Deciphering Co(III)‐Catalyzed Oxidative C−H/C−H Annulation Towards Maleimide‐Fused Imidazopyridine AEEgens†

Abstract

A cobalt(III)‐catalyzed dual C(sp2)−H/C(sp2)−H activation of 2‐arylimidazopyridines and its annulation with N‐substituted maleimides leads to polycyclic aromatic heterocycles. This sustainable oxidative annulation uses earth‐abundant, less toxic, and cost‐effective cobalt(III) catalyst that complement expensive 2nd and 3rd‐row metals. This oxidative annulation features a broad substrate scope with very good functional group tolerance. These maleimide‐fused imidazopyridines display strong fluorescence in the region of 527− 536 nm with a Stokes shift of 83−87 nm and possess an excited state lifetime of 14.6−16.1 ns. Interestingly, such luminescent compounds show aggregation‐enhanced emission (AEE) behavior in the iPr‐OH/hexane mixed solvent system. Furthermore, field emission scanning microscopy (FESEM) reveals their spherical nano‐aggregates with an average diameter of ~216.8 nm. They can also be used as cellular‐imaging and picric acid‐sensing probes.