Isolation and characterization of 2-alkylaminobenzo[b]furans. Evidence for competing O-arylation in Cu-catalyzed intramolecular amidation

2-Alkylaminobenzo[b]furans were isolated and characterized by X-ray crystal structural analysis, for the first time, from the Cu-catalyzed intramolecular amidation of hindered secondary amides under controlled microwave heating. A mechanism was proposed to account for competing Cu-catalyzed intramolecular N- and O-arylation pathways, which were controlled by the bulkiness of substituents on the nitrogen atom of secondary amides.