Theoretical insight into the mechanisms of palladium-catalyzed intramolecular insertion of alkenes into the carbon-nitrogen bond of β-lactam

By employing density functional theory (DFT), we investigate the mechanisms of Pd-catalyzed intramolecular alkene insertion with β-lactam. The catalytic cycle involves oxidative addition, alkene insertion, and reductive elimination. In reaction A, the rate-determining step is the alkene insertion. Compared with reaction A, the higher barriers for reactions B and C could be attributed to the weaker electron-donating ability of ligands and the strong steric repulsion between the ligands and the substrate, respectively. When the methyl group is substituted by the electron-withdrawing phenyl group (reaction D), the alkene insertion becomes more difficult due to the electronic effect, which is consistent with the observation that the yield is low in this reaction.