I2/H2O2 Mediated Synthesis and Photophysical Properties of Imidazole-Fused Heterocycles via [4+1] Cyclization Approach

Graphical We report here a new I 2 /H 2 O 2 co-catalyzed oxidative [4+1] cyclization of benzaldehyde with 2-(aminomethyl)pyridine or o -phenylenediamine/2-aminothiophenol to provide various substituted imidazo[1,5- a ]pyridines and benzimidazoles/thiazole via C(acyl)−N bond construction. Some of heterocyclic products exhibit blue luminescence properties, as well as large Stokes shifts, eminent fluorescence quantum yields (64 %) and long fluorescence lifetimes. An efficient I 2 (10 mmol %)/H 2 O 2 mediated oxidative formal [4+1] cyclization of 2-pyridinemethylamine or o -phenylenediamine (2-aminobenzenethiol) with benzaldehyde via C−N bond formation has been developed. This strategy provides a straightforward approach to imidazo[1,5- a ]pyridines, iodo-substituted imidazo[1,5- a ]pyridines and benzimidazole (benzothiazole) derivatives in yields ranging from 60 % to 98 %, respectively. Several heterocyclic products exhibit promising blue luminous performance with satisfactory fluorescence quantum yields of up to 64 %, large Stokes shifts, and a longer lifetime (7.35 ns). The band gap energies obtained from DFT are also consistent with the absorption spectra.