Theoretical investigations towards the [4+2] cycloaddition of ketenes with 1-azadienes catalyzed by N-heterocyclic carbenes: mechanism and stereoselectivity

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• 作者：Yingying Ran ; Mingsheng Tang ; Yang Wang ; Yanyan Wang ; Xiaoli Zhang ; Yanyan Zhu ; Donghui Wei ; Wenjing Zhang ; ^{zhangwj@zzu.edu.cn" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Density functional theory (DFT) ; N-Heterocyclic carbene (NHC) ; Reaction mechanism ; Stereoselectivity ; [4+2] Cycloaddition
• 刊名：Tetrahedron
• 出版年：2016
• 出版时间：1 September 2016
• 年：2016
• 卷：72
• 期：35
• 页码：5295-5300
• 全文大小：1113 K

文摘

This present work reported a detailed DFT study to the reaction mechanism and stereoselectivities of the NHC-catalyzed [4+2] cycloaddition of ketenes with 1-azadienes. The calculated results reveal that the ‘ketene-first’ mechanism is more energetically favorable than the ‘azadiene-first’ one, and the cycloaddition step is demonstrated to be both the rate- and stereoselectivity-determining step. The Gibbs free energy barrier to afford the product in SS configuration is lower than those in other configurations, which is well consistent with the experimental results. Analyses to the distortion–interaction energies of two key species and the components of the free energy barriers of the step in which the stereocenters generate were conducted, and it was concluded that stereoseletivities of the reaction should originate from differences of enthalpy barriers via the four transition state isomers, rather than the distinctions of barriers stemming from entropy penalties.