Synthetic Method Development Of Heterocycles From Arylazo Compounds

Arylazo compounds are widely used in daily life as dyes.Because arylazo compounds are stable and the majority of them are toxic,the leakage of them into the environment will threat the eco-system and human health.In order to tackle these compounds,two key points should be focused on to convert the azo structure,which are the lone pair of nitrogen and the N=N double bond in the azo moiety.Currently,most methods decompose arylazo compounds into harmless small molecules,or convert them into anilines or imido metal complexes,which are of little value in terms of synthesis.Few reactions involving electrophiles or metals can transform arylazo compounds into relatively valuable heterocycles.This dissertation mainly focuses on the development of heterocycle synthesis based on arylazo coumpounds,using electrophiles to enable the conversion.In the second chapter,a CuI-promoted reaction of azobenzenes with allyl bromides is elucidated for the synthesis of quinolines.This reaction has many advantages such as one-pot procedure,easy manipulation,availability of substrates and good yields.Based on investigation of intermediates of the reaction,a tandem mechanism involving electrophilic reaction and oxidation was proposed.In this process,azobenzenes act both as construction unit and oxidant for quinoline formation.At the start of the reaction,N=N bond is cleaved through reduction by Cu(I)in combination with proton in the system.As the reaction procedes,azobenzene can be continuously reduced to aniline by relevant intermediates in the presence of Cu(I)and proton.In the third chapter,an iodine-mediated sp~3 C-H functionalization process of o-alkyl-azoarenes leading to 2H-indazoles is described.This reaction has simple reaction condition and high yields,and is suitable for variously substituted substrates.By addition of catalytic amount of CuI,an iodine-catalyzed aerobic oxidative procedure was developed,and could be used for gram-scale synthesis of 2H-indazoles.Detailed investigation on the reaction mechanism was conducted.Characterizations like Far-IR and ~1H-NMR suggest that the halogen bonding between azo group and iodine,which can bind iodine to the vicinity of target C-H bond,is crucial for this reaction.In combination with EPR monitoring and DFT calculation,a radical chain mechanism was proposed,in which the key step is an azo-group-assited concomitant transfer of iodine and hydrogen.This step is also the rate-determining step of the reaction,with an activation free energy of around 30 kcal/mol.The outcome of this step is the iodination of the ortho-alkyl,which enables the subsequent nucleophilic cyclization and aromatization to give the final products.The study in this dissertation extended the reaction modes of azo compounds with electrophiles.By using different electrophiles,two sorts of valuable N-containing heterocycles can be obtained.Detailed investigations on the reaction mechanisms in this thesis could function as references for further developments of conversion methods of azo compounds.