Visible-Light-Mediated Photoredox Decarboxylative Couplings And Aerobic Oxidation

Visible light is a kind of widely available and environmentally friendly energy.Comparing with the traditional thermal organic reaction,visible-light-mediated organic reactions exhibit some advantages such as mild conditions,easy operation,high reactivity and good tolerance of functional groups.Decarboxylative couplings are defined as chemical ligations between carboxylic acids and their partners via leaving of carboxyl by liberation of carbon dioxide,and aerobic oxidations are oxidation reactions with oxygen as the oxidant.The two kinds of chemical reactions have been attracting much attention in organic chemical community.In this dissertation,visible-light-mediated photoredox decarboxylative couplings and aerobic oxidations were investigated,and some achievements are obtained as follows:A new method for visible-light-mediated decarboxylative couplings of?-amino acids or peptides with N-heterocycles via formation of C-C bonds has been developed.The protocol used N'-?acetoxy?phthalimide active esters of N-protected?-amino acids and peptides as the radical precursors,Ru?bpy?₃Cl₂ as the photocatalyst,and the cross-couplings between the active intermediates from decarboxylation of the N-protected?-amino acids or peptides and phenanthridine or oxindole derivatives were successfully realized under visible-light irradiation and mild conditions with good tolerance of functional groups.The mechanism investigations showed that the reaction underwent a sequential process including photoredox decarboxylation,generation and trapping of the radicals,and intramolecular cyclization.A novel,convenient,efficient and general photoredox system has been developed for visible-light-mediated thiophenol-assisted decarboxylative couplings of carboxylic acid active esters.The photocatalyst-free decarboxylative arylthiation of carboxylic acid active esters with thiophenols was firstly realized by using the system.The mechanism investigations by ¹⁵N NMR,UV-Visible absorption spectra,Stern-Volmer fluorescence quenching and other experiments showed that the complexes from N-?acetoxy?phthalimide active esters and Cs₂CO₃ acted as the photosensitizers,and thiophenols acted as the organocatalysts and substrates.Furthermore,the photocatalyst-free intermolecular decarboxylative arylation,decarboxylative addition and intramolecular decarboxylative amination were completed by using the similar strategy.Therefore,our newly developed photoredox system?carboxylic acid active esters,Cs₂CO₃ and thiophenols?provides a significant reference for future researches.A novel and highly efficient method for visible-light-mediated aerobic oxidation of N-heterocycles has been developed,and the corresponding pyridones,quinolinones and isoquinolones were sucessfully prepared.The protocol used Eosin Y as the photocatalyst and oxygen from air as the oxidant,and the aerobic oxidation of N-alkylpyridinium salts was effectively realized under irradiation of visible light at room temperature.Furthermore,4-desoxylinomide with various pharmaceutical actvities was conveniently and efficiently sysnthesized by using this strategy.The mechanism investigations indicated that the reaction underwent sequential single-electron transfer,generation of alkdioxyl radicals and radical chain process.The method affords a powerful protocol for the synthesis and activity study of pyridones,quinolinones and isoquinolones.