quaternary pyrazinium salts as well as the protonated pyrazines undergo an intramolecular Diels-Alder reaction under considerably milder conditions than the corresponding neutral pyrazines. The products of the reactions were []-annelated quaternary pyridinium salts and []-annelated protonated pyridinium cations, respectively.
如13 C NMR数据所示,炔基取代的
吡嗪在
二氯甲烷中用四
氟硼酸三乙基氧鎓进行季
铵化仅在N-4处产生3-炔基-1-乙基
吡嗪鎓盐。同样的
吡嗪与
三氟乙酸的质子化也发生在N-4处。季
吡嗪鎓盐以及质子化的
吡嗪在比相应的中性
吡嗪温和得多的条件下进行分子内Diels-Alder反应。反应产物分别为[ ]-退火的季
吡啶鎓盐和[ ]-退火的质子化
吡啶鎓阳离子。