Optically active precursors for quaternary amino acids by addition of N-heteroaromatics to 3-alkylidene-2,5-diketopiperazines

Addition of N-heteroaromatics 3 to 3-alkylidene or 3-benzylidene-2, 4-diket opiperazines 1 in the presence of catalytic amounts of HBr gave access to o ptically active 3-alkyl-2,5-diketopiperazines 4 as potential precursors for quaternary a-amino acids. In addition, unexpected migrations of the C-C-do uble bonds were observed leading to racemic 6-alkylidene-2,5-diketopiperazi nes 6 and 3,6-dialkyl-2,5-diketopiperazines 7.