Stereoselective reductive amination of β-keto esters derived from dipeptides. Stereochemical and mechanistic studies on the formation of 5-carboxymethyl-2-oxopiperazine derivatives

Abstract The stereoselective generation of 3,5-disubstituted and 3,5,6-trisubstituted 2-oxopiperazine derivatives can be accomplished by intramolecular reductive amination of β-keto esters derived from Z-Xaa-Gly-OH and Z-Xaa-Yaa- OH dipeptides, respectively. Differences in the stereoselectivity between the use of NaBH 3 CN and hydrogen as reducing agents are due to the reduction of different intermediates, as deduced from experiments of isotopic labelling with deuterium.