Optically Active Precursors for Quaternary Amino Acids by Addition of N-Heteroaromatics to 3-Alkylidene-2,5-diketopiperazines

Abstract

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