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首页> 外文期刊>Chemistry: A European journal >New Chiral Auxiliaries for Dynamic Kinetic Resolution:From Theory to Experiment
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New Chiral Auxiliaries for Dynamic Kinetic Resolution:From Theory to Experiment

机译：动态动力学拆分的新型手性助剂：从理论到实验

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摘要

New efficient chiral auxiliaries for dynamic kinetic resolution(DKR)of bromides into amines are proposed,based on a theoretical rationalisation of known literature results.One example was synthesized and tested,affording diastereoselectivi-ties up to 100%.Several results of DKR reactions are known,based on oxazolidinone or imidazolidinone units as chiral auxiliaries.Nevertheless,their behaviour was not fully understood until a recent paper that we published.We now used our proposed mechanism to rationalize the behaviour of other similar chiral auxiliaries and to propose small structure changes in imidazolidinone rings which could largely improve their performance.We could show that the good performance of these molecules as chiral auxiliaries for DKR reactions where bromine is the leaving group and a primary or secondary amine is the nucleophile is due,in a first step,to the formation of a hydrogen bond between the amine and the ring carbonyl oxygen and,in a second step,to the strong electrostatic interaction between the leaving bromide and the carbonyl oxygen in the C-3 substituent.Considering the behaviour of this substituent which rotates to minimize the electrostatic repulsion with the bromide when reaching the transition state,we proposed the introduction of a second substituent in the C-4 position of the imidazolidinone ring,which prevents such rotation,thus increasing the energy difference between the transition states of the two dister-eoisomers.With such an auxiliary we were able to increase the best de known in literature(88%),when ben-zylamine is used as nucleophile,to 99,or even 100%,when iodide replaces the bromide in the substrate.
机译：基于已知文献结果的理论合理性，提出了一种新的有效的手性助剂，用于将溴化物动态动力学拆分为胺。合成并测试了一个实例，其非对映选择性高达100％。DKR反应的一些结果是然而，直到我们发表了一篇最近的论文，人们对它们的行为才被完全了解。我们现在使用我们提出的机制来合理化其他类似手性助剂的行为，并提出结构上的细微变化。咪唑烷酮环可大大改善其性能。我们可以证明，这些分子作为DKR反应的手性助剂的良好性能，第一步是溴为离去基团，伯或仲胺为亲核试剂。在胺和环羰基氧之间形成氢键，并在第二步形成强e考虑到C-3取代基中的剩余溴化物与羰基氧之间的静电相互作用。考虑到该取代基在达到过渡态时会旋转以最小化与溴化物的静电排斥，因此我们建议在C中引入第二个取代基咪唑烷酮环的-4位置可防止这种旋转，从而增加了两种二异构体的过渡态之间的能量差。有了这种辅助剂，我们可以提高文献中已知的最佳值（88％）当碘化物取代底物中的溴化物时，苯甲胺被用作亲核试剂，至99％，甚至100％。

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