methyl 2-((1aS,2R,3aS,4aR,6S,7S,8R,8aR,9aR,10aS)-7,8-bis(benzyloxy)-6-(2-oxopropyl)-10a-(triethylsilyl)dodecahydrooxireno[2,3-e]pyrano[2',3':5,6]pyrano[3,2-b]oxepin-2-yl)acetate