Condensed Heteroaromatic Ring Systems. III.^1,2) Synthesis of Naphthyridine Derivatives by Cyclization of Ethynylpyridinecarboxamides

Four kinds of naphthyridinones, i.e. l,6-naphthyridin-5-one, l,7-naphthyridin-8-one, 2,6-naphthyridin-2-one, and 2,7-naphthyridin-l-one derivatives, were commonly synthesized by the intramolecular cyclization of pyridinecarboxamides having an ethynyl group or β,β-dimethoxyethyl group adjacent to the carbamoyl group. The syntheses of the starting pyridine derivatives were easily accomplished by cross-coupling of the corresponding halopyridines with acetylenes.