Stereoselective synthesis of N,N'-diaryl-2,5-dioxopiperazines from homochiral or racemic 2-bromopropananilides

The preparation and characterization of N,N'-diaryl-2,5-dioxopiperazines are described. The stereoselective synthesis involves the self-coupling of 2-bromopropananilides. The reaction can be controlled to favor cis-(R,R) or cis-(S,S)/trans-(R,S) isomers by starting either from a single enantiomer or racemate and by the promoter, aryl substituent and solvent. The six diastereomeric couples have been characterized by 1H NMR spectroscopy and X-ray crystallography.