Propanoic acid, 3-[(1S)-1-[(1S,3aS,4E,7aS)-4-[(2Z)-[(3S,5R)-3,5-bis[[(1,1-dimethylethyl)dimethylsilyl]oxy]-2-methylenecyclohexylidene]ethylidene]octahydro-7a-methyl-1H-inden-1-yl]ethoxy]-, ethyl este