Enantioselective addition of diethylzinc to aldehydes catalyzed by 5-cis-substituted proline derivatives

Abstract

5-Cis-substituted prolinols, prolinamines, and prolinamine sulfonamides proved to be efficient ligands for the enantioselective addition of diethylzinc to aldehydes, providing up to 99% ee. The sense of asymmetric induction can be controlled by the nature of the exocyclic functional group (CPh2OH vs. CH2NHR vs. CH2NHSO3R). The additional 5-cis substituent exerts a strong beneficial effect on the chirality transfer since it rigidifies the catalyst structure. The stereochemical outcome of the reactions is discussed in detail on the respective transition states.