硅杂苯与亲二烯体的Diels-Alder反应

采用密度泛函理论(DFT)在B3LYP/6-311G(d,p)水平上研究了硅杂苯与一些亲二烯体的两类可能的Diels-Alder反应的微观机理、势能剖面、取代基效应和溶剂化效应. 计算结果表明, 所研究反应均以协同的方式进行. 亲二烯体分子碳原子上的苯基取代基对两个新键形成的非同步性和反应的活化能垒的影响取决于苯基在产物中的相对位置, 而硅杂苯分子中硅原子上的CCl3取代基有利于杂Diels-Alder反应的进行. 形成一个C—Si键的杂Diels-Alder反应在热力学和动力学上均远比相应的全碳Diels-Alder反应容易进行, 实验观察到的杂Diels-Alder反应中的区域选择性由动力学因素所控制. 硅杂苯与烯烃的反应比与相应炔烃的反应在动力学上容易进行一些, 但在热力学上后者远比前者容易进行. 苯溶剂对所研究反应的势能剖面影响较小.

Diels-Alder Reactions between Silabenzenes and Dienophiles

The mechanism, potential energy surface, substituent effect and salvation effect of two types of Diels-Alder reactions between silabenzenes and some dienophiles were investigated using density functional theory (DFT) at B3LYP/6-311G(d,p) level. All the studied reactions proceeded in a concerted way. The influence of phenyl at the C atom of dienophiles on the asynchronicity in the bond-formation process and the activation barrier of the reaction were determined by the relative position of phenyl in products. The CCl3 group at the Si atom of the silabenzene molecule favors the hetero-Diels-Alder reactions. The hetero-Diels-Alder reactions associated with the C—Si forming bond proceed much more easily than traditional Diels-Alder reactions both thermodynamically and kinetically. The complete regioselectivity observed experimentally in hetero-Diels-Alder reactions were reproduced well by theoretical calculations and are controlled by kinetic factors. Reactions between silabenzene and olefins proceed more easily than those between silabenzene and corresponding alkynes kinetically, but thermodynamically, this is reversed. Benzene as a solvent only has a trivial influence on the potential energy surface of the studied reactions.