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Two new imidazo[1,2-a]pyridines, 8-hydroxyimidazo[1,2-a]pyridine-2-carboxylic acid (4) and ethyl 8-hydroxyimidazo[1,2-a]pyridine-2-carboxylate (6) were prepared via cyclization of 2-aminopyridin-3-ol (1) with bromopyruvic acid (2) and ethyl bromopyruvate (3), respectively. 8-Hydroxyimidazo[l,2-a]-pyridine-2-carboxylic acid (4) was successfully coupled with various amino acid derivatives via its active ester intermediate into the corresponding amides 22-27. O-protected ethyl 8-hydroxyimidazo[l,2-a]pyridine-2-carboxylate 11 was transformed into its hydrazide 13, acyl azide 14, and amide 15 derivatives.

Indolyl glycinates (3, 7, and 11) were transformed with t-butoxybis(dimethylamino)methane (Bredereck's reagent) into 3-[(dimethylamino)methylidene]-2,3-dihydropyrazino[1,2-a]indole-1,4-dione (4), 3-(dimethylamino)-2-[(1H-indol-3-ylcarbonyl)amino]propenoate (8), and 2-(1-methyl-1H-indol-2-yl)-1,3-oxazol-5(4H)-one derivative (12). Dipeptides (16a-c) were transformed with Bredereck's reagent into the hydantoin (imidazolidine-2,4-dione) derivatives (17a-c).

Methyl (E)-2-[(benzyloxycarbonyl)amino]-3-cyanopropenoate (4) was, as a versatile multifunctional reagent, transformed with hydrazine and monosubstituted aromatic and heteroaromatic hydrazines under various conditions into derivatives of pyridazine (6), pyrrole (7), imidazole-2,4-dione (9), and pyrazole (13).

Ethyl (2E)-3-dimethylamino-2-[(4Z)-4-dimethylaminomethylidene-5-oxo-1-phenyl-4,5-dihydro-1H-pyrazol-3-yl]propenoate (3) was transformed with N-nucleophiles into ethyl 3-oxo-2-phenyl-3,5-dihydro-2H-pyrazolo[4,3-c]pyridine-7-carboxylates (6, 7, 9, 12, and 14).

Methyl 2-benzoylamino-2-oxobutanoate (1) was transformed with aromatic amines (2a-d) into methyl 2-arylamino-2-(benzoylamino)but-2-enoates (3a-d) Cyclization of compounds (3a-c) in polyphosphoric acid affords a mixture ofoxazolo[4,5-c]quinoline derivatives (4a-c) and 1 -aryl-2-phenyl-5-methyl- 1H-imidazole-4-carboxylates (5a-c), while compound 3d gives a mixture of 9-bromo- (4d) and 7-bromooxazolo[4,5-c]quinoline derivative (4d').