ASYMMETRIC-SYNTHESIS OF OPTICALLY-ACTIVE ALCOHOLS WITH 2 CHIRAL CENTERS FROM A RACEMIC ALDEHYDE BY THE SELECTIVE ADDITION OF DIALKYLZINC REAGENTS USING CHIRAL CATALYSTS

Optically active alcohols with two chiral centres have been obtained in good to high e.e.s (enantiomeric excesses) from racemic 2-phenylpropanal 1 by diastereo- and enantio-selective addition of dialkylzinc reagents using (1S,2R)-(-)-N,N-dibutylnorephedrine (DBNE) and (S)-(+)-diphenyl(1-methyl-pyrrolidin-2-yl)methanol (DPMPM) as chiral catalysts. It was found that in the presence of (1S,2R)-(-)-DBNE, dialkylzinc selectively attacked racemic 1 from the Si-face of the aldehyde 1 regardless of the configuration of 1 and that (S)-1 reacted faster with dialkylzinc than did (R)-1.