Bicyclo [3,3,1] nonane approach to pinguisane terpenoids

The total synthesis of (±) pinguisone 1, the sterically crowded unusual [5-6] fused-ring sesquiterpene, was accomplished by synthetic elaboration of the 3β,3aβ,7,7aβ-tetramethylbicyclo [4.3.0] non-6-en-1-one 2a prepared by acid catalyzed rearrangement of the easily accessible 1,4β,5,9-tetramethylbicyclo [3.3.1] nonan-9-hydroxy-2-one 3. This rearrangement constitutes an example of the scarcely observed 1,2 shift of a carbonyl group toward an electron deficient centre.