Effects of Substituents on the Multiple Bonds on Ring-Closing Metathesis of Enynes

In ring-closing metathesis (RCM) reactions of enynes, the substituents on the multiple bonds are quite important. Although RCM of an enyne having a monosubstituted alkene proceeds smoothly using the first-generation ruthenium-carbene complex 1a, that of an enyne having a disubstituted alkene and internal alkyne using 1a does not proceed. However, the second-generation ruthenium-carbene complex 1b or 1c containing an N-heterocyclic carbene as a ligand was found to be very effective for such an enyne, and the two-metathesis products were formed in high yields.