Improvement of the Asymmetric Induction from Lactic Acid Derivatives Enhanced by ZnCl₂

Abstract

Lactic acid methyl ester, lactic acid ethyl ester, and (2S)‐ethyl‐2‐methoxy propanate were used as solvents for acetophenone reduction by boron hydrides. Moderate enantiomeric excess up to 60% was obtained in the presence of stoichiometric amounts of ZnCl₂. There is evidence for an intermediate between the solvents, the Lewis acid and the ketone, as the prerequisite for chirality transfer. The importance of the Lewis acid is to strengthen interaction between solvent and educt compared to the hydroxy group.

Keywords:

• Ketone hydroboration
• lactic acid derivatives
• solvent-induced chirality

Acknowledgment

S. H. H. is grateful for financial support from the ZFE Hochschule Darmstadt.