Visible-Light-Induced C-H Activation Lactonization Promoted By DDQ/TBN System

The construction of C-C bond and C-X bond is an important part of basic organic chemistry.The construction of C-X bond through the oxidative activation of C-H bond has been a hotspot for many scientists nearly years.In order to overcome the high prices of metal reagents,and the problems of metal residue,the non-metal mediated catalyst C-H bond activation reaction attracted more and more attention.2,3-Dichloro-5,6-dicyano-1,4-benzoquinone?DDQ?is a strong oxidizing oxidant.It has been widely used in alcohol oxidation reaction,oxidation deprotection reaction,aromatic in the structure-chemical reaction,etc..Research has found that DDQ can be excited to generate a triplet excited state ³DDQ^*with strong oxidizing ability under visible light irradiation.From the perspective of"environmental friendly chemistry",using oxygen as an oxidant is a good choice in which H₂O is the sole by-product.Based on the reports of related literatures and the existing research works of our group,this paper proposes the application of visible-light-induced DDQ/TBN catalyzed oxidation system to the intramolecular C-H bond activation and C-O bond coupling.First of all,this paper introduces the substituted methyl 2-iodobenzoate and substituted phenylboronic acid were used as raw material through Suzuki coupling reaction to the preparation of corresponding coupling compounds,and then though the hydrolysis reaction to get the corresponding 2-arylaryl formic acid compounds.The corresponding structures were confirmed by NMR nuclear magnetic characterization.Secondly,this paper reports the DDQ/TBN system catalyzed the coupling reaction of arene C?sp²?-H bond oxidation to form C-O bond under visible light irradiation to prepare benzocoumarin.Using 2-arylbenzoic acid as a model substrate,DDQ as a photocatalyst,TBN as a co-catalyst,and oxygen as the sole oxidant,the reaction was performed in an organic solution at normal temperature and pressure and under blue light irradiation.The loading of catalyst,different solvents,presence or absence of oxygen and visible light,and other conditions affect the reaction were explored.With the optimal conditions of 5 mol%DDQ as the photocatalyst,5 mol%TBN as the co-catalyst,4 m L of DCE as solvent,the isolated yield of the corresponding product was 99%in 12 hours.Under the optimized reaction conditions,the range of reaction substrates was expanded,and it was found that the substituted 2-arylaryl formic acid can be converted into the corresponding products well,and the isolated yield were48-99%.Subsequently,on the basis of the above research,we found this reaction could be performed well on gram scale with 98%isolated yield in 18 hours.In addition,the internal lactonization of 4-phenylbutyric acid about?-H was explored.It was found that4-phenylbutyric acid could also react to the corresponding lactone structure products under a certain amount of DDQ/TBN.In conclusion,we have reported DDQ/TBN system catalyzed internal lactonization.It is found that the system has mild reaction conditions,use of green oxidant,and metal-free catalysis,good substrate applicability and other advantages,which has a good application prospect in organic chemistry.