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Synthesis of Condensed Pyrido [1, 2-a] Pyrimidine and Pyrimido [4, 5-d] Pyrimidine Derivatives From Cyanoketene Dithioacetal

Bela Kalwadia, Sarita Ola and D. Kishore

Cyanoketene dithioacetal are known to undergo cyclocondensation with 2-amino pyridyl amines to give pyrimidine derivatives. The aim of the present investigation has been to examine the versatility of cyanoketene dithioacetal in the synthesis of substituted pyrido [1,2-a] pyrimidine and pyrimido [4,5-d] pyrimidine derivatives from 2-aminopyridines. Cyanoketene dithioacetal (1) on reaction with variously substituted 2 -aminopyridine derivatives (2a-f) formed 2-ethoxy-3-cyano-4- oxo-4 –H-pyrido [1,2-a] pyrimidine (3a-f) and 2-ethoxy-(2-methylthio)-3-cyano-4-oxo-4 –H-pyrido [1,2-a] pyrimidine derivatives (4a-f) in high yields. Subsequent reactions of (4) with (i) primary amines (ii) hydrazine hydrate (iii) hydroxyl amine (iv) acetamidine hydrochloride afforded the corresponding pyrimidine derivatives (5-6a-f), pyrazole derivatives (7a-f), isoxazole derivatives (8a-f) and pyrimido [4,5-d] pyrimidine derivatives (9a-f), respectively in good yields.