Imidazole derivatives. VII. Reaction of 1-acylimidazoles with dialkyl acetylenedicarboxylates: synthesis of imidazo[1,2-a]pyridines, (2-imidazolyl)maleates, 1,5-dihydroimidazo[1,2-a]pyridines, furo[2',3':2,3]pyrrolo[1,2-a]imidazoles, furo[2',3':2,3]pyrrolo[1,2-a]benzimidazoles and 7H-pyrrolo[1,2-a]imidazoles.
The reaction of 1-acylimidazoles with dialkyl acetylenedicarboxylates provides novel functionalized imidazole derivs. by a sequence of electrophilic attack on the imidazole azine nitrogen atom and subsequent transprotonations and transacylations of the ylide generated in the first step. Based on this methodol. 1-arylacetylimidazoles were condensed with di-Me acetylenedicarboxylate in acetonitrile providing imidazo[1,2-a]pyridines. Control of the cyclization mode was achieved leading to a different ring system simply by varying the acyl side chain. Solvent and reaction temp. influence these cyclizations strongly, thus allowing the prepn. of further novel imidazole derivs. including the hitherto unknown furo[2',3':2,3]pyrrolo[1,2-a]imidazole framework. Changing the parameters of the reaction of 1-alkanoylimidazoles with electron-deficient acetylenes allows the synthesis of 1,5-dihydroimidazo[1,2-a]pyridine I furo[2',3':2,3]pyrrolo[1,2-a]imidazole II, furo[2',3':2,3]pyrrolo[1,2-a]benzimidazoles, and 7H-pyrrolo[1,2-a]imidazoles, e.g. III. The crystal structures of compds. II and III were detd. by x-ray anal.
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