Efficient Preparation of Biaryl Compounds and Its Application

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Biaryl compounds are important building blocks for naturally occurring materials, and the methods for forming carbon-carbon bond between two aromatic rings have been developed for over 100 years. As a classical method, the Ullmann coupling has been a standard transformation to prepare biaryl molecules although this method often requires the vigorous reaction conditions. Additionally, in the Ullmann coupling, there are some difficulties for the synthesis of unsymmetrical biaryl molecules.For more convenient procedure, Suzuki-Miyaura coupling reaction has widely been utilized for the biaryl synthesis, as well as Stille coupling reaction. For these transformations, the functionalization on both of aromatic rings are necessary, i.e. halogenation on one aromatic ring, and the introduction of boron or tin atom on the other one. However, two aromatic rings, if they are linked with ester or amide group each other, can be coupled using Pd reagent without introduction of the functional group on one aromatic ring. Under such a concept, the intramolecular Pd-mediated biaryl coupling reactions have been developed to synthesize many polycyclic aromatic compounds including some natural products.