Liang Yujie, Jiang Yuan-Ye, Liu Yuxia, Bi Siwei
College of Chemistry and Chemical Engineering, Qufu Normal University, Qufu 273165, P. R. China.
Org Biomol Chem. 2017 Jul 26;15(29):6147-6156. doi: 10.1039/c7ob01021d.
The Pd-catalyzed cross-coupling of aryl iodide, benzoic anhydride and ethyl acrylate provided a useful alternative to synthesize alkenylated aryl ketones with good selectivity and functional-group tolerance. In this manuscript, density functional theory (DFT) calculations were performed to address the detailed reaction mechanism. Computational results support the experimentally proposed Pd(0)-Pd(ii)-Pd(iv) catalytic cycle and further clarify that the rate-determining step is the oxidative addition of benzoic anhydride, the regioselectivity-determining step is the migratory insertion of ethyl acrylate and the following β-H elimination determines the stereoselectivity. The regioselectivity can be attributed to the steric and electronic effect of ethyl acrylate and the stereoselectivity can be explained by the steric repulsion between the toluene moiety and the COEt moiety. Furthermore, we found that norbornene not only acts as the removable scaffold in Catellani-Lautens-type reactions, but also plays the role of suppressing the competitive migratory insertion of ethyl acetate. Norbornene insertion and ethyl acetate insertion are found to have close free energy barriers, which shed light on the origin of using stoichiometric amounts of norbornene.
钯催化的芳基碘化物、苯甲酸酐和丙烯酸乙酯的交叉偶联反应为合成具有良好选择性和官能团耐受性的烯基化芳基酮提供了一种有用的替代方法。在本论文中，进行了密度泛函理论（DFT）计算以阐明详细的反应机理。计算结果支持了实验提出的Pd(0)-Pd(ii)-Pd(iv)催化循环，并进一步阐明了速率决定步骤是苯甲酸酐的氧化加成，区域选择性决定步骤是丙烯酸乙酯的迁移插入，随后的β-H消除决定了立体选择性。区域选择性可归因于丙烯酸乙酯的空间和电子效应，立体选择性可通过甲苯部分与COEt部分之间的空间排斥来解释。此外，我们发现降冰片烯不仅在卡特拉尼-劳滕斯型反应中作为可去除的支架，还起到抑制乙酸乙酯竞争性迁移插入的作用。发现降冰片烯插入和乙酸乙酯插入具有相近的自由能垒，这揭示了使用化学计量的降冰片烯的原因。
