Cu-Mn spinel oxide catalyzed synthesis of imidazo[1,2-a]pyridines through domino three-component coupling and 5-exo-dig cyclization in water

An efficient and eco-friendly synthesis of therapeutically important and structurally diverse imidazo[1,2-a]pyridines using recyclable bimetallic Cu-Mn spinel oxide catalyst in aqueous medium has been developed. The Cu-Mn catalyzed domino three-component coupling of 2-aminopyridines, aldehydes and alkynes followed by 5-exo-dig cycloisomerization produced desired imidazo[1,2-a]pyridines in good yields. The efficiency of this protocol could be attributed to the presence of these metals in multiple oxidation states (Cu2+, Mn2+, Mn3+ and Mn4+) in the bimetallic Cu-Mn catalyst. The advantages of this protocol over previous reports include the use of aqueous medium, recyclable catalyst, shorter reaction times and no requirement of any additive. This is the first method for synthesis of imidazo[1,2-a]pyridines which utilizes water as a reaction medium.