Acta Chimica Sinica ›› 2013, Vol. 71 ›› Issue (12): 1663-1667.DOI: 10.6023/A13080836 Previous Articles     Next Articles

Article

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".

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