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

Abstract

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 a,a-diphenyl-P-amino alcohols, such as (2S,3R) -( -) -2-amino-3-methyl-1,ldiphenylpentanol (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.

Synthesis and Application of a New Fluorous‐Tagged Ammonia Equivalent

“…A range of different reagents have been used for reductive cleavage of N À O bonds, which included Li/4,4'-di-tert-butylbiphenyl (DTBB), [22,23] Na/Hg amalgam, [24,25] SmI 2 , [14,[26][27][28][29][30] TiCl 3 , [31][32][33][34] indium, [8,11] LiAlH 4 , [35,36] BH 3 , [37] [Mo(CO) 6 ], [13,24,[38][39][40][41][42][43][44][45][46][47][48][49] [Co 2 (CO) 8 ], [50] [Fe(CO) 5 ], [13,51] Zn/H +, [43,[52][53][54][55] NiB 2 , [56] Na 2 S 2 O 4 , [57] [TiA C H T U N G T R E N N U N G (iPrO) 4 ]/EtMgBr, [58] NiH 2 , [59] trimethylsilyl chloride/KI, …”

Ligand Design for Catalytic Asymmetric Reduction

“…[117][118][119] This reaction was originally developed as a stoichiometric system consisting of diphenylvalinol and borane, 120 but was later extended to a useful catalytic method. 121 Because of the high efficiency of this reaction, many chiral oxazaborolidines have been synthesized from b-amino alcohols.…”

Stereoselective Synthesis of 8-Trialkylstannylmenthols

“…Compounds 1 and 2 were separated by column chromatography (silica gel 60). The reduction of type 2 ketones with borane in THF using (S)-valinol as a catalyst was carried out according to known procedures [2].…”