Nanosheet-enhanced enantioselectivity in the vanadium-catalyzed asymmetric epoxidation of allylic alcohols.
The use of suitable chiral ligands is an efficient means of producing highly enantioselective transition-metal catalysts. Herein, we report a facile, economic, and effective strategy for the design of chiral ligands that demonstrate enhanced enantioselectivity and catalytic efficacy. Our simple strategy employs naturally occurring or synthetic inorganic nanosheets as huge and rigid planar substituents for, but not limited to, naturally available α-amino-acid ligands; these ligands were successfully used in the vanadium-catalyzed asymmetric epoxidation of allylic alcohols. The crucial role of the inorganic nanosheets as planar substituents in improving the enantioselectivity of the reaction was clearly revealed by relating the observed enantiomeric excess with the distribution of the catalytic centers and the accessibility of the substrate molecules to the catalytic sites. DFT calculations indicated that the LDH layer improved the enantioselectivity by influencing the formation and stability of the catalytic transition states, both in terms of steric resistance and H-bonding interactions.
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Box 98, 15 Beisanhuan Dong Lu, Beijing 100029, PR China.
Li-Wei
LW
Zhao
Hui-Min
HM
Shi
Jiu-Zhao
JZ
Wang
Jing
J
He