Copper-Catalyzed Radical Cyclization of Aryl Amines

Y. Li et al. have reported a Cu(CH₃CN)₄BF₄-catalyzed carbohalogenation via radical cyclization of aryl amines with aqueous hydrogen halides as a halogen source to give 3-halomethyl-2,3-dihydrobenzofuran derivatives with up to 92% yield. They proposed the reaction mechanism through generation of the diazonium salt from starting aryl amines, and the subsequent intramolecular radical cyclization, on the basis of the experimental results using TEMPO as a radical scavenger. This methodology features cheap halogen sources and an easy- to-handle protocol which can be applied to form the dihydrobenzofuran structures.