Ru-Catalyzed ()-Specific -C-H Alkenylation of Arenecarboxylic Acids by Coupling with Alkenyl Bromides.

In the presence of [-cymene)RuCl], ()-configured alkenyl bromides couple with aromatic carboxylates to form -vinylbenzoic acids. This C-H vinylation proceeds in high yields without any activating phosphine ligands and has an excellent functional group tolerance. Starting from commonly available (/ )-mixtures of alkenyl bromides, ()-configured vinyl arenes or dienes are formed exclusively. Mechanistic studies show that this selectivity is achieved because the ()-configured alkenyl bromides undergo a smooth coupling, whereas the ()-isomers are rapidly eliminated with the formation of alkynes.