Microwave-assisted annulation for the construction of pyrido-fused heterocycles and their application as photoluminescent chemosensors

A catalyst-free microwave-assisted annulation protocol for the preparation of biologically interesting pyrido-fused quinazolinones and pyrido[1,2- a ]benzimidazoles is developed. This reaction involves the [3 + 3] annulation of various quinazolinones or benzimidazoles with 3-formylchromones to yield functionalized 11 H -pyrido[2,1- b ]quinazolin-11-one and pyrido[1,2- a ] benzimidazole derivatives. This approach is successfully extended to the construction of various pyrazolo[4,3- d ]pyrido[1,2- a ]pyrimidin-10(1 H )-ones. The present approach is complementary to the existing synthetic methodologies and offers a rapid and facile approach with a broad substrate scope, good yields, catalyst-free conditions, and a high functional group tolerance. The optimal synthesized compound is also employed as an "on-off" photoluminescent probe for the selective detection of Fe 3+ and Ag + metal ions. An efficient and catalyst-free protocol for the synthesis of pyrido-fused heterocycles under microwave irradiation via a [3 + 3] annulation reaction and their application as photoluminescent chemosensors are presented.