Nonlinear Effects in Asymmetric Synthesis and Stereoselective Reactions: Ten Years of Investigation

Who would have thought before 1986 that an enantiomerically impure catalyst could give a product in an asymmetric synthesis with an enantiomeric excess higher than that of the catalyst? Until then it was assumed that the ee value of the product (eeprod) from an asymmetric synthesis was linearly correlated to the ee value of the chiral auxiliary (eeaux)—in fact a large deviation is possible (see diagram). These nonlinear effects are not only of academic interest since they have a variety of practical uses, which are highlighted in this review.