A revised structure for aubergenone, a sesquiterpenoid related to eudesmane: synthesis of 4-epi-aubergenone

Syntheses of 4-epi-aubergenone, a sesquiterpenoid related to eudesmane, are described. One synthesis afforded this sesquiterpenoid as a racemate ( 12 ) whereas another, utilizing (+)-carissone as starting material, afforded an enantiomer ( 12 a). The fact that naturally occurring aubergenone is the C(4) epimer of the thermodynamically more stable synthetic 12 was revealed by the discovery that it was completely converted into the latter by treatment with base. This epimeric relationship is substantiated by comparison of the nmr spectra of the two isomers. Evidence requiring the reformulation of the structure of aubergenone as 13 is adduced.