Abstract
Meldrum's acid as an excellent catalyst for the facile, efficient and one-pot synthesis of N,3-diarylimidazo[1,2-a]pyridin-2-amines
Highlights
Bicyclic heterocycles, especially imidazo[1,2-a]pyridines, which have an amine group on the imidazole ring, are biologically and pharmacologically important.[1,2,3,4,5] In recent years, there has been a strong interest in building a fused imidazole framework.[6]
Several effective initiatives have been reported in the field of intramolecular cyclization, tandem reactions, via radical addition/cyclization reactions,[14] oxidative couplings with the hypervalent iodine(III) reagents,[15] via imidazo[1,2-a]pyridin-2-yl triflate through a Suzuki cross-coupling reaction followed by a direct arylation,[16] two-component cyclization of substituted 2-aminopyridines and substituted phenacyl bromides catalysed by DBU,[17] and multistep approaches.[18,19]
When Meldrum's acid is used as a catalyst for the above reaction, it is proposed that there are two pathways, shown in Scheme 2, for the formation of N,3-diarylimidazo[1,2-a]pyridin-2-amines 4a-k
Summary
Especially imidazo[1,2-a]pyridines, which have an amine group on the imidazole ring, are biologically and pharmacologically important.[1,2,3,4,5] In recent years, there has been a strong interest in building a fused imidazole framework.[6]. In continuation of our previous work on the development of multicomponent reactions for the synthesis of imidazole compounds,[29] we describe a facile and efficient strategy for the synthesis of N,3-diarylimidazo[1,2-a]pyridin-2-amines via the one-pot, three-component reaction of aryl glyoxals, arylamines, and 2-aminopyridine in the presence of Meldrum's acid in ethanol at room temperature. A mixture of an aryl glyoxal (1, 1.0 mmol), an arylamine (2, 1.0 mmol), and 2aminopyridine (3, 1.0 mmol) were reacted together in EtOH, from which products N,3-diarylimidazo[1,2a]pyridin-2-amine 4a-j and 3-aryl-N-(pyridin-2-yl)imidazo[1,2-a]pyridin-2-amine 5a-c were isolated and purified (Table 1).
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