Visible-light-driven Amination Of Alkenes For The Synthesis Of Nitrogen-containing Heterocycles

Olefins are not only bulk chemicals in chemical industry but also essential building blocks in organic synthesis.The olefin functionalization provides a simple convenient means for the construction of structurally useful organic frameworks from relatively simple starting materials.Nitrogen-containing heterocycles constitute important scaffolds that are ubiquitous in natural products,medicines,agrochemicals and polymer materials.Olefin amination reactions are highly valuable for the preparation of nitrogen-containing compounds and nitrogen heterocycles,and this methodology can be effectively implemented by taking advantage of the high reactivity of nitrogen-centered radicals to enable C-N bond formation that may be difficult with other types of reactions.Important progress has been made recently on radical olefin amination reactions as a result of wide applications of photoredox catalysis,which not only enables the generation of N-radicals under mild from readily accessible precursors,but also greatly facilitates radical transformations via efficient redox catalytic cycle.This dissertation deals with on construction of heterocylces via visible-light-driven radical amination reactions of alkenes with secondary alkyl amines and amidopyridinium salts as nitrogen radical precursors,and the content is divided into the following four parts:In chapter 1,we briefly described the basic properties of aminium radicals and amidyl radicals,and summarized the research progress of C-H amination and addition reaction of alkenes involving aminium radicals and amidyl radicals.Chapter 2 to Chapter 4 described research work conducted during the Ph.D study.They are summarized as follows.(1)A visible-light-induced amination/cyclization of aryl acrylamides with commonly used secondary alkyl amine as aminium radical precursors was developed.In this reaction,the aminium radicals were generated by a two-step sequence which involves the in-situ N-chlorination of secondary alkyl amines with assistance of NCS(N-chlorosuccinimide)and subsequent reductive N-Cl cleavage under visible-light irradiation.This method provides a convenient access to aminated oxindoles.(2)New aryl,heteroaryl and alkyl amidyl pyridinium salts were prepared and used as primary amidyl radical precursors to affect the radical alkene amination reactions for the construction of amidated oxindoles.The pyridinium salts were converted to the corresponding amidyl radicals via N-N bond cleavage by photoredox catalysis.Trapping of the amidyl radicals by arylacrylamides,followed by intramolecular arylation delivered C-3 amidated oxindole successfully.(3)Visible-light-driven annulation reactions of benzoamidyl radicals with alkenes were investigated by using benzoamidyl pyridinium salts as the amidyl radical precursors.Two distinct annulations were realized depending on the nature of alkenes.When vinyl arenes were reacted with benzoamidyl pyridinium salts,the [3+2] annulation products were generated in good yield;when alkyl-substituted akenes were used as the substrates,on the other hand,the reaction proceeded following a pattern of formal [4+2] cycloaddition.The reactions are potentially useful for the preparation of oxazolines and dihydroisoquinolinone compounds.The reaction mechanisms and the key factors determining the reaction patterns of alkenes were elucidated by experiments and theoretical calculations.