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■ A Novel 1,6-Cyclization of Imidazolium N-Allylides (2): Formation of the Mesomeric Betaine, 7-Iminoimidazo[1,2-a]pyridiniumide

Yoshiro Matsuda,* Hiromi Gotou, Keisuke Katou, Hiroshi Matsumoto, Makoto Yamashita, Kimitoshi Takahashi, Shizuki Ide, Kazuki Furuno, and Katsura Torisu

*School of Pharmaceutical Sciences, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

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).