Systèmes aromatiques à 10 électrons π dérivés de l'aza-3a-pentalène. XI. Etude par résonance magnétique nucléaire de l'imidazo [1,2-b] pyrazole et du pyrazolo [1,5-a] benzimidazole

Abstract

Nuclear magnetic resonance spectroscopy has allowed us to determine the annular tautomerism in two [5,5]-heteroaromatic systems and the position of the acetyl group in their acetyl derivatives. In each case, the more stable compound is the one in which the imidazolic nitrogen atom is bearing H or COCH3. We have also found unusual couplings with the N—H in the N-unsubstituted compounds and abnormally high barriers for the azolides. These observations agree well with the hypothesis of a decrease in the aromaticity of the imidazolic part.