tert-butyl N-(2-oxoethyl)carbamate → methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(2-(tert-butoxycarbonylamino)ethylamino)-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

Participants

Reaction Steps

To 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 (1.00 g, 1.84 mmol) in DCE (5 mL) was added tert-butyl 2-oxoethylcarbamate (1.17 g, 7.36 mmol) and tetraisopropoxytitanium (0.700 mL, 2.39 mmol). The reaction mixture was stirred for 1 h, then sodium triacetoxyborohydride (1.17 g, 5.52 mmol) was added. The reaction mixture was stirred for 18 h. The reaction mixture was quenched with sodium bicarbonate and was extracted with DCM (3×40 mL). The combined organic layers were dried over sodium sulfate, filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography using ethyl acetate and hexanes (20-100%) as the eluent to provide the title compound as a pale yellow oil. (900 mg, 71%). LCMS: m/e 688.24 (M+H)+, 2.51 min (method 11).

Provenance & Evidence