Enantioselective Friedel-Crafts alkylation of pyrrole with chalcones catalyzed by a dinuclear zinc catalyst.
A highly enantioselective Friedel-Crafts (F-C) alkylation of pyrrole with a wide range of simple nonchelating chalcone derivatives catalyzed by a chiral (Zn2EtL)n (L = (S,S)-1) complex has been developed. The catalyst (Zn2EtL)n complex was prepared in situ by reacting the chiral ligand (S,S)-1 with 2 equiv of diethylzinc. A series of β-pyrrole-substituted dihydrochalcones were usually formed mostly in excellent yields (up to 99%) and excellent enantioselectivity [up to 99% enantiomeric excess (ee)] by using 15 mol % catalyst loading under mild conditions. The absolute stereochemistry of the products was determined to be the S-configuration by X-ray crystallographic analysis of 13g. Meanwhile, a weak negative nonlinear effect was observed. On the basis of the experimental results and previous reports, a possible mechanism was proposed to explain the origin of the asymmetric induction.
College of Chemistry and Molecular Engineering, Zhengzhou University , No. 75, Daxue Street, Zhengzhou City, Henan Province 450052, P. R. China.
Yuan-Zhao
YZ
Hua
Xing-Wang
XW
Han
Xiao-Chao
XC
Yang
Xixi
X
Song
Min-Can
MC
Wang
Jun-Biao
JB
Chang