A new approach for the synthesis of fluorescent pyrido[1,2-a]benzimidazoles

Abstract

A facile synthesis of new pyrido[1,2-a]benzimidazoles through a one-pot multicomponent reaction of malononitrile, electron-deficient aryl aldehydes and heterocyclic enamines followed by a nitrous acid release under mild condition, is reported. Depending on the substituents on heterocyclic enamine, newly synthesized products have been obtained either as an inseparable mixture of regioisomers or as a single regioisomer. A plausible mechanism can be proposed for the formation of pyrido[1,2-a]benzimidazoles via this unfamiliar transformation with the HNO₂ extrusion. The structures of all title compounds were elucidated using spectroscopic methods and physical characteristics involving single crystal X-ray diffraction and TOF-MS measurements. In addition, among all the products, CN- and CF₃-substituted ones showed promising absorption and fluorescent properties.

Graphical Abstract

Keywords:

• Heterocyclic enamine
• multicomponent reaction
• pyrido[1,2-a]benzimidazole

Acknowledgement

Special thanks to Dr. Murat Olutas and Dr. Muhammet Yıldırım for interpreting fluorescent measurements and valuable discussions throughout this study.

Additional information

Funding

Bolu Abant İzzet Baysal University, Directorate of Research Projects Commission [BAP grant no. 2018.03.03.1348] are gratefully acknowledged for financial support.