2-锗萘与2,3-二甲基丁二烯杂Diels-Alder反应的研究

Studies on the hetero-Diels-Alder reactions between 2-germanaphthalenes and 2,3-dimethyl-butadiene

采用密度泛函理论(DFT)在B3LYP/6-311G(d,p)水平上,研究2-锗萘作为亲二烯体与2,3-二甲基丁二烯的杂Diels-Alder反应的微观机理和势能剖面,考察反应的取代基效应和溶剂效应。计算结果表明,所研究反应均以协同非同步的方式进行,且C-Ge键总是先于C-C键形成。发生在C1,Ge2位上的反应中,形成2个新键的非同步性比发生在Ge2-C3位上的大,且前者在热力学和动力学上都比后者容易进行,与实验完全一致。exo进攻方式在动力学上都比相应的endo容易,但二者在热力学上的差别一般比较小。锗原子上的CCl_3和NH_2取代基,一般有利于反应,而C(CH_3)_3取代基则相反。苯溶剂对所研究反应的势能剖面影响较小。

Density functional theory（DFT） calculation,at the B3LYP/6-311G（d,p） level of theory,were performed to investigate the mechanism,potential energy surface,substituent effect and solvent effect of hetero-Diels-Alder reactions of 2-germanaphthalenes with 2,3-dimethyl-butadiene.It can be observed that all of studied reactions proceed in a concerted but nonsynchronous way and the formations of C-Ge bond always keep ahead the formation of C-C bond.The reactions taking place at C1-Ge2 positions are more asynchronous and more favorable both thermodynamically and kinetically than those occurring at Ge2-C3 positions, which is in good agreement with experimental observations.It seems that the exo approach is kinetically favored over corresponding endo one,but the difference in the thermodynamic properties between exo and endo approaches is not obvious.The substituent CCl_3 or NH_2 at Ge atom is in favor of reactions,while C（CH_3）_3 as a substituent has opposite effect.Benzene,as a poor polar solvent,has only trivial influence on the potential energy surface of the studied reactions.