Seven-membered oxacycles are structural units that are present in a wide variety of bioactive natural products, 1., , , , , , and including the monocyclic zoapatanol, 2., , and the polycyclic hemibrevetoxin B 3., , and (Fig. 1) and more complex polyether toxins such as ciguatoxin 4., and and brevetoxins A and B. 5 Because of their unusual molecular architecture, these molecules are challenging synthetic targets for organic chemists. ... We recently described the synthesis of seven- ...