enantioselective synthesis of the polyhydroxylatedchaincommon to marine natural products oscillariolide and phormidolidesA–C is described herein. This chain represents a synthetic challenge that needs to be solved before the total synthesis of this family of natural products can be approached. It contains seven stereocenters, six of them having a syn-hydroxylated functionality, and a tricky terminal (E)-bromomethoxydiene