Toward an integrated route to the vernonia allenes and related sesquiterpenoids

The synthesis of a model endocyclic allene related to the vernonia allenes is described. Fragmentation of a suitable decalin derivative gave the simplified germacrane scaffold. Computational analysis of this and related substrates provides insight into the stereoelectronic requirements of C-C fragmentation. The overall strategy to access these and other sesquiterpenes and the key steps in the present sequence are also discussed.