Asymmetric Protonation through Reactive Chiral Gadolinium Enolates

Significance

The authors have demonstrated that the chiral polynuclear gadolinium complexes derived from L2 and L3 are efficient catalysts for two types of asymmetric protonation reactions: protonation of silyl enol ethers and conjugate ­cyanation-protonation of N-acyl pyrroles. It is believed that both protonation reactions proceed through chiral gadolinium enolates, which are generated by either protonolysis of silyl enol ethers or conjugate addition of cyanide. Proton source is either bulky phenol or HCN.