3.16 Synthetically Derived Auxiliaries: Amines (including Diamines), Hydrazines and Hydroxylamines, and Amino Alcohols

Abstract

Chiral, synthetically derived amines, hydrazines, hydroxylamines, and aminoalcohols are valuable chiral auxiliaries which have shown high efficiency in a wide array of asymmetric transformations. They are prepared by asymmetric synthesis, or more often as a racemic mixture then resolved. Chiral amines include 1-phenylethylamine and derivatives thereof, C2 symmetric amines such as 2,5-disubstituted pyrrolidines, as well as the very important subclass of chiral 1,2-diamines. Chiral hydrazines and hydroxylamines are generally derived from similar structures. Asymmetric synthesis using these chiral auxiliaries generally involve reactions of imine or N-acyl derivatives and include nucleophilic additions, cycloadditions, and reactions of enolate derivatives. Aminoalcohols such as tert-leucinol, cyclic aminoalcohols of the Betti base may be used as such, or after transformations into heterocyclic structures. These chiral auxilairies have been widely used for cycloadditions or reactions of enolate derivatives (enolate alkylation or aldol reactions) with very high levels of stereoselectivity. In all cases, cleavage of the chiral auxiliary after reaction is accomplished in high yields and without racemization.