Pyrrolidine as an efficient organocatalyst for direct aldol reaction of trifluoroacetaldehyde ethyl hemiacetal with ketones |
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Authors: | Fanglin Zhang Saihu Liao |
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Institution: | a Department of Chemistry, Huazhong University of Science and Technology, Hubei 430074, China b Department of Chemistry, Jiangxi Normal University, Nanchang 330027, China |
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Abstract: | Pyrrolidine-catalyzed aldol reaction of trifluoroacetaldehyde ethyl hemiacetal (1) with ketones or aldehydes was described. In the presence of 20 mol % of pyrrolidine, the reaction proceeded smoothly at room temperature to afford the aldol products in good to excellent yields (up to 95%). Pyrrolidine showed a much higher catalytic activity than piperidine in the reaction with less reactive ketones. GC analysis clearly indicated that the catalyst and the enamine intermediates were kept at extremely low concentration during the reaction. Based on these observations, we suggested that formation of the enamine would be a rate-determining step for the catalytic aldol reaction. In addition, the asymmetric aldol reaction of 1 with cyclohexanone catalyzed by l-proline derivatives was also discussed. |
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Keywords: | Pyrrolidine Organocatalysis Aldol reaction Trifluoroacetaldehyde ethyl hemiacetal |
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