Prochiral guest

CDx and in particular 7-CDx are known to accommodate two aromatic moieties under certain circumstances. Hence if two appropriate prochiral guest molecules are included in the same CDx cavity, regio- and enantioselective bimolecular photoreactions are expected to occur [108]. Indeed, it is known that the presence of CDx not only accelerates the rate but also modifies the product distribution of photocyclodimerizations of anthracene derivatives [109-111], coumarin derivatives [113-115], stilbene derivatives [116,117], stilbazole [118], and tranilast [119]. For instance, Tamaki and coworkers reported significantly enhanced quantum yields of photodimerization of anthracenesulfonates and anthracenecarboxyl-ates in the presence of 3- and 7-CDx [109-111]. These anthracene derivatives form 2 2 and 2 1 guest-host complexes with (3- and 7-CDx, respectively, and... 

When the oxidation reaction of a prochiral guest is carried out in inclusion crystals with a chiral host, enantioselective oxidation of the guest can be expected. For example, enantioselective oxidation of (3-ionone 2 to optically active epoxide 3 was... 

It is not easy to control the steric course of photoreactions in solution. Since molelcules are ordered regularly in a crystal, it is rather easy to control the reaction by carrying out the photoreaction in a crystal. However, molecules are not always arranged at an appropriate position for efficient and stereoselective reaction in their crystals. In these cases inclusion chemistry is a useful technique, as it can be employed to position molecules appropriately in the host-guest structure. Chiral host compounds are especially useful in placing prochiral and achiral molecules in suitable positions to yield the desired product upon photoirradiation. Some controls of the steric course of intramolecular and intermolelcular photoreactions in inclusion complexes with a host compound are described. 

In the last twenty five years there has been a number of studies devoted to the reactions of the organic solids subjected either to a physical agent (light, heat) or a chemical one which can be a solid, a liquid or a gas The molecular constituents of a highly ordered medium such as a crystal lattice may undergo physical or chemical modifications which are far more selective than those experienced in solution or in the gas-phase. In the bimolecular crystalline edifices of the clathrates, attention is turned to the guest molecules as incipient reactive species. For example, it has recently been reported that inclusion polymerization of prochiral... 

K. Hatton, K. Takahashi, M. Uematsu, N. Sakai, Multiple interactions between host cyclodextrin and guest compound assisting asymmetrically selective reduction with NaBH4 in aqueous media, Chem. Lett., 1990, 19, 1463-1466 K. Hattori, K. Takahashi, N. Sakai, Enantioface differentiating reduction of keto-acid in the presence of 6-deoxy-6-amino-j3-cyclodextrin with NaBHi in aqueous media. Bull. Chem. Soc. Jpn., 1992,65,2690-2696 K. Hattori, K. Takahashi, Asymmetric reduction of prochiral inclusion complex in aqueous media, Supramol. Chem., 1993, 2, 209-213. 

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