Synthetic studies of yessotoxin, a polycyclic ether implicated in diarrhetic shellfish poisoning: convergent synthesis of the BCDE ring system via an alkyne intermediate

A convergent synthetic route to the BCDE ring system of yessotoxin, a polycyclic ether marine toxin related to diarrhetic shellfish poisoning, has been developed. The key feature of the present synthesis is the alkylation of acetylene with the B and E ring units, which were prepared from a common intermediate. The alkyne functionality was directly converted to a 1,2-diketone by ruthenium oxidation. Acid treatment of the diketone led to the formation of a tetracyclic dihemiketal structure. O-Methylation of the hydroxyl groups of the dihemiketal and reductive etherification completed the synthesis of the BCDE ring system of yessotoxin.