Enantioselective Friedel鈥揅rafts Alkylation of Pyrrole with Chalcones Catalyzed by a Dinuclear Zinc Catalyst

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• 作者：Yuan-Zhao Hua ; Xing-Wang Han ; Xiao-Chao Yang ; Xixi Song ; Min-Can Wang ; Jun-Biao Chang
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：December 5, 2014
• 年：2014
• 卷：79
• 期：23
• 页码：11690-11699
• 全文大小：429K
• ISSN：1520-6904

文摘

A highly enantioselective Friedel鈥揅rafts (F鈥揅) 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 尾-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.