化学学报 ›› 2013, Vol. 71 ›› Issue (12): 1663-1667.DOI: 10.6023/A13080836 上一篇    下一篇

研究论文

烯丙基类不对称醚异构化反应机理的理论研究

王红b, 何桥a, 谭凯a   

  1. a 厦门大学化学化工学院 厦门 361005;
    b 青海民族大学化学与生命科学学院 西宁 810007
  • 收稿日期:2013-08-08 出版日期:2013-12-14 发布日期:2013-10-09
  • 通讯作者: 谭凯 E-mail:ktan@xmu.edu.cn
  • 基金资助:

    项目受国家自然科学基金(No. 21273177)和西部之光计划资助.

A Theoretical Study of the Mechanism for Allylic Ether Isomerization

Wang Hongb, He Qiaoa, Tan Kaia   

  1. a College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005;
    b College of Chemistry and Life Science, Qinghai University for Nationalities, Xining 810007
  • Received:2013-08-08 Online:2013-12-14 Published:2013-10-09
  • Supported by:

    Project supported by the National Natural Science Foundation of China (No. 21273177) and "Western Light".

采用MP2和密度泛函M06-2X方法,在6-31++G(d,p)基组水平上对烯丙基类不对称醚异构化反应机理进行了计算研究. 揭示了其可能的反应途径,预测了互变异构吉布斯自由能,活化能等性质. 计算结果表明,在没有金催化剂的条件下,尽管有醇溶剂时异构化活化能垒有所降低,异构化反应依然不容易进行. 相反,存在金催化剂并且有醇溶剂情况下,烯丙基类不对称醚异构化反应活化自由能大大降低,仅为7.5 kcal/mol. 通过比较有无醇溶剂和金催化剂对异构化的影响,揭示了金烯烃络合和醇分子参与反应以质子转移的异构化反应机理,很好解释了实验中观察的现象. 计算结果还表明:醇分子不仅参与反应提供质子转移,它还能与醚竞争金催化剂络合,因此在高浓度醇条件下会抑制异构化反应进行.

关键词: 烯丙基不对称醚, 异构化反应, 反应机理

The reaction mechanism of allylic ether isomerization has been investigated by MP2 and DFT method (different functionals) with 6-31++G(d,p) basis set. The calculated results show that M06-2X method that designed to treat dispersion and hydrogen-bonded systems do better than traditional functional-B3LYP for the calculated energetic and structural properties of allylic ether isomerization. The optimal structures of allylic ether and transition states were located and the reaction Gibbs free energy barriers were predicted at the MP2 and M06-2X level. Furthermore, the possible reaction pathways and mechanisms were proposed to explain the origin of regioselectivity observed in experiment. The calculation results show that the isomerization reaction will not readily occur in the absence of catalysis by Au. The computed potential energy barrier is quite high, and things get better when alcohol molecules are introduced, resulting in the decrease of calculated activation free energy from 67.1 to 48.6 kcal/mol. However, the Au(I)-catalyzed addition of another molecule of alcohol to an allylic ether can occur readily. A protonated diether intermediate was stabilized by a hydrogen bond and the activation energies of allylic ether isomerization were dramatically decreased, only 7.5 kcal/mol. By contrast the isomerization effect under with and without alcohol, gold catalysis, the results indicate that the allylic ether isomerization involve cationic gold coordination and proton shift reaction process, which form the intermediate that allows the interconversion of the products. This reaction mechanism can successfully explain the observed regioselectivity for the thermodynamic product. Meanwhile, the results also show that the isomerization was completely inhibited with the excess alcohol due to competing gold coordination between alcohol and ether. The discovery of gold catalysts in allylic ether isomerization not only contributes to the development of catalysts from the usual transition metals to noble metals, but also shows the potential catalytic activities by switching the reaction conditions.

Key words: allylic ether, isomerization, reaction mechanism