Substituent effects on the tautomer ratios between the hydrazone imine and diazenyl enamine forms in side‐chained quinoxalines

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<jats:title>Abstract</jats:title><jats:p>The 3‐(arylhydrazono)methyl‐2‐oxo‐1,2‐dihydroquinoxalines <jats:bold>9–11</jats:bold> were synthesized by the reaction of the quinoxalines <jats:bold>6–8</jats:bold> with various <jats:italic>p</jats:italic>‐substituted benzenediazonium salts. Compounds <jats:bold>9–11</jats:bold> showed the tautomeric equilibria between the hydrazone imine <jats:bold>A</jats:bold> and diazenyl enamine <jats:bold>B</jats:bold> forms in dimethyl sulfoxide media. The substituent effect on the tautomer ratios of <jats:bold>A</jats:bold> to <jats:bold>B</jats:bold> was studied by the nmr spectroscopy to clarify that the presence of the ester group R<jats:sup>2</jats:sup> on the hydrazone carbon and electron‐donating <jats:italic>p</jats:italic>‐substituent R<jats:sup>1</jats:sup> on the side chain benzene ring exhibited a tendency to increase the ratios of the tautomer <jats:bold>A</jats:bold>.</jats:p>

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