ENANTIOSELECTIVE ADDITION OF DIETHYLZINC TO ALDEHYDES CATALYZED BY POLYMER-SUPPORTED CHIRAL OXAZABOROLIDINE

Two new polymers containing chiral oxazaborolidines as pendant groups have been prepared by chemical modification of crosslinked 2-vinylthiophene copolymers. The polymers are used as chiral auxiliaries in the catalysis of asymmetric addition of diethylzinc to aldehydes. We found that when these new catalysts are used in the alkylation of benzaldehyde (ratio catalyst/aldehyde 0.15/1), the ee obtained are between 51 and 28%, whereas with the corresponding model compounds the ee obtained at a ratio catalyst/aldehyde 0.1/1 are in the range of 75-65%. We have also discussed the influence of several parameters (solvent, temperature, amount and loading of the catalyst, nature of the oxazaborolidine, nature of the aldehyde and recycling of the supported catalyst) on the enantiomeric excess.