Palladium-Catalyzed Reaction Of C_aryl-C_aryl Bond Formation By Ligand Regulation

Biaromatic skeleton as an important structural unit is frequently found in naturalproducts, performance materials and chemical products. Palladium-catalyzed C-Cbond forming reactions have emerged as powerful tools for the synthesis of biarylderivatives. So the development of simple, efficient and mild reaction conditions isstill in demand. In this paper, palladium-catalyzed reactions of Caryl-Caryl bondformation by ligand regulation for the synthesis of biaryl derivatives are reported,such as Suzuki coupling reaction and direct functionalization of polyfluoroarenes.In the first part, a convenient approach has been developed to preparepolyfluorobiphenyl by Pd(OAc)2/PCy3catalyzed direct arylation of polyfluoroareneswith aromatic halides in the presence of Cs2CO3as base and toluene as solvent. Inmost cases, the desired arylated products of aromatic bromides were obtained in goodto excellent yields at80oC, and aryl chlorides also gave modest to good yields ofarylated products at110oC. According to this efficient C-C bond-forming method,polyfluorobiphenyl liquid crystal compounds were prepared by Pd-catalyzed directarylation reactions of polyfluoroarenes with long alkyl chain substituted aryl bromidesin62-96%yields.In the second part, an efficient tandem route to the synthesis ofpolyfluoroterphenyls derivatives has been developed. The target compounds wereobtained in moderate to good yields by a Pd(OAc)2-catalyzed three-componentcoupling reaction involving Suzuki coupling reaction and direct C-H activation ofperfluoroarenes.In the third part, a series of4-vinylbiphenyl derivatives were synthesized byPd(OAc)2/PCy3-catalyzed Suzuki-Miyaura reaction in the presence of K3PO4·3H2O asbase in toluene at80°C for only10-30min, and the corresponding products achieved65-98%yields. According to this efficient C-C bond-forming method, the obtainedyields of4-vinylbiphenyl liquid crystal compounds were up to92-96%. In addition,the different ligands such as PCy3·HBF4and PPh3, could inducible Suzuki coupling of4-bromobenzyl chloride with aryl boronic acid in ifferent C-X bond. WhenPCy3HBF4as ligand, the coupling product by C(sp2)-Br activation is obtained. Andthe coupling product affored by C(sp3)-Cl activation is the major when the ligand isPPh3. Then, Suzuki coupling reaction of4-bromobenzyl bromide for the synthesis of the symmetrical or unsymmetrical diaryl derivates is investigated. A range of arylboronic acids can serve as arylating for the double Suzuki coupling reactions,affording the desired products in excellent yields. A variety of arylboronic acidspossess good tolerance of functional groups and broad substrate scope, and give morethan90%yields.In summary, various biphenyl derivatives are obtained by palladium-catalyzeddirect arylation of polyfluoroarenes and Suzuki reaction under ligand regulation. Theadvantages of these methods are simple, mild reaction conditions, broad substratescope, and high yields.