Substituent effects on the Z/E-selectivity in cross-metathesis of conjugated enynes.
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.
Kang
Byungman
B
Center for Molecular Design and Synthesis, Department of Chemistry and School of Molecular Science (BK21), Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.
Lee
Ji Min
JM
Kwak
Jaesik
J
Lee
Yoon Sup
YS
Chang
Sukbok
S