An efficient asymmetric hydrophosphonylation of unsaturated amides catalyzed by rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with phenoxy-functionalized chiral prolinols

Abstract

An asymmetric hydrophosphonylation reaction of diethyl phosphite with α,β-unsaturated amides catalyzed by [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ (RE = Sc (1), Y (2), La (3), Yb (4) and Lu (5)) with H₂Lⁿ ((S)-2,4-R₂-6-[[2-(hydroxydiphenylmethyl)pyrrolidin-1-yl]methyl]phenol) (R = ^tBu (H₂L¹); R = 1-cumyl (H₂L²) and R = 1-adm (H₂L³)) was disclosed. The effects of different central metals and proligands on the addition reaction were tested and it was found that the combination of Sc complex 1 and ligand H₂L² gave the best results. An excellent chemical yield (up to 99%) and good to high enantioselectivities (varied from 73 to 89%) were achieved with a relatively broad scope of the unsaturated amides. The active species in the current system was also discussed.