Nanosheet‐Enhanced Asymmetric Induction of Chiral α‐Amino Acids in Catalytic Aldol Reaction |
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Authors: | Li‐Wei Zhao Hui‐Min Shi Jiu‐Zhao Wang Prof Jing He |
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Institution: | State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, P.?O. Box 98, 15 Beisanhuan Dong Lu, Beijing 100029 (P.R. China), Fax: (+86)?10‐64425385 |
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Abstract: | An efficient ligand design strategy towards boosting asymmetric induction was proposed, which simply employed inorganic nanosheets to modify α‐amino acids and has been demonstrated to be effective in vanadium‐catalyzed epoxidation of allylic alcohols. Here, the strategy was first extended to zinc‐catalyzed asymmetric aldol reaction, a versatile bottom‐up route to make complex functional compounds. Zinc, the second‐most abundant transition metal in humans, is an environment‐friendly catalytic center. The strategy was then further proved valid for organocatalyzed metal‐free asymmetric catalysis, that is, α‐amino acid catalyzed asymmetric aldol reaction. Visible improvement of enantioselectivity was experimentally achieved irrespective of whether the nanosheet‐attached α‐amino acids were applied as chiral ligands together with catalytic ZnII centers or as chiral catalysts alone. The layered double hydroxide nanosheet was clearly found by theoretical calculations to boost ee through both steric and H‐bonding effects; this resembles the role of a huge and rigid substituent. |
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Keywords: | asymmetric catalysis chiral ligands heterogeneous catalysis inorganic nanosheets planar substituents |
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