Spontaneous transfer of chirality in an atropisomerically enriched two-axis system.
Spontaneous transfer of chirality in an atropisomerically enriched two-axis system.
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也许手性分子中最广为人知的立体生成元素是具有四个不同取代基的sp型杂化碳原子。然而，手性轴也可能存在于带有受阻旋转障碍的键上，导致立体异构体被称为阿托品。了解这些系统的动力学可能是有用的，例如，在设计单一阿托品药物或分子开关和马达时。对于表现出单一手性轴的分子，当体系达到平衡时，围绕该轴的旋转会导致外消旋。我们在这里报告了一个两轴系统，其中产生四个立体异构体(两个对映体对)的对映选择性反应显示了更复杂的情景。在催化不对称转化之后，我们观察到一个受动力学控制的产物分布，该分布基本上从系统的平衡位置扰动。值得注意的是，当体系经历异构化时，观察到其中一个非对映异构体对自发地漂移到较高的对映体比率。以补偿的方式，另一个非对映异构体对也转换成改变的对映体比率，在大小上比初始比率降低。这些观察结果发生在一类不对称的酰胺中，它表现出两个不对称的轴-一个通过苯甲酰胺亚结构定义，另一个隐含着不同的N，N-二取代酰胺。这些底物的立体动力学提供了一个机会来观察动力学和热力学之间的奇怪的相互作用，这些动力学和热力学是限制在部分平衡情况下的立体异构体系统所固有的。
Perhaps the most well-recognized stereogenic elements within chiral molecules are sp-hybridized carbon atoms possessing four different substituents. However, axes of chirality may also exist about bonds with hindered barriers of rotation, leading to stereoisomers known as atropisomers. Understanding the dynamics of these systems can be useful, for example, in the design of single-atropisomer drugs or molecular switches and motors. For molecules that exhibit a single axis of chirality, rotation about that axis leads to racemization as the system reaches equilibrium. We report here a two-axis system in which an enantioselective reaction that produces four stereoisomers (two enantiomeric pairs) displays a more complex scenario. Following a catalytic asymmetric transformation, we observe a kinetically controlled product distribution that is substantially perturbed from the system’s equilibrium position. Notably, as the system undergoes isomerization, one of the diastereomeric pairs is observed to drift spontaneously to a higher enantiomeric ratio. In a compensatory manner, the other diastereomeric pair also converts to an altered enantiomeric ratio, reduced in magnitude from the initial ratio. These observations occur within a class of unsymmetrical amides that exhibits two asymmetric axes – one defined through a benzamide substructure, and the other implicit with differentially N,N-disubstituted amides. The stereodynamics of these substrates provide an opportunity to observe a curious interplay of kinetics and thermodynamics intrinsic to a system of stereoisomers that is constrained to a situation of partial equilibration.
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影响因子：
2.9
作者：
Campomanes, P;Menéndez, MI;Sordo, TL
通讯作者：
Sordo, TL
影响因子：
2
作者：
Erol, Sule;Dogan, Ilknur
通讯作者：
Dogan, Ilknur
影响因子：
1.7
作者：
Zhao, Yan;Truhlar, Donald G.
通讯作者：
Truhlar, Donald G.
影响因子：
56.9
作者：
Wang, Jiaobing;Feringa, Ben L.
通讯作者：
Feringa, Ben L.
DOI：
10.1002/cber.19871200519
发表时间：
1987-05-01
期刊：
CHEMISCHE BERICHTE-RECUEIL
影响因子：
--
作者：
CUYEGKENG, MA;MANNSCHRECK, A
通讯作者：
MANNSCHRECK, A