Substituent Effects on the <i>Z/E</i>-Selectivity in Cross-Metathesis of Conjugated Enynes
作者:Byungman Kang、Ji Min Lee、Jaesik Kwak、Yoon Sup Lee、Sukbok Chang
DOI:10.1021/jo048883q
日期:2004.10.1
Cross-metathesis of a range of conjugated enynes with alkenes turns out to proceed with preferential formation of Z-isomers over E-isomers up to >25:1. Careful studies including substrate modification and control experiments revealed that the reaction proceeds under kinetic rather than thermodynamic control. Driving forces for this substrate-dependent Z-selectivity are attributed to the steric hindrance between substituents on the reacting enynes and NHC ligand of the ruthenium catalyst in the putative metallacyclobutane, as well as chelation effects of suitably positioned functional groups to Ru, which is strongly supported by ab initio calculations.