NBS-Enabled Rapid Cyclization of 5,6-Diaryl Dipyrroethenes to Access meso-Tetraaryl Porphycenes

We introduce the concept of N-bromosuccinimide (NBS)-mediated rapid macrocyclization of 5,6-diaryl dipyrroethenes (DPEs) to access meso-tetraaryl porphycenes in a seconds time frame. This fastest strategy for porphycene synthesis not only eliminates the requirements of reactive p-TSA, sacrificial oxidant, and sophisticated techniques associated with the previous methods but also enables the reaction to be performed under "open air" with significantly improved reaction yields up to 76%, while minimizing other byproducts. Moreover, this protocol is well compatible with six- and five-membered aryl substituents at the meso-positions and achieved up to gram-scale synthesis of meso-tetratolyl porphycene. Combined experimental and computational studies highlight that the NBS-mediated umpolung modification of the DPE core is the key step in driving the reaction in the forward direction with such exclusive selectivity and yield in a short time.