Synthesis of medium ring ethers. Part 3. Disproof of the proposed 2,8-disubstituted oxocane structure for gloeosporone. Synthesis of pseudo-gloeosporone

Synthesis of the cis- and trans-2,8-disubstituted oxocane derivatives 2 and 3(carrying the unusual γ,δ-diketohexanecarboxylic acid side chain) by ozonolysis of the alkynes 14 and 18(prepared respectively from the alcohols 11 and 15) demonstrated unequivocally that neither of these compounds nor their hydroxy-γ-lactone ring (lactol) tautomers 1 corresponded to the naturally occurring fungal self germination inhibitor gloeosporone. A study of 4,5-dioxohexanoic itself 9 revealed a remarkably low tendency to exist as its hydroxy-γ-lactone (lactol) tautomer 10.