Novel pyrido[l,2-a]pyrimidine derivatives; 2,3-dihydro-4H-furo[2,3-d]pyrido[l,2-a]pyridimidine- 4-ones were prepared by acidic cyclisation of 3-(2-methyl prop-l-enyl)-2-hydroxy-4H-pyrido[l,2-a] pyrimidin-4-ones, which were obtained from condensation reaction of 2-aminopyridines with diethyl alkylmethylene malonates.