Synthesis of pyrido[2,3-d]pyrimidines via palladium-catalyzed reaction of iodouracil with acetylenes

The reactions of iodouracils having a formamidine or acetamidine moiety 1 with various acetylenes 2 in DMF at 120°C using potassium carbonate and a catalytic amount of palladium acetate gave a mixture of pyrido[2,3-d]pyrimidine derivatives in good to high yields. Addition of lithium chloride to the reaction solution resulted in a change of reaction selectivity.