THERMAL-REACTION OF IMIDAZOLIUM N-VINYLIMINO YLIDES - FORMATION OF MESOMERIC BETAINES, IMIDAZOPYRIDAZINIUMIDES, VIA BACK-DONATED 1,6-CYCLIZATION

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-vinylimi no 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 olefi ns (2e, 3d) in the presence of K2CO3 gave pyrazoles (11a,b). The forma tion of mesomeric betaines is suggested to proceed via back-donated 1, 6-cyclization.