Annelation of 2,3-dimethylcyclohexanone. Synthetic proof for the stereochemistry of the sesquiterpene aristolone

An efficient annelation of 2,3-dimethylcyclohexanone is described. The key step of this process involves the reaction of the enol lactone 16 with methyllithium, under carefully controlled conditions. The completely stereoselective conversion of the sesquiterpene (−)-aristolone (1) into the levorotatory decalone 22b is described. Comparison of the latter with the unambiguously synthesized racemic decalone 22a conclusively establishes the relative stereochemistry of aristolone (1).