Enantioselective C–H Amination Catalyzed by Nickel Iminyl Complexes Supported by Anionic Bisoxazoline (BOX) Ligands
作者:Yuyang Dong、Colton J. Lund、Gerard J. Porter、Ryan M. Clarke、Shao-Liang Zheng、Thomas R. Cundari、Theodore A. Betley
DOI:10.1021/jacs.0c09839
日期:2021.1.20
Investigation of 6 via single-crystal X-ray crystallography, NMR and EPR spectroscopies, and computations revealed a Ni(II)-iminyl radical formulation, similar to its dipyrrinato congener. Complex 4 exhibits enantioselective intramolecular C-H bond amination to afford N-heterocyclic products from 4-aryl-2-methyl-2-azidopentanes. Catalytic C-H amination occurs under mild conditions (5 mol % catalyst, 60 °C)
将三苯甲基取代的双恶唑啉 (TrHBOX) 制备为先前报道的能够进行闭环胺化催化的联吡啶镍系统的手性类似物。用二价 NiI2(py)4 进行配体金属化,然后还原钾石墨,得到一价 (TrHBOX)Ni(py) (4)。将 1.4 equiv 的 1-金刚基叠氮化物的苯溶液缓慢添加到 4 中生成四叠氮基 (TrHBOX)Ni(κ2-N4Ad2) (5) 和末端亚胺基加合物 (TrHBOX)Ni(NAd) (6)。通过单晶 X 射线晶体学、NMR 和 EPR 光谱学和计算对 6 进行的研究揭示了一种 Ni(II)-亚胺基自由基配方,类似于其双吡喃酮同系物。配合物 4 表现出对映选择性分子内 CH 键胺化,可从 4-aryl-2-methyl-2-azidopentanes 得到 N-杂环产物。催化 CH 胺化在温和条件下(5 mol% 催化剂,60 °C)发生,并以适中的产率(29%-87%)提供吡咯烷产物,ee