Thermal reaction of imidazolium N-vinylimino ylides: Formation of mesomeric betaines, imidazopyridaziniumides, via back-donated 1,6-cyclization

Article abstract of DOI:10.1248/cpb.42.454

The reaction of N-aminoimidazolium salts (4,5) with polarized olefins (2a- d, 3a, b) in the presence of K₂CO₃ in EtOH gave the corresponding imidazolium N-vinylimino ylides (6, 7). Thermolyses of the N-vinylimino ylides (6c-f. 7a-c) afforded mesomeric betaines (8a-d, 9a,b, 10a,b). Treatment of the salt (5) with polarized olefins (2b-d. 3c) in the presence of K₂CO₃ in EtOH directly yielded mesomeric betaines (9c-d, 10c), while in EtOH, the reaction of the salt (5) with polarized olefins (2e, 3d) in the presence of K₂CO₃ gave pyrazoles (11a, b). The formation of mesomeric betaines is suggested to proceed via back-donated 1,6-cyclization.

Full text of DOI:10.1248/cpb.42.454

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