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.