Study Of Visible Light-induced Ketone Photosensitizers-Catalyzed Chemical Reactions

Due to the relatively high triplet energy and long triplet lifetime of the excited aromatic ketone,the aromatic ketones are efficient energy transfer sensitizers in photochemical reactions.The excited aromatic ketone also can take or give the electrons from the additional reductant or oxidant to produce free radical intermediates with higher redox activity and then transfer electrons to the substrates to complete the photocatalytic redox reaction.Besides,the excited aromatic ketones can generate radicals by extracting hydrogen atoms from hydrogen donors.Aromatic ketones are inexpensive and usually resistant to photodegradation.However,aromatic ketones in photochemical reactions are relatively underused.Moreover,most of the light used is high-energy ultraviolet or violet light,which requires that the reaction substrate has sufficient light stability and maybe be harmful to the researchers' health.Structural modification of photocatalyst for higher efficiency is important for photochemical chemists.This thesis mainly explores some unique properties of ketone compounds.After structural modifications,it can be used as an excellent photocatalyst for some visible light-excited chemical reactions and enrich the field of photochemistry.The thesis includes the following five parts:Part 1.A series of new photocatalysts based on the xanthone and thioxanthone have been synthesized,and their physical and chemical properties were investigated.We found that thioxanthone can significantly improve the reaction rate,and adding halogen and higher conjugation can also increase the reaction rate.In this chapter,the(E)-styrene derivatives are used as the substrates,and benzo thioxanthone is served as the photocatalyst,the E to Z isomerization could be obtained by the energy transfer pathway between the photocatalyst and the substrates;the Z/E ratio can be up to99%/1%.It should be noted that the aromatic ketone is not only inexpensive and accessible available but also simple in structure and non-heavy metal used.Part 2.We successfully achieved the photooxidation cycloaddition reaction to produce coumarin at room temperature using cinnamic acids or phenylpropionic acids as the substrates,xanthone as the catalyst,and Selectfluor as the oxidant.Under similar conditions with a large amount of Selectfluor,the cycloaddition reaction takes place with cinnamate as the substrate to synthesize regioselective lignin.The reaction system has good substrate tolerance in good yields(up to 91%).It is worth noting that the aromatic ketone catalyst has excellent light stability and oxidation tolerance.Part 3.We report a widely applicable photocatalytic radical generation method using a 2-chloro thioxanthone/DMAc binary catalytic system.Under the standard conditions,redox-active radical precursors can effectively generate a variety of radicals,such as alkyl(primary,secondary,and tertiary)radicals,sulfur radicals,carbonyl radicals,halogen radicals,and fluoroalkyl radicals.The method is suitable for various types of radical acceptors,such as quinoxalinones,coumarins,nitrogen-containing heterocyclic compounds,electron-deficient or electron-rich olefins,etc.Part 4.We report an effective photocatalytic decarboxylation radical addition/cyclization strategy to synthesize imidazo-isoquinolinone or indoleisoquinolinone derivatives using N-methacryloyl-2-phenylbenzimidazole or Nmethacryloyl-2-phenylindole as substrates.This strategy uses DMAc/ACN(1/30)as the solvent to inhibit the DMAc radicals generated in the reaction from reacting with the substrate.This method is suitable for alkyl radicals derived from Nhydroxyphthalimide esters and aryl radicals derived from diazonium salts.Part 5.We report an environmentally friendly and chemically selective photocatalytic method to synthesize sulfoxides and sulfones from thioethers.It is carried out by using air or oxygen as an oxidant at ambient temperature.This method uses a cheap 2-chloro thioxanthone as the photocatalyst and hexafluoro-2-propanol as the reaction solvent to give the sulfoxide compound with excellent chemical yield(up to 96%)and good functional group tolerance.Acetonitrile is used as the reaction solvent to give the sulfone compounds.