Synthesis of Naphthyridines

The application of the Skraup reaction, utilizing sulfo mix, to the appropriate aminopyridines affords these compounds in variable yields. Recent reaction condition improvements3 in some of these syntheses afford the naphthyridines in up to 90% yields. 

It is again1 pointed out that no 1,7-naphthyridine is obtained by potential cyclization into the 4-position of 3-aminopyridine, 1,5-naphthyridine (1) being the lone naphthyridine product. Only when the 2-position is blocked by electron-donating groups are 1,7-naphthyridines obtained.1 

The well-known reaction of 3-aminopyridines (e.g., 10) with ethoxy- 

Some 1,3-dicarbonyl compounds, when condensed with 2,6-diaminopyridine, afford 2-amino-5,7-disubstituted l,8-naphthyridines.4a 

When 4-amino-3-carboxaldehyde derivatives of pyridine are employed, 2-amino-l,6-naphthyridines (16) are obtained.6 

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