New Synthetic Methodology in Sesquiterpene Chemistry

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In contrast to the elegant multiple-annulation procedures of carbocyclic chemistry, there have been few efforts to incorporate similar strategies in the synthesis of natural products containing furan rings. Dr. Jacobi has pioneered new highly compact syntheses of these latter materials which are important in certain medicinal compounds. This grant in the Organic and Macromolecular Chemistry Program will further develop the concept of bis-heteroannulation, in which fused ring furans are readily prepared with complete regiochemical control. The key element of this approach involves an intramolecular Diels-Alder reaction between an oxazole and an acetylene. This is currently being employed for the synthesis of the guaiane sesquiterpene geigerin and the butenolide-alkaloid norsecurinine. In addition are described the direct conversion of either acetylenic alcohols or enones to methylenecyclopentenones or to phenols via tandem sigmatropic rearrangements. These transformations are of considerable mechanistic interest and could be utilized in the synthesis of materials as diverse as the acoranes, methyleneomycin antibiotics, hirsutanes and various naturally occurring phenols. The syntheses of methyleneomycins B and A, the antitumor agent sarkomycin, acorone, hirsutene and juncusol are planned as representative examples.