Palladium Catalyst for the Synthesis of 2,4,5-Trisubstituted Imidazoles

Bis(1,10-phenanthroline)palladium(II) bis(hexafluorophosphate) (1) is a palladium complex used in the C-H arylation of azoles.¹⁾ For instance, in the presence of catalytic amount of 1, 1-methylimidazole is regioselectively substituted by treatment with 1 equivalent of aryl halides at 5th position. When excess amount of aryl halides is used, further C-H arylations proceed at 2 and 4 positions to give trisubstituted imidazoles. Furthermore, when multiple aryl halides are added in sequence, regioselective arylations proceed to afford trisubstituted imidazoles bearing all different aryl substituents. This reaction can be also operated in one-pot.²⁾ 1 can be used as a catalyst for the synthesis of multi-substituted heterocyclic compound and is anticipated to be used in the development of medicines and agrochemicals.