Amino Acid Mediated Borane Reduction of Ketones II^a

Summary.

 Acetophenone, 2,2-dimethylcyclopentanone, 3,3-dimethyl-2-butanone, 3-methyl-2-butanone, and 2-pentanone were reduced with borane mediated by (S)-alanine, (S)-methionine, (S)-leucine, (S)-valine, and (S)-isoleucine in very good yields giving predominantly alcohols of (R)-configuration (ee = 23–89%). A molecular topology based model was developed for describing the influence of the substituents, both in the oxazaborolidine type reagent and in the ketone, on the observed chiral induction.