Highly enantioselective Friedel-Crafts alkylation of indoles with ¦Á,¦Â-unsaturated ketones with simple Cu(II)-oxazoline-imidazoline catalysts

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• 作者：Assem Barakat ^{ambarakat@ksu.edu.sa} ; Mohammad Shahidul Islam ; ^{mislam@ksu.edu.sa} ; ^{shahid.10amui@gmail.com} ; Abdullah M.A. Al Majid ^{amajid@ksu.edu.sa} ; Zeid Abdullah Al-Othman ^{zaothman@ksu.edu.sa}
• 关键词：Asymmetric catalysis ; Oxazoline&ndash ; imidazoline ligands ; Friedel&ndash ; Crafts alkylation ; Indoles
• 刊名：Tetrahedron
• 出版年：2013
• 出版时间：24 June, 2013
• 年：2013
• 卷：69
• 期：25
• 页码：5185-5192
• 全文大小：432 K

文摘

A series of novel chiral ligands L1-L4 with an imidazoline-oxazoline framework have been developed as new type of non-symmetric N,N-bidentate ligands. All the chiral ligands were prepared from 2,2-diethylmalonic acid and enantiomerically pure (S)-2-amino-3-methyl-1-butanol in four steps with excellent optical purity. These newly developed ligands efficiently affect the copper-catalyzed enantioselective addition of indole to ¦Á,¦Â-unsaturated ketones, yielding the corresponding adducts in good yield and high enantiomeric excess. The fine-tuning capability of these ligands plays a significant role in achieving high enantioselectivity in the asymmetric alkylation (up to 99 % ee). The higher enantioselectivity of the reaction could be due to the activation and asymmetric induction of chiral Lewis acid metal complex coordinated by enones through a concerted mechanism of 1,4-metal bonding model.