CATALYZED ASYMMETRIC REACTION OF ALDEHYDES WITH DIALKYLZINC IN THE PRESENCE OF CHIRAL PYRIDYL ALCOHOLS AS LIGANDS

The synthesis of homochiral pyridyl alcohols (1,2,3a-c) and a catalytic asymmetric addition of dialkylzinc to various aldehydes using 1-3 as ligands are described. Although the reaction of benzaldehyde with Et2Zn in the presence of (S)-1 and (R,R)-2 gave (S)- and (R)-1-phenyl-1-propanol, respectively, in moderate enantiomeric excess (e.e.), tridentate ligands (3a-c) accelerated the reaction to produce the corresponding alcohols in high e.e. Particularly, (S)-3b was found to be the most efficient catalyst, for which asymmetric reactions of various aldehydes with dialkylzinc gave the corresponding alcohols in good to high e.es. (up to 95% e.e.).