Asymmetric Michael addition of malonates to unsaturated ketones catalyzed by rare earth metal complexes bearing phenoxy functionalized chiral diphenylprolinolate ligands

Abstract

A simple, efficient catalytic asymmetric Michael addition of malonates to unsaturated ketones has been successfully developed. This process was promoted by rare earth metal complexes 1–4 bearing a chiral phenoxy functionalized prolinol ligand at room temperature [L1RE(L1H) (H2L1=(S)-2,4-di-tert-butyl-6-((2-(hydroxydiphenylmethyl)pyrrolidin-1-yl)methyl)phenol, RE=Yb 1, Y 2, Sc 3 and L2Sc(L2H) 4 (H2L2=(S)-2,4-di-dimethylbenzyl-6-((2-(hydroxydiphenylmethyl)-pyrrolidin-1-yl)methyl)phenol)]. Complex 3 was the best catalyst in the transformation and the products were obtained in up to 99% yield and with 90% ee. In addition, the molecular structures of the catalysts were well characterized, including X-ray determination of complex 3.