Enantioselective synthesis of the medium ring ethers, tetrahydrooxepin, oxocane and hexahydrooxonin, of ciguatoxin. Extensive ring-expansion and chemoenzymatic desymmetrization strategy

The extensive ring-expansion strategy for the synthesis of tetrahydrooxepin, oxocane, and hexahydrooxonin, which correspond to the D(E), I and F rings of ciguatoxin (CTX1B, 1). respectively, has been established. Chemoenzymatic acylation of the meso alcohols using a lipase provides an expeditious entry for the enantiomeric building blocks.