Reaction Steps
To a suspension of ethyl 2-(diethoxyphosphoryl)propanoate (3.12 g, 13.09 mmol) in DMF (35 mL) stirred under nitrogen at 0° C. was added NaH (0.60 g, 80 wt %, 20 mmol) during 5 min and stirred for 10 mins. The solution was warmed to rt and stirred for 30 mins before (3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-formyl-1-isopropyl-5a,5b,8,8,11a-pentamethyl-2-oxo-3,3a,4,5,5a,5b,6,7,7a,8,9,10,11,11a,11b,12,13,13a-octadecahydro-2H-cyclopenta[a]chrysen-9-yl acetate (5.0 g, 10 mmol) was added to above mixture. After overnight, the reaction was quenched with water and washed with saturated NaHCO3 and water. The solid was solved into EtOAc, dried over Na2SO4, filtered and concentrated to remove the majority of solvent. The residue was recrystallized from petroleum ether/EtOAc (8:1), filtered and the filtrate was concentrated to give the residue, which was purified by silica gel eluting with petroleum ether/EtOAc (15:1-10:1) to obtain the product (E)-ethyl 3-((3aS,5aR,5bR,7aR,9S,11aR,11bR,13aS)-9-acetoxy-1-isopropyl-5a,5b,8,8,11a-pentamethyl-2-oxo-3,3a,4,5,5a,5b,6,7,7a,8,9,10,11,11a,11b,12,13,13a-octadecahydro-2H-cyclopenta[a]chrysen-3a-yl)-2-methylacrylate (1.0 g, 1.291 mmol, 12.82%) as a yellow solid.
