Kinetic Insight into Specific Features of the Autocatalytic Soai Reaction

The addition of diisopropylzinc to prochiral pyrimidine carbaldehydes (Soai reaction) is the onlyknown example of spontaneous asymmetric synthesis in organic chemistry. It serves as a model systemfor the spontaneous occurrence of chiral asymmetry from achiral initial conditions. This review describesthe possible kinetic origin of specific experimental features of this reaction. It is shown that generickinetic models, including enantioselective autocatalysis and mutual inhibition between the enantiomers,are adequate to describe a variety of the astonishing properties of the Soai reaction. Namely, theseare the unprecedented strong chiral amplification, extreme sensitivity to the presence of very small amountsof chiral initiator, mirror-symmetry breaking when starting from achiral conditions, and the reversal ofenantioselectivity of chiral catalysts by addition of achiral additives. The described kinetic approachallows a closer insight into the nonlinear dynamics of the Soai reaction. It also reveals that a numberof open questions concerning the detailed reaction mechanism are still to be solved and that further experimentalstudies are required.