Primary amine catalyzed direct asymmetric aldol reaction assisted by water |
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| Affiliation: | 1. Ghent University, Laboratory for Chemical Technology, Technologiepark 914, 9052 Ghent, Belgium;2. Georgia Institute of Technology, School of Chemical & Biomolecular Engineering, 311 Ferst Drive, Atlanta, GA 30332-0100, USA;3. Ghent University, Department of Inorganic and Physical Chemistry, Center for Ordered Materials, Organometallics & Catalysis, Krijgslaan 281 (S3), 9000 Ghent, Belgium;1. Department of Chemistry, School of Science, Tianjin University, Tianjin, 300072, PR China;2. Key Laboratory of Inorganic-Organic Hybrid Functional Materials Chemistry, Ministry of Education, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Tianjin Normal University, Tianjin, 300387, PR China;1. College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, Henan, China;2. Key Laboratory of Ministry of Education for Special Functional Materials, Henan University, Kaifeng 475004, Henan, China;1. Ghent University, Department of Chemical Technology, Laboratory for Chemical Technology, Technologiepark 914, 9052 Ghent, Belgium;2. Ghent University, Department of Inorganic and Physical Chemistry, Center for Ordered Materials, Organometallics & Catalysis, Krijgslaan 281 (S3), 9000 Ghent, Belgium |
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| Abstract: | 
l-Valine was found to be an active catalyst in the asymmetric direct aldol reaction. The aldol reaction of a variety of aromatic aldehydes with acetone was catalyzed by 20 mol % of l-valine at 35 °C with the aldol products obtained in moderate to good yields (48–83%) and enantiomeric excesses (42–72%). The reaction was more efficient catalytically with best results observed in the presence of 1 mol equiv of water, with respect to the aldehyde, in either DMSO or DMF as solvent. The effect of water concentration on the reaction rate and enantioselectivity was also investigated. Thus, with increasing water concentration in DMSO there was decreasing enantioselectivity. However, the reaction in the presence of l-phenylalanine showed a lower level of reactivity and enantioselectivity to afford the aldol in 25% with 31% ee. In marked contrast, reaction with l-phenylglycine resulted in the negligible formation of the aldol (<5%). Our results, suggest a new strategy in the design of new bioorganic catalysts for direct asymmetric aldol reactions. |
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