**6. Prospects for new asymmetric reaction using crystal**

New aspects of chemistry are deployed by effectively utilizing the unique nature of crystals. In this chapter, a new approach to asymmetric chemistry using chiral crystals found in our research groups is introduced. We succeeded in transferring the chirality expressed by chiral crystallization of achiral substrate to products in a variety of reactions in homogeneous systems. Stereoselective reaction using chiral crystals was limited to the topochemical solidstate photoreaction, and the reactions expanded in a homogeneous system were able to achieve the highly stereoselective asymmetric reaction. Some readers may think that chiral molecules possessing memory effects introduced in this chapter are like acrobats using a very narrow energy band. Figure 19 shows an energy diagram for racemization of chiral molecules that express chirality by spontaneous crystallization or by Crystallization-Induced Enantiomer Transformation (CIET). We can effectively use molecules with

Fig. 19. Energy diagram for racemization of axially chiral and achiral materials available for asymmetric synthesis via spontaneous chiral crystallization

activation free energy of racemization from 10 to 30 kcal mol-1 for chiral memory. It is not an unusual technique, but a rather typical approach that can be widely utilized in asymmetric reactions. We have found many more applications to this method using chiral memory; we will present them in future work. In addition, this method could be applied to the diastereoselective reaction using chiral memory derived from CIDT. These findings suggest that the molecular information in the crystal can be widely applied to a variety of chemistry, in addition to organic asymmetric reaction.
