(2S,11aR)-2β,5β,6α,11β-Tetraacetoxy-2,3,4,4a,5,6,10,11-octahydro-4aα,7α,12,12-tetramethyl-1-methylene-7H-6aα,10α-methano-1H-benz[c]azulen-8(9H)-one