Cyclo[8]pyrrole: A Simple-to-Make Expanded Porphyrin with No Meso Bridges

Easily obtained in a single step from bipyrrolic precursors in yields over 70 %, cyclo[8]pyrroles represent a new class of porphyrin analogues that display the classic disklike structure of porphyrins. The X-ray crystal structure of one of the cyclo[8]pyrroles obtained (see picture) shows that the macrocycle acts as a formal diprotonated receptor and forms eight hydrogen bonds to a sulfate ion bound within its core.