Regioselective one-pot three-component synthesis of quinoline based 1,2,4-triazolo[1,5-a]quinoline derivatives

A one-pot three-component approach for the synthesis of 2-(piperidin-1-yl) quinoline based 1,2,4-triazolo[1,5- a ]quinoline derivatives ( 4a–l ) has been described by the reaction of aldehyde ( 1a–f ), methyl 2-cyanoacetate ( 2 ) and enaminones ( 3a–b ). Different regioselectivities of the reaction are attained with different catalysts and the highest regioselectivity is achieved by l -proline. This new procedure provides an efficient method to construct fused tricyclic heterocycles containing 1,2,4-triazole analogues. In this regard, we have used the least amount of amphoteric catalyst, like l -proline, ammonium acetate and a mixture of pyrolidine with acetic acid, to obtain the 1,4-dihydroquinoline derivative 5a as a by-product. The salient features of this protocol are the mild reaction conditions, high yield (75–85%) and higher regioselectivity toward the desired products 4a–l . The structures of the title compounds were confirmed by FT-IR, 1 H NMR, 13 C NMR and mass spectrometry.