methyl (2aR,2a1R,4S,4aR,7aS,8S,10R,10aS)-4-((1S,2R,4S,6S)-6-(benzoyloxy)-3-oxobicyclo[2.2.1]heptan-2-yl)-4-methyl-3,5-dioxo-8,10-bis((triethylsilyl)oxy)octahydro-1H,7H-naphtho[1,8-bc:4,4a-c']difuran-10a(8H)-carboxylate