Guest, achiral, inclusion with

Optical Resolution by Inclusion Complexation with an Achiral Guest Compound... 

Resolution of some hosts can be accomplished by inclusion complexation with an achiral guest compound. 

By inclusion complexation with a chiral host compound, achiral guest molecules can be ordered in a chiral manner, and photoirradiation of the complex gives optically active reaction products. The inclusion complexation can also be accom-... 

Another use of TADDOL inclusion compounds is to carry out a solid-state reaction with a TADDOL crystal containing an achiral guest molecule, such that the latter is converted to a chiral product. There are again numerous highly successful applications of this procedure by the Toda group [50]. Especially intriguing are enantioselective photoreactions with inter- and intramolecular C,C-bond formation, for which three examples are shown in Scheme 8. 

Circular Dichroism (CD) Spectroscopy New circular dichroism (CD) bands can be induced in the absorption bands of the achiral guest molecule when it is included within the asymmetric locus of the cyclodextrin cavity which consists of chiral glucose units [62]. Chiral guest molecules may also show changes in circular dichroism (CD) spectra upon the formation of inclusion complexes with cyclodextrin [63]. 

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. 

It was found that the title achiral host molecules (134) are arranged in a chiral form in their inclusion complex with a guest. By using this phenomenum, some rac-guests were resolved by complexation with achiral 134. 

In a related host-guest based chiral synthesis, the molecule 16b was used to make a 1 1 inclusion compound with 21. Just tis in the case of 19, 21 is achiral, contains q two oxygens on adjacent carbon atoms and undergoes a photorearrangement. 

The title achiral molecule (108) was found to be arranged in a chiral form in its inclusion complex with a guest compound. By using this phenomenon, some mc-guests were separated into their enantiomers by complexation with achiral 108 [45]. 

---