DABCO‐Promoted Selective Photochemical C−N Coupling: Access to Unsymmetrical Azahelicenes

Abstract

A multifaceted study on the effect of various factors on the efficiency of photocyclization of naphthofuran O‐acyl oximes was performed. It showed that without any additives or in the presence of electron acceptors, the reaction occurs by a radical pathway and with low chemoselectivity, while DABCO promotes intramolecular cyclization to give naphthofuroquinolines (NFQs) in 34‐87% yields. The iminyl radical formed under UV irradiation in the presence of DABCO due to single electron transfer (SET) and N–O bond cleavage undergoes selective intramolecular homolytic aromatic substitution (HAS) with formation of a new C–N bond. This route to quinoline‐annulated scaffolds is based on the use of DABCO both as an electron transfer agent and a proton acceptor.