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