Pd(II)-Catalyzed Direct ortho-C-H Acylation of Aromatic Ketones by Oxidative Decarboxylation of α-Oxocarboxylic Acids.

A Pd-catalyzed decarboxylative acylation of aromatic ketones with α-oxocarboxylic acids was developed, and 1,2-diacylbenzenes were formed in up to 90% yield with excellent ortho-selectivity. This work demonstrates the first successful attempt to direct C-H acylation of aromatic ketones without the need for prederivatization to imines. The acylation reaction was inhibited by radical scavengers such as TEMPO, and 2,2,6,6-tetramethylpiperidin-1-yl benzoate, the adduct of TEMPO and a benzoyl radical, has been isolated and characterized. This finding is compatible with the intermediacy of acyl radicals. A mechanism involving the reaction of the palladacyclic complexes of aryl ketones with acyl radicals is proposed.