Switching of the Diastereomer Deposited during the Crystallization of N-[(S)-1-Phenylethyl]-2鈥?carbamoyl-1,1鈥?binaphthalene-2-carboxylic Acid: Investigation of the Mechanism of Dielectri

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• 作者：Yuichi Kitamoto ; Kazumi Suzuki ; Naoya Morohashi ; Kenichi Sakai ; Tetsutaro Hattori
• 刊名：The Journal of Organic Chemistry
• 出版年：2013
• 出版时间：January 18, 2013
• 年：2013
• 卷：78
• 期：2
• 页码：597-605
• 全文大小：520K
• 年卷期：v.78,no.2(January 18, 2013)
• ISSN：1520-6904

文摘

Dielectrically controlled resolution (DCR) has been achieved during the crystallization of (S)-1-phenylethylamides of racemic 1,1鈥?binaphthalene-2,2鈥?dicarboxylic acid (RS_a,S)-1. For example, a water well-shaped plot is obtained for the diastereomeric excess (de) of the deposited amide versus the solvent permittivity (蔚) for the crystallization of (RS_a,S)-1 from three-component mixed solvents, consisting of 25 vol % of dichloromethane and 75 vol % of varying ratios of two solvents (i.e., an alcohol and either hexane or water). The de value drastically changes within two narrow 蔚 ranges and diastereomerically pure crystals of either (R_a,S)-1 (13.9 鈮?蔚 鈮?17.9) or (S_a,S)-1路CH₂Cl₂ (蔚 鈮?11.9 and 蔚 鈮?21.8) deposit, depending on the solvent permittivity. X-ray crystallographic analyses reveal that the major difference between the crystal structures of (S_a,S)-1 and (R_a,S)-1 is the presence of solvent molecules that fill the spatial voids in the (S_a,S)-1 crystals. The 蔚-dependence of the chemical shifts of (S_a,S)-1 and (R_a,S)-1 suggests that their aggregation states are similar in the same solvents and change discontinuously at two 蔚 values. The 蔚-dependence of the C鈺怬 stretching vibrations suggests that the lower 蔚 is a transition point where the amide molecules, which aggregate through intermolecular hydrogen bonds in low-permittivity solvents, begin to dissociate. An absorption experiment suggests that dichloromethane is easily incorporated into solvent-free (S_a,S)-1 crystals in high-permittivity solvents. On the basis of these observations, a feasible molecular mechanism is proposed for the present DCR phenomenon.