THE PHOTOCHEMICAL REACTION AND THE ABSOLUTE ASYMMETRIC SYNTHESIS IN THE CHIRAL CRYSTALLINE ENVIRONMENT

长期以来，在没有任何外部手性试剂的情况下，从非手性试剂开始实现不对称合成一直是化学家们感兴趣的挑战，也是自然界光学活性起源问题的核心。非手性材料形成的手性晶体的立体定向固体板化学反应被定义为“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，得到手性产物。我们证明了立体控制的光化学苯基迁移也可以在固态发生。由邻苯甲酰氯和邻甲基硫酚合成的硫代酯在手性空间群P2_12_12_1中结晶。研究了这两种对映体在KBr中的圆二色谱。当硫代酯的对映体晶体被照射成白色粉末时，分离出具有光学活性的苯酞。苯酞的形成可以用苯环上的芳硫基迁移-迁移过程来解释。通过手性晶格对产物和非手性分子的绝对-绝对构型关联研究，确定了苯环的迁移机理，部分邻苯甲酰苯甲酸酯也在手性空间群中结晶，固相光解通过C(=O)-O键裂解生成苯酞类化合物，涉及与硫代酯不同的机理。N，N-二取代邻苯甲酰基苯甲酰胺的光反应也可用于绝对不对称合成，这一领域的发展与有机固相化学领域的进展以及对晶体分子堆积方式的深入理解密切相关。

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-slate chemical reactions of chiral crystals formed by achiral materials are defined as "absolute" asymmetric synthesis. This asymmetric synthesis involves two aspects : generating chiral crystals and performing topochemically controlled solid-state reactions, which yield chiral products.We demonstrated that the stereo-controlled photochemical phenyl migration could also occur in the solid state. Thioester prepared from o-benzoylbenzoylchloride and o-methylthiophenol crystallized in a chiral space group P2_12_12_1. The circular dichroism (CD) spectra of the two enantiomorphs in KBr were presented. When the enantiomorphic crystals of the thioester was irradiated as white powders, an optically active phthalide was isolated. The formation of phthalide is explained in terms of either arylthio-migration of phenyl-migration process. The phenyl-migration mechanism was confirmed on the basis of the absolute-to-absolute configuration correlation studies of both product and an achiral molecule influenced by chiral crystal lattice.Some of o-benzoylbenzoic acid esters also crystallized in chiral space group, and the photolysis in solid-state gave phthalide derivatives via a cleavage of C(=O)-O bond, which involved the different mechanism from that of thioesters. The absolute asymmetric synthesis was also performed by the photoreaction of N,N-disubstituted o-benzoylbenzamides.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.