Pd-catalyzed C-H Activation Arylation Of Perfluoroarenes With Aromatic Heterocycles

In the past decade, palladium-catalyzed C-H activation/C-C bond-forming reactions have emerged as promising new catalytic transformations; however, development in this field is still at an early stage compared to the state of the art in cross-coupling reactions using aryl and alkyl halides. Among the myriad of important transition metal catalyzed synthetic transformations, palladium catalyzed cross-coupling (Heck, Suzuki, Stille, Negishi, Sogashira), using organohalides and other surrogates are particularly valuable tools in synthetic chemistry. A common and critical feature of these catalytic processes is the formation of aryl or unstable alkyl palladium(II) intermediates, which greatly limit their applications in organic synthetic. From the viewpoint of synthetic analysis, such reactions using unactivated C-H bonds offer not only complementary reactivity, but also represent novel synthetic disconnections in a given synthetic plan when the regioselective introduction of halides into molecules is not straightforward.Perfluorinated aromatic rings are a prominent structural motif found in numerous functional materials of importance in various application fields. In particular, because of the strong electronwithdrawing effect of perfluorinated aryl groups, this induces a significant lowering of the HOMO and LUMO energy levels with respect to the nonfluorinated counterparts. Molecules containing the perfluoroarene thiophene structure play a primary role as active materials in electronic devices, such as organic light-emitting diodes (OLEDs) and field-effect transistors (FETs). Generally, such a structural moiety is achieved by cross-coupling of organometallic aryls with aryl halides. The direct functionalization of electron-deficient perfluoroarenes is still a great challenge, and only rare examples have been reported. Hence, we have developed a new coupling of Pd-catalyzed C-H activation arylation of perfluoro- arenes with aromatic heterocycles.This paper describled the author's effort on these topics:Firstly, A general review was provided for the development of palladium- catalyzed C-H activation/C-C Cross-Coupling reactions, and the author summarized the recent applications of perfluoroarenes in C-H activation coupling reactions.Secondly, Palladium-catalyzed C-H activation/C-C coupling reactions were studied. After examining various ratios of catalys, base and the oxidant,solution, reaction temperature and time, the author has found the optimized reaction conditions for this transformation.Thirdly, the application scope of Pd-catalyzed C-H activation arylation of perfluoroarenes with aromatic heterocycles was expanded.Fourthly, achieving regioselective functionalization at either the 2- or 3-position of heterocycles through the coupling reaction can be obtained. We have identified the stucture of the subtances obtained by the new coupling reactions.In conclusion, we have developed a straightforward and practical method for the direct Pd(OAc)₂ catalyzed oxidative cross-coupling of electron-deficient perfluoro- arenes with aromatic heterocycles via twofold C-H functionalization, using Ag₂O or Ag₂CO₃ as base and oxidant, in DMF and 5% DMSO.