Ligand-Enabled, Palladium-Catalyzed β-C(sp)-H Arylation of Weinreb Amides.

We report the development of Pd(II)-catalyzed C(sp)-H arylation of Weinreb amides. This work demonstrates the first example of using Weinreb amide as a directing group for transition metal-catalyzed C(sp)-H activation. Both the inductive effect and the potential bidentate coordination mode of the Weinreb amides pose a unique challenge for this reaction development. A pyridinesulfonic acid ligand is designed to accommodate the weak, neutral coordinating property of Weinreb amides via preserving the cationic character of Pd center through zwitterionic assembly of Pd/ligand complexes. DFT studies of the C-H cleavage step indicate that the superior reactivity of 3-pyridinesulfonic acid ligand compared to pyridine, Ac-Gly-OH, and ligandless conditions originates from the stabilization of overall substrate-bound Pd species.