Zou Hongyan, Wang Zhong-Liang, Huang Genping
Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin, 300387, P.R. China.
Department of Chemistry, School of Science, National Demonstration Center for Experimental Chemistry & Chemical engineering Education, National Virtual Simulation Experimental Teaching Center for Chemistry & Chemical engineering Education, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin, 300072, P.R. China.
Chemistry. 2017 Sep 12;23(51):12593-12603. doi: 10.1002/chem.201702316. Epub 2017 Aug 9.
The nickel-catalyzed intermolecular cycloadditions of benzocyclobutenones with 1,3-dienes developed by Martin and co-workers are featured with the exclusive proximal C-C bond cleavage and a high chemoselectivity of the [4+4] over the [4+2] cycloaddition. In this report, the detailed reaction mechanism and the origins of the selectivities were investigated by means of density functional theory calculations. The results show that the reaction is initiated by a C-C oxidative addition of the benzocyclobutenone to form the five-membered nickelacycles. A subsequent exo 1,4-insertion/C-C reductive elimination and an endo 1,4-insertion/C-C reductive elimination lead to the [4+4] and [4+2] cycloaddition products, respectively. The 1,4-insertion of the 1,3-diene into the Ni-C bond was calculated to be the rate- and selectivity-determining step of the reaction. The calculations reproduced quite well the experimentally observed exclusive proximal C-C bond cleavage and the high chemoselectivity of the [4+4] over the [4+2] cycloaddition. In particular, it was found that the steric repulsion between the phosphine ligand and the α-substituent of the benzocyclobutenone has a dramatic impact on the 1,4-insertion, which enables the experimentally observed selectivities.
马丁及其同事所开发的镍催化苯并环丁烯酮与1,3 - 二烯的分子间环加成反应，其特点是具有独特的近端碳 - 碳键断裂以及[4 + 4]环加成相对于[4 + 2]环加成的高化学选择性。在本报告中，通过密度泛函理论计算研究了详细的反应机理和选择性的来源。结果表明，反应由苯并环丁烯酮的碳 - 碳氧化加成引发，形成五元镍杂环。随后的外向1,4 - 插入/碳 - 碳还原消除和内向1,4 - 插入/碳 - 碳还原消除分别导致[4 + 4]和[4 + 2]环加成产物。计算得出1,3 - 二烯插入镍 - 碳键的1,4 - 插入是反应的速率和选择性决定步骤。计算结果很好地再现了实验观察到的独特的近端碳 - 碳键断裂以及[4 + 4]环加成相对于[4 + 2]环加成的高化学选择性。特别地，发现膦配体与苯并环丁烯酮的α - 取代基之间的空间排斥对1,4 - 插入有显著影响，这使得能够实现实验观察到的选择性。
