Photocatalytic Arene C-H Bond Functionalization:Aryl C-O/C-N Bond Formation Via Hydrogen-Evolution Cross-Couplings

Arenes are tremendous importance in chemical industrial applications.Direct functionalization of aryl C-H bonds can provide efficient access to arenes with diverse structural and chemical properties.Therefore,the development of methodologies for aryl C-H fumctionalization carry the promise of practical syntheses of high-value chemicals.However,it is still a great challenge to achieve aryl C-H bonds transformation in a sustainable way which possesses step-economy,atom-economy,mild reaction contions and use of simple and abundant materials.In this context,photocatalytic hydrogen-evolution cross-coupling(HECC)reactions provide a new and ideal strategy for aryl C-H bond functionalization.Photocatalytic HECC is a reaction that directly couples two different C-H bonds or one C-H bond with one X-H bond to contruct C-C bond or C-X bond.Without any sacrificial oxidant,this type of reactions can carry out in unprecedented mild reaction conditions and the sole side product is an equivalent amount of hydrogen gas.Based on these characteristics,photocatalytic HECC reactions may be a sustainable strategy for aryl C-H bond functionalization.Thus,in this dissertation photocatalytic HECC strategy was used for the direct coupling of ary C-H bond with O-H bond and with N-H bond to form the ary C-O bond and C-N bond respectively with the evolution of H2.The following creative results are achieved:1.By utility of photocatalytic HECC strategy,phenol was produced from benzene and water with evolution of hydrogen gas.Without any sacrificial oxidant,this reaction was carried out under unusually mild conditions.After 5 h irradiation,the conversion of benzene,yield of phenol and the reaction selectivity is 90%,90%and 100%,respectively.This procedure was also applied for the preparative scale syntheis of phenol.In addition,substituents on benzene were tolerated in this reaction.2.Aryl C-0 bond was successfully constructed by direct coupling of aryl C-H bond with alcohol O-H bond via photocatalytic HECC strategy.Without any sacrificial oxidant,etherification of aryl C-H bond was proceed smoothly under mild reaction conditions,and the sole by-product was hydrogen gas.This reaction exhibited a large range of substrate scope.Generally,good to excellent yields were obtained.Moreover,this methodology was also demonstrated applicable for the de novo synthesis of local anesthetic butoxycaine from benzene.Furthermore,intramolecular C-H etherification of 3-phenylpropanols also was performed well using this protocol.3.Without any directing group,direct coupling of aryl C-H bond with various alkyl and aryl carboxamides N-H bond via photocatalytic HECC were accomplished under mild reaction conditions.Holo-alidation of benzamides were achieved with ortho-selectivity.This strategy has been applied to the synthesis of 2-phenylquinazolin-4-one,a key skeleton of pharmaceuticals and bioactive natural products,from simple benzamides.4.Without any sacrifical oxidant,aniline can be synthesized directly from benzene and ammonia with evolution of hydrogen gas under unprecedent mild conditions.Irradiation of acetonitrile solution containing benzene,ammonia,1-methylquinolinum ion,dimethylglyoxime and BF3,37%aniline was produced with 41%benzene conversion and 90%selectivity,and no byproduct except for hydrogen gas was yielded.