The reaction of 3-ethoxycarbonyl-6-methyl-4-oxo-6,7,8,9-tetrahydro-4H-pyrido [1,2-a]pyrimidine (I) with glyoxilic acid (II) in ethanolic HCl gives 3-ethoxycarbonyl-6-methyl-4-oxo-9-carboxymethylen-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine (IIIa-b), which is reduced with H2 over Pd/C in ethanol.