Chiral crystal environment

The chiral crystallization of achiral materials and the asymmetric transformation in the chiral crystal environment are described. Many successful examples are presented however, it is still rare to find materials which show this behavior. Recently, new asymmetric reactions using chiral crystals in homogeneous conditions have been developed. [39],[40] These reactions used the frozen chirality generated by chiral... 

Imgartinger, H., Fettel, P. W., and Siemund, V. (1998) Diastereo- and enantioselective 6-H abstraction in die solid state of l-benzoyl-8-benzylnaphthalene. Absolute asymmetric synthesis due to a chiral crystal environment, Kur. J. Org. Chem., 2079-2082. 

S. (1995) "Absolute" Asymmetric Synthesis Using die Chiral Crystal Environment Photochemical Hydrogen... 

Solid-state photochemistry absolute asymmetric oxetane synthesis from an achiral acyclic imide using die chiral crystal environment, J. Org. Chem., 58, 3476-3477. (b) Sakamoto, M., Takahashi, M., Fujita, T.,... 

Koura, T. and Ohashi, Y. (2000) Asymmetric Induction in Cobaloxime Complex Crystals Due to Chiral Crystal Environment, Tetrahedron, 56, 6769-6779. 

Absolute asymmetric synthesis using the chiral crystal environment photochemical hydrogen abstraction from achiral acyclic monothioimides in the solid state. Journal of Organic Chemistry, 60 (22), 7088-7089 ... 

Scheme 2 First example of absolute asymmetric synthesis in the chiral crystal environment of 4,4 -dimethylchalcone 1.

There are two ways of obtaining chiral substances using a chiral crystal environment. One is to produce the chiral compounds from the prochiral ones, and the other is to obtain the chiral compounds from racemic ones. The former method is called absolute asymmetric synthesis, since the asymmetry is introduced from the physical conditions such as the chiral crystal environment. Several examples [ 1 -7] have been reported since the first example of the chiral polymer produced in the photopolymerization of the chiral monomer crystal [8]. We also observed that chiral 3-lactam compounds were produced from the prochiral oxoamide crystals [9,10]. 

Interestingly, the chiral (S)- +)-sec-butyl "handle" did exert a slight but measurable solution phase asymmetric induction. The solid state results are quite different. In both cases the chiral crystal environment led to a dramatic increase in the formation of one substituted dibenzosemibullvalene configuration over the other (80% ee). A similar large effect was found on the regioselectivity of the solid state reaction. Remarkably, the regioselectivities were found to be different for crystals of (+)-sec-butyl-26 as compared to the ( )-26 samples. This is no... 

Chiral thietane-fused (3-lactam from an achiral monothioimide using the chiral crystal environment. /. Am. Chem. Soc., Vol. 115, p. 818 (b) Takahashi, M. Sekine, N. Fujita, T. Watanabe, S. Yamaguchi, K. Sakamoto, M. (1998). Solid-state photochemistry of o-aroylbenzothioates Absolute asymmetric phthalide formation involving 1,4-aryl migration. /. Am. Chem. Soc., Vol. 49, pp. 12770-12776... 

The chiral 1-ce group was produced from the achiral 2-ce group in the photoisomerization as shown in Scheme 5.1. This gave an idea that the asynunetric induction would be observed if the isomerization occurs in the chiral crystal environment. A very high optical yield ( 82 % ee) was observed using / -2-amino-2-phenylethanol as an axial base ligand [14]. This section describes the chirality generation in the two types of 2-ce complex crystals with perpendicular and parallel conformations. 

Sekine, A., Hori, K., Ohashi, Y, Yagi, M., and Toda, R, X-ray structural studies of chiral P-lactam formation from an achiral oxo amide using the chiral-crystal environment,/.Am. Chem. Soc., Ill, 697, 1989. 

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