A NOVEL 1,6 CYCLIZATION OF IMIDAZOLIUM N-ALLYLIDES - FORMATION OF MESOMERIC BETAINES, 8-OXOIMIDAZO[1,2-A]-PYRIDINIUMIDES

Treatment of imidazolium N-allylides (3a,b) in refluxing xylene resulted in 1,5-dipolar cyclization to give pyrroloimidazoles (4a,b), whereas heating of N-allylides (3c,d,e) in refluxing xylene gave the mesomeric betaines, 8-oxoimidazo[1,2-a]pyridiniumides (5a,b,c), with 1,6 cyclization. Furthermore, treatment of the N-aminoimidazolium salt (9) and ketene dithioacetal (2c) with potassium carbonate in dimethyl sulfoxide (DMSO) directly afforded the mesomeric betaine, imidazo [1,2-b]pyridaziniumide (11). The benzimidazolium salt (12) and diethyl ethoxymethylenemalonate (2d) were treated with potassium carbonate in CHCl3 to also produce the mesomeric betaine, 4-oxobenz[b]imidazo-[1,2-a]pyridiniumide (14). © 1990.