Abstract 6-Methyl-6, 7, 8, 9-tetrahydro-4H-pyrido [1, 2-a] pyrimidin-4-ones 1-5 were subjected to Vilsmeier-Haack acylation with complexes of phosphoryl chloride and different amides. Acylation at position 9 of the pyridopyrim-idines was successful with the iminium salt formed in situ from N-formylpiperidine, N-methylformanilide or N, N-diethylbenzamide, but unsuccessful with the iminium salt formed from N, N-diethylacetamide or N, N-di- ...