Asymmetric synthesis using chirally modified borohydrides. Part 3. Enantioselective reduction of ketones and oxime ethers with reagents prepared from borane and chiral amino alcohols

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.