Reaction Steps
To a suspension of ethyl 2-(diethoxyphosphoryl)acetate (7.80 g, 34.8 mmol) in anhydrous N,N-Dimethylformamide (DMF) (20 ml) and Tetrahydrofuran (THF) (10 ml) stirred under nitrogen at 0° C. was added NaH (1.288 g, 32.2 mmol) dropwise during 5 min and stirred for 10 mins. The solution was warmed to rt and stirred for 30 mins before (3aS,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-formyl-1-isopropyl-5a,5b,8,8,11a-pentamethyl-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 (4.2 g, 8.70 mmol) was added to above mixture. After sitting overnight, the reaction was quenched by water and washed with saturated NaHCO3, water and brine. The organic fraction was dried over sodium sulfate, filtered and concentrated to give a residue, which was purified on a silica gel column (petrol ether/EtOAc=10:1) to obtain the pure product (E)-ethyl 3-((3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-9-hydroxy-1-isopropyl-5a,5b,8,8,11a-pentamethyl-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)acrylate (3.1 g, 69%) as a white foam. 1H NMR (400 MHz, CHLOROFORM-d) δ=7.01-6.84 (m, 2H), 5.64 (d, J=16.1 Hz, 1H), 4.20 (q, J=7.3 Hz, 2H), 3.26-3.07 (m, 3H), 2.40-2.11 (m, 5H), 2.08-1.91 (m, 2H), 1.89-0.61 (m, 43H).
