Diastereotopos-differentiation in the Rh-catalyzed amination of benzylic methylene groups in the α-position to a stereogenic center.
Diastereotopos-differentiation in the Rh-catalyzed amination of benzylic methylene groups in the α-position to a stereogenic center.
复制标题
α-位苄基亚甲基在 Rh 催化胺化反应中的非对映异构分化为立构中心
DOI：
10.1021/ja3066682
复制
发表时间：
2012
影响因子：
15
通讯作者：
T. Bach
中科院分区：
文献类型：
--
作者：
A. Nörder;S. E. Warren;E. Herdtweck;S. M. Huber;T. Bach
Rh催化的C-H胺化的非对映选择性用18种手性开链底物和4种手性环四氢化萘进行了研究，其中18种手性开链底物在立体异构中心（−CHMeX）的α-位具有苄基亚甲基，其中立体异构中心位于碳原子C2。以三氯乙氧磺酰基取代胺（H2 NTces）为氮源，二酰氧基碘苯为氧化剂，双[（α，α，α′，α′-四甲基-1，3-苯二丙酸）铑] [Rh 2（esp）2]为催化剂，进行C-H胺化反应。对于无环底物，如果取代基X是Br、PO（OEt）2、SO2 Ph或OOCCF 3，则发现高顺式非对映选择性（dr > 95/5）（8个实例）。对于X = NO2、OAc、COOMe和CN，发现中等至良好的顺式选择性（dr = 80/20至91/9）（8个实施例）。只有两种底物的非对映选择性较低。动力学同位素效应（KIE）实验表明，当用−CDMeCOOMe取代−CHMeCOOMe时，没有次级KIE，但在苄基亚甲基位置有显著的初级KIE（4.8 ± 0.7）。氘代实验提供的证据表明，该反应进行立体特异性与保留的配置。提出了一个优选的构象，这解释了反应的结果。在这种构象中，X取代基是C-H键的反周面，C-H键被非对映选择性攻击，并且在立体异构中心和前立体异构中心处的剩余取代基之间的空间应变被最小化。DFT计算支持这一模型。然而，他们认为反应不是协同的，而是通过氢原子的提取和随后的自由基反弹发生的。进一步的支持，相对于一个给定的取代基X = Br，COOMe，或CN的反周平面攻击得到相应的2-取代的四氢化萘。在C1的进攻几乎完全提供转胺产物。如果X取代基的大小增加[Br < CN < COOMe < PO（OEt）2]，则碳原子C4上的进攻占优势，在该位置产生相应的转胺产物。
The diastereoselectivity of the Rh-catalyzed C–H amination was examined with 18 chiral open-chain substrates, which bear a benzylic methylene group in the α-position to a stereogenic center (−CHMeX), and with four chiral cyclic tetralins, in which the stereogenic center was positioned at carbon atom C2. The C–H amination was performed using trichloroethoxysulfonyl-substituted amine (H2NTces) as the nitrogen source, a diacyloxyiodobenzene as the oxidant, and bis[rhodium(α,α,α′,α′-tetramethyl-1,3-benzenedipropionate)] [Rh2(esp)2] as the catalyst. For acyclic substrates a high syn diastereoselectivity (dr > 95/5) was found if the substituent X was Br, PO(OEt)2, SO2Ph, or OOCCF3(eight examples). Moderate to good syn selectivities (dr = 80/20 to 91/9) were found for X = NO2, OAc, COOMe, and CN (eight examples). Only two substrates gave a low diastereoselectivity. Kinetic isotope effect (KIE) experiments revealed that there is no secondary KIE when replacing −CHMeCOOMe by −CDMeCOOMe, but there is a significant primary KIE at the benzylic methylene position (4.8 ± 0.7). Deuteration experiments provided evidence that the reaction proceeds stereospecifically with retention of configuration. A preferred conformation is proposed, which explains the outcome of the reaction. In this conformation the X substituent is antiperiplanar to the C–H bond, which is diastereoselectively attacked, and steric strain between the remaining substituents at the stereogenic and the prostereogenic center is minimized. DFT calculations support this model. They suggest, however, that the reaction is not concerted but occurs via hydrogen atom abstraction and subsequent radical rebound. Further support for an antiperiplanar attack relative to a given substituent X = Br, COOMe, or CN was obtained with the respective 2-substituted tetralins. Attack at C1 provides almost exclusively the trans-amination product. If the size of the X substituent increases [Br < CN < COOMe < PO(OEt)2], attack at the carbon atom C4 prevails, delivering the respective trans-amination products at this position.
热亚硫酸盐-亚砜重排：自由基对机制
DOI：
--
发表时间：
2000
期刊：
影响因子：
--
作者：
Jérôme Amaudrut and;O. Wiest
通讯作者：
O. Wiest
DOI：
--
发表时间：
1979
期刊：
影响因子：
--
作者：
D. Defrees;W. Hehre;D. E. Sunko
通讯作者：
D. E. Sunko
影响因子：
4.3
作者：
Huard, Kim;Lebel, Helene
通讯作者：
Lebel, Helene