Rare reactions are being explored to find ways to make building blocks for organic synthesis. 

A useful organic building block is the five-membered ring. These rings are made by cycloaddition reactions, typically involving a [3+2] or [2+2+1] addition of components, with the numbers indicating the number of atoms that each component contributes to the ring. But researchers from France are investigating the less common [4+1] process. 

Jan Szymoniak and co-workers from the Université de Reims Champagne-Ardenne have shown the first example of a titanium-mediated cycloaddition of diene and nitrile groups, forming five-membered carbon rings in high yields. Their technique is particularly useful because it is simple and the starting materials are readily available. 

Szymoniak hopes that in future the synthetic potential of both titanium and zirconium cycles can be exploited, and that a catalytic version of this reaction can be developed. 

Richard Kelly