JS-aminoalcohols

Isoxazolidine (149) was converted into jS-aminoalcohol (151) via reductive N—O bond cleavage of the quaternary salt (150) with Zn and aqueous acetic acid (Scheme 27) <85JCS(Pi)26i>. 

Kinetic analysis of the decomposition of t-24 by (+)-ephedrine and other jS-aminoalcohols was examined in detail at different temperatures and the activation and discrimination parameters were defined. An entropy of... 

As an extension of this study, Hamada s group applied these conditions to the asymmetric hydrogenation of aromatic a-aminoketone hydrochlorides. Surprisingly, no reaction took place under similar conditions. However, it was discovered that the presence of a catalytic amount of NaBARF in addition to sodium acetate in toluene was essential for this hydrogenation catalysed by the same homogeneous nickel catalyst. In these adapted conditions, the synthesis of a series of anti jS-aminoalcohol hydrochlorides was achieved with moderate to high yields, almost complete anti diastereoselectivity in all cases of substrates and high enantioselectivities of up to 96% ee, as shown in Scheme 2.70. 

Due to sharp and selective reduction in bond dissociation energy of radical cations [106,107], the cleavage of strong -C-C- or C heteroatom bonds has been observed during PET reactions. In this context, examples of -C-C- bond cleavage from jS-phenylethers [108], bibenzyls and pinacols [25,109,110] may be mentioned. In an extensive study, Whitten et al. [Ill, 112] have reported clean -C-C- bond cleavage from the reaction of /J-aminoalcohols and vinylog-ous amino alcohols. 

Most chiral organoboron Lewis acids reported to date are based on an organoborane that is attached to a chiral organic moiety such as a diol, aminoalcohol, or other readily available chiral substrates.Organoboron derivatives recently used as catalysts in enantioselective Diels-Alder reactions include the family of chiral acyloxyboranes (CAB) with (196) and (197) as representative examples and various cyclic boronic esters such as (198) and (199). An interesting system that combines the favorable Lewis acid properties of fluorinated arylboranes with a chiral Bronsted acid has been developed by Ishihara and Yamamoto. The Bronsted acid-assisted chiral Lewis acids (BLA) (200) was found to be highly effective in enantioselective cycloadditions of Q ,jS-enals with various dienes. The presence of the Bronsted acid functionality leads to significant acceleration of the reaction. 

The jS-CD inclusion complexes of aryloxyepoxides with amines afforded amino-alcohols enantioselectively in the solid state. When carried out in water as the reaction medium, nearly racemic aminoalcohols were produced. 

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