关于Birch还原反应产物的探讨

Theoretical Study About Products of the Birch Reduction

Birch还原反应产物为非共轭的烯烃,其原因在各种基础有机化学教材中都未有明确探讨。现有机理表明,决定产物双键位置的一步是芳香族化合物获得2个电子后形成的负离子中间体的质子化。基于量子化学计算与其他文献的报道对质子化的区域选择性做出了探讨。结论从定性与定量2方面指出,上述质子化的反应位点是中间体HOMO中轨道系数最大的碳原子,即该反应的区域选择性由动力学因素控制。

The Birch reduction converts aromatic compounds possessing a benzenoid ring into products derived from 1,4-cyclohexadienes, which has rarely been explicitly concluded in various organic chemistry textbooks. Current mechanisms indicate that the step determining the position of the carbon-carbon double bonds in the product is the protonation of the anion intermediate after capturing two electrons. This article studied the regional selectivity in the protonation step on the base of quantum chemical calculations and reports of other literature. The results demonstrate both qualitatively and quantitatively that the protonation site is mainly the carbon atom with the largest orbital coefficient in the intermediate＇s HOMO, which means the regional selectivity is resulted from chemical kinetics factors.