Reactivity of 4‐phenylthiazoles in ruthenium catalyzed direct arylations

The reactivity of the phenyl substituent of 4‐phenylthiazoles in Ru‐catalyzed direct arylation was studied. 4‐Phenylthiazole was found to be unreactive; whereas, the introduction of an aryl unit at C5‐position of 4‐phenylthiazole enhances its reactivity, allowing the selective mono‐arylation of the phenyl unit of 4‐phenylthiazoles in moderate to high yields using 5 mol% of Ru(p‐cymene)Cl₂]₂ catalyst precursor associated to KOPiv as base. These results reveal that the conformation and electronic properties of 4‐phenylthiazoles are crucial to allow the formation of suitable intermediates in the course of the catalytic cycle. The reaction tolerated both electron‐rich and electron‐poor aryl bromides allowing the straightforward tuning of the electronic properties of the arylated 2‐methyl‐4‐phenyl‐5‐arylthiazoles.