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首页> 外文期刊>Chemistry: A European journal >Autocatalytic Enantiomerisation at the Crystal Surface in Deracemisation ofScalemic Conglomerates
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Autocatalytic Enantiomerisation at the Crystal Surface in Deracemisation ofScalemic Conglomerates

机译：在Scalemic团块的脱硝过程中晶体表面的自催化对映异构化

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Deracemisation of racemic or scalemic conglomerates of intrinsi-, cally chiral compounds appears to be a promising method of chiral resolution.By combining the established methodsof asymmetric synthesis and the physi-cal process of crystal growth, we wereable to achieve a complete deracemisa-tion (with 100 % ee) of an asymmetricMannich product conglomerate—vigo-rously stirred in its saturated solu-tion—from a starting enantiomericexcess value of 15.8 % in the presenceof pyrrolidine (8 mol %) as an achiralcatalyst for the CC bond-forming reac-tion. Strong activation of this deracem-isation process was observed on mild isothermal heating to only 40 °C, result-ing in dramatic acceleration by a factorof about 20 with respect to the resultsobtained at room temperature. Despitethe fact that the racemisation half-lifetime of the nearly enantiopure Man-nich product (with 99 % ee) in the ho-mogenous solution at the reaction tem-perature is eight days, the deracemisa-tion process took only hours in a small-scale experiment. This apparent para-dox is explained by a proposed rapidenantiomerisation at the crystal/solu-tion interface, which was corroboratedby a 13C labelling experiment that con-firmed the involvement of rapid enan-tiomerisation. Frequent monitoring ofthe solution-phase ee of the slowly rac-emising compound further revealedthat the minor enantiomer dominatedin solution, supporting an explanationbased on a kinetic model. A generalisa-tion of the process of "aymmetric auto-catalysis" (resulting in automultiplica-tion of chiral products in homogenousmedia) to encompass heterogeneoussystems is also suggested.
机译：本征的，手性的手性化合物的外消旋或规模化团聚体的脱硫似乎是一种有前途的手性拆分方法。通过结合已建立的不对称合成方法和晶体生长的物理过程，我们能够实现完全的脱硫（含有100％ee）的不对称曼尼希产品集团-在饱和溶液中剧烈搅拌-在吡咯烷（8 mol％）作为手性催化剂形成CC键反应的手性催化剂中，对映体起始过量值为15.8％。 tion。在温和的等温加热至仅40°C的条件下，观察到了该脱硝过程的强烈激活，相对于室温下获得的结果，加速了约20倍。尽管在反应温度下，均相溶液中几乎对映纯的曼尼希产品（具有ee达99％ee）的消旋半衰期为8天，但在小体积的脱氨过程中，消旋过程仅花费了数小时。规模实验。这种明显的悖论可以通过晶体/溶液界面的快速对映异构化来解释，该现象被13 C标记实验所证实，该实验证实了快速的对映异构化的参与。频繁监测缓慢外消旋的化合物的溶液相ee进一步揭示，对映体占主导地位的溶液，支持基于动力学模型的解释。还建议将“阳图自动催化”过程的一般化（导致手性产物在均相介质中自动繁殖）以涵盖异质系统。

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