6.5 C-C Bond Formation: Aldol Reaction with Non-Proline Derivatives

The aldol reaction is one of the most important carbon-carbon bond-forming reactions in organic synthesis. Since the discovery of intra- and intermolecular aldol reactions catalyzed by proline, organocatalyst-mediated aldol reactions have been developed extensively. Currently, asymmetric organocatalytic aldol reactions can be classified into four major categories, differentiated by their reaction mechanisms: (1) enamine mechanisms; (2) ion-pair mechanisms; (3) chiral enolate mechanisms; and (4) electron acceptor activation by Brønsted acids. In this chapter, the authors describe these four types of aldol reactions; herein, the authors limit their discussion to reactions catalyzed by nonproline derivatives, whereas in the previous chapter, aldol reactions catalyzed by proline and proline derivatives are reviewed.