[Rh(CO)2Cl]2 is as an effective catalyst for endo-selective cyclizations and cascades of epoxy-(E)-enoate alcohols, thus enabling the synthesis of oxepanes and oxepane-containing polyethers from di- and trisubstituted epoxides. Syntheses of the ABC and EF ring systems of (-)-brevisin via all endo-diepoxide-opening cascades using this method constitute a formal total synthesis and demonstrate the utility of this methodology in the context of the synthesis of marine ladder polyether natural products.