Cui Wei-Chen, Zhao Wenxuan, Gao Ming, Liu Wei, Wang Shaozhong, Liang Yong, Yao Zhu-Jun
State Key Laboratory of Coordination Chemistry, Jiangsu Key Laboratory of Advanced Organic Materials, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, P. R. China.
Chemistry. 2019 Dec 20;25(72):16506-16510. doi: 10.1002/chem.201903440. Epub 2019 Nov 27.
A visible-light-driven radical silylative cyclization of aza-1,6-dienes featuring an acrylonitrile or acrylate moiety and an electron-neutral olefin was developed, which allows for stereoselective synthesis of densely functionalized piperidines in a highly atom-economical manner. Depending on the substitution pattern of the electron-neutral olefin, poor-to-excellent diastereoselectivity was observed. It was suggested that the 6-exo-trig cyclization was initiated by a chemoselective addition of silyl radical toward electron-deficient olefin and the geometry of the remaining olefin is closely associated with the cis-stereoselectivity. DFT calculations supported that a transition state with a cyano group locating at the axial position of the forming piperidine ring might be involved, in which either the increase of 1,3-diaxial repulsion or the lack of hydrogen bonding interaction will diminish diastereoselectivity.
开发了一种可见光驱动的含丙烯腈或丙烯酸酯部分以及电子中性烯烃的氮杂-1,6-二烯的自由基硅氢化环化反应，该反应能够以高度原子经济的方式立体选择性地合成功能密集的哌啶。根据电子中性烯烃的取代模式，观察到了从差到优异的非对映选择性。有人提出，6-外向-三取代环化反应是由硅基自由基向缺电子烯烃的化学选择性加成引发的，剩余烯烃的几何结构与顺式立体选择性密切相关。密度泛函理论计算支持可能涉及氰基位于形成的哌啶环轴向位置的过渡态，其中1,3-二轴向排斥力的增加或氢键相互作用的缺乏都会降低非对映选择性。
