Synthesis and antioxidant activity evaluation of new 7-aryl or 7-heteroarylamino-2,3-dimethylbenzo[b]thiophenes obtained by Buchwald–Hartwig C–N cross-coupling Original Research Article

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 β-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 Ctriple bond; length of mdashN), on the presence of a pyridine ring and on the position of its nitrogen atom relative to the N–H bond.