Entropy-Driven Diastereoselectivity Improvement in the Paternò-Büchi Reaction of 1-Naphthyl Aryl Ethenes with a Chiral Cyanobenzoate through Remote Alkylation
作者:Keisuke Nagasaki、Yoshihisa Inoue、Tadashi Mori
DOI:10.1002/anie.201801330
日期:2018.4.23
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
由于光环加成反应机理的复杂性以及高反应性和短寿命中间体的参与,对光环加成反应的精确立体控制仍然是一个巨大的挑战。迄今为止,已经尝试通过结构上的修改,主要是通过引入空间冲突来增加焓屏障之间的差异。本文中,我们证明了熵在影响Paternò-Büchi反应的非对映选择性中起着至关重要的作用。远程元供体的烷基化引起其光物理性质以及衍生自其的激基复合物的光物理性质的名义上的变化。但是,氧杂环丁烷产物的非对映异构体过量大大改善了约40%。这种增强没有伴随光物理性质的任何显着变化,很难通过基于排斥性空间和/或有吸引力的分子间相互作用以及电子扰动的常规焓控制概念来合理化。差异激活参数和补偿焓-熵关系表明,非对映选择性的增强不仅是焓,而且在起源上也是熵。