Palladium-Catalyzed Direct Arylation of Polyfluoroarenes for Accessing Tetra- ortho-Substituted Biaryls: Buchwald-type Ligand Having Complementary -PPh₂ Moiety Exhibits Better Efficiency

The first general examples of direct C-H arylation of electron-deficient polyfluoroarenes with challenging di-ortho-substituted aryl(heteroaryl) chlorides for tetra-ortho-substituted biaryl synthesis are reported. Key to success is the use of Buchwald-type biaryl phosphine ligand, notably with inexpensive -PPh₂ moiety (instead of -PCy₂ group). Pd(OAc)₂ associated with ligand L9 exhibits even higher efficiency than the corresponding SPhos toward this reaction. A wide range of sterically hindered di-ortho-substituted chloroarenes bearing electron-donating or -withdrawing groups are found applicable. Excellent product yields are obtained under mild reaction conditions, and the catalyst loading down to 0.25 mol % of Pd can also be achieved.