Iron-Catalyzed Azide Aryl Migration And Intramolecular C-H Amination

Nitrenes are highly reactive intermediates that can undergo a variety of reactions,including addition to unsaturated bonds,C-H insertion and coupling with heteroatoms.However,these reactions only find limited applications in organic synthesis because of the difficulty in controlling the selectivity of nitrene-mediated reactions.Metal nitrenoids have similar chemical properties to nitrenes,but they are less reactive and much more selective in reactions.Therefore,the chemistry of metallonitrenes is very useful for the preparation of nitrogen-containing compounds.Much attention has been made recently on the metal nitrenoid-mediated cycloaddition and C-H insertion,and important breakthroughs have been made to expand the scopes of these reactions in organic synthesis.Iron-catalyzed aminations of azides is a current research interest in nitrene chemistry.Organic azides are commonly used nitrene precursors which have the merits of high atom economy.Iron salts can react with azides to form imido-iron（or iminyl-iron）intermediates,which can undergo nitrene transfer reactions such as cycloaddition,C-H insertion and coupling with heteroatoms.However,there are only a small number of reports concerning this topic,and more studies need to be done to fully exploit the synthetic potential of these reactions.In this thesis,we investigated the iron-catalyzed aryl migration of alkyl azides and intramolecular C-H amination of acyl azides,and the results are summarized as follows.（1）The catalytic system of FeCl₂/SIPr?HCl was applied to convert diphenyl tertiary azides to imines via 1,2-phenyl migration.One-pot reduction of the thus formed imines by Na BH₄ provides aniline products in high yield.The electronic effect of the substituent at the phenyl group affects its migrating capability.The more electron-rich the phenyl ring,the larger its migrating capacity.（2）A novel skeleton rearrangement was engendered when2-azido-N,N-dibenzamide was treated with FeCl₂/SIPr?HCl in the presence of triethylamine and water.The reaction proceeds following a pattern of 1,4-phenyl migration from the amido nitrogen to the azido nitrogen,while at the same time the phenyl ring is expanded to give an azepine ring.The key step involves cycloaddition of an iron-imido intermediate to the benzene ring.This reaction not only represents an unprecedented type of rearrangement,but also constitutes the first example of cycloaddition of benzene by alkyl azides.Moreover,it provides a new method for the activation of the benzene ring and for the synthesis of structurally important azepine derivatives.（3）The intramolecular C（sp~2）-H amination of acyl azides was explored under iron catalysis.It was found that the system of FeCl₂/i-Pr-Pybox is capable of effecting the reaction of phenyl carbonazidate,which leads to the formation of benzazolone in high yield.A variety of benzoxazolone compounds were prepared by using this method.The method can also be used to prepare benzimidazole from diphenylcarbamoyl azide.