Synthesis of new pyrido[2,3-d]pyrimidin-5-one, pyrido[2,3-d]pyrimidin-7-one, and pyrimidino[4,5-d][1,3]oxazine derivatives from 5-acetyl-4-aminopyrimidines

Methods were developed for the synthesis of new pyrido[2,3- d ]pyrimidine and pyrimidino[4,5- d ][1,3]oxazine derivatives. When heated under reflux with MeONa in BuOH, 5-acetyl-4-aminopyrimidines, acylated with carboxylic anhydrides or acid chlorides, are transformed into pyrido[2,3- d ]pyrimidin-5-one derivatives, i.e., the acetyl methyl group and the amide carbonyl moiety are involved in the cyclization. In the presence of an activated CH 2 group (e.g . , PhCH 2 ) in the amide moiety, the cyclization involves this group and the acetyl carbonyl giving rise to pyrido[2,3- d ]pyrimidin-7-one derivatives. The reaction of 5-acetyl-4-aminopyrimidines with carboxylic acid chlorides under reflux in xylene followed by addition of a base affords pyrimidino[4,5- d ][1,3]oxazines.