Synthesis of medium-sized cyclic allylic ethers by ring-closing metathesis and subsequent elaboration to sub-units found in the brevetoxins and ciguatoxins

Construction of fused polycyclic ethers by strategies involving ring-closing metathesis

Large fused polycyclic ether natural products of marine origin are some of the most complex and formidable synthetic targets found in Nature, and they continue to fascinate and inspire those engaged in target-directed synthesis and the development of new synthetic methods. Novel strategies for the rapid and stereoselective assembly of fused polyethers have been devised in which ring-closing metathesis reactions are used to accomplish cyclic ether construction. Two-directional and iterative ring construction approaches involving ring-closing metathesis are being employed to assemble polyether sequences found in marine natural products such as the ciguatoxins and gambieric acids.

Synthesis of the carbocyclic core of the cornexistins by ring-closing metathesis

An advanced intermediate in the synthesis of the phytotoxins cornexistin and hydroxycornexistin has been synthesized. Sequential palladium-mediated sp(2)-sp(3) fragment coupling and ring-closing diene metathesis have been used to construct the nine-membered carbocyclic core found in the natural products. [reaction--see text]

C-glycosides to fused polycyclic ethers. A formal synthesis of (+/-)-hemibrevetoxin B

This paper describes a formal total synthesis of the marine ladder toxin hemibrevetoxin B from Danishefsky's dienes. This approach couples the generation of C-glycosides from cyclic enol ethers with metathesis or acid-mediated annulation reactions. The result is a highly efficient synthesis of the tetracyclic ring system of hemibrevetoxin B.