(E)-4-((4aR,5aS,6aR,8S,9R,10aS,11aR,13aS)-2,2,9,10a-Tetramethyl-9-trimethylsilanyloxy-dodecahydro-1,3,5,7,11-pentaoxa-benzo[4,5]cyclohepta[1,2-b]naphthalen-8-yl)-but-2-enoic acid benzyl ester