With Ammonia or Amines on o-Acylamino Acids

3-Acetamidopyridine-2-carboxylic acid, when refluxed with acetic anhydride for 90 min, gave an excellent yield of 2-methylpyrido[3,2-d][l,3]-oxazin-4-one (165). At room temperature this is immediately converted to pyridines of the type 166 by ammonia, aliphatic or aromatic amines, hydrox-ylamine, or hydrazine. These products spontaneously cyclize to the pyrido-[3,2-d]pyrimidin-4-ones 167 in excellent overall yields. When the starting material is 3-benzamidopyridine-2-carboxylic acid, the ring-opened stage (analogous to 166) is stable and requires phosphoryl chloride to cyclize it 

3-Acetamidothiophene-2-carboxylic acid, condensed with aniline and phosphorus trichloride, gave only a low yield of 2-methyl-3-phenylthieno-[3,2-d]pyrimidin-4-one (see 14).305 

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