ORGN 533

We will describe the synthesis of a family of 4,4’-substituted 2,2’-bis(diphenylphosphino)- 1,1’-binaphthyl (4,4’-BINAPs) and their applications in highly enantioselective asymmetric catalytic processes. These 4,4’-modified BINAPs coordinate with Ru(II) centers to form Ru(4,4’-BINAP)(diamine)Cl₂ complexes which serve as excellent precatalysts in Ru-catalyzed hydrogenation of aromatic ketones, with e.e. values of up to 99.5%. This level of enantioselectivity for Ru(4,4’-BINAP)(diamine)Cl₂ is far superior to that afforded by their BINAP analogs. X-ray single crystal structure studies showed that the steric effect of 4,4’-groups is responsible for this enantioselectivity enhancement. 4,4’-Substituted BINAPs were also applied in Ru-catalyzed asymmetric hydrogenation of b-aryl-b-ketoesters with e.e. values of 99.5% for the hydrogenation of ethyl benzoylacetoacetate, a value that is much higher than that of BINAP analog (85% e.e. under identical conditions). This catalyst system also has a wide substrate scope with e.e. values ranging from 97.8% to 99.6% for a variety of b-aryl-b-ketoesters. Applications of these 4,4’-modified BINAPs in other metal-catalyzed asymmetric catalytic processes will also be reported.