Acetic Acid → (E)-3-(2,5-difluoro-phenylamino)-but-2-enoic acid ethyl ester

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A mixture of 2,5-difluoroaniline (7.5 ml) and ethyl acetoacetate (9.6 ml) were combined in toluene (15 ml) containing acetic acid (1.5 ml). The mixture was boiled under Dean-Stark azeotrope conditions, cooled and solvent removed at reduced pressure to give crude (E)-3-(2,5-difluoro-phenylamino)-but-2-enoic acid ethyl ester (16.17 g). (E)-3-(2,5-Difluoro-phenylamino)-but-2-enoic acid ethyl ester (2 g) was refluxed in Dowtherm-A (40 ml) for 3 h. After cooling the Dowtherm was diluted with pentane (40 ml) and the precipitated title compound isolated by filtration. (Method A). 1H NMR δ: 2.34 (3H, s), 5.91 (1H, s), 6.96 (1H, m), 7.53 (1H, m), 11.48 (1H, brs).

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