The effect of direct steric interaction between substrate substituents and ligand substituents on enantioselectivities in asymmetric addition of diethylzinc to aldehydes catalyzed by sterically congested ferrocenyl aziridino alcohols

The direct strong steric interaction between substrate substituents and ligand substituents was first discovered in asymmetric addition of diethylzinc to aldehydes catalyzed by sterically congested ferrocenyl aziridino alcohol derivatives. In addition, this nonbonded steric repulsion influenced significantly enantioselectivities of this reaction, and even led to inversion of the absolute configuration. This fact was further confirmed by the theoretical calculations and the design of a new chiral ferrocenyl aziridino alcohol ligand. A plausible mechanism for this asymmetric reaction was also proposed.

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Methyl (2S,3S)-N-ferrocenylmethyl-allo-l-threomine esterC16H21FeNO3[α]D20=-40.8 (c 1.00, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2S,3S)

Methyl (2S,3R)-1-ferrocenylmethyl-3-methylaziridine-2-carboxylateC16H19FeNO2[α]D20=-86.6 (c 0.77, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2S,3R)

(2S,3R)-1-Ferrocenylmethyl-3-methylaziridin-2-yl(diphenyl)methanolC27H27FeNO[α]D20=-10.0 (c 0.46, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2S,3R)