Research On Visible Light Indued Functionalization Reactions Of Phenols

One of the pivotal goals in the field of catalysis is to develop new methods to activate inert molecules and to improve the reaction efficiency of used resource and energy as well as the yield of product through new bonding mode.In the past decades,the renascence of radical chemistry in organic synthesis has also revived researchers' interest in photochemistry.Special open-shell reactive intermediate can be formed during the photocatalytic process,which can hardly be accessed by other non-photocatalysis.Furthermore,the inherent properties of visible-light such as high abundance,environment-friendly and sustainable make photochemistry meet the requirement of green chemistry in this era.Phenols and their derivatives are very important pharmaceutical intermediates and chemical materials.Bromophenols are common synthetic intermediates and play important roles in industrial production such as materials,medicine and pesticides.Compounds containing dihydrobenzofuran that stemmed from phenols have potential biologic activities such as anti-inflammatory,anti-oxidant and anti-cancer;and they are found to be existed in many natural products.Benzoxazinones constructed by o-aminophenol/alcohol constitute very important parts in the realm of biology,medicine and pesticides.For example,Efavirenz,a kind of anti-HIV drug,has a core of benzoxazinone skeleton.This thesis focused on the study of visible-light-induced functionalization reactions of phenol such as bromination,[3+2] cycloaddition,esterification/amidation and direct amination under mild conditions.In the visible-light-enabled bromination reaction of phenol,CBr4 was served as the oxidative quencher and brominating agent by employing Ru?bpy?₃Cl₂ as the photocatalyst.Bromophenols were condidered to be formed via electrophilic bromination between phenols and the in-situ generated Br2 from Br-.Besides,alkenes were able to produce di-bromoproducts under the same conditions,which further demonstrated the formation of Br2 during the reaction.This bromination method provided a greener and more effective route by applying the stable CBr4 as brominating source thus avoiding the highly toxic Br2 as usual.Benzofuran has been synthesized in moderate yields from [3+2] cycloaddition between phenol and alkene by using sodium persulfate as the oxidant under photo or thermo conditions.Moreover,the natural product Corsifuran A was synthesized in a single-step reaction.The strong oxidative SO₄^·-derived from the photolysis or thermolysis of S₂O₈^2-was able to oxidize phenol to enable the following [3+2]cycloaddition with alkene.This route has been proved to be more economic and benign than traditional ways that using strong acid or heavy metals.A series of five-or six-member benzoxazinones were constructed by photocatalytic three-component reactions of o-aminophenol/alcohol,CBr4 and moisture by using Ru?bpy?₃Cl₂.Moreover,continuous flow technique was applied to scale up the reaction and recycle the photocatalyst.This synthetic method was highlighted in building the carbonyl group of product with two separate components,namely C-atom from CBr4 and O-atom from water,which averted the use of hazardous phosgene and its derivate as well as resulted waste.Direct cross-dehydrogenative-coupling?CDC?amination between phenol and heterocyclic diarylamine has been adopted to synthesize cyclic triarylamine by using potassium persulfate as oxidant under visible-light irradiation.It was featured in achieving high yield and absolute selectivity without additional catalysis under very mild conditions.Most importantly,it enabled the formation of new C-N bond from two coupling partners in direct dehydrogenative way to avoid pre-activation step.Further investigation on the performance of acyclic ones was conducted.Herein,the first CDC amination of phenol and acyclic diarylamine was realized to construct triaylamine unit in the presence of organic photocatalyst at room temperature.A mechanism involving radical/radical cross-coupling was proposed based on the fluorescent quenching and EPR experiments.Moreover,determining quantum yield clarified the existence of radical chain propagation process during the amination reaction.This route innovatively broadened the scope of aminating substrate and also prevented from high temperature,metal catalysis and pre-activation that required in conventional amination ways.Both amination reactions proceeded through radicals cross coupling between the oxidized phenol radical and nitrogen atom radical.