Dihalogentriphenylphosphoranes in the Synthesis of Heterocycles, 29.1  A  Simple Synthesis of Pteridin-4-ones, from Methyl 3-Amino-2-pyrazinecarboxylate  and Pyrazino[3,1]oxazin-4-ones  Methyl 3-amino-2-pyrazinecarboxylate(3) affords the synthetically useful  3-aroylaminopyrazin-2-carboxylates 5a-f with aroyl chlorides, which are converted with  dibromotriphenylphosphorane into 2-arylpyrazino[2,3-d][3,1]oxazin-4-ones  6a-f. Nucleophilic attack at the carbonyl function of these oxazinones  results in ring cleaved amides which can be recyclized with  dibromotriphenylphosphorane to afford 2-arylpteridin-4-ones  7a-f.
                                    对
苯基膦盐在杂环合成中的应用,29.1 简单合成4-氮杂
嘧啶酮,从甲基3-
氨基-2-
吡嗪羧酸酯和
吡嗪[3,1]噁嗪-4-酮。甲基3-
氨基-2-
吡嗪羧酸酯(3)与酰
氯反应生成合成上有用的3-酰
氨基吡嗪-2-
羧酸酯5a-f,随后与
二溴三苯基膦反应,生成2-芳基
吡嗪[2,3-d][3,1]噁嗪-4-酮6a-f。对这些噁嗪酮的羰基官能团进行亲核攻击,产生开环的酰胺,这些酰胺可以与
二溴三苯基膦再循环,生成2-芳基4-氮杂
嘧啶酮7a-f。