Study of the Reaction of Bis- and Tris-pyrylium and -thiopyrylium Cations with Methoxide Ion. Electronic Effects of the Heterocyclic Rings as Substituents
作者:Barbara Branchi、Giancarlo Doddi、Gianfranco Ercolani
DOI:10.1021/jo050884a
日期:2005.8.1
5-pentanediones 6 and 8. Their reaction with CD3ONa in CD3OD was studied by 1H NMR at −40 °C and at +25 °C. At low temperature, kinetically controlled mixtures of 2H and/or 4H adducts were detected, whereas at room temperature the mixtures equilibrated to yield, in all of the cases, the more stable 2H adducts exclusively. A spectrophotometric study of the reactions with sodium methoxide in methanol was carried
的双-和三-吡喃鎓和硫代吡喃鎓阳离子1 - 4在克规模通过heterocyclization制备相应的双-和三-1,5- pentanediones 6和8。它们与CD反应3 ONA在CD 3 OD,研究了1在-40℃1 H NMR,在25℃。在低温下,检测到2 H和/或4 H加合物的动力学控制混合物,而在室温下,混合物平衡,在所有情况下均产生更稳定的2 H专门加成。用在甲醇中的甲醇钠反应的分光光度研究是在25.0℃下进行与确定用于添加的MeO的逐级平衡常数的目的-在杂芳族环的α位。所获得的平衡常数使得能够评价硫属吡啶鎓和2 H-硫属吡喃亚基作为取代基的电子效应。尽管电子效应的不同的灵敏度,吡喃鎓和噻喃环具有与σ类似吸电子效应+ p〜0.8和σ +米约0.5。除了预期的由于正电荷引起的感应效应的重要性外,这两个值之间的差异还表明了共振贡献的重要性。相反,中性的2 H-吡喃基环和硫代吡喃基环