Add time:08/23/2019         Source:sciencedirect.com

2-(Trifluoroacetyl)chromones were obtained in good yields via the Claisen condensation of 2-hydroxyacetophenones with methyl 2-methoxytetrafluoropropionate, followed by sulfuric acid-mediated deprotection of the reaction products. These compounds react with ethylenediamine in the presence of acetic acid in methanol to produce the target 2-salicyloylmethylene-3-(trifluoromethyl)-1,2,5,6-tetrahydropyrazines in 48–61% yield. In a similar manner, their reactions with o-phenylenediamine and 2,3-diaminonaphthaline in refluxing acetic acid gave a mixture of ketoenamine and ketoimine tautomers of the corresponding quinoxaline derivatives in excellent yields. The regioisomeric and tautomeric composition of the pyrido[2,3-b]pyrazines prepared from 2-(trifluoroacetyl)chromones and 2,3-diaminopyridine was also investigated.

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