Solid-State Asymmetric Reaction by Use of Chiral Crystal Environment

在可见光照射下，3-氰丙基钴酰肟配合物可发生固态特异性、单向光异构化和手性晶格控制的不对称（γ→β→α）光异构化。对映选择性最高可达91%。总的来说，第二步（β→α）的反应速度比第一步（γ→β）快得多，第二步的对映选择性也比第一步高得多。在对这类反应的广泛研究中，我们还发现了几个不寻常的例子，其中第一步的反应速度比第二步快，或者第一步的对映体选择性比第二步高。研究发现，在所有实验中，根据晶体结构绘制的反应腔的形状可以预测α -配合物的主要对映体的构型，并且从反应腔的形状也可以解释不寻常的结果。最后，我们研究了一个有趣的例子的中间反应阶段的x射线晶体结构分析，其中主要对映体的构型可能在从β-配合物到α-配合物的异构化过程中被逆转。因此，我们可以直接观察到中间β -取代丙基配合物的主要对映体，其构型和构象与3-取代丙基配合物的反应腔形状预测一致。通过在平面乙氧肟配体上引入苯基或糠基等大取代基，可以极大地提高一系列2-氰乙基配合物的反应速率，也极大地提高了一系列2-甲氧基羰基乙基配合物的对映选择性。

Solid state-specific and unidirectional photoisomerization and chiral lattice-controlled asymmetric (γ→β→α) photoisomerization of 3-cyanopropyl cobaloxime complexes were found to occur on visible light-irradiation of 3-cyanopropylcobaloxime complexes. Maximum enantioselectivities reached up to 91%ee. In general, the reaction rate of the second step (β→α) was much faster than that of the first step (γ→β) and the enantioselectivity of the second step was much higher than that of the first step.In extensive investigations of this type of reactions, we also found several unusual examples in which the reaction rate of the first step was faster than that of the second step or the enantioselectivity of the first step was higher than that of the second step.The configuration of the major enantiomer of alpha-complexes produced was found to be predictable from the shape of the reaction cavity drawn based on the crystal structure, in all cases examined, and the unusual results were also elucidated from the shape of the reaction cavity. Finally, we investigated X-ray crystal structure analyses of intermediate reaction stages of an interesting example in which the configuration of the major enantiomer had presumably been reversed on isomerization from the β-complex to the α-complex. Thus, we could directly observe the major enantiomer of the intermediate beta-substituted propyl complex, whose configuration and conformation agreed with those predicted from the shape of the reaction cavity of the 3-substituted propyl complex. By introducing large substituents such as phenyl or furyl group on the planar glyoxime ligand, the reaction rate was extremely enhanced in a series of 2-cyanoethyl complexes, and also enantioselectivity was extremely improved in a series of 2-methoxycarbonylethyl complexes.