(3aS,4R,5R,6S,7R,7aS)-6'-Bromo-4-isocyanato-7'-methoxy-2,2-dimethyl-6,7-bis-triethylsilanyloxy-3a,4,5,6,7,7a-hexahydro-[5,5']bi[benzo[1,3]dioxolyl]