Cycloparaphenylenes via [2+2+2] cycloaddition.

The [2+2+2] cycloaddition (CA) offers great potential as an atom economic method for the formation of substituted aromatic rings. In this article, we highlight the application of this versatile method in synthetic approaches towards substituted cycloparaphenylenes (CPPs). The [2+2+2] CA can take over different tasks within the synthesis depending on the targeted CPP. These approaches were divided into three key steps: aromatization (which finalises the CPP), macrocyclization (the formation of a strain-reduced macrocycle) and the [2+2+2] CA. Based on this analysis the strategies were categorised into four classes based on which task the [2+2+2] CA fulfills. We point out the benefits and drawbacks of each synthesic strategy and summarize our findings to provide the reader with an easy insight into this research field.