Recent Advances in the Synthesis of trans-Fused Polycyclic Ethers by Hydroxy-Epoxide-Cyclization and Ether-Ring-Expansion Reactions

Natural trans-fused polycyclic ethers, produced by marine sources such as dinoflagellates, are hypothesized to be constructed efficiently from the corresponding polyepoxide precursors by a cascade of ring-closure reactions. The efficiency of the biogenetic pathway has been attractive for synthetic chemists and has prompted them to develop new methods for the construction of cyclic ethers from epoxides. In this review, recent advances in the synthesis of trans-fused polycyclic ethers by hydroxy-epoxide-cyclization reactions via monocyclic epoxonium ion intermediates and ether-ring-expansion reactions via bicyclic epoxonium ion intermediates are described.