Theoretical Insights into the Synthesis of 2,3-Dihydropyridines from Unsaturated Oximes by Rh^III-Catalyzed C-H Activation - A DFT Study

详细信息    查看全文

• 作者：Xiang-Biao Zhang ; Zhen-Yuan Hu ; Gui-E Zhou and Song Wang
• 刊名：European Journal of Organic Chemistry
• 出版年：2017
• 出版时间：January 10, 2017
• 年：2017
• 卷：2017
• 期：2
• 页码：397-408
• 全文大小：4094K
• ISSN：1099-0690

文摘

A density functional theory study is performed on the reactions of α,β-unsaturated oxime pivalates and alkenes through Cp*Rh^III-catalyzed (Cp* = pentamethylcyclopentadienyl) C–H activation. The catalytic cycle involves reversible metalation–deprotonation, migratory alkene insertion, pivaloyl transfer to the Rh center, and reductive elimination, among other steps. The results show that the migratory alkene insertion is rate-determining and that the reductive elimination to form the product-ligated species makes the reaction irreversible (exergonic by 60 kcal/mol). If the electron-donating ability of the substituents on the cyclopentadienyl (Cp) ligand is increased or an electron-withdrawing group is introduced into the terminus of the alkene, the apparent activation energy of the reaction increases. In contrast, if a stronger electron-donating group is introduced at the 2-position of the α,β-unsaturated oxime pivalate, the apparent activation energy of the reaction decreases greatly, and the reaction can be performed at room temperature. On the other hand, for phenyl groups at the 2-position, the introduction of a more electron-deficient p-CF₃-phenyl group increases the apparent activation energy. Finally, the diastereoselectivity of the reaction with cyclohexylethylene as the substrate is attributable to a clash between the cyclohexyl group and the α,β-unsaturated oxime pivalate.