Chirality, that is, the handedness of compounds, has attracted the broad interest of many scientists. One of the most characteristic features of chirality is that all living organisms on earth are composed of highly enantioenriched L-amino acids and D-sugars. Prebiotic processes which lead to these compounds being highly enantiomerically enriched are a significant issue. The origin of chiral homogeneity of biomolecules has attracted much attention because this chiral homogeneity of biomolecules has been considered to be relevant to the origin and evolution of life. 1 Several mechanisms have been proposed as the origins of the chirality of organic compounds, such as circularly polarized light (CPL), quartz, and statistical fluctuation. However, enantiomeric enrichments of organic compounds induced by these proposed mechanisms have been very low, usually below 2% ee. Thus, an amplification process of enantiomeric enrichment is required. However, processes reaching a very high enantiomeric enrichment of organic compounds remain an unsolved issue.
In usual asymmetric catalysis, asymmetric catalysts C* provide the enantioenriched products P*, whose structures are generally different from those of the asymmetric catalysts. 2 In contrast, in asymmetric autocatalysis, the chiral catalyst P* produces itself (P*) and the chiral product P* acts as a chiral catalyst for its own production (Scheme 1). 3 The process is an automultiplication of chiral compound.
Asymmetric autocatalysis has the following intrinsic advantages over nonautocatalytic catalysis: (i) because the process is an automultiplication, the efficiency is high; (ii) no decrease in the amount of catalyst and in the catalytic activity should be observed because the amount of catalyst (i.e., product) increases during the reaction; (iii) separation of the catalyst from the product is not required because their structures are identical. Frank proposed a mathematical model of asymmetric autocatalysis without mentioning actual compound or actual reaction. 4 However, the experimental realization of asymmetric autocatalysis had to wait until our discovery of asymmetric autocatalysis.
In this review, we describe the discovery of highly enantioselective asymmetric autocatalysis with amplification of chirality and asymmetric autocatalysis initiated by chiral triggers. 3 We have also found spontaneous absolute asymmetric synthesis in combination with asymmetric autocatalysis. Asymmetric autocatalysis has significant implications in the correlations between the origin of chirality and the homochirality of organic compounds.