Mechanism Of Electrophilic Reaction With Hypervalent Iodine Reagent And Theoretical Study Based On Nitrogen Heterocycle Control

Hypervalent iodine(III)reagents have been developed as very important and useful reagents in organic chemistry due to mild reaction conditions and green chemistry properties,and have been used in various reactions such as oxidation,cyclization,halogenation,and atom transfer reactions.Although hypervalent iodine(III)reagents have obtained certain achievements in the application,some important reaction mechanisms are still unclear,such as electrophilic fluorocyclization.At the same time,the strong oxidizing properties and high Lewis acidity of hypervalent iodine(III)reagents have been recognized,but the research on its participation in the reaction as a Lewis acid,regulation of structural characteristics and structure-activity relationship is still in its infancy.Therefore,this thesis focuses on the mechanism of electrophilic fluorocyclization of hypervalent iodine(III)reagents and the theoretical research on the regulation of electrophilic reactivity,which mainly includes the following two parts:(1)The selective electrophilic fluorocyclization of unsaturated carboxylic acids and unsaturated alcohols promoted by hypervalent iodine(III)reagents was revealed by DFT calculations to systematically compare the previously proposed mechanism of“fluorination first and cyclization later”.The results indicated that two substrates undergo different reaction mechanisms.Unsaturated carboxylic acids complete the fluorocyclization undergo the“cyclization first and fluorination later”mechanism,while unsaturated alcohols complete the fluorocyclization undergo the“fluorination first and cyclization later”mechanism.In further study,the effect of the acidity coefficient of the substrate was explained and a linear relationship between the acidity coefficient and the relative free energy of cyclization was confirmed.It is expected to provide effective research ideas on fluorocyclization reactions and electrophilic reactions mediated by hypervalent iodine(III)reagents.(2)Combining common nitrogen heterocyclic structures and cyclic aryliodonium salt structures,121 dicationic iodonium salts containing nitrogen heterocycles were designed.The ³¹P NMR chemical shifts of these structures in acetonitrile were systematically established by theoretical calculations,and the relative Lewis acidity scale was derived.The effects of N-heterocyclic substituents on the Natural population analysis(NPA)charge of the iodine atom,changes in molecular surface electrostatic potential,and the interaction between iodine and N-heterocyclic substituents were analyzed using the NBO(Natural Bond Orbital)method.Three rules are summarized:(a)the larger the chemical shift value,the greater the degree of polarization within the structure,and the more positive the NPA charge of iodine;(b)The larger the chemical shift value,the more concentrated the positive electrostatic potential is on the“?holes”which on both sides of the iodine atom.Otherwise the positive electrostatic potential is concentrated on the N-heterocyclic substituents;(c)The linear relationship between the energy value and the chemical shift value of the main interaction between the iodine(III)center and the N-heterocyclic substituent proves that the N-heterocyclic The stronger the interaction that exists between the ring substituent and the iodine(III)center,the greater the Lewis acidity will result.This is expected to provide an effective quantitative theoretical reference and new research ideas for design and synthesis of hypervalent iodine(III)reagents with high Lewis acidity.