Experimental and Theoretical Conformational Analysis of 5‐Benzylimidazolidin‐4‐one Derivatives – a ‘Playground’ for Studying Dispersion Interactions and a ‘Windshield‐Wiper’ Effect in Organocatalysis
Experimental and Theoretical Conformational Analysis of 5‐Benzylimidazolidin‐4‐one Derivatives – a ‘Playground’ for Studying Dispersion Interactions and a ‘Windshield‐Wiper’ Effect in Organocatalysis
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5-苄基咪唑烷-4-酮衍生物的实验和理论构象分析——研究有机催化中分散相互作用和“挡风玻璃雨刷”效应的“游乐场”
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
Christian Mück‐Lichtenfeld
中科院分区：
文献类型：
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作者：
D. Seebach;Uroš Grošelj;W. Schweizer;S. Grimme;Christian Mück‐Lichtenfeld
制备了2位不同取代基的5-苄基-1-异丙基-和5-苄基-1-肉桂基-3-甲基咪唑烷-4-酮1（方案）的PF6盐，得到了适于x射线结构测定的14个此类化合物的单晶，即2-10和12-16（装置）。2 - 5)。在其中9个结构中，苯基的Ph环位于杂环之上。与C(2)上的顺式取代基接触（交错构象A：图1-3）；在三种结构中，Ph环位于最小pi平面上方（交错构象B，图1和图4）；在这两种结构中，苯基C-C键具有重叠构象（C；图1和图5），这使得Ph环同时与相邻的CO基团、N=C-pi体系和杂环C(2)上的顺式取代基保持最大距离。定性构象分析（图6）表明，苯基C-C键的三个交错构象都受到不利的空间相互作用，因此重叠构象可能是一种“逃逸”。采用最先进的量子化学方法，利用大的AO基本集（接近极限）进行单点计算，计算了14个亚胺离子中7个的结构，即3、4/12、5-7、13和16（表）在A和B两个交错构象中，苯基Ph基团分别在环上和在亚胺pi体系上。在所有情况下，更稳定的计算构象（“孤立分子”结构）对应于晶体中存在的构象（在rig中覆盖）。7）. 能量差很小（<= 2 kcal/mol），加上其中一个结构的苯基C-C键周围旋转的势能曲线计算结果16（图8），表明苯基在室温下或多或少是自由旋转的。证明了分子内伦敦色散（苯环与构象A的顺式取代基“接触”）对DFT和其他量子化学计算的重要性；苯基咪唑烷酮1似乎是检测苯环和烷基或芳基CH之间分散贡献的理想体系。本文研究的乙烯基离子类型是对映选择性有机催化共轭加成、Diels-Alder反应和许多其他涉及α， β -不饱和羰基化合物的转化的活性中间体。从5-苄基咪唑烷酮对映选择性催化剂的性能出发，讨论了实验和理论结果。
The PF6 salts of 5-benzyl-1-isopropylidene- and 5-benzyl-1-cinnamylidene-3-methylimidazolidin-4-ones 1 (Scheme) with various substituents in the 2-position have been prepared, and single crystals suitable for X-ray structure determination have been obtained of 14 such compounds, i.e., 2-10 and 12-16 (rigs. 2-5). In nine of the structures, the Ph ring of the benzyl group resides above the heterocycle. in contact with the cis-substituent at C(2) (staggered conformation A: Figs. 1-3); in three structures, the Ph ring lies above the iminium pi-plane (staggered conformation B; Figs. 1 and 4); in two structures, the benzylic C-C bond has an eclipsing conformation (C; Figs. 1 and 5) which places the Ph ring simultaneously at a maximum distance with its neighbors, the CO group, the N=C-pi-system, and the cis-substituent at C(2) oft lie heterocycle. It is suggested by a qualitative conformational analysis (Fig. 6) that the three staggered conformations of the benzylic C-C bond are all subject to unfavorable steric interactions, so that the eclipsing conformation may lie a kind of 'escape'. State-of-the-art quantum-chemical methods, with large AO basic sets (near the limit) for the single-point calculations, were used to compute the structures of seven of the 14 iminium ions, i.e., 3, 4/12, 5-7, 13, and 16 (Table) in the two staggered conformations, A and B, with the benzylic Ph group above the ring and above the iminium pi-system, respectively. In all cases, the more stable Computed conformer ('isolated-molecule' structure) corresponds to the one present in the crystal (overlay in rig. 7). The energy differences are small (<= 2 kcal/mol) which, together with the result of a potential-curve calculation for the rotation around the benzylic C-C bond of one of the structures, 16 (Fig. 8), suggests that the benzyl group is more or less freely rotating at ambident temperatures. The importance of intramolecular London dispersion (benzene ring in 'contact' with the cis-substituent in conformation A) for DFT and other quantum-chemical computations is demonstrated; the benzyl-imidazolidinones 1 appear to be ideal systems for detecting dispersion contributions between a benzene ring and alkyl or aryl CH groups. Enylidene ions of the type studied herein are the reactive intermediates of enantioselective organocatalytic conjugate additions, Diels-Alder reactions, and many other transformations involving alpha,beta-unsaturated carbonyl compounds. Our experimental and theoretical results are discussed in view of the performance of 5-benzyl-imidazolidinones as enantioselective catalysts.
影响因子：
5.2
作者：
Brazier, John B.;Evans, Gareth;Tomkinson, Nicholas C. O.
通讯作者：
Tomkinson, Nicholas C. O.