The aldol addition reaction has become a strategically important, reliable transformation that is widely employed in the asymmetric synthesis of complex molecules. It can be counted on not only to provide access to polyketide fragments with their characteristic 1,3-oxygenation pattern, but also to numerous other classes of compounds, such as oxo-heterocycles, alpha and beta-amino acids, and nucleosides.
Two general approaches have emerged for aldol reaction: (1) diastereoselective additions, wherein stoichiometric quantities of a covalently bound, chiral controlling element shepherds the stereochemical course of the reaction and, alternatively, (2) enantioselective methods wherein a chiral catalyst functions as the stereochemical controlling element. Diastereoselective methods remain dominant. Enantioselective methods are new on the scene. However, explosive development has led to complex molecule assembly via catalytic asymmetric aldol transformations. Such reactions are described here.