Halogen-Bond-Promoted Radical Isocyanide Insertion of <i>o</i>-Diisocyanoarenes with Perfluoroalkyl Bromides under Visible Light Irradiation

Abstract

A halogen-bond-promoted double radical isocyanide insertion of o-diisocyanoarenes with perfluoroalkyl bromides is reported, in which perfluoroalkyl bromides as halogen bond donors and organic bases as halogen bond acceptors. Fluoroalkyl radicals can be generated by a visible-light-induced single electron transfer (SET) process. Fluoroalkyl radicals are trapped by o-diisocyanoarenes to give 2-fluoroalkylated quinoxaline derivatives. These reactions could be carried out under mild conditions with good chemical yields and broad substrate scope. A broad range of fluoroalkyl bromides with different functionalities could undergo this reaction to give the corresponding quinoxaline derivatives in good yields. A variety of o-diisocyanides could be fluoroalkylated to give quinoxalines under our established conditions. The radical nature of this reaction was confirmed by electron paramagnetic resonance (EPR) experiments using tert-butyl--phenylnitrone (PBN) as a spin trap. When PBN was introduced into the reaction mixture, a spectrum signal attributed to the spin adduct C 8 F 17 -PBN appeared as a triplet of doublets. Without light and amine, almost no signal was observed. These phenomena strongly suggested that the perfluoroalkyl radical was the key intermediate and the generation of the intermediate heavily relied on the presence of light and amine. A series of deuteration experiments were performed and these results suggested that both the amine and solvent could serve as the hydrogen source and solvent was the major source.