New synthesis of pyrido[2,3‐d]pyrimidines. III. Nucleophilic substitution on 4‐amino‐2‐halo and 2‐amino‐4‐halo‐5,6‐dihydropyrido[2,3‐d]pyrimidin‐7(8H)‐ones

As the third step of a new general synthesis of pyrido[2,3‐d]pyrimidines, the substitution of the halogens by several nucleophiles has been carried out. Yields are between good and high in every case, even when 4‐halogenated compounds have a neighbouring methyl group in C5.