Enantioselective total syntheses of the novel tricyclic sesquiterpene hydrocarbons (+)- and (-)- kelsoene. Absolute configuration of the natural product

Abstract

Simple and preparatively efficacious lipase-catalysed kinetic resolution of endo,endo-cis-bicyclo[3.3.0]octane-2,6-diol rac-3 has provided ready access to bicyclo[3.3.0]octane-2,6-diones (-)-2 and (+)-2 of high enantiomeric purity. These C₂-symmetric diones have been further elaborated to the sesquiterpene hydrocarbon (+)-kelsoene 1 and ent-kelsoene (-)-1, respectively, thereby establishing the absolute configuration of the natural product. In the light of these results, the absolute configuration assigned earlier to (+)-kelsoene needs to be revised as (+)-1.