Spontaneous chiral crystallization of achiral materials and absolute asymmetric transformation in the chiral crystalline environment

Recently, the combination of chiral crystallization and the solid-state photoreaction has provided many successful examples of absolute asymmetric synthesis.[1] In these reactions achiral materials adopted chiral arrangement only by spontaneous crystallization, and optically active products are obtained from the topochemically controlled reaction with high ees (Figure 1).[2,3] This method incurs a problem in crystallization of achiral molecules in chiral space groups, while rare and unpredictable. However, crystal engineering and the solid-state reaction in recent years to a variety of new systems has progressed to such extent that it can now be regarded as an important branch of organic chemistry. The achievement of an asymmetric synthesis starting from an achiral reagent and in the absence of any external chiral agent has long been an intriguing challenge to chemists and is also central to the problem of the origin of optical activity on Earth.[4] In this chapter, a general method of chiral crystallization and asymmetric synthesis using the chiral crystals will be described.