化学
环加成
化学选择性
路易斯酸
有机催化
电泳剂
废止
催化作用
立体选择性
密度泛函理论
组合化学
计算化学
有机化学
对映选择合成
作者
Min Zhang,Yan Wang,Shijun Li,Xinghua Wang,Qianqian Shi,Xue Li,Lingbo Qu,Donghui Wei,Yu Lan
标识
DOI:10.1021/acscatal.0c05511
摘要
Although breakthroughs in the N-heterocyclic carbene (NHC)-catalyzed inert C–C bond activation strategy have been achieved, understanding the role of the catalyst as well as the origin of its chemo- and stereoselectivities is still one of the most challenging questions in the field of organocatalysis. Herein, we propose an NHC and NHC·H+ cooperative catalytic model for these kinds of reactions and perform density functional theory calculations in the case of an NHC-catalyzed [4 + 2] annulation reaction of conjugated dienal and α-aryl ketone. The calculated results indicate that the organocatalyst either works as a Lewis base to prevent the bad frontier molecular orbital overlap mode, promoting [2 + 2] cycloaddition, or as a noncovalent organocatalyst to provide a hydrogen bonding network to facilitate the release of CO2. The latter is remarkably different from its well-known role as a Lewis base. In addition, we devised an atomic electrophilicity index to correctly predict the site of the stereoselective C–C bond formation involved in [4 + 2] cycloaddition. Further analysis results show that hydrogen bonds significantly contribute to the favorable stereoselective pathway, which was associated with axial chirality of the main final product in an experiment. The obtained insights should be valuable for the prediction and rational design of organocatalytic inert C–C activations with special chemoselectivity and high stereoselectivity.
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