Highly unsaturated hydrocarbons are often very reactive, and tetravinylethylene (TVE) looks, on paper, to be no exception. It is the smallest possible vinylic molecule that is both cross-conjugated and through-conjugated, and its synthesis has only been reported once before, using a four-step sequence to give an overall yield of 0.1%. As with similar molecules that contain multiple alkenes, it is potentially useful in the formation of complex hydrocarbon skeletons using Diels–Alder cascades, and so a simpler synthetic procedure to give TVE with higher yields is desirable.
Now, the combined efforts of a team led by Anthony Willis and Michael Sherburn from the Australian National University and Michael Padden-Row from the University of New South Wales have resulted in the discovery of a deceptively simple synthesis of TVE. Starting from tetrachloroethylene, four Stille cross-coupling reactions with vinyltributyltin in one solvent-free step gives a TVE yield of 64%, in batches of up to 7 grams at a time. In contrast to what might be assumed based on the instability of similar dendralenes and other related structures, they found that neat TVE was stable in air and at ambient temperatures. The same synthetic strategy could also be used to make a family of five substituted symmetrical TVE-based molecules.
Tetravinylethylene can also be used as a precursor to divinyl cyclohexadiene (DVC) by thermally promoted electrocyclization. Both TVE and DVC were found to participate as dienes in sequences of Diels–Alder reactions with N-methylmaleimide (NMM) to create several fused cyclic hydrocarbon ring systems (pictured). Not only were much higher regio- and stereoselectivities observed than with dendralene — similar to both TVE and DVC in terms of size and number of C=C bonds — but unexpected Diels–Alder reaction sequences were also observed and rationalized using density functional theory calculations. Simple methods to create complex fused ring structures with multiple stereocentres and substituents are a boon to synthetic chemists, and TVE looks like it could be a welcome addition to the toolbox of small-molecule precursors for such systems.
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Hansell, C. Vinyl destination. Nature Chem 6, 558 (2014). https://doi.org/10.1038/nchem.1992