Palladium-Catalyzed Decarboxylative Ortho-Acylation of Tertiary Benzamides with Arylglyoxylic Acids

A palladium-catalyzed ortho-acylation of tertiary benzamides using arylglyoxylic acids has been described. Unlike the palladium insertion reported to occur in the distorted N-C(O) amide bond of tertiary benzamides, the current study unveils ortho C-H palladation in acylic or cyclic N,N-dialkylbenzamides affording ortho-acylated tertiary benzamides in good to excellent yields. Our experimental study on the mechanism provides information on the tendency of the amide nitrogen toward weak coordination with palladium as opposed to oxygen. However, density functional theory calculations suggest coordination of amide oxygen to palladium, which makes the mechanism especially interesting. A Pd(II)/Pd(III) catalytic cycle and nucleophilic attack by the acyl radical rather than arylglyoxylate anion are supported by mechanistic studies.