Application Of Gem-difluoroolefin In The Synthesis Of Heterocyclic Compounds

Owing to their unique physical and chemical properties,fluorine containing compounds have been widely used in different areas such as medicine,pesticides,energy,dyes,materials.Therefore,revealing and application new modes of reactivity of organofluorine compounds has been actively sought after in modern organic synthesis.The gem-difluoroalkenes is a class of versatile intermediate with unique molecular structure.In this dissertation,we have conducted research on the syntheses and applications of fluorinated oximes and fluorinated hydrazines that are derived from gem-difluoroalkenes.The main contents are as the following:First,we have developed a new method for the synthesis of 1,2,4,5-tetrazine compounds from gem-difluoroalkene and hydrazine hydrates.Different from the existing methodologies that utilize [4+2] cycloaddition,this method proceeds via a formal [3+3] cycloaddition reaction.As only air was used as the oxidant,this method could be viewed as a green one for the synthesis of both symmetric and asymmetric 1,2,3,4,-tetrazines.The NMR experiments conducted provided solid proof that the fluorinated hydrazine is the key intermediate in this transformation.Second,we have also developed a new method for the synthesis of nitrile oxides based on the in-situ generation of fluorinated oximes using gem-difluoroalkenes.Control and NMR experiments indicated that the reaction proceeds via the following sequence: addition of hydroxylamine followed by elimination of the first fluorine yields the fluorinated oxime,elimination the second fluorine then form the nitrile oxide.In this work,we have proved for the first time that fluorine atom could be used as the leaving group for the synthesis of nitrile oxides.The work carried out in this dissertation provides valuable information regarding the stability and reactivity of a C-F bond on a C=N and should be useful for those who work this area.