A Chiral Bisthiourea as a Chiral Solvating Agent for Carboxylic Acids in the Presence of DMAP

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• 作者：Guangling Bian ; Hongjun Fan ; Shiwei Yang ; Huifeng Yue ; Huayin Huang ; Hua Zong ; Ling Song
• 刊名：Journal of Organic Chemistry
• 出版年：2013
• 出版时间：September 20, 2013
• 年：2013
• 卷：78
• 期：18
• 页码：9137-9142
• 全文大小：382K
• 年卷期：v.78,no.18(September 20, 2013)
• ISSN：1520-6904

文摘

A simple chiral bisthiourea has been used as a highly effective and practical chemical solvating agent (CSA) for diverse 伪-carboxylic acids in the presence of DMAP. Excellent enantiodiscrimination based on well-resolved 伪-H NMR signals of the enantiomers of carboxylic acids can be obtained without interference from the chiral bisthiourea and DMAP. To check the practicality of the chiral bisthiourea/DMAP for enantiomeric determination, the ee values of mandelic acid (MA) samples over a wide ee range were determined by integration of the 伪-H signal of MA in ¹H NMR. A discrimination mechanism is proposed, that the formation of two diasteromeric ternary complexes between the chiral bisthiourea and two in situ formed enantiomeric carboxylate-DMAPH⁺ ion pairs discriminates the enantiomers of carboxylic acids. Computational modeling studies show that the chemical shift value of 伪-H of (S)-MA is greater than that of (R)-MA in ternary complexes, which is consistent with experimental observation. 1D and 2D NOESY spectra demonstrate the intermolecular noncovalent interactions between the protons on the aromatic rings of chiral bisthiourea and 伪-H of the enantiomers of racemic 伪-methoxy phenylacetic acids in the complexes.