Studies On The Photochemical Reactions Of Nitrogen-containing Substrates

N-contained compounds are widely imbedded in structures of natural products and active pharmaceuticals.Meanwhile,they also served as a kind of ligands of common metal catalysts.Due to the relative low bond energy of N-X(X = N/C/O)bonds,N-contained compounds have always been employed as a kind of important reactants in organic synthesis.Traditional strategies for activating the N-X bonds involve the pre-functionalization of substrates,the use of metal-catalysts,and the reactions often were conducted under high temperature,moisture-/oxygen-free conditions.Visible-light-induced organic reactions have attracted enormous attentions because of the advantages such as mild reaction conditions and simple operation.Previously reported visible-light-mediated reactions required tedious steps to introduce active groups into N-contained compounds to improve their reactivity,which are not incompatible with atomic economy as well.In this thesis,three types of easily prepared N-contained compounds(benzotriazoles,cyclic ketone oxime esters,sulfonyl azides)were chosen as research objects.With the aid of photocatalysts to activate N-N or N-O bonds,three different types of active N-contained intermediates were obtained,which respectively coupled with phosphites,heteroarenes and amines with high atom-/step-economy.Phosphonates,which contain C(sp2)-P bonds,were prepared by the denitrogenative coupling of benzotriazole derivatives with triphosphites under photocatalytic conditions.In this protocol,[Ir(ppy)2(dtbbpy)]PF6 was used as photocatalyst.Substrate scope screening disclosed the reaction exhibited good tolerance towards various functional groups,such as methoxyl,halogen,trifluoromethyl,amide,ester,etc.Furthermore,the utility of this protocol was successfully realized by a gram-scale reaction.Fluorescence quenching experiments suggested the reaction proceeded via a reductive quenching process.Electron spin resonance(ESR)together with the isolated N-benzoyl aniline byproduct indicated an aryl radical intermediate was generated in the reaction process.A series of β-and γ-cyano alkyl heteroaromatics were prepared from cycloketone oxime and N-heterocycles via Minisci-type reactions under mild visible light conditions.By employing cycloketone oximes as terminal alkylcyano precursors,the use of highly toxic cyanide reagents was avoided.ESR experiment suggested the reaction proceeded via a radical pathway.The radical capture experiment by TEMPO intuitively proved a sequential cleavage of N-O and C-C bonds of four-or five-membered cycloketone oximes under the action of photocatlyst and ring tension,and which could afford cyano alkyl radical intermediate via radical cascade reaction.This also provides theoretic evidence for the highly site-selective reactions of asymmetric cycloketone oximes.Under visible light conditions,the catalytic performance of naphthalene derivatives was compared systematically through the reactions of sulfonyl azides and alkyl amines.A variety of sulfonyamidines were obtained from aryl/alkyl sulfonyl azides and amines using nitroacenaphthene as photocatalyst.The products were obtained with steady yields in the catalyst-recycling experiments,which showed there was no activity decrease of catalysts.This result and the gram-scale reaction demonstrated the potential industrial application of the photocatalyst.The redox potential of the catalyst was measured by UV-vis spectra and cyclic voltammetry,together with the ESR experiment and the fluorescence quenching experiment,provided evidence for the photocatalytic redox cycle.The verification test of intermediate indicated the generation of N-vinyl-N,N-diethylamine.Mechanistic studies suggested when the alkyl of amine contained two or more than two carbon atoms,an enamine intermediate was involved in the reaction process.When one of the alkyls in amines was methyl,the reaction proceeded via an imine cation intermediate.