Visible-light-induced metal and reagent-free oxidative coupling of sp2 C–H bonds with organo-dichalcogenides: synthesis of 3-organochalcogenyl indoles

Abstract

Here, a unique visible-light-induced method for the organochalcogenation of the sp² C–H bonds of indoles and aniline has been presented using diaryl dichalcogenides (S, Se, and Te) and oxygen as an oxidant avoiding a photocatalyst, base, catalyst, and reagent in acetone at room temperature. This benign protocol allows one to access a wide range of 3-arylselenylindoles, 3-arylthioindoles and even 3-aryltelluroindoles with good to excellent yields. Various functionalities namely, methoxy, and halo either on indoles or aryl dichalcogenides showed amenability to the developed reaction. Furthermore, thiocyanation of the sp² C–H bonds of indoles has been accomplished by this visible light induced method. A mechanistic understanding by UV-visible, EPR spectroscopy, and cyclic voltammetry suggests that light induces electron transfer from the electron rich arene to oxygen providing an arene radical cation and a superoxide radical anion. Subsequently, reaction of the radical cation with aryl dichalcogenides provides a diaryl chalcogenyl cation which upon removal of protons gave unsymmetrical 3-indolyl aryl chalcogenides.