Sites of protonation in cardiotonic polyazaindolizines by NMR spectroscopy
The pKa, values of six sulmazole analogues were measured spectrophotometrically. The major protonation sites for most of these bridgehead nitrogen heterocycles were determined by 1H and 13C NMR methods. The aryl‐substituted imidazo[1,2‐a]pyrimidine (4), 8‐methoxyimidazo[1,2‐a]pyrazine (6), imidazo[1...
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Veröffentlicht in: | Magnetic resonance in chemistry 1991-05, Vol.29 (5), p.468-475 |
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Sprache: | eng |
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Zusammenfassung: | The pKa, values of six sulmazole analogues were measured spectrophotometrically. The major protonation sites for most of these bridgehead nitrogen heterocycles were determined by 1H and 13C NMR methods. The aryl‐substituted imidazo[1,2‐a]pyrimidine (4), 8‐methoxyimidazo[1,2‐a]pyrazine (6), imidazo[1,2‐b]pyridazine (9) and imidazo[1,2‐b][1,2,4]triazine (11) undergo protonation at the imidazo nitrogen. The imidazo[1,2‐a]pyrazine (5) protonates mainly at N‐7. In some cases differences in basicity properties between these aryl analogues and the bridgehead heterocycles have been observed. |
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ISSN: | 0749-1581 1097-458X |
DOI: | 10.1002/mrc.1260290511 |