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 diortho-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.