Mechanism and Enantioselectivity of Dirhodium-Catalyzed Intramolecular C-H Amination of Sulfamate
Mechanism and Enantioselectivity of Dirhodium-Catalyzed Intramolecular C-H Amination of Sulfamate
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铑催化氨基磺酸分子内C-H胺化反应的机理及对映选择性
DOI：
10.1021/jo402101h
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发表时间：
2013
影响因子：
3.6
通讯作者：
Zhao Cunyuan
中科院分区：
文献类型：
--
作者：
Zhang Xiting;Ke Zhuofeng;DeYonker Nathan J.;Xu Huiying;Li Zhi-Feng;Xu Xianyan;Zhang Xuepeng;Su Cheng-Yong;Phillips David Lee;Zhao Cunyuan
用密度泛函理论BPW 91计算方法研究了铑（Rh 2L 4，L =甲酸根，N-甲基甲酰胺，S-nap）催化的3-苯丙氨基磺酸酯分子内C-H胺化反应的机理和对映选择性.由Rh 2 II，II催化剂催化的反应从Rh 2 II，II二聚体氧化成三重混合价Rh 2 II，III-氮烯自由基开始，这应该有助于自由基H原子的提取。然而，在铑2（甲酸）4促进的反应，作为一个最小能量交叉点（MECP）之间的单线态和三线态配置文件的结果，一个直接的C-H键插入被假定。Rh 2（N-甲基甲酰胺）4反应表现出完全不同的机理特征，通过两步过程发生，包括（i）在三重态上的分子内H-提取以产生双自由基中间体和（ii）通过从三重态到开壳层单重态的系间交叉形成C-N。Rh 2（S-nap）4催化的3-苯丙基氨基磺酸酯反应也遵循分步反应机理，双自由基中间体也是竞争步骤的起点，而竞争步骤的选择性取决于C-N形成的单重态过渡态.该机理建议得到了对映体过量（94.2%ee）的支持，产物的绝对立体化学为R，与实验结果（92.0%ee）良好一致。
The mechanisms and enantioselectivities of the dirhodium (Rh2L4, L = formate,N-methylformamide,S-nap)-catalyzed intramolecular C–H aminations of 3-phenylpropylsulfamate ester have been investigated in detail with BPW91 density functional theory computations. The reactions catalyzed by the Rh2II,IIcatalysts start from the oxidation of the Rh2II,IIdimer to a triplet mixed-valent Rh2II,III–nitrene radical, which should facilitate radical H-atom abstraction. However, in the Rh2(formate)4-promoted reaction, as a result of a minimum-energy crossing point (MECP) between the singlet and triplet profiles, a direct C–H bond insertion is postulated. The Rh2(N-methylformamide)4reaction exhibits quite different mechanistic characteristics, taking place via a two-step process involving (i) intramolecular H-abstraction on the triplet profile to generate a diradical intermediate and (ii) C–N formation by intersystem crossing from the triplet state to the open-shell singlet state. The stepwise mechanism was found to hold also in the reaction of 3-phenylpropylsulfamate ester catalyzed by Rh2(S-nap)4.Furthermore, the diradical intermediate also constitutes the starting point for competition steps involving enantioselectivity, which is determined by the C–N formation open-shell singlet transition state. This mechanistic proposal is supported by the calculated enantiomeric excess (94.2%ee) with the absolute stereochemistry of the product asR, in good agreement with the experimental results (92.0%ee).