THE ABSOLUTE AYMMETRIC SYNTHESIS IN THE CHIRAL CRYSTALLINE ENVIRONMENT AND THE MOLECULAR DINAMICS

从非手性试剂出发，在没有任何外部手性试剂的情况下实现不对称合成一直是化学家们感兴趣的挑战，也是自然界中光学活性起源问题的核心。由非手性物质形成手性晶体的立体定向固相化学反应被定义为“绝对”不对称合成。这种不对称合成包括两个方面：生成手性晶体和进行拓扑化学控制的固相反应，生成手性产物。(1)We证明了立体控制的光化学反应也可以在固态下发生。由2-苯甲酰基苯甲酸和相应的酰胺反应得到的许多非手性2-苯甲酰基苯甲酰胺都是手性空间群P2_12_12_1或P2_1。在固态下对芳香酰胺类化合物的对映体晶体进行辐照，得到了光学活性的苯酞类化合物。苯酞的形成是通过酰胺键的均质断裂形成的自由基对中间体的苯胺基迁移来解释的。另一方面，N-苄基酰胺的照射促进氢提取，导致氢化苯酞。(2)A在均相条件下利用手性化合物进行了一种新的绝对不对称合成。发现氮原子上有大取代基的非手性非环酰亚胺以手性空间群结晶，在低温THF中溶解时仍保持手性构象，在-20 ° C以下与正丁基锂反应得到光学活性的丁基加成物和氢化产物。该反应提供了在均相条件下使用手性晶体进行绝对不对称合成的第一个例子。该领域的未来与有机固态化学的一般领域的进展以及对晶体分子堆积模式的更深入理解密切相关。

The achievement of an asymmetric synthesis starting from an achiral reagent and in the absence of any external chiral agent has long been an intriguing challenge to chemists and is also central to the problem of the origin of optically activity in nature. Stereospecific solid-state chemical reactions of chiral crystals formed by achiral materials are defined as "absolute" asymmetric synthesis. This asymmetric synthesis involves two aspects : generating chiral crystal and performing topochemically controlled solid-state reactions, which yield chiral products.(1)We demonstrated that the stereo-controlled photochemical reaction could also occur in the solid state. Many achiral 2-benzoylbenzamides prepared from 2-benzoylbenzoic acid and the corresponding amides crystallized in chiral space group, P2_12_12_1 or P2_1. When the enantiomorphic crystals of the aromatic amides were irradiate in the solid-state, optically active phthalides were obtained. The formation of phthalide is explained in terms of anilino-group-migration via radical pair intermediate formed by the homolitic cleavage of amide bond. On the other hand, the irradiation of the N-benzyl amide promoted hydrogen abstraction leading to hydrogenated phthalides.(2)A new absolute asymmteric synthesis in homogeneous conditions using chiral christals were demonstrated. We found achiral acyclic imides with bulky substituents on the nitrogen atom crystallized in chiral space group, and maintain the chiral conformation when the crystals dissolved at low-temperature THF.The reaction with n-butyllithium below -20°C gave optically active butyl adduct and hydrogenated product. This reaction provides the first example of absolute asymmetric synthesis using chiral crystals in homogeneous conditions.The future of this field is intimately connected with progress in the general area of organic solid-state chemistry as well as with deeper understanding of the molecular packing modes of crystals.