Pd-catalyzed Decarboxylative Coupling Of Aromatic Carboxylic Acids With Phenyl Boronic Acid

The biaryl moiety is an important structural motif in a large number of biologically active compounds and functional polymers. Chemists have always been looking for a simple and effective method to synthesize such biphenyl compounds. Cross-coupling reactions are among the most widely used carbon-carbon bond-forming reactions in organic synthesis. In the past decades, transition metal-catalyzed cross-coupling reactions developed fast due to the organic researchers'work. Suzuki cross-coupling reaction is one of the most important reactions in these reactions. Its reaction condition is soft and its yield is often very high as well. Additionally arylboron reagents are easy to prepare and easy to keep. People have maken great achievement in Suzuki cross-coupling reaction to synthesis a great deal of useful chemicals by organoboron reagents and aryl halides.It is an advantage that aromatic carboxylic acids could easily be obtained at low cost in the commercial market. Additionally, the only by-product of decarboxylation procedure is carbon dioxide which is much more environmental friendly compared to the heavy polluting by-products generated from traditional coupling reaction. For these reasons, the development of aromatic carboxylic acids as new substrates of coupling reaction has become a research focus in recent years.This paper described the author's recent works on these topics, with focus on the development of biaryl synthesis via Palladium-catalyzation.Firstly, the author summarized the recent developments of biaryl synthesis. A general review is provided for reactions catalyzed by Copper, Iridium, Ruthenium, Rhodium and Palladium.Secondly, Palladium-catalyzed decarboxylative coupling reactions were studied. After examining various ratios of reagent, reaction temperature and time, the author has found the optimized reaction conditions for this transformation. With the optimized conditions, several unsymmetrical biaryls products were prepared. Additionally, a possible mechanism was proposed to explain the reaction.Through the above works, an efficient Palladium-catalyzed decarboxylative coupling reaction for preparing biaryl from aromatic carboxylic acids and substitut phenyl boronic acid has been developed. The procedure shown in this paper extended not only the application scope of Pd-catalysis, but also the application of aromatic carboxylic acids and substitut phenyl boronic acid in coupling reaction.