Pi Zongxin, Li Shuhua
School of Chemistry and Chemical Engineering, Institute of Theoretical and Computational Chemistry, Laboratory of Mesoscopic Chemistry, Nanjing University, Nanjing, 210093, People's Republic of China.
J Phys Chem A. 2006 Jul 27;110(29):9225-30. doi: 10.1021/jp062320w.
The reaction mechanism of the Diels-Alder reaction between 2-methylacrolein and cyclopentadiene catalyzed by a cationic oxazaborolidine Lewis acid has been characterized using density functional theory calculations. The solvent effect on the studied reaction is taken into account by optimizing all stationary points in CH(2)Cl(2) using the polarizable-continuum model. Our calculations show that the presence of this cationic oxazaborolidine catalyst changes the molecular mechanism of the studied reaction from concerted to stepwise, and lowers the activation barrier by more than 10.0 kcal/mol. A comparison of the results obtained for four different reaction channels reveals that the studied reaction is energetically favorable to occur along the exo/s-cis channel, which reasonably explains the stereoselectivity of the title reaction observed in related experiments. The electronic effect of this cationic oxazaborolidine complex in catalyzing the title reaction is found to be very similar to that of the commonly used Lewis acid BF(3).
采用密度泛函理论计算方法，对阳离子恶唑硼烷路易斯酸催化2-甲基丙烯醛与环戊二烯之间的狄尔斯-阿尔德反应的反应机理进行了表征。通过使用极化连续介质模型在CH₂Cl₂中优化所有驻点，考虑了溶剂对所研究反应的影响。我们的计算表明，这种阳离子恶唑硼烷催化剂的存在将所研究反应的分子机理从协同反应转变为逐步反应，并使活化能垒降低了超过10.0 kcal/mol。对四个不同反应通道获得的结果进行比较后发现，所研究的反应在能量上有利于沿着外型/顺式-顺式通道发生，这合理地解释了在相关实验中观察到的该反应的立体选择性。发现这种阳离子恶唑硼烷配合物在催化该反应中的电子效应与常用的路易斯酸BF₃非常相似。
