• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>RSC Advances >Mechanism of the Paal-Knorr reaction: the importance of water mediated hemialcohol pathway
【24h】

Mechanism of the Paal-Knorr reaction: the importance of water mediated hemialcohol pathway

机译：Paal-knorr反应的机制：水介导的血红蛋油途径的重要性

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The Paal-Knorr synthesis of furan, pyrrole and thiophene rings is one of the most important methods of generating these very important heterocycles, but the mechanism of this reaction is not well understood. Though several mechanistic paths are suggested, the exact energy requirements of this reaction, the structural features of transition states associated with the cyclization step, have not been established, especially for furan and thiophene synthesis. In this work, we explore the mechanism of the Paal-Knorr method and establish the energy requirements, using quantum chemical methods. The Paal-Knorr reaction to give furans is endergonic by 3.7 kcal mol(-1) whereas the same reaction is exergonic for pyrrole and thiophene generation by 16.4 and 15.9 kcal mol(-1), using G2MP2 method. The cyclization step is associated with high energy barrier, however, explicit water participation reduces the barrier significantly. For example, under the neutral condition two water mediated pathways - (i) monoenol and (ii) hemiketal, are possible on the reaction leading to furan. The cyclization step in these two pathways require 28.9 and 27.1 kcal mol(-1), respectively. The ring formation step becomes highly favorable in the presence of H3O+ with a barrier of only 11.5 kcal mol(-1) (solvent phase) from the monoenol to dihydrofuran derivative and 5.5 kcal mol(-1) (solvent phase) from hemiketal to dihydroxy dihydrofuran derivative. Similarly, a water mediated pathway involving the intermediacy of hemialcohols has been found to be energetically preferred mechanism for pyrrole and thiophene also.
机译：呋喃，吡咯和噻吩环的Paal-Knorr合成是产生这些非常重要的杂环的最重要方法之一，但该反应的机制尚不清楚。尽管提出了几条机制路径，但这种反应的确切能量要求，尚未确定与环化步骤相关的过渡状态的结构特征，特别是对于呋喃和噻吩合成。在这项工作中，我们使用量子化学方法探索了Paal-Knorr方法的机制并建立了能量要求。 Paal-knorr对呋喃的反应是脱衣性3.7 kcal mol（-1），而使用G2MP2方法，相同的反应是吡咯和噻吩的出现和噻吩生成的。使用G2MP2方法，是16.4和15.9kcal摩尔（-1）。环化步骤与高能量屏障相关联，然而，显着的水参与显着降低了屏障。例如，在中性条件下，两种水介导的途径 - （I）单烯醇和（II）的半鸟，可以在导致呋喃的反应中进行。这两种途径中的环化步骤分别需要28.9和27.1kcal（-1）。在H3O +存在下，环形成步骤在H3O +存在下具有11.5kcal摩尔（-1）（溶剂相）的屏障，从单烯醇与二氢呋喃衍生物和5.5kcal摩尔（-1）（溶剂相）从半鸟嘌呤中到二羟基二氢呋喃衍生物。类似地，已经发现涉及血红蛋白中间体的水介导的途径是吡咯和噻吩的能量优选的机制。

著录项

  • 来源
    《RSC Advances》 |2015年第107期|共14页
  • 作者

    Abbat Sheenu; Dhaked Devendra; Arfeen Minhajul; Bharatam Prasad V.;

  • 作者单位

    Natl Inst Pharmaceut Educ &

    Res Dept Pharmacoinformat Sas Nagar India;

    Natl Inst Pharmaceut Educ &

    Res Dept Med Chem Sas Nagar India;

    Natl Inst Pharmaceut Educ &

    Res Dept Med Chem Sas Nagar India;

    Natl Inst Pharmaceut Educ &

    Res Dept Med Chem Sas Nagar India;

  • 收录信息
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 化学;
  • 关键词

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号