Catalytic Asymmetric Reactions Means of Attractive Interactions

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Asymmetric reactions catalyzed by transition metal complexes containing optically active phosphine ligands have attracted significant interest for their synthetic utility. One of the most exciting and challenging subjects in research on the catalytic asymmetric synthesis is development of the chiral ligand which will fit in with a given reaction efficiently in enantioselectivity as well as in catalytic activity. In designing chiral ligands we have attached importance to introduction of a functional group into the ligand that, where possible, would be expected to interact attractively with a functional group in the substrate. The attractive interactions will enhance the enantioselectivity in catalytic asymmetric reactions by increased steric interactions between the chiral ligand and a prochiral substrate. We have developed new chiral ligands bearing some functional groups on the backbone : 1) 2- (Diphenylphosphino) -1,1'-binaphthyls (MOPs) which have carboxyl, hydroxy, alkoxy, and amino groups on the 2'-position. 2) Ferrocenyl-and ruthenocenylbisphosphines containing amino and hydroxy groups on the metallocene side chain. 3) Several kinds of functional groups were introduced into 3-and 3'-positions of 2,2'-bis [4- (alkyl) oxazol-2-yl] -1,1'-binaphthyls (boxax). These functionalized chiral ligands have been used for palladium-catalyzed asymmetric reactions including allylic substitutions and Wacker-type cyclization.