Copper-Catalyzed Intermolecular Oxidative Cyclization of Haloalkynes: Synthesis of 2-Halo-substituted Imidazo[1,2-a]pyridines, Imidazo[1,2-a]pyrazines and Imidazo[1,2-a]pyrimidines

An efficient copper-catalyzed method for the synthesis of 2-haloimidazopyridines with aminopyridines and haloalkynes using molecular oxygen as oxidant in a one-pot manner has been developed. In this process, the reaction appears to be very general and suitable for the construction of a variety of 2-halo-substituted imidazopyridines, imidazopyrazines and imidazopyrimidines. The intermolecular oxidative diamination of haloalkynes was achieved for the first time. Importantly, the mild reaction conditions and the efficient conversion of the alkyl-substituted haloalkynes are great improvements over the existing methods. Moreover, the resultant 2-haloimidazo[1,2-a]pyridines could be efficiently converted to other functionalized imidazopyridine products via substitution, coupling reactions and other transformations, which further indicates potential applications of this method in synthetic and pharmaceutical chemistry.