Radical Cyclisation of Dienes; Part IV.1Enantiomerically Pure Building Blocks from (R)-(-)- and (S)-(+)-Carvone for the Synthesis of Naturally Occurring Triquinanes

All articles of this category 6a-Methyl-3,3a,4,6a-tetrahydro-2 H -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-2 H -cyclopenta[ b ]furan-2-one ( 3a ) in high yield. Transformation of 3a by standard reactions leads to the unsaturated lactone 9 .