3-[4-benzyloxy-3-(4-methoxy-benzyloxy)-3,4,4a,6,9,9a-hexahydro-2H-1,5-dioxa-benzocyclohepten-2-yl]-2-[6-(tert-butyl-diphenyl-silanyloxy)-7-(tert-butyl-diphenyl-silanyloxymethyl)-2-vinyl-oxepan-3-yloxy]-propionic acid tert-butyl ester