Investigation of naphthyridines. 16. Synthesis of derivatives of 2,5-dioxo-1,2,5,6,7,8-hexahydro-1,6-naphthyridine-3-carboxylic acids from anilides (hydrazides) of 6-oxo-2-styrylnicotinic acids
Heating anilides (hydrazides) of 5-cyano-6-oxo-2-styrylnicotinic acids in polyphosphoric acid (PPA) leads to amides of 7-aryl-2,5-dioxo-6-phenyl(amino)-1,2,5,6,7,8-hexahydro-1,6-naphthyridine-3-carboxylic acids, which on heating with perchloric acid in acetic acid give the corresponding acids.