New 7-aryl or 7-heteroarylamino-2,3-dimethylbenzo[b]thiophenes were prepared by palladium-catalyzed Buchwald-Hartwig cross-coupling of 7-bromo or 7-amino-2,3-dimethylbenzo[b]thiophenes, previously prepared by us, with substituted (4-methoxy or 3,4-dimethoxy) anilines and 3-aminopyridine or with substituted (3-methoxy or 4-cyano) bromobenzenes and 2-bromopyridine, respectively, using Pd(OAc)2, rac-BINAP or Xantphos as ligands, and Cs2CO3 as base. Their antioxidant properties were evaluated by several methods: reducing power, scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals, inhibition of erythrocyte hemolysis and inhibition of lipid peroxidation using the beta-carotene linoleate system. EC50 values for all the methods were determined and it was possible to establish some structure-activity relationships (SARs) based on the presence and position of different substituents on the phenyl ring (1 or 2 OMe and CN), on the presence of a pyridine ring and on the position of its nitrogen atom relative to the N-H bond.