Solid-State Asymmetric Reaction by Use of Chiral Crystal Environment

3-氰基丙基钴肟配合物在可见光照射下发生了固相特定的单向光致异构化和手性晶格控制的不对称(γ→β→α)光致异构化。最大对映体选择性高达91%ee。一般来说，第二步(β→α)的反应速度比第一步(γ→β)快得多，第二步的对映体选择性也比第一步高得多。在对这类反应的广泛研究中，我们还发现了几个罕见的例子，第一步的反应速度快于第二步的反应速度，或第一步的对映体选择性高于第二步的反应速度。根据晶体结构绘制的反应腔的形状可以预测生成的α-络合物的主要对映体的构型。从反应腔的形状也可以解释这种不寻常的结果。最后，我们对一个有趣的例子进行了中间反应阶段的X射线晶体结构分析，在这个例子中，主要对映体的构型可能在从β-络合物异构化到α-络合物的过程中发生了逆转。因此，我们可以直接观察到中间体β-取代丙基络合物的主要对映体，其构型和构象与从3-取代丙基络合物的反应腔形状预测的结果一致。通过在平面乙二酮肟配体上引入苯基或呋喃基等大取代基，大大提高了一系列2-氰乙基化合物的反应速度，也极大地提高了一系列2-甲氧基酮乙基化合物的对映选择性。

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.