Construction of a carbapenam skeleton using palladium-catalyzed cyclization

When a THF solution of β-lactam having propargyl phosphate was warmed in the presence of 5 mol% of Pd2(dba)3·CHCl3, 20 mol% of bidentate ligand and sodium acetate (1.5 equiv.) at 40°C for 22 h, carbapenam was produced in high yield. In this reaction, the lactam nitrogen attacked the central sp carbon of a σ-allenylpalladium complex, which was formed from propargyl phosphate and Pd(0).