Supramolecular catalysis of the enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylate by γ-cyclodextrin
Supramolecular catalysis of the enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylate by γ-cyclodextrin
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DOI：
10.1021/ja016238k
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发表时间：
2003-01-29
影响因子：
15
通讯作者：
Inoue, Y
中科院分区：
文献类型：
--
作者：
Nakamura, A;Inoue, Y
2-蒽甲酸（AC）与γ-环糊精（γ-CDx）形成非常稳定的1：2包合物（K-1 = 161 +/- 25 M-1，K-2 = 38 500 +/- 3300 M-1，25 ℃）。1：2包合物的形成加速了AC的光环化二聚反应。通过紫外可见光谱、CD光谱和1H-1 NMR光谱可以清楚地证实1：2包合物。虽然这些光谱提供的包合物的结构异构体的信息很少，应该有几个结构异构体的1：2包合物，具有不同的纵向取向的客体分子在空腔中。光二聚产物的异构体分布主要取决于光反应前基态中1：2包合物的这些取向异构体的数量，因为在激发单重态的寿命中，交换取向是不可能的。光二聚反应的对映选择性来源于1：2包合物的非对映异构体对的稳定性差异，它们是特定手性环嵌体的对映异构体的前体。手性环限制物2在25 ℃时的ee为32%，并通过将温度降低至0 ℃时的41%而增强。这是溶液中不对称光二聚反应的最高值。
2-Anthracenecarboxylic acid (AC) makes a very stable 1:2 inclusion complex with gamma-cyclodextrin (gamma-CDx) (K-1 = 161 +/- 25 M-1, K-2 = 38 500 +/- 3300 M-1 at 25 degreesC). The formation of the 1:2 inclusion complex accelerated the photocyclodimerization of AC. The 1:2 inclusion could be clearly verified by UV-vis, CD, and H-1 NMR spectroscopies. Although these spectroscopies provide little information about the structural isomers of the inclusion complex, there should be several structural isomers of the 1:2 inclusion complex which have a different longitudinal orientation of the guest molecules in the cavity. The isomer distribution of the photodimerization product primarily depends on the population of these orientational isomers of the 1:2 inclusion complex in the ground state before photoreaction, because, in the lifetime of the excited singlet state, exchanging the orientation is impossible. The enantioselectivity of the photodimerization originates from the difference in the stability of the diastereomeric pair of orientational isomers of the 1:2 inclusion complex in the ground state, which are the precursors of the enantiomers of a specific chiral cycloclimer. The ee of a chiral cycloclimer 2 was 32% at 25 degreesC and was enhanced by lowering the temperature to 41% at 0 degreesC. This is the highest value reported for the asymmetric photodimerization in solution.