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Combined Theoretical and Experimental Studies Unravel Multiple Pathways to Convergent Asymmetric Hydrogenation of Enamides
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2021-12-14 , DOI: 10.1021/jacs.1c09573
Jianping Yang 1 , Luca Massaro 1 , Suppachai Krajangsri 1 , Thishana Singh 2 , Hao Su 3 , Emanuele Silvi 1 , Sudipta Ponra 1 , Lars Eriksson 4 , Mårten S G Ahlquist 3 , Pher G Andersson 1, 2
Affiliation  

We present a highly efficient convergent asymmetric hydrogenation of E/Z mixtures of enamides catalyzed by N,P–iridium complexes supported by mechanistic studies. It was found that reduction of the olefinic isomers (E and Z geometries) produces chiral amides with the same absolute configuration (enantioconvergent hydrogenation). This allowed the hydrogenation of a wide range of E/Z mixtures of trisubstituted enamides with excellent enantioselectivity (up to 99% ee). A detailed mechanistic study using deuterium labeling and kinetic experiments revealed two different pathways for the observed enantioconvergence. For α-aryl enamides, fast isomerization of the double bond takes place, and the overall process results in kinetic resolution of the two isomers. For α-alkyl enamides, no double bond isomerization is detected, and competition experiments suggested that substrate chelation is responsible for the enantioconvergent stereochemical outcome. DFT calculations were performed to predict the correct absolute configuration of the products and strengthen the proposed mechanism of the iridium-catalyzed isomerization pathway.

中文翻译:

结合理论和实验研究揭示了烯酰胺聚合不对称氢化的多种途径

我们提出了一种由 N,P-铱配合物催化的E / Z烯酰胺混合物的高效收敛不对称氢化,并得到机理研究的支持。发现烯烃异构体(EZ几何形状)的还原产生具有相同绝对构型的手性酰胺(对映收敛氢化)。这允许以优异的对选择性(高达 99% ee)。使用氘标记和动力学实验的详细机理研究揭示了观察到的对映收敛的两种不同途径。对于 α-芳基烯酰胺,双键发生快速异构化,整个过程导致两种异构体的动力学拆分。对于 α-烷基烯酰胺,没有检测到双键异构化,竞争实验表明底物螯合是对映收敛立体化学结果的原因。进行 DFT 计算以预测产物的正确绝对构型并加强提出的铱催化异构化途径的机制。
更新日期:2021-12-29
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