By condensing alicyclic β‐ketocarboxylates with substituted 2‐aminopyridines in polyphosphoric acid or phosphoryl chloride‐polyphosphoric acid, numerous 2,3‐tri‐, tetra‐, penta‐ and hexamethylene‐4H‐pvrido[1,2‐a]pyrimidin‐4‐ones were synthesized for pharmacological purposes. The stability and several reactions of the title compounds were studied. The 6‐substituted‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones were transformed into 1,8‐naphthyridines in good yields independent of the ring size of ring C. The characteristic differences in the ir and uv spectra of the pyrido‐pyrimidines and the corresponding naphthyridines are discussed. Catalytic hydrogenation of the pyrido[1,2‐a]pyrimidin‐4‐ones furnished the corresponding 6,7,8,9‐tetrahydropyrido‐[1,2‐a]pyrimidin‐4‐one derivatives. It was found that the A and C rings attached to the pyrirnidinone ring in solutions of unsubstituted tetrahydropyrido[1,2‐a]pyrimidin‐4‐ones are flexible, whereas in the 6‐methyl derivatives the conformer containing the 6‐methyl group in axial position predominates.
ASJC Scopus subject areas
- Organic Chemistry