Ru-Catalyzed C-H Arylation of Acrylic Acids with Aryl Bromides
Florian Belitz, Ann-Katrin Seitz, Jonas F. Goebel, Zhiyong Hu and Lukas J. Gooßen*
*Department of Chemistry and Biochemistry, Ruhr-Universität Bochum, NC 2/170, Universitätsstrasse 150, 44801 Bochum, Germany, Email: lukas.goossenrub.de
F. Belitz, A.-K. Seitz, J. F. Goebel, Z. Hu, L. K. Goossen, Org. Lett., 2022, 24, 3467-3470.
The combination of [Ru(p-cymene)Cl2]2/triethylphosphine/lithium carbonate catalyzes a coupling of aryl bromides with unprotected 2-arylacrylic acids to form (Z)-diarylacrylic acids in high yields. The reaction tolerates a wide range of functional groups. The vinylic C-H activation proceeds via base-assisted cyclometalation rather than a Heck-type mechanism, which explains its stereoselectivity.
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Synthesis and Characterization of Products
An oven-dried 20 mL vial was charged with 2-arylacrylic acid (1.00 mmol, 1.0 equiv.) and Li2CO3 (89.6 mg, 1.2 equiv.), and sealed with a septum cap. After the vial was flushed with three alternating vacuum and nitrogen purge cycles, the catalyst stock solution (4.0 mL) and aryl bromide (2.00 mmol) were added via syringe. The resulting mixture was stirred at 100 °C for 19 h. After the reaction was complete, the mixture was allowed to cool to room temperature. MeCN (8.0 mL), K2CO3 (276 mg, 2.0 equiv.) and MeI (320 μL, 5.0 equiv.) were added, and the mixture was stirred at 60 °C for 2 h. The mixture was allowed to cool to room temperature, EtOAc (50 mL) was added and the resulting mixture was washed with aqueous LiCl solution (20%). The aqueous phase was extracted with EtOAc (2×50 mL). The combined organic layers were washed with brine (50 mL), dried over MgSO4, filtered, and the volatiles were removed under reduced pressure. The residue was purified by column chromatography.