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

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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.