Simple amphiphilic isosteviol–proline conjugates as chiral catalysts for the direct asymmetric aldol reaction in the presence of water |
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Authors: | Ya-Jie An Yun-Xiao Zhang Ya Wu Zhao-Min Liu Chao Pi Jing-Chao Tao |
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Institution: | 1. Department of Chemistry, New Drug Research and Development Center, Zhengzhou University, Zhengzhou 450052, PR China;2. School of Pharmacy, Henan College of Traditional Chinese Medicine, Zhengzhou 450008, PR China |
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Abstract: | Two novel amphiphilic catalysts 3 and 4 were synthesized by the condensation of isosteviol with l-proline in a one-pot process. With only 1 mol % loading, the catalyst 3 showed excellent activity (up to >99% yield) and stereoselectivity (up to 99:1 dr, >99% ee) for the direct aldol reaction of cyclohexanone and substituted benzaldehydes at room temperature in the presence of water. In addition, solvent effects, catalyst loading, substrate scope, temperature, and the influence of water on the reactions were investigated. These results demonstrate that the catalysts with a chiral concave and hydrophobic substituent in the 4-position of l-proline furnished high activity and stereoselectivity for the reaction. |
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