Mono-, di-, tri-, and tetraarylated thieno[3,2 -b]thiophenes were synthesized by direct site-selective Pd-catalyzed C−H activation reactions with various aryl bromides in the presence of a phosphine-free Pd(OAc)2/KOAc catalyst system in N, N-dimethylacetamide (DMAc). The arylation of 2-arylthieno[3,2 -b]thiophene took place at the C3 position if the 2-aryl substituents possessed electron-withdrawing groups and at the C5 position if they were bulky and possessed electron-donating groups. [ABSTRACT FROM AUTHOR]