Ru-Catalyzed C–H Arylation of Acrylic Acids with Aryl Bromides

In the presence of a [Ru(p-cymene)Cl₂]₂/triethylphosphine/lithium carbonate catalyst system, aryl bromides undergo (Z)-selective couplings with unprotected 2-arylacrylic acids to form (Z)-diarylacrylic acids. This vinylic C-H functionalization proceeds in high yields of up to 94% and (Z/E)-ratios of up to 99:1, tolerating a wide range of functional groups. Mechanistic studies indicate that the vinylic C-H activation proceeds via base-assisted cyclometalation rather than via a Heck-type mechanism, which explains its orthogonal stereoselectivity.