Mixed oxazoline-carbenes as stereodirecting ligands for asymmetric catalysis

Whereas initially the use of chiral N-heterocyclic carbene (NHC) ligands in asymmetric catalysis met with very limited success, several novel structural concepts have emerged which have led to a rapid expansion of the field since the beginning of this decade. One concept in the design of new chiral NHC-containing molecular catalysts is the incorporation of oxazolines. These may play a secondary structural role in the design of monodentate chiral NHCs which are either employed as organocatalysts or as stereodirecting spectator ligands in transition metal complexes. Alternatively, oxazolines may be ligating units which are combined with NHCs to give polydentate stereodirecting ligands. Both approaches have been applied successfully and are reviewed in this article.