Kinetically controlled synthesis of rotaxane geometric isomers
Kinetically controlled synthesis of rotaxane geometric isomers
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DOI：
10.1039/d3sc04412b
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发表时间：
2024-02-01
期刊：
影响因子：
8.4
通讯作者：
Schneebeli，Severin T.
中科院分区：
文献类型：
--
作者：
McCarthy，Dillon R.;Xu，Ke;Schneebeli，Severin T.
机械联锁体系中的几何异构——当机械联锁分子的轴是定向的，而大环成分是表面不对称的——可以为定向运输和聚合催化提供增强的功能。我们现在引入一种动力学控制策略来控制[2]轮烷的几何异构体。我们的合成提供了具有高选择性的主要几何异构体，拓宽了这种互锁结构的合成途径。从具有对称轴的易于接近的[2]轮烷开始，两个塞子中的一个被环组分上的取代基选择性地激活以进行塞子交换。在这些反应中，通过耦合导致主要产物的选择性生成反应和次要产物的反选择性消耗反应，实现了高选择性。具体来说，在我们的反应系统中，需要的（主要）产物在第一步形成得更快，而不需要的（次要）产物随后在第二步反应得更快。符合详细动力学模型的定量1H NMR数据表明，这种效应（在概念上与次要对映体回收和相关过程密切相关）可以显著提高反应的内在选择性。我们的结果证明了多个选择性反应步骤如何协同工作，以增强合成过程的立体选择性，形成复杂的机械联锁分子。
Geometric isomerism in mechanically interlocked systems—which arises when the axle of a mechanically interlocked molecule is oriented, and the macrocyclic component is facially dissymmetric—can provide enhanced functionality for directional transport and polymerization catalysis. We now introduce a kinetically controlled strategy to control geometric isomerism in [2]rotaxanes. Our synthesis provides the major geometric isomer with high selectivity, broadening synthetic access to such interlocked structures. Starting from a readily accessible [2]rotaxane with a symmetrical axle, one of the two stoppers is activated selectively for stopper exchange by the substituents on the ring component. High selectivities are achieved in these reactions, based on coupling the selective formation reactions leading to the major products with inversely selective depletion reactions for the minor products. Specifically, in our reaction system, the desired (major) product forms faster in the first step, while the undesired (minor) product subsequently reacts away faster in the second step. Quantitative 1H NMR data, fit to a detailed kinetic model, demonstrates that this effect (which is conceptually closely related to minor enantiomer recycling and related processes) can significantly improve the intrinsic selectivity of the reactions. Our results serve as proof of principle for how multiple selective reaction steps can work together to enhance the stereoselectivity of synthetic processes forming complex mechanically interlocked molecules.