organic layer was collected and the aqueous layer was extracted with CH2Cl2 (2×20 ml). The combined organic phase was dried over Na2SO4. The solvent was removed in vacuo to afford methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(aminomethyl)-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 an off-white solid (˜800 mg). The crude material was used in the next step without further purification. LCMS: m/e 558.5 (MH+), 2.53 min (method 2).
