Research On Oxazolone-Directed C-H Activation

Transition-metal-catalyzed C-H activation has emerged as an exercisable,flexible,efficient and practical organic synthetic tool,which is widely used to construct C-C or C-hetero bonds and also has made remarkable achievements in designing the structures of target molecules.Among them,the designation of directing groups(DGs)is particularly important because DGs are usually used to initiate a C-H activation reaction and decide the basic structure of target products.In this thesis,Rh(Ⅲ)-catalyzed structurally similar oxazolones-directed C-H activation reactions for preparing products with different structures are presented as well as the exploratory research of conjugated polymers like poly(m-phenylene vinylene)s(PPVs)and poly(heteroarylene)s.Chapter One:Overview the previous reports on cyclic DGs-directed C-H activation.Based on the effect of DGs in reactions and the structures of products,immutable cyclic DGs and alterable cyclic DGs are distinguished.Several N-heterocyclic compounds with strong coordination ability and stable structure such as pyridine,pyrimidine,quinoline,indole,et al are unchanged as DGs during the C-H activation reactions.DGs are retained to the products as whole and additional equivalent oxidants like Cu or Ag salts are needed in reaction,which are representatives of immutable cyclic DGs.With a long-term development(from 1994),a great many of research achievements have been reported,in which pyridine is usually as the research subject and pyrimidine,quinoline et al are as supplementary substrates.So the reports based on pyridine-directed C-H activation are main content of this chapter.When indole is the DG,the exposed N-H bond leads to a different reaction mode from pyridine-directed reactions,which is important supplementary instruction to the immutable cyclic DGs.Recently,the C-H activation followed "redox-neutral" mode gradually becomes predominating,which shows excellent environmental friendliness and atom-economy with labile N-O and N-N bond to oxidative regenerate the active species of the catalysts,so the equivalent heavy mental salts are needless.N,O-heterocyclic compounds such as oxazoles,oxadiazoles,oxazolones et al are used as DGs can realize the "redox-neutral" C-H activations,which represent the alterable cyclic DGs.However,only a few works have been reported during the short development time.On the other hand,the cyclic DGs for "redox-neutral" C-H activations is the starting point and innovation point of this thesis,which act as important supplementary and outlook content in this chapter.Chapter Two:Rh(Ⅲ)-catalyzed oxazolone-directed C-H activation between 4-aryloxazol-2(3H)-ones and internal alkynes to prepare spiro[indene-1,4’-oxazo-lidin]-2’-ones.After migration of alkynes,Rh(Ⅲ)complex doesn’t undergo the traditional "reductive elimination-oxidation regeneration" process but acidolysis followed by a formal two-step migration to C=C double bond to access to the spiro structure.Compared with several reports about other double bonds such as C=N,C=O and C=C-mediated C-H activation reactions,our work shows broad substrate scope,high atomic conversion and good step-economy.The mechanism study indicates that C-H activation is reversible and the rate-limiting step,and the catalytic reaction follows the concerted metallization and deprotonation(CMD)mechanism.Chapter Three:Rh(Ⅲ)-catalyzed isooxazolone-directed C-H activation between 3-arylisooxazol-5(4H)-ones and internal alkynes to prepare 1-substituted isoquinol-ines.The labile N-O bond in isooxazolone acts as an internal oxidant and 1-methyl-isoquinolines are achieved with the removal of CO2 under the optimized conditions.The yields are up to 97%with wide substrate scope and mind conditions.Furthermore,the model reaction obtains high product yield under both acidic and alkaline condition and in several solvents such as 1,1,1,3,3,3-hexafluoro-2-propanol(HFIP)and N,N-dimethylacetamide(DMAc),and the scope of appropriate reaction temperature is from room temperature(r.t.)to 60℃.So the reaction conditions are also explored for 2-(isoquinolin-1-yl)acetic acid without the removal of CO2 because the C-Carbonyl bond is stable.The mechanism study indicates that C-H activation is reversible and the rate-limiting step,and the catalytic reaction follows the concerted metallization and deprotonation(CMD)mechanism.Chapter Four:Rh(Ⅲ)-catalyzed exploratory research about conjugated polymers prepared by N-nitroso,N-chloride amide and isooxazolone-directed C-H activation.The first two can react with olefins and internal alkynes while the latter can react with internal alkynes efficiently.AA-type directing substrates are prepared for the copolymerization with BB-type coupling substrates and AB-type amphibious mono-mers for self-polymerization.To out delight,the successful self-polymerization of the AB-type monomers containing N-nitroso and alkenyl is achieved for several PPV-type conjugated polymers.The thermal and fluorescence properties are detailed studied and one of them is found a strong fluorescence quenching corresponding to Hg2+,which offers a new method to detect the environmentally harmful species.