Visible Light Induced Synthesis Of 3-acylindoles

Acylindoles are common structural motifs in many natural products,pharmaceuticals and bioactive compounds.Acylindoles are also versatile starting materials for the synthesis of a variety of indole derivatives.The synthesis of 3-acylindoles have been studied by chemists for a long time.Traditional methods suffer from the following disadvantages: stoichiometric Lewis acid is required as promoters and strict exclusion of moisture;usage of large amounts of environmentally unfriendly POCl3,and lacking of the amides used as carbonyl sources;some functional groups are sensitive to strong nucleophiles because Grignard reagents are used in these reactions.Therefore a novel and mild protocol to 3-acylindoles is highly desirable.Recently visible light has attracted widespread attention as an environmentally friendly and sustainable source of energy for activating chemical transformations.In this paper,synthesis of 3-acylindoles via radical decarboxylative coupling of α-amino acids under visible light was investigated.Compared with tradional methods,this reaction proceed under mild conditions with high regioselectivity and show good functional group compatibility.Substrates with different substitutions have been developed,and the target products have been obtained with moderate yields under the given conditions.In addition,on the basis of the observed experimental results,we tentatively proposed a plausible mechanism.It is hypothesized that the reaction would be a photon-induced intramolecular single electron transfer(SET)oxidation decarboxylation coupling reaction mechanism.It was verified by isotope labeling experiments,cyclic voltammetry and free radical capture experiments.16 different substituents 3-acylindoles have been successfully synthesized,and all of the products were characterized by GC-MS,NMR,HRMS and IR analysis.