A series of new 6,8-dichloro-imidazo[1,2-a]pyridine derivatives incorporating pyridine, thiazole, and pyrazole ring systems was synthesized. The synthetic strategy of imidazopyridinyl-pyridine hybrids 2 and 3 involves one pot reaction of the precursor 3-acetyl-6,8-dichloro-2-methylimidazo[1,2-a] pyridine (1) with aldehydes, malononitrile, and/or ethyl cyanoacetate. Treatment of 1 with thiosemicarbazide and/or bromine followed by subsequent cyclization with ethyl bromoacetate, chloroacetone, phenacyl chloride, and/or thiourea was applied as synthetic routes for accessing the imidazopyridinyl-thiazole hybrids 5, 6, and 8–10. The reaction of 1 with dimethylformamide-dimethylacetal followed by subsequent treatment with hydrazine was employed to prepare the imidazopyridinyl-pyrazole motif 12. The antibacterial potency of these imidazopyridine hybrids has been evaluated against some model bacteria. The results indicated that the imidazopyridine-thiazole hybrids revealed remarkable antibacterial activities.

Syntheses and reactions of 2-amino-4-substituted-1,3-thiazoles are reviewed in a formal way. The title compounds are most easily accessible by various approaches, and even waste-free solid-state procedures have been developed. The substitution in 4-position has synthetic reasons and therefore most interest accumulates around these derivatives of 2-aminothiazole. The high reactivity of both the amino group and the positions 3 and 5 of the 1,3-thiazole ring are used for numerous syntheses in a comprehensive way. The reactions are subdivided in groups that cover reactions at the amino substituent without touching the thiazole ring, reactions which involve both nitrogens in the formal amidine system to give thiazolo-pyrimidinones and -imidazoles as well as more involved polycondensed N,S-heterocycles with multiple possibilities for substituents, and substitution reactions at the 5-position of the thiazole ring. Most of the imaginable reaction types have been successfully applied and used, as many of the synthesized compounds exhibit interesting biological activity in various fields.