Department Chemie, Ludwig-Maximilians-Universität München , Butenandtstrasse 5-13, 81377 München, Germany.
J Am Chem Soc. 2014 Oct 8;136(40):14263-9. doi: 10.1021/ja508065e. Epub 2014 Sep 24.
X-ray structures of enamines and iminium ions derived from 2-tritylpyrrolidine (Maruoka catalyst) and 2-(triphenylsilyl)pyrrolidine (Bolm-Christmann-Strohmann catalyst) have been determined. Kinetic investigations showed that enamines derived from phenylacetaldehyde and pyrrolidine (R = H) or 2-(triphenylsilyl)pyrrolidine (R = SiPh3) have similar reactivities toward benzhydryl cations Ar2CH(+) (reference electrophiles), while the corresponding enamine derived from 2-tritylpyrrolidine (R = CPh3) is 26 times less reactive. The rationalization of this phenomenon by negative hyperconjugative interaction of the trityl group with the lone pair of the enamine nitrogen is supported by the finding that the trityl group in the 2-position of the pyrrolidine increases the electrophilic reactivity of iminium ions derived from cinnamaldehyde by a factor of 14. The consequences of these observations for the rationalization of the reactivity of the Jørgensen-Hayashi catalyst (diphenylprolinol trimethylsilyl ether) are discussed.
已确定 2-三苯甲基吡咯烷（Maruoka 催化剂）和 2-（三苯基甲硅烷基）吡咯烷（Bolm-Christmann-Strohmann 催化剂）衍生的亚胺和亚胺离子的 X 射线结构。动力学研究表明，苯乙醛和吡咯烷（R = H）或 2-（三苯基甲硅烷基）吡咯烷（R = SiPh3）衍生的亚胺对苯甲叉阳离子 Ar2CH(+)（参考亲电试剂）具有相似的反应性，而来自 2-三苯甲基吡咯烷（R = CPh3）的相应亚胺的反应性则低 26 倍。通过三苯甲基与亚胺氮的孤对负超共轭相互作用对这一现象进行合理化，发现吡咯烷 2 位上的三苯甲基基团使肉桂醛衍生的亚胺离子的亲电性反应性提高了 14 倍。讨论了这些观察结果对 Jørgensen-Hayashi 催化剂（二苯脯氨醇三甲基硅醚）反应性的合理化的影响。
