Studies on Pyrimidine Derivatives. XXVIII. Synthesis of Pyridopyrimidine Derivatives by Cross-coupling of Halopyrimidines with Olefins and Acetylenes

Three kinds of pyridopyrimidines were synthesized from appropriate pyrimidine derivatives. Cross-coupling of 4-amino-5-iodopyrimidines with α,β-unsaturated carboxylic esters followed by ring-closure afforded pyrido[2,3-d]pyrimidines. Ammonolysis of 4-ethoxycarbonyl-5-phenylethynyl- and 5-ethoxycarbonyl-4-phenylethynyl-pyrimidines which were obtained by cross-coupling of the corresponding halopyrimidines with phenylacetylene, gave pyrido[3,4-d]- and pyrido[4,3-d]-pyrimidines, respectively.