5-Benzyl-3-methylimidazolidin-4-one-Derived Reactive Intermediates of Organocatalysis - A Comforting Resemblance of X-Ray, NMR, and DFT Solid-Phase, Liquid-Phase, and Gas-Phase Structures
5-Benzyl-3-methylimidazolidin-4-one-Derived Reactive Intermediates of Organocatalysis - A Comforting Resemblance of X-Ray, NMR, and DFT Solid-Phase, Liquid-Phase, and Gas-Phase Structures
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DOI：
10.1002/hlca.200800432
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发表时间：
2009-01-01
影响因子：
1.8
通讯作者：
Seebach, Dieter
中科院分区：
文献类型：
--
作者：
Groselj, Uros;Schweizer, W. Bernd;Seebach, Dieter
报道了 5-苄基-3-甲基咪唑烷-4-酮（2,2-二甲基-、顺-2-（叔丁基）-和顺-2-苯乙烯基取代；分别为 2-4）的三种 (E)-1-肉桂亚胺 PF6 盐的 X 射线晶体结构（图 3,5）。在2,2-二甲基和顺式-2-苯乙烯基衍生物中，分别为2和4，2位顺式取代基的C-H键指向五元环上方苯甲基的苯环中心（图6，a和b）。 NMR 测量（图 8）提供的证据表明溶液中存在相同的结构，并且这种类型的第四种衍生物 5（方案）在 C-N 键周围具有 (Z)-构型，而不是 (E)-构型。在顺式-2-(叔丁基)衍生物3中，苄基位于亚胺π-系统上(图4和6,c)。与 DFT 计算的巴豆亚基类似物 A 和 B 的叠加表明理论和实验结构几乎是重叠的（图 9 和表）。鉴于它们在有机催化中作为反应中间体的作用以及合成有机化学家可能从理论中获得的帮助，对这些结构进行了讨论，
The X-ray crystal structures of three (E)-1-cinnamoylidene iminium PF6 salts of 5-benzyl-3-methylimidazolidin-4-ones (2,2-dimethyl-, cis-2-(tert-butyl)-, and cis-2-styryl-substituted; 2-4, resp.) are reported (Figs. 3,5). In the 2,2-dimethyl and in the cis-2-styryl derivative, 2 and 4, respectively, a C-H bond of the cis-substituent in 2-position points to the center of the benzene ring of the benzyl group above the five-membered ring (Fig. 6,a and b). NMR Measurements (Fig. 8) provide evidence that the same Structure is present in solution, and that a fourth derivative of this type, 5 (Scheme), has (Z)-instead of (E)-configuration around the C-N bond. In the cis-2-(tert-butyl) derivative 3, the benzyl group is located over the iminium pi-system (Figs. 4 and 6,c). Overlays with DFT-calculated crotonylidene analogs, A and B, show that the theoretical and experimental structures are almost superimposable (Fig. 9 and Table). The structures are discussed in view of their role as reactive intermediates in organocatalysis and in view of the help synthetic organic chemists may experience from theory,