Asymmetric Autocatalysis: The Soai Reaction
Living creatures on Earth have two characteristic features. One is the ability to self-replicate at the molecular, cellular, and individual levels. The second is the overwhelming one-handedness (homochirality) of biomolecules such as l-amino acids and d-sugars. No known life-form can exist without homochiral components. Ever since Pasteur discovered molecular chirality in 1848, the origins and the processes that can lead to enantiopure organic compounds have attracted broad attention. Indeed, Pasteur himself stated in his lecture notes that he tried to induce chirality using a magnet or by inversed movement of sunlight. Thus, research on the origin of chirality of organic compounds has been a historically venerable theme. Although several theories have been proposed to explain the origins of chirality of organic compounds, such as the influence of circularly polarized light or quartz, the enantiomeric excesses (ee) induced by these mechanisms have been very low or below detection levels. Thus, a mechanism by which the very low or even below detection levels of ee induced by the proposed mechanism of the origins of chirality can be amplified to the corresponding highly enantioenriched compounds is crucial.
Asymmetric autocatalysis is a reaction in which a chiral compound acts as a chiral catalyst for its own formation. The process constitutes a catalytic automultiplication of the chiral compound. In 1995, Soai and co-workers discovered asymmetric autocatalysis of 5-pyrimidyl alkanol with amplification of ee in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde. Along with automultiplication, asymmetric autocatalysis is capable of amplifying ee from extremely low to near enantiopure levels in the absence of any other chiral factor. Mislow referred to this phenomenon as the Soai reaction, and it has attracted much attention from competent research groups around the world.
This book illustrates recent developments in asymmetric autocatalysis: the Soai reaction. An overview of the Soai reaction is presented with an examination of the origins of chirality in conjunction with asymmetric autocatalysis and its application to absolute asymmetric synthesis. The influence of circularly polarized light, chiral inorganic crystals, chiral isotopomers, and chiral organic crystals composed of achiral compounds are also discussed. Reaction models of the Soai reaction that have been developed, such as structures of asymmetric autocatalysts, elucidation of the reaction pathways, application of asymmetric autocatalysis to chiral discrimination, and some unusual aspects of chirality induction detected by using the Soai reaction are also described.
Kenso Soai, Tsuneomi Kawasaki and Arimasa Matsumoto