ChemInform Abstract: Two Methods for Catalytic Generation of Reactive Enolates Promoted by a Chiral Poly Gd Complex: Application to Catalytic Enantioselective Protonation Reactions

A chiral polynuclear Gd complex derived from Gd(OiPr)3 and FujiCAPO (2 or 3) catalytically generated Gd enolates through two distinct methods; transmetalation from enol silyl ethers and conjugate addition of cyanide to α,β-unsaturated N-acyl pyrroles. These chiral enolates can be enantioselectively protonated by a proton in an asymmetric environment in the polynuclear catalyst. Thus, catalytic enantioselective protonation of enol silyl ethers was promoted by the Gd catalyst (5−10 mol %) in the presence of a stoichiometric amount of 2,6-dimethylphenol. Kinetic studies and dependencies of the enantioselectivity on the silyl group structure and the proton source suggest that the reaction proceeds through a Gd enolate generated through transmetalation. Moreover, the same Gd complex (5−10 mol %) promoted conjugate addition of a cyanide−enantioselective protonation sequential reaction from α,β-unsaturated N-acyl pyrroles. Because Gd isocyanide was determined to be the active nucleophile in the conjugate additio...