Green Initiation Of Iminoxyl Radical And Research On Cyclization Of Internal Alkenes And Alkynes

The cyclization reaction is one of most versatile and powerful methods for the construction of mono-and polycyclic systems,in which radical cyclization of alkenes and alkyne is an important strategy to achieve such cyclization reaction,widely used in organic synthesis.Although the carbon-centered radical cyclizations of alkenens and alkynes have been well studied,those involving O-/N-atom-centered radicals are rarely reported.Iminoxyl radicals,as a classicalσ-nitroxide,can not only cyclize with oxygen atoms,but also be capable of cyclizing with nitrogen atoms,which have recently been widely used to synthesize a series of heterocyclic compounds.Focus on the initiatation of iminoxyl radicals participating in the cyclization of intramolecular alkenes and alkynes in green,this thesis studied the oxyoximation,aminooximation and dioxidation of unactivated alkenes and the cyclization of iminoxyl radical onto alkynes for the first time to achieve trifunctionalization of the alkynes.These reactions provide an efficient and convenient method for the synthesis of a series of important isoxazoline compounds and cyclic nitrone compounds.Specific research results are summarized as follows:In chapter one,a brief introduction of the free radical,involved classification of radicals,generation of radicals,C-centered radicals,heteroatom-centered radicals,cyclization rules.And briefly summarizes the structural properties of iminoxyl radicals and their participation in the organic cyclization reaction.In chapter two,we developed a novel iminoxyl radical-involved metal-free approach to vicinal oxyoximation and aminooximation of unactivated alkenes.This method utilizes the dichotomous reactivity of the iminoxyl radical to furnish a general difunctionalization on alkenes using simple tert-butyl nitrite（TBN）as the iminoxyl radical initiator as well the carbon radical trap.By using this protocol,oxime featured 4,5-dihydroisoxazoles and cyclic nitrones were facilely prepared fromβ,γ-andγ,δ-unsaturated ketoximes,respectively.In chapter three,a novel,efficient iminoxyl radical-involved approach to synthesis isoxazoline has been achieved by NHPI catalyzed dioxygenation and ketooxygenation of alkenes of unsaturated ketoximes.This method utilized the iminoxyl radical derived from the initiation ofβ,γ-unsaturated ketoximes to provide the general difunctionalization of alkenes using simple NHPI as iminoxyl radical initrator,oxygen as carbon radical trap as well terminal oxidant.By using this protocol,a series of useful hydroxyl-and keto-featured isoxazolines were efficient prepared.In chapter four,a facile,mild and efficient dioxygen activation for the synthesis of isoxazoline/cyclic nitrone-featuredα-ketols has been achieved by Cu-catalyzed trifunctionalization of internal unactivated alkynes of unsaturated ketoximes at room temperature.¹⁸O isotope tracing and DFT calculation disclose that a cascade iminoxyl radical dichoto-mous 5-exo-dig cyclization/oxygen activation/peroxy radical 4-endo-trig cyclization process was involved in the reaction.