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

In the presence of a [Ru( p -cymene)Cl ₂ ] 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.