P. Thapa, Philip M. Palacios, T. Tran
Jan 13, 2020
Citations
0
Influential Citations
24
Citations
Journal
The Journal of organic chemistry
Abstract
Benzimidazoles are common in nature, medicines, and materials. Numerous strategies for preparing 2-arylbenzimidazoles exist. In this work, 1,2-disubstituted benzimidazoles were prepared from various mono- and di-substituted ortho-phenylenediamines (OPD) by iron-catalyzed oxidative coupling. Specifically, O2 and FeCl3●6H2O catalyzed the cross dehydrogenative coupling and aromatization of diarylmethyl- and dialkyl- benzimidazole precursors. N,N'-disubstituted-OPD substrates were significantly more reactive than their N,N-disubstituted isomers, which appears to be relative to their propensity for complexation and charge transfer with Fe3+. The reaction also converted N-monosubstituted OPD substrates to 2-substituted-benzimidazoles; however, electron-poor substrates produce 1,2-disubstituted benzimidazoles by intermolecular imino-transfer. Kinetic, reagent, and spectroscopic (UV-Vis and EPR) studies suggest a mechanism involving metal-substrate complexation, charge transfer, and aerobic turn over, involving high-valent Fe(IV) intermediates. Overall, comparative strategies for the relatively sustainable and efficient synthesis of 1,2-disubstituted benzimidazoles are demonstrated.