Rigid and Sterically Regular Chiral 1,1'-Binaphthyl Polymers in Asymmetric Catalysis

摘要

Optically active 1,1'-binaphthyl structures have been used to synthesize novel, rigid and sterically regular polymeric catalysts for asymmetric catalysis.Good to excelent enantioselectivties have been achieved for reactions including the organozinc addition to aldehydes, the reduction of ketones with catecholborane, the hetero-Diels-Alder reaction of ethyl glyoxylate with a conjugated diene, the epoxidation fo #alpha#,#beta#-unsaturated ketones, and the 1,3-dipolar cycloaddition of nitrones with alkenes. The studies on the use of polymers (R)-4, (R)-8, (R)-9, and (R)-15 and monomer (R)-11 in asymmetric catalysis have introduced two new concepts for the development of enantioselective polymer catalysts:1) the microenvironment of the catalytic sites in rigid and sterically regular polymers can be systematically modified to produce highly enantioselective polymeric catalysts; 2) the enantioselectivity of a monomeric catalyst can be maintained ina polymer catalyst by the use of a rigid and sterically regular polymer backbone. Compared with the traditional polymer-supported catalysts for which flexible and sterically 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 also can be further extended to construct polymeric chiral catalysts that are capable of multiple asymmetric catalytic reactions by incorporating different catalytic species in a polymer chain.