Agura Kazushi, Hayashi Yukiko, Wada Mari, Nakatake Daiki, Mashima Kazushi, Ohshima Takashi
Graduate School of Pharmaceutical Sciences, Kyushu University, CREST, Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan.
Department of Chemistry, Graduate School of Engineering Science, Osaka University, CREST, Toyonaka, Osaka, 560-8631, Japan.
Chem Asian J. 2016 May 20;11(10):1548-54. doi: 10.1002/asia.201600062. Epub 2016 Apr 14.
The electronic effects of tetranuclear zinc cluster catalysts on transesterification were investigated by changing the carboxylate ligands in the clusters. High catalyst activity crucially depended on the balance between Lewis acidity and Brønsted basicity of the catalyst; this was consistent with the dual activation of both the electrophile and nucleophile by the cooperative zinc centers. In addition, tetranuclear zinc cluster catalysts achieved the transesterification of β-keto esters with unprecedented levels of broad substrate generality, in which a newly developed pentafluoropropionate-bridged zinc cluster and 4-dimethylaminopyridine additive greatly improved the reactivity of sterically congested α- and α,α-disubstituted β-keto esters.
通过改变四核锌簇催化剂中的羧酸盐配体，研究了其对酯交换反应的电子效应。高催化剂活性关键取决于催化剂的路易斯酸性和布朗斯特碱性之间的平衡；这与锌中心协同对亲电试剂和亲核试剂的双重活化是一致的。此外，四核锌簇催化剂实现了β-酮酯的酯交换反应，具有前所未有的广泛底物通用性，其中新开发的五氟丙酸桥连锌簇和4-二甲氨基吡啶添加剂极大地提高了空间位阻较大的α-和α,α-二取代β-酮酯的反应活性。
