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Synlett 1991; 1991(11): 785-786
DOI: 10.1055/s-1991-20874
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Radical Cyclisation of Dienes; Part IV.1 Enantiomerically Pure Building Blocks from (R)-(-)- and (S)-(+)-Carvone for the Synthesis of Naturally Occurring Triquinanes

Klaus Weinges* , Hans Reichert
  • *Organisch-Chemisches Institut der Universität, Im Neuenheimer Feld 270, D-6900 Heidelberg, Germany
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Publication Date:
07 March 2002 (online)

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6a-Methyl-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-2-one (9), an intermediate in the synthesis of triquinanes, can be prepared simply and in either enantiomeric form, from commerically available (R)-(-)- and (S)-(+)-carvone (5-isopropenyl-2-methyl-2-cyclohexen-1-one), respectively. The first step is the radical cyclisation of carvone to the bicyclic ketone 2a (endo-6-hydroxy-2,6-dimethylbicyclo[3.2.1]octan-3-one), which is converted with 3-chloroperoxybenzoic acid (MCPBA) to 5-acetoxy-6a-methyl-3,3a,4,5,6, 6a-hexahydro-2H-cyclopenta[b]furan-2-one (3a) in high yield. Transformation of 3a by standard reactions leads to the unsaturated lactone 9.