A robust and highly active homogeneous chiral nickel-phosphine complex for the asymmetric hydrogenation of aliphatic γ- and δ-ketoacids has been discovered. The hydrogenation could proceed smoothly in the presence of 0.0133 mol% catalyst loading (S/C=7500). The coordination chemistry and catalytic behavior of Ni(OTf) 2 with (S,S)-Ph-BPE were explored by 1 H NMR and HRMS. The mechanistic studies revealed that a proton promoted the activation of the substrate C=O bond and controlled the stereoselectivity through hydrogen bonds. A series of chiral γ- and δ-alkyl substituted lactones were obtained in high yields with excellent enantioselectivities (up to 98 % yield and 99 % ee). In addition, this catalytic system also demonstrated that levulinic acid produced from a biomass feedstock was converted into chiral γ-valerolactone without loss of ee value.
Keyphrases
- ionic liquid
- room temperature
- metal organic framework
- reduced graphene oxide
- capillary electrophoresis
- solid state
- magnetic resonance
- visible light
- transition metal
- oxide nanoparticles
- crystal structure
- wastewater treatment
- gold nanoparticles
- single cell
- molecular docking
- carbon nanotubes
- mass spectrometry
- amino acid