Chemoselective Activation of sp3 vs sp2 C-H Bonds with Pd(II)

The first selective coupling of a carbon nucleophile with methyl, ethyl, propyl, and butyl arenes in the absence of a directing group is described. Pd(OAc)(2) double C-H activation displays remarkable selectivity for the terminal methyl sites in alkyl arenes, rather than the more commonly observed arene sp(2) C-H activation. Mechanistic studies indicate the intermediacy of an azlactone dimer, obtained from oxidation with Pd(OAc)(2), and are consistent with a Pd-catalyzed C-H activation vs a radical process. The observed reactivity establishes that typical reaction solvents (e.g., toluene) can readily participate in C-H activation chemistry.