Xin Shuang, Liao Jibang, Tang Qi, Feng Xiaoming, Liu Xiaohua
Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University Chengdu 610064 P. R. China
Chem Sci. 2024 Oct 14;15(44):18557-63. doi: 10.1039/d4sc05642f.
The asymmetric dicarbofunctionalization of alkenes a radical relay process can provide routes to diverse hydrocarbon derivatives. Three-component carboalkynylation, limited to particular alkyl halides and using readily available cycloketone oxime esters as redox-active precursors, is restricted by the available pool of suitable chiral ligands for broadening the redox potential window of copper complexes and simultaneously creating the enantiocontrol environment. Herein, we report a new hybrid tridentate ligand bearing a guanidine-amide-pyridine unit for photoinduced copper-catalyzed cyanoalkylalkynylation of alkenes. Leveraging the copper catalyst's redox capability is achieved merging the electron-rich ligand with a readily organized configuration and enhanced absorption in the visible light range, which also facilitates the enantioselectivity. The generality of the catalyst system is exemplified by the efficacy across a number of alkenes, terminal alkynes and cycloketone oxime esters, working smoothly to give alkyne-bearing nitriles with good yields and excellent enantioselectivity. A mechanistic study reveals that the chiral copper catalyst meets the requirements of possessing sufficient reduction ability, good light absorption properties, and appropriate steric hindrance.
烯烃的不对称双碳官能化——一种自由基接力过程，能够为多种烃类衍生物提供合成路线。三组分碳炔基化反应，限于特定的卤代烃，并使用易于获得的环酮肟酯作为氧化还原活性前体，受到合适手性配体种类的限制，这些配体需要拓宽铜配合物的氧化还原电位窗口并同时创建对映体控制环境。在此，我们报道了一种带有胍基-酰胺-吡啶单元的新型混合三齿配体，用于光诱导铜催化的烯烃氰基烷基炔基化反应。通过将富电子配体与易于构建的构型以及在可见光范围内增强的吸收相结合，利用了铜催化剂的氧化还原能力，这也促进了对映选择性。该催化剂体系的通用性通过其对多种烯烃、末端炔烃和环酮肟酯的有效性得到例证，反应顺利进行，以良好的产率和优异的对映选择性得到含炔腈类化合物。机理研究表明，手性铜催化剂满足具有足够还原能力、良好光吸收性能和适当空间位阻的要求。
