By the reactions of ketimines bearing a pyridyl or a picolyl group on a nitrogen atom of the imine moiety with tosylisocyanate, 4H-pyrido [1, 2-a] pyrimidin-4-one derivatives could be obtained in quantitative yields. In these reactions, tosylisocyanate acts as a carbonyl precursor. The pyridyl or picolyl group is a key functional group because it is not only the constituent structure of the 4H-pyrido [1, 2-a] pyrimidin-4-one framework but also the ...