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Synthesis 1992; 1992(1/2): 74-82
DOI: 10.1055/s-1992-34160
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Annulations via Bifunctional Reagents. Total Syntheses of (±)-Methyl Cantabrenonate and (±)-Methyl Epoxycantabronate

Edward Piers* , Johanne Renaud
  • *Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
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Publication Date:
18 September 2002 (online)

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Total syntheses of the angularly fused triquinane sesquiterpenoids (±)-methyl cantabrenonate (10) and (±)-methyl epoxycantabronate (11) are described. The bicyclic enone, (RS)-5-methylbicyclo-[3.3.0]oct-1 (8)-en-2-one (18), was readily obtained from 3-methyl-2-cyclopenten-1-one (20). The highly stereoselective conversion of 18 into the tricyclic oxo alkene, (1R*,5R*,8R*)-5-methyl-9-methylenetricyclo [6.3.0.01,5]undecan-2-one (19), was achieved via a one-pot process involving the reaction of 18 with the novel lower order bifunctional cuprate reagent lithium (4-chloro-1-buten-2-yl)-cyanocuprate (15). The key intermediate 19 was transformed into the tricyclic enone (1R*,5R*,8S*, 9R*)-2,5,9-trimethyltricyclo-[6.3.0.01,5]undec-2-en-4-one (44), by means of a straightforward sequence of reactions. Hydrogenation of 44 gave a single ketone 45, which was converted, in two synthetic operations, into (±)-10. Treatment of 10 with hydrogen peroxide/sodium hydroxide provided, stereoselectively, (±)-11.