Origins of Opposite Syn−Anti Diastereoselectivities in Primary and Secondary Amino Acid-Catalyzed Intermolecular Aldol Reactions Involving Unmodified α-Hydroxyketones

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• 作者：Aiping Fu ; Hongliang Li ; Shuping Yuan ; Hongzong Si ; Yunbo Duan
• 刊名：Journal of Organic Chemistry
• 出版年：2008
• 出版时间：July 18, 2008
• 年：2008
• 卷：73
• 期：14
• 页码：5264 - 5271
• 全文大小：1603K
• 年卷期：v.73,no.14(July 18, 2008)
• ISSN：1520-6904

文摘

The effects of different amino acid catalysts on the stereoselectivity of the direct intermolecular aldol reactions between α-hydroxyketones and isobutyraldehyde or 4-nitrobenzaldehyde have been studied with the aid of density functional theory methods. The transition states of the crucial C−C bond-forming step with the enamine intermediate addition to the aldehyde for the proline and threonine-catalyzed asymmetric aldol reactions are reported. B3LYP/6-31+G** calculations provide a good explanation for the opposite syn vs anti diastereoselectivity of these two kinds of amino acid catalysts (anti-selectivity for the secondary cyclic amino acids proline, syn-selectivity for the acyclic primary amino acids like threonine). Calculated and observed diastereomeric ratio and enantiomeric excess values are in good agreement.