LATTICE-CONTROLLED SOLID STATE-SPECIFIC AND ENANTIOSELECTIVE REACTIONS

在此之前，我们在光学活性烷基钴胺配合物的光消旋反应中发现了溶胶态特异性现象。我们还发现固态特异性和单向（β到α）光异构的2取代乙基钴胺配合物。本研究旨在阐明上述固体特异现象的机理，寻找手性晶格控制的不对称（betha to alpha）光异构化，得到如下结果[(1)-(3)]。(1)光学活性的烷基钴胺配合物在光消旋反应中的固相特异性现象归因于分子间相互作用（如氢键）对反应基的不对称限制。(2) 2-氰乙基、2-甲氧基羰基乙基和n -取代2-氨基乙基钴酰肟与手性轴配体配合，在可见光照射下产生具有光学活性的1-取代乙基钴酰肟配合物，具有中高的对映选择性（高达88%ee），对同一分子中反位的反应基没有不对称影响，但作为形成手性晶格的手性手柄。(3)对一系列2-氰乙基和2-甲氧基羰基乙基钴酰肟的x射线晶体学分析表明，具有高对映选择性的配合物中的2取代乙基易于形成与面内配体平行的构象，并在手性晶格的作用下被迫形成手性构象，而具有低对映选择性的配合物中的活性基团则形成与面内配体垂直的构象。

Previously, we found solia state-specific phenomenon in the photoracemization of optically active alkyl cobaloxime complexes. We also found solid state-specific and unidirectional (betha to alpha) photoisomerization of 2-substituted ethyl cobaloxime complexes.This study was carried out to clarify the mechanism for the above mentioned solid state-specific phenomenon and to find chiral lattice-controlled asymmetric (betha to alpha) photoisomerization, and the following results [ (1)- (3)] were obtained.(1) The solid state-specific phenomenon in the photoracemization of optically active alkyl cobalocime complexes was attributed (ascribed) to an unsymmetrical restriction of the reactive group by an intermolecular interaction such as hydrogen bonding.(2) Solid-state asymmetric photoisomerization occurred to afford optically active 1-substituted ethyl cobaloxime complexes with moderate to high enantioselectivities (up to 88%ee) upon visible light-irradiation on 2-cyanoethyl, 2-methoxycarbonylethyl, and N-substituted 2-carbamoylethyl cobaloximes coordinated with chiral axial ligand which has no asymmetric effect on the reactive group at the trans position in the same molecule but serves as the chiral handle for forming the chiral lattice.(3) The X-ray crystallographic analyzes of a series of 2-cyanoethyl and 2-methoxycarbonylethyl cobaloximes revealed that the 2-substituted ethyl group in a complex bringing about high enantioselectivity is apt to take a conformation parallel to the inplane ligand and is also forced to take a chiral conformation by chiral lattice, while the reactive group in a complex bringing about low enantioselectivity take a conformation perpendicular to the inplane ligand.