New approaches for the synthesis of imidazopyridine carboxamide and pyridopyrimidine carboxamide derivatives

Heterocyclic compounds, especially nitrogen containing heterocycles, are important natural and synthetic materials. Among them, imidazo[1,2-a]pyridine derivatives display a diverse range of biological activities such as antibacterial, antiinflammatory, antifungal, anthelmintic, antiviral, antiprotozoal, analgesic, antipyretic, hypnoselective, anxioselective [1], and pyrido[1,2-a]pyrimidine derivatives exhibit promising antiviral, antibacterial, anti-AIDS, and antinociceptive activities [2]. During recent years, the use of 1,1-bis(methylthio)-2-nitroethene in organic synthesis has attracted great interest from many chemists [3]. Herein we report an efficient synthesis of imidazopyridine carboxamide and pyridopyrimidine carboxamide derivatives, via a one-pot, four-component reaction of nitro ketene aminals derived from the addition of various 1,n-diamines 1 to 1,1-bis(methylthio)-2-nitroethene 2 with aromatic aldehydes 3 and cyanoacetamide 4 in EtOH as solvent under reflux condition in excellent yields (Fig 1). This protocol has the advantages of simple workup, mild reaction conditions, absence of catalyst and provides an entry point to fused heterocyclic structures. All structures were confirmed by IR, MS, 1H- and 13CNMR analyses.