(E)-3-[(2R,3S,4aR,6S,7R,8aS)-7-Benzyloxy-6-(2-benzyloxy-ethyl)-3-(tert-butyl-dimethyl-silanyloxy)-2,6,8a-trimethyl-octahydro-pyrano[3,2-b]pyran-2-yl]-acrylic acid methyl ester