Revisiting Secondary Interactions in Neighboring Group Participation, Exemplified by Reactivity Changes of Iminylium Intermediates
Revisiting Secondary Interactions in Neighboring Group Participation, Exemplified by Reactivity Changes of Iminylium Intermediates
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重新审视邻近群体参与中的次级相互作用，以亚胺鎓中间体的反应性变化为例
DOI：
10.1039/c6ob02719a
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发表时间：
2017
影响因子：
3.2
通讯作者：
and Tomohiko Ohwada
中科院分区：
文献类型：
--
作者：
Yingtang Ning;Tomoya Fukuda;Hirotaka Ikeda;Yuko Otani;Masatoshi Kawahata;Kentaro Yamaguchi;and Tomohiko Ohwada
邻基参与被定义为取代基通过与反应中心形成键或部分键来稳定过渡态或中间体的作用。除了与最近邻基团的主要相互作用之外，原则上还可能发生涉及另一个或多个相邻基团的次要相互作用。在这里，我们重新审视这个问题，通过检查二级相互作用的影响，对稳定性和反应性的推定iminylium阳离子中间体，形成N-O键裂解的1-四氢萘酮肟系统。直接观察的peri-bromo-iminylium中间体在溶液中支持的iminylium阳离子的参与和稳定作用的二级相互作用所产生的远端串联取代基。实验和计算结果都支持这样的想法，即在主要的周围杂原子（Br，Cl和O（Me））-亚胺鎓键合相互作用上的串联相邻基团的次级相互作用，即，弱的卤素键合相互作用（酯（硝基）氧-卤素键合）和硝基氧原子与CH 3 O氢原子之间前所未有的氢键相互作用是反应途径的关键决定因素，导致肟官能团的压倒性选择性顺式迁移或在酸催化的贝克曼重排条件下形成共价键。
Neighboring group participation is defined as the action of a substituent to stabilize a transition state or an intermediate by forming a bond or a partial bond with the reaction center. In addition to the primary interaction with the nearest neighboring group, secondary interactions involving another neighboring group(s) could also occur in principle. Here, we revisit this issue by examining the influence of secondary interactions on the stability and reactivity of the putative iminylium cation intermediates, formed by N–O bond cleavage of 1-tetralone oxime systems. A direct observation of a peri-bromo-iminylium intermediate in solution supported the involvement of iminylium cations and the stabilizing effect of secondary interactions arising from a distal tandem substituent. Both experimental and computational findings support the idea that secondary interactions of a tandem-neighboring group on the primary peri-heteroatom (Br, Cl, and O(Me))-iminylium bonding interaction, i.e., a weak halogen bonding interaction (ester (nitro) oxygen–halogen bonding) and an unprecedented hydrogen bonding interaction between a nitro oxygen atom and a CH3O hydrogen atom, are crucial determinants of the reaction pathway, leading to either overwhelmingly selective syn-migration of the oxime functionality or covalent bond formation under acid-catalyzed Beckmann rearrangement conditions.