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Heterocyclic betaines. Aza analogues of sesquifulvalene. 2. Azolium
Azolate Inner Salts: Synthesis, Reactivity, and Structure of a 1:1 Adduct
With Dimethy1 Acetylenedicarboxylate
Ermitas Alcaldeand Immaculada Dinarés
Laboratorio de quimica organica, facultad de farmacia, Universidad de Barcelona, E-08028-Barcelona, spain received july 20, 1990
Reaction of an activated 2- chloroazole withseveral N-alkylazoles afforded the N-azolylazolium salts,deprotonation of which results in a series of the little mesomeric betaines 7 and 8. Their reactivity toward electrophiles and dipolarophilesunder mild.conditions reflects the highly dipolar structures of 7 and 8. The thermal stability and dequaternization reactions of some of their corresponding N-azolylimidazolium and –pyrazolium saltshave also been studied.

of the vas variety of structures that conjugated heterocyclic mesomeric betaines adopt,1 few reports have appeared of aza analogues of the N-ylide 1 and the dipolar resonanceform of sesquifulvalene (2B). several re

The highly dipolar character of mesomeric betaines 3 and 4 has a dominant influence upon their chemistry, which merits study. These systems are suited to astudy of their behavior as dipoles, where the dipolar moiety contains more than four electrons, and their reactions with dipolarophiles should be a potentially attractive route for the synthesis of avariety of heterocyclic structures, as well as novel polycyclic ring systems.
As to quaternary salts of nitrogen heteroaromatic compounds, these are usually stable and their dealkylation reactions areof interest. In this context, pyridinium salts, and to a lesser extent, condensed systems derived from six-membered nitrogen heterocycles, are by far the most commonly investigated. This ispresumably due to the fact that such studies were directed toward seeking insight into fundamental topic of heteroaromatic chemistry 8a such as aliphatic nucleophilic substitution reactions,forward and...