Entropy-Driven Diastereoselectivity Improvement in the Paterno-Buchi Reaction of 1-Naphthyl Aryl Ethenes with a Chiral Cyanobenzoate through Remote Alkylation
Entropy-Driven Diastereoselectivity Improvement in the Paterno-Buchi Reaction of 1-Naphthyl Aryl Ethenes with a Chiral Cyanobenzoate through Remote Alkylation
复制标题
通过远程烷基化提高 1-萘基芳基乙烯与手性氰基苯甲酸酯的 Paterno-Buchi 反应的熵驱动非对映选择性
DOI：
10.1002/anie.201801330
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Mori Tadashi
中科院分区：
文献类型：
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作者：
Nagasaki Keisuke;Inoue Yoshihisa;Mori Tadashi
光环加成反应的精确立体控制仍然是一个巨大的挑战，因为它们的机理复杂，而且涉及高活性和短寿命的中间体。到目前为止，人们一直试图通过结构修改，主要是通过引入立体冲突来增加热势垒之间的差异。在此，我们证明了熵在影响Paternó-Büchi反应的非对映选择性中起着至关重要的作用。给体的远程烷基化导致其光物理性质及其衍生的激基络合物的名义上的变化。然而，氧杂环己烷产品的非对映异构体过量得到了很大的改善，提高了约40 %。这种增强并不伴随着光物理性质的任何显著变化，很难用传统的基于排斥空间和/或吸引分子间相互作用以及电子微扰的焓控制概念来合理化。微分活化参数和补偿焓-熵关系表明，非对映选择性的增强不仅是简单的焓增强，而且是起源的熵增强。
The precise stereocontrol of photocycloaddition reactions is still a significant challenge owing to their mechanistic complexity and the involvement of highly reactive and short‐lived intermediates. Attempts have hitherto been made through structural modifications, mostly by introducing steric conflicts, to increase the difference between the enthalpic barriers. Herein, we show that entropy plays a crucial role in influencing the diastereoselectivity of a Paternò–Büchi reaction. Remotemetaalkylation of the donor caused nominal changes in its photophysical properties as well as those of the exciplexes derived thereof. Nevertheless, the diastereomeric excess of the oxetane product was greatly improved by about 40 %. This enhancement, which is not accompanied by any significant changes in the photophysical properties, is difficult to rationalize by conventional enthalpic control concepts based on repulsive steric and/or attractive intermolecular interactions as well as electronic perturbations. Differential activation parameters and compensatory enthalpy–entropy relationships revealed that the diastereoselectivity enhancement is not simply enthalpic but also entropic in origin.