Synthesis of diarylamines in the benzo[b]thiophene series bearing electron donating or withdrawing groups by Buchwald-Hartwig C-N coupling

Abstract

Diarylamines in the benzo[b]thiophene series bearing electron donating or withdrawing groups, were prepared by Buchwald-Hartwig C-N coupling in moderate to high yields. The conditions used were Pd(OAc)2 (3mol %), BINAP as ligand (4mol %) and Cs2CO3 as base (1.4 equiv.), in toluene at 100 oC, being 6-bromo or amino benzo[b]thiophenes coupled respectively with substituted anilines or phenylbromides. The 6-aminobenzo[b]thiophene derivatives were also prepared by palladium catalyzed C-N coupling of the corresponding 6-bromo compounds with benzophenone imine, followed by acidic hydrolysis of the imino derivatives. When 4-nitrobromobenzene and 4-bromobenzonitrile were used as coupling components, triarylamines were also isolated in small amounts. The presence of a fluorine atom on the phenylbromide highly increases the diarylamine yields.