DDQ-promoted synthesis of 2-benzoylbenzofurans and benzofuro[2,3-c]pyridines using 2′-hydroxy ethyl cinnamate and phenacyl bromides

Abstract

A cascade oxidation, cyanation/cyclization facilitated by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), has been developed as an efficient synthetic route for producing a range of 2-benzoylbenzofurans and benzofuro[2,3-c]pyridines from 2′-hydroxyethyl cinnamate and phenacyl bromides. Mechanistic studies indicate that the CN radical, generated through the homolytic cleavage of the C–C bond of DDQ, served as a key intermediate in the reaction. DDQ-mediated single-electron transfer initiates the cascade process of radical addition, and 1–2 addition of DDQ promotes cyclization. A wide range of bicyclic and tricyclic ring systems of benzofuran and benzofuropyridine are obtained in this methodology with moderate to good yields. This transformation features a broad substrate scope, operates under organometallic catalyst-free conditions, utilises readily accessible starting materials, and demonstrates potential for scale-up. Additionally, it allows for the simultaneous formation of two new C–C and C–N bonds in a single operation.