Synthesis of fused pyrido[2,3-d]pyrimidines by thermal lsomerization of 4-amino-5-vinylpyrimidines

Article abstract of DOI:10.1016/S0040-4020(97)10334-9

4-dialkylamino-5-(2,2-dicyanovinyl)pyrimidines 4a-c react thermally in DMSO via [1,5] hydrogen transfer followed by carbon-carbon bond formation to yield fused pyrido[2,3-d]pyrimidines 6a-c. 4-alkylarylamino-5-(2,2- dicyanovinyl)pyrimidines 5a-c lend themselves more readily to thermal electrocyclic ring-closure followed by aromatization, to give tetracyclic fused pyrido[2,3-d]pyrimidines 7a-c.