(2E)-2-Methyl-2-butenoic Acid (2aR,4S,4aS,6R,9S,11S,12S,12aR,12bS)- 12b-(acetyloxy)-2a,3,4,4a,5,6,9,10,11,12,12a,12b-dodecahydro-4,6,9,11-tetrahydroxy-4a,8,13,13-tetraMethyl-5-oxo-7,11-Methano-1H-cyclodeca[3,4]benz[1,2-b]oxet-12-yl Ester