NBS mediated protocol for the synthesis of N-bridged fused heterocycles in water

A facile and environmental friendly protocol for the synthesis of N-bridged fused bicyclic compounds such as imidazo1,2-a]pyridines, imidazo1,2-a]pyrimidines, and imidazo2,1-b]thiazole, from commercially available starting materials has been developed. The reaction proceeds via NBS mediated in situ formation of α-brominated intermediate of corresponding aromatic ketones, 1,3-diketones, β-keto esters, followed by trapping with suitable nucleophiles to provide these versatile imidazole fused bicyclic heterocycles in good yields under metal-free conditions.