Asymmetric borane reduction of prochiral ketones using imidazolium-tagged sulfonamide catalyst

A novel sulfonamide catalyst based on a room temperature ionic liquid (RTIL) has been developed for the enantioselective reduction of ketones in refluxing toluene. The optically active secondary alcohol products were obtained in good enantiomeric excess and excellent yields. The imidazolium-tagged sulfonamide catalyst can be readily recovered and reused four times without any significant loss of catalytic activity.

Figure optionsDownload as PowerPoint slide

(R)-1-PhenylethanolC8H10OEe = 73%[α]D25=-38.4 (c 1.32, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: R

(R)-1(2-Chlorophenyl)-ethanolC8H9OClEe = 94%[α]D25=-49.3 (c 1.12, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: R

(S)-2-Bromo-1-(2,4-dimethylphenyl)-ethanolC10H13OBrEe = 95%[α]D25=+41.5 (c 1.06, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: S