Highly diastereoselective Staudinger reaction on 5,6-dihydropyrazin-2-(1H)-ones. Synthesis of enantiopure fused oxopiperazino-β-lactams

The highly diastereoselective synthesis of fused oxopiperazino-β-lactams 2 by Staudinger reaction between functionalized ketenes and 5,6-dihydropyrazin-2(1H)-ones 1 has been carried out. Further cleavage of the β-lactam ring produced 2-oxopiperazine-3-acetic acid derivatives 7 with no epimerization and in good yields.

Diastereoselective [2+2] cycloaddition onto 5,6-dihydropyrazin-2(1H)-ones produces enantiopure oxopiperazino-β-lactams, precursors to enantiopure 2-oxopiperazine 3-acetate derivatives by methanolysis.