The asymmetric reduction of aromatic and aliphatic ketones, halogeno ketones, hydroxy ketones, keto esters, and ketone oxime ethers with reagents prepared from borane and chiral amino alcohols has been investigated. When α,α-diphenyl β-amino alcohols, such as (2S,3R)-(–)-2-amino-3-methyl-1,1 -diphenylpentanol (2d), were used as a chiral auxiliary, very high enantioselectivities (ca. 90 % e.e.) were obtained in the reduction of various ketones and oxime ethers.

Asymmetric reduction of prochiral aromatic ketones with the reagent prepared from (S)-(–)-2-amino-3-methyl-1,1-diphenylbutan-1-ol [(S)-(1)] and borane afforded the corresponding aromatic secondary alcohols in high optical (94–100% enantiomeric excess) and chemical (100%) yields.