Rigid and sterically regular chiral 1,1 '-binaphthyl polymers in asymmetric catalysis

Optically active 1,1'-binaphthyl structures have been used to synthesize no vel, rigid and sterically regular polymeric catalysts for asymmetric cataly sis. Good to excellent enantioselectivties have been achieved for reactions including the organozinc addition to aldehydes, the reduction of ketones w ith catecholborane, the hetero-Diels-Alder reaction of ethyl glyoxylate wit h a conjugated diene, the epoxidation of alpha,beta-unsaturated ketones, an d the 1,3-dipolar cycloaddition of nitrones with alkenes. The studies on th e use of polymers (R)-4, (R)-8, (R)-9, and (R)-15 and monomer (R)-11 in asy mmetric catalysis have introduced two new concepts for the development of e nantioselective polymer catalysts: 1) the microenvironment of the catalytic sites in rigid and sterically regular polymers can be systematically modif ied to produce highly enantioselective polymeric catalysts; 2) the enantios electivity of a monomeric catalyst can be maintained in a polymer catalyst by the use of a rigid and sterically regular polymer backbone. Compared wit h the traditional polymer-supported catalysts for which flexible and steric ally irregular polymers are used, this new approach can better preserve the catalytic environment of the monomeric catalysts in the polymer as long as the catalytically active species are not aggregates of the monomers. These strategies not only make it possible to obtain easily reusable and highly enantioselective polymeric catalysts for many asymmetric reactions, but als o can be further extended to construct polymeric chiral catalysts that are capable of multiple asymmetric catalytic reactions by incorporating differe nt catalytic species in a polymer chain.