6‐ And 7‐Substituted 4H‐Pyrido[1,2‐a] pyrimidin‐4‐ones. Synthesis via the Acid‐catalyzed Isomerization of 2‐(Acetoacetamido)pyridines

Abstract

A novel procedure has been developed for converting a variety of substituted 2‐(aceto‐acetamido)pyridines into substituted 4H‐pyrido[1,2‐a]pyrimidin‐4‐ones. The reaction involves an acid‐catalyzed isomerization of the 2‐(acetoacetamido)pyridine derivatives into the corresponding enamines, under conditions that permit the latter to undergo cyclization to the 4‐one, in situ. The method has been employed to prepare a number of hitherto unknown 2,6‐ and 2,7‐di‐ and 2,7,9‐trisubstituted 4H‐pyrido[1,2‐a]pyrimidin‐4‐ones.