The α-tertiary amine motif drives remarkable selectivity for Pd-catalyzed carbonylation of β-methylene C-H bonds.

The selective C-H carbonylation of methylene bonds in the presence of traditionally more reactive methyl C-H and C(sp(2))-H bonds in a-tertiary amines is reported. The exceptional selectivity is driven by the bulky alpha-tertiary amine motif, which we hypothesise orientates the activating C-H bond proximal to Pd in order to avoid an unfavourable steric clash with a second alpha-tertiary amine on the Pd centre, promoting preferential cyclopalladation at the methylene position. The reaction tolerates a range of structurally interesting and synthetically versatile functional groups, delivering the corresponding beta-lactam products in good to excellent yields.