Visible light-induced radical cyclization of o-alkenyl aromatic isocyanides with thioethers: direct synthesis of 2-thioquinolines

Abstract

A novel visible-light-induced photoredox-catalyzed regioselective radical cyclization reaction of isocyanides with thioethers has been developed for the first time. This reaction provides a novel and efficient method for the construction of 2-thioquinolines from readily available starting materials. Moreover, this visible-light-induced radical cyclization strategy was further extended to the α-C(sp³)–H activation reaction of Boc-S-benzyl-L-cysteine. Mechanistic studies indicate that in situ generation of a sulfide radical cation or an α-thio alkyl radical, radical addition to isocyanides and the following intramolecular cyclization/intermolecular nucleophilic substitution might be involved in the process.