Asymmetric epoxidation of α,β-unsaturated ketones catalyzed by rare-earth metal amides RE[N(SiMe3)2]3 with chiral TADDOL ligands

Abstract

The catalytic asymmetric epoxidation of α,β-unsaturated ketones by tert-butylhydroperoxide (TBHP) has been well established using rare-earth metal amides RE[N(SiMe₃)₂]₃ (RE = La(1), Nd(2), Sm(3), Y(4), Yb(5)) with chiral TADDOL ligands. It was found that the combination of Yb[N(SiMe₃)₂]₃ and chiral TADDOL ligand H₂L² ((4S,5S)-2,2-dimethyl-α,α,α′,α′-tetra-3,5-bis(trifluormethylphenyl)-1,3-dioxolane-4,5-dimethanol) in a 1 : 1 molar ratio was the optimal choice, which provided the desired epoxides in excellent yields (89–99%) and good to high enantioselectivities (57–94% ee), using DBU as an additive. Various substrates were proved to have functional group tolerance. In addition, gram-level experiments and derivatization experiments were also studied.