Study On The Palladium- And Ruthenium-Catalyzed Directed Carbonylation And Fluoromethylation

Over the past years,transition-metal catalyzed C-H activation has been widely applied for the synthesis and preparation of organic materials,natural products,bioactive molecules,and some fine chemicals.Among these reactions,ligand-directed C-H activation has specially aroused chemists' extensive interests owing to its unnecessary prefunctionalization,which would effectively decrease the reaction steps and improve the efficiency of reaction.Despite numerous examples have been reported,the C-H activation still remains significant challenges.On one hand,the energy of C-H is higher than that of C-C,C-X and H-X.Therefore,how to overcome the higher energy barrier to realize the C-H activation is a very important issue.On the other hand,the selectivity of the reaction is difficult to control because of the similarity of the energy between different C-H bonds.Late transitioin metals can easily realize the C-H activation owing to their unoccupied molecular orbitals,which could bond with lone electron pair or ? electron.Therefore,the selection and introduction of directing groups are crucial.This dissertation is focused on the Pd-catalyzed or Ru-catalyzed N-ligand-directed sp2 C-H activation,and consists of the following parts:Firstly,azo compound has been developed as the directing group for the palladium-catalyzed decarboxylative acylation.This protocol provides a series of orrtho-acylated unsymmetrical azo compounds,tolerating a wide range of functional groups such as chloro,bromo,iodo,and methoxy groups.In addition,para,ortho and disubstituted as well as unsymmetrical azo compounds can be employed in this reaction.Secondly,a novel and efficient protocol for the palladium-catalyzed ethoxycarbonylation by using potassium oxalate monoester as the ethoxycarbonylation source via C-H activation has been realized.This method extends the scope of the recently popular ethoxycarboxylation.Different kinds of directing groups such as oxime and pyridine can be utilized in this transformation.In addition,this new protocol also tolerates a wide range of functional groups.The products of this reaction can be further converted into ketoesters and lactones.Thirdly,palladium-catalyzed C-H decarboxylative ortho-ethoxycarbonylation of 2-arlyoxypyridines has been achieved by using potassium oxalate monoester.This reaction can afford a series of ethyl salicylate derivatives.Furthermore,as a common and easily handled protocol,this reaction provides a new strategy and idea for the synthesis of aspirin derivatives.Fourthly,the first example of the Ru-catalyzed ligand-directed meta-selective C-H fluoromethylation of 2-phenylpyridines,2-phenylpyrimidines,and 1-phenylpyrazoles has been developed.The present work expands the scope of the recently popular fluoromethylation and ruthenium-catalyzed meta-selective C-H activation.In addition,this method can be extended to non-fluoromethylation with ethyl bromoacetate as the partner.