The thermal ring transformation of 2-substituted 4-oxo-4H-pyrido[1,2-a]pyrimidine-3-acrylates gave 2-substituted 1,8-naphthyridine-3-acrylates, pyrano-1,8-naphthyridines and anthyridine, depending upon the nature of the 2-substituent. A longer reaction period and a higher reaction temperature favored the formation of tricyclic products from 1,8-naphthyridine-3-acrylate after isomerization of the side-chain at position 3. The products were characterized by means of uv, ir and ¹H nmr spectroscopy.