Potassium tert-butoxide → (3R,5R,8S,10S,13S,14S,Z)-17-Ethylidene-10,13-dimethyl-2,3,4,5,6,7,8,10,12,13,14,15,16,17-tetradecahydro-1H-cyclopenta[A]phenanthren-3-OL

Participants

Reaction Conditions

Reaction Steps

A solution of potassium tert-butoxide in THF (1 M, 230 mL, 231 mmol) was added drop wise to a suspension of ethyltriphenylphosphonium bromide (88.7 g, 239 mmol) in THF (150 mL) over 1 h at 25° C. The resulting dark red colored mixture was stirred for an additional 1 h at 25° C. A solution of compound 1.3 (23.0 g, 79.7 mmol) in THF (230 mL) was added slowly to the red-colored mixture at 25° C. The resulting mixture was stirred for 3-4 h, at which point it was determined to be complete by TLC. The reaction was quenched by adding saturated aqueous NH4Cl solution (75 mL). The phases were separated and the aqueous layer was extracted three times with EtOAc (3×150 mL). The organic fractions were combined, washed with saturated brine solution (100 mL), dried over Na2SO4 (75 g), and filtered. The filtrate was concentrated under vacuum and the crude solid was purified by column chromatography [49 mm (W)×600 mm (L), 60-120 mesh silica, 300 g] eluting with ethyl acetate/hexanes (1:9). The fractions containing product were combined and concentrated, providing compound 1.5 (19.1 g, 80.0%) as a white solid.

Provenance & Evidence