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首页> 外文期刊>Chemistry: A European journal >Elucidating the mechanism of the asymmetric aza-Michael reaction
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Elucidating the mechanism of the asymmetric aza-Michael reaction

机译：阐明不对称AZA-Michael反应的机制

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摘要

The mechanism of the palladium-catalysed asymmetric aza-Michael addition of aniline to a,p-unsaturated N-imide was examined from several aspects using a combination of techniques, including X-ray crystallography, mass spectrometry, NMR, UV/Vis spectroscopy, and kinetic studies. The binding of aniline to the dicationic palladium(II) metal centre was found to occur in two consecutive steps: The binding of the first aniline is fast and reversible, whereas the binding of the second aniline is slower and irreversible. This occurs in competition with the binding of the N-imide, which forms a planar six-membered chelate ring with the metal centre; coordinating through the 1,3-dicarbonyl moiety. Isotopic labelling revealed that the addition of N-H occurs in a highly stereoselective manner, allowing the synthesis of optically active beta(2)- and beta(2,3)-amino acid derivatives. The stereochernistry of the addition is postulated to be syn. in situ kinetic studies provided evidence for product inhibition. The binding of the N-imide to the catalyst was found to be the rate-limiting step. Aniline was found to be an inhibitor of the pre-catalyst. The study culminated in the design of a new reaction protocol. By maintaining a low concentration of the aniline substrate during the course of the reaction, significant enhancement of yield and enantioselectivity can be achieved.
机译：使用技术组合的几个方面检查钯催化的不对称AZA-micha-micha-micha-michael加入苯胺至a，p-不饱和N-酰亚胺的机制，包括X射线晶体学，质谱法，NMR，UV / Vis光谱，和动力学研究。发现苯胺与Daticic钯（II）金属中心的结合在两个连续步骤中发生：第一苯胺的结合是快速且可逆的，而第二苯胺的结合是较慢的并且不可逆。这发生在竞争中与N-酰亚胺的结合，形成与金属中心的平面六元螯合环;通过1,3-二羰基部分配位。同位素标记显示，添加N-H以高度立体化的方式发生，允许合成光学活性β（2） - 和β（2,3） - 氨基酸衍生物。添加的立体声istronsishristrishsissish istrishsissishsissishsistrys是syn。原位动力学研究提供了产品抑制的证据。发现N-酰亚胺与催化剂的结合是速率限制步骤。发现苯胺是预催化剂的抑制剂。该研究在新的反应协议设计中有效。通过在反应过程中保持低浓度的苯胺衬底，可以实现产率和对映选择性的显着提高。

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