Study On The Synthesis Of Polycyclic Aromatic Hydrocarbons By Palladium Catalyzed Suzuki Coupling Reaction

A wide range of natural products, pharmaceutical intermediates, and polymers in functional materials contain aromatic compounds with biphenyl, terphenyl and diarylmethane structural units. Therefore, to seek an efficient and rapid construction method has been one of the active hot spots in the research of organic chemistry.In recent decades, transition metal-catalyzed cross-coupling reactions of aromatic compounds have made significant progress. Suzuki coupling reaction provides a powerful tool for the synthesis of complex organic molecules, such as multi aromatic hydrocarbon compounds by Pd-catalyzed coupling reaction of aryl boronic acid with aryl halides. Aryl boronic acid is often used as one of the important reagents for the synthesis of multi aromatic hydrocarbon compounds attributed to its advantages including water and air stability, easy availability, low toxicity, and good functional group tolerance. Therefore, the main objective of this study was to explore a more moderate "Pd-ligands" Suzuki coupling reaction catalyzed system for aromatic hydrocarbons, in particular, in the synthesis of terphenyl compounds. The main content included three parts as follows:Synthesis of symmetrical terphenyl derivatives by PdCl2-catalyzed Suzuki–Miyaura reaction of dibromobenzene using 3-（diphenylphosphino） propanoic acid as a ligand. In the presence of PdCl₂（1 mol%）, L2（2 mol%）, K₃PO4·H₂O（4 equiv.） in DMSO as solvent and at temperature below 100 °C, 22 terphenyl derivatives were synthesized in 14–95% yields, and the substrates were characterized by ¹HNMR and ¹³ CNMR. Moreover, the reaction of propylbenzene with 1,4-dibromobenzene was also conducted in gram scale.Synthesis of terphenyl derivatives by Pd-catalyzed Suzuki–Miyaura reaction of dibromobenzene using 2N₂O-Salen as a ligand was conducted in aqueous solution. Through systematic explorations, we obtained the optimal reaction conditions: Na₂PdCl₄（0.5 mol%）, L3（0.5 mol%）, solvent: H2O/EtOH（V:V = 4:1）, base: NaOH, temperature: 100 °C, time: 8 hour, and ultimately obtained 28 products in 20–97% yields. The structures were characterized by ¹HNMR, ¹³ CNMR, ¹⁹ FNMR, and high resolution mass spectrometry（HRMS, EI）. Furthermore, the reaction of 1,4-bromobenzene with 4-methylphthalic acid was conducted in gram scale.Synthesis of 4-arylmethyl-biphenyl derivatives via one-pot, multi-step, multi-component reactions of 4-acetylbiphenyl derivatives, tosylhydrazide, with arylboronic acids was performed. Based on the Valdés Barluenga’s study, through explorations, we obtained the optimal reaction conditions: Pd（OAc）₂（1 mol%）, Pcy3·HBF4（4 mol%）, solvent: 1,4-dixoane, base: K₂CO₃, temperature:（i） 80 °C,（ii） 110 °C, and（iii） 110 °C, time:（i） 2 h,（ii） 5 h, and（iii） 12 h; and ultimately we obtained 25 products in 18–94% yields. Moreover, the reaction of 1-（4-bromophenyl）ethanone with m- tolylboronic acid acid was performed in gram scale.In summary, in this study based on transition-metal Pd-catalyzed Suzuki cross coupling reaction, a series of polycyclic aromatic hydrocarbons were synthesized. In particular, terphenyl derivatives were obtained by simple, effective, sustainable, and facile method, which provided an important supplement and perfection to C–C bond formation.