Highly efficient and regioselective synthesis of keto-enamine Schiff bases of 7-hydroxy-4-methyl-2-oxo-2H-benzo[h]chromene-8,10-dicarbaldehyde and 1-hydroxynaphthalene-2,4-dicarbaldehyde |
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Authors: | Koneni V Sashidhara Jammikuntla N Rosaiah |
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Institution: | Division of Medicinal and Process Chemistry, Central Drug Research Institute, Lucknow 226 001, India |
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Abstract: | A series of novel Schiff bases has been synthesized by reacting 7-hydroxy-4-methyl-2-oxo-2H-benzoh]chromene-8,10-dicarbaldehyde 3 and 1-hydroxynaphthalene-2,4-dicarbaldehyde 8 with several primary alkylamines in ethyl alcohol at room temperature within 1-2 min. Schiff bases 4a-i and 9 were formed regioselectively by condensation with only one aldehyde, which is in chelation with a hydroxyl group. Extensive 2D NMR spectroscopic studies revealed that all the compounds 4a-i and 9 exist in the keto-enamine tautomeric form at room temperature. The high reactivity, regioselectivity and stable keto-enamine tautomeric form are due to the presence of an electron-withdrawing aldehyde group. |
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Keywords: | Coumarins synthesis Schiff bases Imine-enamine tautomerism NMR spectroscopy Regioselectivity |
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