A NOVEL 1,6-CYCLIZATION OF IMIDAZOLIUM N-ALLYLIDES .2. FORMATION OF THE MESOMERIC BETAINE, 7-IMINOIMIDAZO-[1,2-A]PYRIDINIUMIDE

Treatment of imidazolium N-allylide (3) in refluxing 1,2,4-trimethylbenzene resulted in 1,6-cyclization to give the mesomeric betaine, 7-iminoimidazo[1,2-a]pyridiniumide (4). On the other hand, heating of 1-cyanoimidoylmethylimidazolium N-ylide (6) in refluxing 1,2,4-trimethylbenzene underwent 1,6-cyclization and debenzylation to give 8-aminoimidazo [1,2-a]pyrazine (7). Furthermore, treatment of the imidazolium salt (1a) and ethyl ethoxymethylenenitroacetate (2d) with K2CO3 in DMSO afforded the mesomeric betaine, imidazo[1,2-a]pyridiniumide (12), whereas the reaction of 1a and nitroketene dithioacetal (2e) with K2CO3 in DMSO resulted in 1,5-dipolar cyclization to produce pyrrolo[1,2-a]imidazole (13) and pyrrolo[1,2-a]pyrazine (14).