Visible-Light-Induced Regioselective Insertion Reactions Of Arynes

Arynes are highly active organic intermediates,which can be achieved by eliminating two ortho hydrogen atoms in the aromatic ring.Due to the existence of carbon-carbon triple bonds in the six-membered ring of aromatic hydrocarbons,the unhybridized p orbitals are distorted and no longer parallel to each other like ordinary alkynes.The intramolecular strain caused by the triple bond in the rings makes them highly reactive.Therefore,the kinetically unstable intermediate can react with a variety of anions and uncharged nucleophiles to obtain ortho-disubstituted arynes.Arynes have found wide applications in organic synthesis for their unique activity,especially in the fields of biology,pesticides,medicine and dyes.In recent years,the reseach on photocatalysis and C–H bond activation have received much attention and become hot topics in organic synthetic chemistry.In this paper,some insertion reactions using arynes are designed,which are described as follows:?1?With 450 nm blue LEDs as light soure,a mild cascade reaction of benzamides and arynes using Pd?OAc?₂/Na₂-eosin Y dual catalysis under an oxygen atmosphere has been estblished.Results show that cesium fluoride as a base plays a critic role in the formation of arynes.A series of phenanthrone compounds can be obtained by this[4+2]cycloaddition reaction in which both the alkynyl carbon paticicpated into the insertion reactions on the N and benzene rings of the benzamide,respectively.Compared to the previous reports,this catalytic system successfully employs the visible light as a green energy,which obviates the use of heavy metal salts as oxidants.?2?Upon blue LEDs irradiation?450 nm?,a regioselective three-molecule insertion reaction of 1-toluenesulfonyl aziridines,arynes and acetonitriles would occure in the presence of cesium fluoride as a base.Remarkblely,acetonitrile used in this reaction play a dual role,acting both as a reactant and a solvent.This mild three-molecule cascade reaction provides a new method for the synthesis of long-chained organic nitriles.