Abstract
The well-known tricyclic sesquiterpenoid (−)-sativene, isolated in 1965 from Helminthosporium sativum and shown to possess structure and absolute configuration as indicated by structure 1 3, has been implicated3,4 as an intermediate in the biogenesis of the fungal toxin (−)-helminthosporal (2)5. Two total syntheses of the racemic modification of sativene have been reported6,7. A closely related sesquiterpenoid, (+)-cyclosativene, was isolated from Abies magnifica A. Murr. and was shown to possess structure 3 8,9. The absolute configuration of this material, although not established unambiguously, has been proposed10 as indicated by formula 3. The total synthesis of cyclosativene has not as yet been achieved directly, although it has been obtained indirectly via acid-promoted rearrangement of sativene8,9,11,12. We report herein a total synthesis of (+)-sativene (4) and (+)-cyclosativene (3) via a stereoselective route which unambiguously establishes the absolute configuration of both natural products.