Palladium-Catalyzed Direct Arylation of Polyfluoroarenes for Accessing Tetra-<i>ortho</i>-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.本工作首次报道了可用于四邻位取代联芳烃合成的、极具挑战性的双邻位取代芳基（杂芳基）氯与缺电子多氟芳烃的直接C-H芳基化（C–H arylation）通用实例。该反应成功的核心在于采用布赫瓦尔德型联芳基膦配体（Buchwald-type biaryl phosphine ligand），尤其可使用廉价的二苯基膦基（−PPh2）取代传统的二环己基膦基（−PCy2）。与配体L9配位的乙酸钯[Pd(OAc)2]对该反应的催化效率甚至优于经典配体SPhos。多种带有给电子或吸电子取代基的空间位阻型双邻位取代氯代芳烃均可适用于该反应体系。在温和的反应条件下即可获得优异的产物收率，且钯催化剂的负载量可低至0.25 mol%。