Furfural → methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(furan-2-ylmethylamino)-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 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)benzoate (30 mg, 0.055 mmol) in DCE (0.5 mL) was added furfural (5.71 μL, 0.069 mmol) and titanium(IV) isopropoxide (0.020 mL, 0.069 mmol). The mixture was stirred at rt for 1 h and sodium triacetoxyborohydride (23.38 mg, 0.110 mmol) was added. After stirring the mixture for 16 h at rt an additional 5 μL of furfural was added along with an additional 0.025 g of sodium triacetoxborohydride. After stirring the mixture overnight at rt, it was purified by passing through a plug of silica gel and washing with 0-25% EtOAc in hexanes. The fractions containing the product were combined and concentrated under reduced pressure to give the title compound (31 mg, 0.050 mmol, 90% yield) as a light-yellow film. The product was used in the next step with no additional purification. LCMS: m/e 625.6 (M+H)+, 3.08 min (method 2).

Provenance & Evidence