A synthetic route to the AB ring system of verrucarol is described. After two routes employing intramolecular cyclization failed, the Diels-Alder reaction of methyl coumalate and isoprene afforded bicyclic lactone 13. Transformation of 13 into hydroxy lactone 16 involved cuprate addition, hydroxylation, and oxidation. The conversion of 16 into desired keto alcohol 14 was accomplished by enol ether formation, reduction of the lactone and ester, and hydrolysis of the enol ether. The successful nine-step sequence proceeded in an overall yield of 7.9% from methyl coumalate.
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