CHIRAL AUXILIARIES FOR ASYMMETRIC-SYNTHESIS - ENANTIOSELECTIVE ADDITION OF DIALKYLZINCS TO ALDEHYDES CATALYZED BY CHIRAL 1,2-DISUBSTITUTED FERROCENYL AMINO-ALCOHOLS

Chiral 1,2-disubstituted ferrocenyl amino alcohols derived from (R)- and (S)-N,N-dimethyl-1-ferrocenyl-ethylamines 1 and 9 catalyze the enantioselective addition of dialkylzincs to aldehydes to afford optically active S and R secondary alcohols. The degree of enantioselectivity increases with increased bulk of substituents near the C-O and C-N bonds of the catalyst. Catalysts with R chirality at the carbon bearing the amino group and planar S chirality at the ferrocene nucleus afford S alcohols, regardless of the chirality of the carbon bearing the hydroxy group. Catalyst 8o is the most effective in ethylating benzaldehyde, and it alkylates aromatic and highly branched aliphatic aldehydes in greater-than-or-equal-to 90% ee. Only moderate selectivities are obtained in the ethylation of aliphatic aldehydes without an alpha substituent.