A convenient synthesis of 1,3-disubstituted 4-thioxo-3,4-dihydropyrido〔2,3-d〕pyrimidin-2(1H)-ones and 4-thioxo-3,4-dihydropyrido〔4,3-d〕pyrimidin-2(1H)-ones

An efficient and simple method for the synthesis of the compounds (V) and (IX) starting from the readily available starting materials (I) and (VI) is presented.