Transition metal-catalysed [2+2+2] cycloaddition is well known as an efficient way to construct six-membered rings. However, enantioselective cycloadditions are less common in the literature. In this article, Takanori Shibata and Kyoji Tsuchikama at Waseda University, Japan, summarise their strategies and achievements in this emerging area of chemistry. Shibata describes more about his article below. 

1. Please explain, for a non-specialist, the significance of your article. 

[2+2+2] Cycloaddition is the most atom-economical protocol for the synthesis of multi-substituted six-membered ring compounds. We revealed that the chiral iridium- or rhodium-catalyzed reactions are powerful tools of the highly enantioselective syntheses of a wide range of chiral compounds. Moreover, our methods can be also applied to the synthesis of structurally complex molecules such as helix-shaped polyaryls, intricate tricyclic compounds, and so on. 

2. What has motivated you to conduct this work? 

[2+2+2] Cycloaddition is well-known as an efficient synthetic method, but there had been no practical example of enantioselective variants. Therefore enantioselective [2+2+2] cycloaddition could be a new and versatile approach to chiral libraries. 

3. Where do you see this work developing in the future? 

Our work showed that enantioselective [2+2+2] cycloadditions could be applied to the syntheses of diverse chiral compounds. As the next stage, we wish to use our methods for target-oriented syntheses, such as electronic materials and pharmaceutical agents. 

4. Are there any particular challenges facing future research in this area? 

Iridium and rhodium are expensive rare metals and their prices will further increase in the future. It will be necessary for us to recycle their complexes or to develop alternative metal catalysts, which are much cheaper than iridium and rhodium ones.