Asymmetric Conjugate Addition to Enones and Imines

In 1994 Chinchilla and coworkers [34] identified and synthesized a chiral guanidine for the asymmetric catalytic addition of nitroolefins to aldehydes. Since this initial discovery, numerous developments in the field of asymmetric Brmsted base catalysis have utilized chiral guanidines. 

Upton and coworkers [32] reported the use of a cyclic dipeptide guanidine catalyst for the asymmetric Strecker reaction. In a comparison between an imidazole moiety and a guanidine moiety for the Bronsted basic unit of the catalyst, a large discrepancy in the reactivity became evident The highly basic guanidine 

Another structurally modified guanidine, catalyst 57, was reported by Ishikawa et al. [36] for asymmetric Michael additions of glycine imines to acrylates under neat conditions. The high conversion and selectivity was attributed to the relative configuration of the three chiral centers of the catalyst in the absence of any solvent interactions. A reversal of stereochemistry may be achieved when the chiral center 

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