Radical differentiation of two ester groups in unsymmetrical diazomalonates for highly asymmetric olefin cyclopropanation.
Radical differentiation of two ester groups in unsymmetrical diazomalonates for highly asymmetric olefin cyclopropanation.
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DOI：
10.1016/j.checat.2021.11.018
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发表时间：
2022-02-17
期刊：
影响因子：
--
通讯作者：
Zhang, X Peter
中科院分区：
文献类型：
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作者：
Wang, Jingyi;Xie, Jingjing;Lee, Wan-Chen Cindy;Wang, Duo-Sheng;Zhang, X Peter
重氮膦酸盐已被证明是通过Co(II)-金属催化（MRC）进行不对称自由基烯烃环丙烷化的有效的亲金属试剂。在d2对称手性氨基卟啉配体的支持下，Co（II）基金属化体系可以有效激活不对称甲基苯基重氮丙酸酯（MPDM），使其两个酯基有效分化，进行不对称环丙化反应，从而可以立体选择性地构建具有两个连续手性中心的1,1-环丙二酯，包括全碳季立体中心。Co（II）催化的不对称环丙烷化反应在室温下进行，无需缓慢加成重氮化合物，通常适用于范围广泛的烯烃，并且具有多种官能团，可以以高非对映选择性和高对映选择性的流线型合成手性1,1-环丙二酯。计算和实验相结合的研究支持了Co（II）催化环丙烷化的潜在逐步自由基机制。对映体富集(E)-1,1-环丙二酯除了作为形成五元结构的1,3偶极子外，还可以作为立体选择性合成不同环丙烷衍生物的有用构件。此外，对映体富集的(E)-1,1-环丙二酯可以立体选择性地转化为(Z)-非对映体。基于钴（II）的金属催化（MRC）已经成功地应用于第一个催化系统的开发，该系统对不对称重氮酸酯（一类以前未被利用的稳定重氮化合物）的不对称烯烃环丙烷化非常有效。该Co（II）基催化体系由最佳的d2对称手性酰胺卟啉配体支撑，通常适用于多种具有不同官能团的烯烃底物，可以立体选择性合成多种1,1-环丙二酯，具有优异的非对映选择性和对映选择性。
Diazomalonates have been demonstrated as effective metalloradicophiles for asymmetric radical olefin cyclopropanation via Co(II)-metalloradical catalysis (MRC). Supported by D2-symmetric chiral amidoporphyrin ligand, Co(II)-based metalloradical system can efficiently activate unsymmetrical methyl phenyl diazomalonate (MPDM) with effective differentiation of the two ester groups for asymmetric cyclopropanation, enabling stereoselective construction of 1,1-cyclopropanediesters bearing two contiguous chiral centers, including all-carbon quaternary stereogenic center. The Co(II)-catalyzed asymmetric cyclopropanation, which operates at room temperature without slow addition of the diazo compound, is generally applicable to broad-ranging olefins and tolerates various functionalities, providing a streamlined synthesis of chiral 1,1-cyclopropanediesters in high yields with both high diastereoselectivity and enantioselectivity. Combined computational and experimental studies support the underlying stepwise radical mechanism for Co(II)-catalyzed cyclopropanation. In addition to functioning as 1,3-dipoles for forming five-membered structures, enantioenriched (E)-1,1-cyclopropanediesters serve as useful building blocks for stereoselective synthesis of different cyclopropane derivatives. In addition, the enantioenriched (E)-1,1-cyclopropanediesters can be stereoselectively converted to (Z)-diastereomers. Cobalt(II)-based metalloradical catalysis (MRC) has been successfully applied for the development of the first catalytic system that is highly effective for asymmetric olefin cyclopropanation with unsymmetrical diazomalonates, a class of stable diazo compounds that have not been previously utilized. Supported by an optimal D2-symmetric chiral amidoporphyrin ligand, the Co(II)-based catalytic system is generally applicable to a broad range of olefin substrates with different functionalities, enabling stereoselective synthesis of diverse 1,1-cyclopropanediesters in high yields with both excellent diastereoselectivity and enantioselectivity.