Asymmetric organocatalytic direct aldol reactions of ketones with alpha-keto acids and their application to the synthesis of 2-hydroxy-gamma-butyrolactones
| Autor: | Lin Feng Cun, Liu-Zhu Gong, Shi Wei Luo, Yanzhao Wang, Zhuo Tang, Xiao-Ying Xu |
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| Rok vydání: | 2007 |
| Předmět: |
chemistry.chemical_classification
Models Molecular Ketone Molecular Structure Proline Carboxylic acid Organic Chemistry Enantioselective synthesis Aminopyridines Stereoisomerism Ketones Chemical synthesis Keto Acids Butanones Catalysis chemistry.chemical_compound chemistry Aldol reaction 4-Butyrolactone Amide Pyridine Organic chemistry Aldol condensation |
| Zdroj: | The Journal of organic chemistry. 72(26) |
| ISSN: | 0022-3263 |
| Popis: | A variety of organocatalysts for the asymmetric direct aldol reactions of ketones with alpha-keto acids were designed on the basis of molecular recognition and prepared from proline and aminopyridines. The organic molecule 8e, derived from proline and 6-methyl-2-amino pyridine, was the best catalyst, affording excellent enantioselectivities (up to 98% ee) for the direct aldol reactions of acetone or 2-butanone with a wide range of alpha-keto acids and for the reactions of various acyclic aliphatic ketones with 3-(2-nitrophenyl)-2-oxopropanoic acid. The aldol adducts could be converted to 2-hydroxy-gamma-butyrolactones by reaction sequences of diastereoselective reduction and lactonization. Experimental and theoretical studies on the transition states revealed that the amide N-H and the pyridine N of the organocatalyst selectively form hydrogen bonds with the keto oxygen and the carboxylic acid hydroxy of the alpha-keto acid, respectively. These two hydrogen-bonding interactions are important for the reactivity and enantioselectivity of the direct asymmetric aldol condensation. |
| Databáze: | OpenAIRE |
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