Angew. Chem. Int. Ed. http://dx.doi.org/10.1002/anie.201105541 (2011)

Synthetic methods that rapidly create molecular complexity from simple molecules are greatly prized. Highly unsaturated hydrocarbon structures, for example, are often extremely reactive. This reactivity can make them difficult to isolate — but when that is possible, they can become the basis for surprisingly simple routes to complex molecules. Now, Michael Sherburn and co-workers from the Australian National University along with Michael Padden-Row from the University of New South Wales, have isolated 1,1-divinylallene for the first time, and performed some initial experiments on its reactions.

There are only a few examples of such π-bond-rich hydrocarbons not stabilized by steric protection. Previous attempts by other researchers to prepare 1,1-divinylallene had resulted in isolation of a rearranged product. Sherburn and co-workers suspected that this was as a result of the high-temperature requirements of the methodology used, and first confirmed this by performing accurate ab initio calculations. These calculations suggested that in concentrated solution, 1,1-divinylallene would have a half-life of only minutes. After several failed attempts, they identified a method — with the key step being a Grieco–Sharpless elimination from a selenide — of preparing their target in dilute solution and at low temperature.

In a demonstration of the synthetic utility of such highly unsaturated molecules, Sherburn and co-workers then showed that this molecule could react in a cascade of three Diels–Alder reactions. The molecule acts as the diene partner for the reaction in each case, with each cycloaddition occurring at a chemically distinct site, and in the process creates a new diene for the next part of the cascade. This cascade creates six carbon–carbon bonds, three rings and eight stereocentres in a single step.