Enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylate catalyzed by 6A,6X-diamino-6A,6X-dideoxy-γ-cyclodextrins:: Manipulation of product chirality by electrostatic interaction, temperature and solvent in supramolecular photochirogenesis
Enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylate catalyzed by 6A,6X-diamino-6A,6X-dideoxy-γ-cyclodextrins:: Manipulation of product chirality by electrostatic interaction, temperature and solvent in supramolecular photochirogenesis
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DOI：
10.1016/j.jphotochem.2005.04.017
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发表时间：
2005-07-15
影响因子：
4.3
通讯作者：
Inoue, Y
中科院分区：
文献类型：
--
作者：
Yang, C;Fukuhara, G;Inoue, Y
合成了6（A），6（X）-双脱氧-6（A），6（X）-二氨基-γ-环糊精（X=B，C，D和E）5a-d作为手性主体，催化2-蒽甲酸（ACA）的[4+4]对映异构化光环化二聚反应。5a-d与ACA之间的静电相互作用有效地影响了两个ACA分子在γ-CD空腔内的预组装，并提高了头对头环二聚体的产率。通过降低反应温度或溶剂极性，静电相互作用进一步增强。通过改变主体从5a到5d（随着CD边缘上两个氨基之间的距离增加），头对头异构体的反-顺比逐渐增加，表明在该超分子光反应体系中具有良好的结构-功能关系。所得光产物的手性和对映体过量受溶剂组成和反应温度的显著影响，甚至反转。这种温度和溶剂控制的手性切换行为被证明是源于非零微分熵（Δ Δ S-双刃剑）的对映体分化过程中的贡献。这一发现是在非敏化不对称光反应中由熵相关因素（如溶剂和温度）驱动的手性反转的第一个例子。Δ Δ S-双匕首的符号由溶剂的组合物切换，并表现出对微分焓（Δ Δ H-双匕首）的良好补偿关系，揭示了光对映体分化不仅受焓，而且还受熵，而且对映体分化机制在整个系统中不变化，无论条件的变化。(c)2005 Elsevier B. V.保留所有权利。
6(A),6(X)-Dideoxy-6(A),6(X)-diamino-gamma-cyclodextrins (X=B, C, D and E) 5a-d were synthesized as chiral hosts for catalyzing the enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylic acid (ACA). The electrostatic interaction between 5a-d and ACA efficiently affected the preorganization of two ACA molecules within the gamma-CD cavity, and improved the yields of head-to-head cyclodimers. By lowering the reaction temperature or solvent polarity, the electrostatic interaction was further enhanced. The anti-to-syn ratio of the head-to-head isomers gradually increased by changing the host from 5a to 5d (with increasing distance between the two amino groups on the CD rim), demonstrating a good structure-function relationship in this supramolecular photoreaction system. The chiral sense and enantiomeric excess of the photoproducts obtained are significantly affected, and even inverted, by solvent composition and reaction temperature. This temperature- and solvent-controlled chirality switching behavior is proven to originate from the contribution of non-zero differential entropy (Delta Delta S-double dagger) in the enantiodifferentiating process. This finding is the first example of a chirality inversion driven by entropy-related factors, such as solvent and temperature, in a non-sensitized asymmetric photoreaction. The sign of Delta Delta S-double dagger was switched by the composition of solvent and exhibited an excellent compensatory relationship against the differential enthalpy (Delta Delta H-double dagger), revealing that the photoenantiodifferentiation is governed not only by enthalpy but also by entropy, and also that the enantiodifferentiation mechanism does not vary throughout the whole system, irrespective of the condition changes. (c) 2005 Elsevier B.V. All rights reserved.