Multiple dendritic catalysts for asymmetric transfer hydrogenation.
The first and second generation multiple dendritic ligands based on chiral diamine were synthesized in a convergent approach and were well-characterized by NMR and MS techniques. Their ruthenium complexes prepared in situ had good solubility in the reaction medium (azeotrope of formic acid and triethylamine) and demonstrated high catalytic activity and enantioselectivity comparable to monomeric catalysts in the asymmetric transfer hydrogenation of ketones and imines. Quantitative yields and for some cases a slightly higher enantioselectivity (up to 98.7% ee) were obtained in the dendritic catalysis. Considering the high local catalyst concentrations at the periphery, diones were tested for the possible synergic reactivity between catalytic units at the surface, while no apparent differences were noted.
Union Laboratory of Asymmetric Synthesis, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China.
Ying-Chun
YC
Chen
Tong-Fei
TF
Wu
Jin-Gen
JG
Deng
Hui
H
Liu
Xin
X
Cui
Jin
J
Zhu
Yao-Zhong
YZ
Jiang
Michael C K
MC
Choi
Albert S C
AS
Chan