Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Cover Picture (Angew. Chem. Int. Ed. 21/1998)
The cover picture shows two examples of enantioselective catalytic reactions, where L* stands for an enantioimpure catalyst. The addition of Et2Zn to benzaldehyde catalyzed by a β-amino alcohol gives a strong asymmetric amplification; that is, the product of the reaction has a much higher enantiopurity than that calculated by the proportionality between the ee value of the product (eeprod) and the ee value of the chiral auxiliary. The second example is the (S)-proline-catalyzed intramolecular aldol reaction of a triketone, which is characterized by a moderate asymmetric depletion. More can be found on nonlinear effects, especially for catalytic reactions, in the review by H. B. Kagan and C. Girard on pages 2922–2959. The cover picture was designed by Timo Luukas.