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■ Synthesis of Mesomeric Betaines, [1,2,4]Triazolo[2,3-a]pyridiniumides, via Back-donated 1,6-Cyclization

Yoshiro Matsuda,* Keisuke Katou, Chieko Motokawa, and Takashi Uemura

*Faculty of Environmental Studies, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

The reaction of [1,2,4]triazolium salts (4a,b) with polarized alkenes (1a,b, 2a) in the presence of K₂CO₃ in CHCl₃-EtOH gave the corresponding triazolium N-allylides (5a-c). Thermolyses of the N-allylides (5a-c) afforded the 7-imino[1,2,4]triazolo[2,3-a]pyridiniumide derivatives (6a,b) and the 7-oxo-[1,2,4]triazolo[2,3-a]pyridiniumide derivative (7a). Similar treatment of the salts (4a,b) with alkenes (1c, 2b) directly yielded mesomeric betaines (7b,c), while the reaction of the salt (4b) with alkene (2c) gave the pyrrolo[2,1-f][1,2,4]triazine derivative (8).