Novel Rearrangements of Guaiane Sesquiterpenes

Guaiane sesquiterpenes are an important class of biologically active natural products. Several oxygenated bicyclic but also tricyclic derivatives show unprecedented olfactory activity with great importance in perfumery. Their in vivo syntheses are largely controlled by the intrinsic selectivities of terpene synthases and only a few rearrangements of their hydroazulene skeletons were reported, mostly resulting into terpenoids with decalin motives. Using α-guaiene and bulnesene, complex rearrangements into novel tri and tetracyclic terpenoids are described herein. The cationic rearrangement mechanisms of their formation based on subsequent 1,2-H and alkyl shifts promoted by substoichiometric amounts of ethylaluminum dichloride.