A new synthesis of pyridones and unsaturated lactams

The condensation of diethyl glutaconate (I) with imines leads to unsaturated ester lactams which, in some cases, can be isomerized to pyridones. Thus I with N-benzylidenemethylamine yields ester lactam (IV) and I with benzalaniline yields IVa. Saponification of IV and IVa produces the isomerize pyridone carboxylic acids VI and VIa respectively which can be decarboxlated to pyridones (IX and IXa). The sequence involving saponification of IV followed by Fischer esterification gives the pyridone VIII, isomeric with IV.

Alternatively, the ester lactam (IV) can be converted to the corresponding thiolactam (V) with P₂S₅, or to the pyridone (XII) via bromination followed by treatment with ethanolic KOH. Both IV and IVa can be reduced catalytically to the piperidones X and Xa. Condensation of I with diphenylketimine gives the ester lactam (XIV) which does not isomerize under saponifying conditions, but leads to the acid (XV) and benzophenone.