Arylation of the heteroaromatic compounds

Heteroaromatic compounds are important structural moieties with an extensive history of diverse applications in a variety of fields, such as biology or material sciences, since, numerous economically important pharmaceuticals or agrochemicals have bi(hetero)aryl units as indispensable substructures. The direct arylation of heteroarenes with aryl halides has become the most valuable method for the formation of C(sp2)-C(sp2) bonds in contemporary organic synthesis. Therefore, the direct coupling between aryl halides and heteroarenes is advantageous with respect to a minimization of reaction steps and a reduction of byproduct formation. In recent years, a wide variety of studies in this field focused on the developments of new C-H bond transformations. After this development, various methods for direct arylation of other valuable heteroarenes such as pyrroles, azoles, (benzo)thiophenes and (benzo)furans have been developed N-Heterocyclic carbene (NHC) ligands are electronically and sterically tunable, and they generally form thermally stable compounds with different metal ions. The strong σ-donating but poor π-accepting ability of NHC ligands lead also to the formation of many stable palladium(II)-NHC complexes. Due to activity, stability and selectivity of palladium(II)-NHC complexes, they have been widely used as highly reactive and rather selective catalysts for numerous direct arylation reactions. For this purpose new carbene precursors and their palladium complexes were synthesized and catalytic activities of the heteroaromatic compounds were investigated in this thesis. The finding can be explained in three sub-step: 1) Benzimidazolium salts (1a-1k) were synthesized using alkyl halides with 1-(2-ethylhexylbenzimidazole) and their structures were elucidated by appropriate spectroscopic methods. 2) The synthesized benzimidazolium salts were reacted with PdCl2 and Pd(OAc)2 under appropriate conditions to synthesize Pd-NHC complexes(2a-2g and 3a-3c) and their structures were elucidated by appropriate spectroscopic methods. 3) The catalytic activity of synthesized Pd-NHC complexes in the arylation reaction of heteroaromatic compounds were investigated.