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 beta-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. (C) 2018 Elsevier B.V. All rights reserved.