Epimerization Reaction of a Substituted Vinylcyclopropane Catalyzed by Ruthenium Carbenes: Mechanistic Analysis
作者:Xingzhong Zeng、Xudong Wei、Vittorio Farina、Elio Napolitano、Yibo Xu、Li Zhang、Nizar Haddad、Nathan K. Yee、Nelu Grinberg、Sherry Shen、Chris H. Senanayake
DOI:10.1021/jo061587o
日期:2006.11.1
A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction rate strongly depends on the presence of ruthenium ligands in solution. When the first-generation Grubbs catalyst is employed, a 5.3:1 equilibrium ratio of epimers is established quickly, but when a first-generation Hoveyda catalyst is employed, epimerization is observed only if an additional phosphine
报道了一种新型的钌卡宾催化的乙烯基环丙烷差向异构化反应。反应速率很大程度上取决于溶液中钌配体的存在。当使用第一代Grubbs催化剂时,迅速建立了5.3:1的差向异构体平衡比,但是当使用第一代Hoveyda催化剂时,仅在添加额外的膦或氮配体的情况下才观察到差向异构。NMR和动力学研究表明,异构化反应是通过钌环戊烯的中间体发生的。该观察结果表明,合成实用性的环丙基亚甲基钌卡宾可以通过经由其他途径获得的钌-环戊烯来获得。