Efficient Chirality Switching in the Addition of Diethylzinc to Aldehydes in the Presence of Simple Chiral alpha-Amino Amides

摘要

Chiral catalysis is one of the most efficient approaches for the preparation of enantiopure compounds. For practical applications, the chiral ligands need to be accessible from simple starting materials and the process has to provide access to both enantiomers of the product, to guarantee that the desired isomer can be obtained. This last condition can be fulfilled through the preparation of both enantiomers of the corresponding ligand. A more challenging approach is the dual stereocontrol over the outcome of the reaction by modification of the reaction conditions or the nonchiral structural components, thereby allowing the preparation of either of the enantiomers from a single configuration of the chiral elements of the catalyst. This chirality switching has been achieved by using different Lewis acids coordinated to the ligands by modification of the solvent system, and by introduction of structural features that modify the catalytic mechanism or the structure of the catalytic site, including variations in the nature of the support in heterogeneous catalysis.