β-Arylaminoacrolein Derivatives. I. The Investigation of Combes Reaction and the Syntheses of β-Arylaminoacrolein Derivatives as the Possible Reactant

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The limitations of Combes reaction were reinvestigated. 4-(p-Chloroanilino)-3-penten-2-one (III), hitherto believed to be insusceptible to cyclodehydration in sulfuric acid, reacted at a higher temperature to give 2, 4-dimethyl-6-chloroquinoline (IV). 4-Anilino-3-buten-2-one (V), however, was sulfonated in concentrated sulfuric acid and no quinolines were detected in the reaction mixture. 4-(p-Chloroanilino)-3-buten-2-one (VI) was cyclodehydrated to give 6-chloroquinaldine (VIII) in dioxane containing sulfuric acid in low yield. β-Anilinoacrolein (X), a pussible reactant of Combes reaction, and its derivatives were synthesised for further studies, and their structure was confirmed by chemical evidences and by their infrared and nuclear magnetic resonance (NMR) spectra. The conformational analysis of β-arylaminoacroleins in three solvents was carried out using their NMR spectra.