Synthesis of pyrrolidine-2,4-diones from urethane N-carboxyanhydrides (UNCAs)

In the presence of a base in aprotic medium, UNCAs lead to N-urethane protected-3,5-dialkyl-3-amino pyrrolidine-2,4-diones as racemic cis/trans mixtures. Consequently the choice of the base should be carefully considered to optimize yields and avoid side products when UNCAs are used in peptide synthesis.