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

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. image