Studies On The Iminyl Radical-involved C-N Bond Forming Reactions

Iminyl radicals are an important type of reaction intermediates,which are useful in the synthesis of nitrogen heterocycles.This thesis describes our studies on applying the iminyl radical cyclization reactions to the synthesis of several classes of nitrogen-containing heterocyclic compounds.This thesis is composed of five chapters.In the first chapter the recent applications of iminyl radical-involved reactions in organic synthesis are reviewed along with a brief introduction of generation and general properties of iminyl radicals.The other four chapters describe our results obtained in our own study.They are summerized as follows:?1?The oxidizing system of tert-butyl hydroperoxide?TBHP?and tetrabutylammonium iodide?TBAI?was found to be capable of generating ?-?arylaminocarbonyl?iminyl radicals from ethyl 2-?N-arylcarbamoyl?-2-iminoacetates.These iminyl radicals preferably underwent intramolecular ipso-attack on the benzene ring to give azaspirocyclohexadienyl radicals,which were readily captured by molecular oxygen under an oxygen atmosphere to yield azaspirocyclohexadienones.By contrast,ethyl 2-?N-arylcarbamoyl?-2-iminoacetates were transformed into quinoxalin-2-ones in high yield through intramolecular homolytic aromatic substitution by using the oxidation system of t-BuOCl,TBAI and tetrabutylammonium chloride?TBAC?.?2?Visible light irradiation with Ru?phen?3Cl2 as photocatalyst could induce ethyl 2-?N-arylcarbamoyl?-2-chloroiminoacetates to undergo N-Cl cleavage to give ?-?aminocarbonyl?iminyl radicals.The subsequent cyclization of the thus formed iminyl radicals afforded quinoxalin-2?1H?-one products in good yield in the presence of an inorganic base such as Na2CO3.The reactions proceeded very well even without using a photocatalyst when DMF was used as the solvent.?3?The N-arylenamines could be converted to quonoxalines via tandem azidation/intramolecular C-H amination under visible light irradiation by using 1-azidyl-1,2-benziodoxole?Zhdankin's reagent?as the azidating agent.The substituents in the enamines were found to have a critical influence on the reaction: the conversion N-aryl-3-arylenamine esters to the corresponding quonoxalines proceeded well under metal-free conditions,whereas Cu?OAc?2 was required when N-aryl-3-trifluoromethyl enamine esters was used as the substrates.This method was also extended to prepare 2,3-diarylquinoxalines by using Ru?bpy?3Cl2 as photocatalyst.?4?Ethyl 2-?N-arylcarbamoyl?-2-iminoacetates were found to undergo intramolecular Friedele-Crafts cyclization to afford 3-aminooxindoles in high yield by the catalysis of an acid such as BF₃?OEt2.?-Aryl-?-azido-N-arylamides,on the other hand,were transformed to 3-arylaminooxindoles via a tandem 1,2-aryl migration-dinitrogenation and cyclization by the action of triflic acid.