Direct C5-Arylation Reaction between Imidazoles and Aryl Chlorides Catalyzed by Palladium Complexes with Phosphines and N-Heterocyclic Carbenes

Palladium(II) acetate complexes bearing phosphines and carbene ligands, Pd(L)(PR3)(OAc)2 (1a, R = Ph; 1b, R = Cy; L = 1,3-dibenzylimidazol-2-ylidene), were prepared by salt metathesis reactions of their chloro complexes with AgOAc in good yields. The electron-rich 1b was efficient in catalyzing C-5 direct arylation of imidazoles with aryl halides. Most significantly, the catalytic system allows a range of aryl chlorides as substrates. Microwave irradiation effectively promotes the reactions, with good yields obtainable in only 2 h. In combination with the classical method of C–C bond formation reactions, novel imidazole derivatives featuring biaryl and styryl subunits were successfully obtained from 1,4-dichlorobenzene and 1-bromo-4-chlorobenzene.