Synthese von Pyridonen aus Enaminen und Cyanessigsäuren

Reaction of enamines1 a–e with cyanoacetic acids2 a,b in acetic anhydride at about 100°C yields the α-cyanoacetylated enamines3 a–g. Under the same conditions methyl 4-cyano-2-(2-pyridyl)-acetoacetate3 h is obtained from methyl 2-pyridylacetate and2 a. Compounds3 are cyclized in hydrochloric acid yielding the 4-hydroxy-2-pyridones4; on the other hand in ethanolic sodium ethoxide solution the 2-amino-4-pyridones are obtained. The esters5 a,b andd are saponified to give the acids7 a–c which decarboxylate at 250°C to8 a–c.