A SYNTHESIS OF (+)-OBLONGOLIDE

The absolute configuration of natural oblongolide is reassigned as cta hydro-7,9b-dimethylaphtho[1,2-c]furan-1(3H)-one 2 by a 7-stage synthes is of its enantiomer 1 from (+)-citronellol involving a regioselective reduction and an intramolecular Diels-Alder reaction (IMDA) as the ke y steps. (+)-Citronellol was converted into methyl S)-(+)-11-tert-buto xycarbonyl-7-methyl-undeca-2,4, 10-trienoate 7 by sequential Lemieux-J ohnson oxidation, Wittig reaction, pyridinium chlorochromate oxidation , and Wadsworth-Emmons-Horner alkenation. A regioselective reduction o f the methoxycarbonyl group in 7 afforded tert-butyl (2E,8E, +)-2,6-di methyl-12-hydroxy-dodeca-2,8,10-trienoate 8 from which (+)-oblongolide was readily obtained via an IMDA reaction.