Selective Reductions. 40. A Critical Examination of the Relative Effectiveness of Various Reducing Agents for the Asymmetric Reduction of Different Classes of Ketones

Article abstract of DOI:10.1021/jo00233a019

Among a wide variety of highly promising asymmetric reducing agents recently reported in the literature, 20 promising reagents were selected for critical examination.All of the data for the asymmetric reductions of prochiral ketones by these 20 reagents were compiled.The various ketones were organized into 10 distinct classes.However, direct comparison of the relative effectiveness of these 20 reagents for individual classes of ketones proved not possible because of the wide variation in the individual ketones used to test each reagent.In the hope of making possible such comparison, we selected one representative ketone for each of the 10 different classes of ketones.Then, six of the most promising reagents were selected: B-isopinocampheyl-9-borabicyclo<3.3.1>nonane, B-Ipc-9-BBN (neat); diisopinocampheylchloroborane, Ipc2BCl; a mixed reagent of 2 equiv of BH3 with (S)-(-)-2-amino-3-methyl-1,1-diphenylbutan-1-ol, BH3-AMDPB (2:1); NB-Enantride; K-Glucoride; and Binal-H.These six reagents were applied to the 10 selected standard ketones.On the basis of results obtained for the six reagents and the 10 selected ketones, preferred reagents are suggested for the asymmetric reduction of individual classes of ketones.