Asymmetric radical cyclopropanation of alkenes.
Asymmetric radical cyclopropanation of alkenes.
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DOI：
10.1016/j.trechm.2022.06.003
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发表时间：
2022-09
影响因子：
15.7
通讯作者：
Zhang XP
中科院分区：
文献类型：
--
作者：
Lee WC;Zhang XP
在D2-对称手性氨基卟啉配体的支持下，Co（II）基金属自由基体系在温和的条件下以低催化剂负载量操作，可以活化不同种类的重氮化合物，而不需要缓慢添加不同类型的烯烃作为限制试剂的不对称环丙烷化反应。可以高产率合成相应的环丙烷，并且可以出色地控制非对映选择性和对映选择性。广泛的基板范围和独特的催化性能的Co（II）催化的环丙烷化是由于基本的逐步自由基的机制，已建立通过结合实验和计算研究。作为金属自由基催化剂的卟啉的Co（II）配合物可以均裂活化重氮化合物，同时在释放双氮气体时将原始自由基特征从金属中心转移到α-碳原子，导致α-Co（III）-烷基自由基I的产生。初始产生的α-Co（III）-烷基自由基中间体I代表了一类全新的金属稳定的有机自由基，在动力学上能够与烯烃进行自由基加成，导致生成γ-Co（III）-烷基自由基II，同时形成第一个C-C键。由于Co-C键比C-C键弱得多，所得的γ-Co（III）-烷基自由基中间体II优先进行分子内自由基取代（3-exo-tet自由基环化），而不是与另一个烯烃分子的分子间自由基加成，从而通过形成第二个C-C键同时再生Co（II）-金属自由基催化剂来选择性地产生环丙烷。与已知的协同反应机理不同，基于Co（II）的自由基环丙烷化反应在C-C键形成的两个连续步骤中分别控制对映选择性和非对映选择性.
With the support of D2-symmetric chiral amidoporphyrin ligands, the Co (II)-based metalloradical system, which operates under mild conditions with low catalyst loadings, can activate different classes of diazo compounds without the need of slow addition for asymmetric cyclopropanation of diverse types of alkenes as the limiting reagents. The corresponding cyclopropanes can be synthesized in high yields with excellent control of both diastereoselectivity and enantioselectivity. The broad substrate scope and the unique catalytic profile of the Co (II)-catalyzed cyclopropanation are attributed to the underlying stepwise radical mechanism that has been established through combined experimental and computational studies. The Co (II) complexes of porphyrins as metalloradical catalysts can activate diazo compounds homolytically while translocating the original radical character from the metal center to the α-carbon atom upon releasing dinitrogen gas, resulting in the generation of α-Co (III)-alkyl radicals I.The initially-generated α-Co (III)-alkyl radical intermediates I, which represent a fundamentally new class of metal-stabilized organic radicals, are kinetically competent to undergo radical addition to alkenes, leading to the generation of γ-Co (III)-alkyl radicals II while forming the first C–C bond. Since Co–C bonds are significantly weaker than C–C bonds, the resulting γ-Co (III)-alkyl radical intermediates II preferentially proceed intramolecular radical substitution (3-exo-tet radical cyclization) over intermolecular radical addition to another alkene molecule, giving rise to selective production of the cyclopropanes by forming the second C–C bond while regenerating the Co (II)-metalloradical catalysts. Different from the well-known concerted mechanism, the Co (II)-based radical cyclopropanation controls enantioselectivity and diastereoselectivity separately during two consecutive steps of C–C bond formation.
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影响因子：
23.5
作者：
Cindy Lee WC;Wang DS;Zhang C;Xie J;Li B;Zhang XP
通讯作者：
Zhang XP
DOI：
10.1016/j.checat.2021.11.018
发表时间：
2022-02-17
期刊：
CHEM CATALYSIS
影响因子：
--
作者：
Wang, Jingyi;Xie, Jingjing;Lee, Wan-Chen Cindy;Wang, Duo-Sheng;Zhang, X Peter
通讯作者：
Zhang, X Peter
影响因子：
7.3
作者：
Chirila, Andrei;Brands, Maria B.;de Bruin, Bas
通讯作者：
de Bruin, Bas
影响因子：
2.8
作者：
Fantauzzi, Simone;Gallo, Emma;Cenini, Sergio
通讯作者：
Cenini, Sergio
影响因子：
16.6
作者：
Roy, Satyajit;Das, Sandip Kumar;Chattopadhyay, Buddhadeb
通讯作者：
Chattopadhyay, Buddhadeb