Chiral bipyridine derivatives in asymmetric catalysis

The current review presents a systematic outline of the types of chiral bipyridines known to-date, in particular the methods of their preparation and their application in selected catalytic enantioselective processes. The first part deals with the main structural types of chiral bipyridines, based on the topological origin of chirality of these systems, namely central, axial, planar, and helical, or any combination of these. The sp(2) nitrogens can be oxidised to the corresponding N-oxides, and that not only alters the electronic and steric properties of the system but also allows different modes of coordination. The synthetic approaches are illustrated for each structural type. Several applications of chiral bipyridine derivatives in enantioselective catalysis are reviewed. The most successful transformations where chiral bipyridine-type compounds are employed as the ligands, include copper-catalysed cyclopropanation and allylic oxidation, and palladium- catalysed allylic substitution. Enantioselective nucleophilic catalysis is a new emerging area where chiral bypiridine N-oxides have recently made a considerable impact; a substantial progress has been made in the enantioselective allylation of aromatic aldehydes with allyltrichlorosilanes.