(2aR,4S,4aS,6R,9S,11S,12S,12aR,12bS)-12b-acetoxy-11-hydroxy-4a,8,13,13-tetramethyl-5-oxo-4,6,9-tris((triethylsilyl)oxy)-2a,3,4,4a,5,6,9,10,11,12,12a,12b-dodecahydro-1H-7,11-methanocyclodeca[3,4]benzo[1,2-b]oxet-12-yl 3,3-dimethylpent-4-enoate