| The exploration of environmentally-benign,energy-saving,and operationally-safe chemical process plays a prominent role in modern green chemistry.The past decade has witnessed a great development of visible-light photoredox catalysis,and so far it has become a powerful tool in organic synthesis.Radicals or radical ions,which are highly reactive species,could be generated via single-electron transfer in visible-light photoredox catalyzed reactions under mild conditions.This dissertation aims at designing enviromentally-benign photocatalytic reaction routes,reducing the amount of hazardous materials or reagents,and developing operationally-simple,effecient,and sustainable photocatalytic system for valuable transformations to meet the standards of green chemistry.Firstly,the photoredox catalyzed difunctionalization of alkenes or alkynes was researched under aerobic conditions.Radicals generated by photoredox catalysis undergo radical addition to unsaturated carbon-carbon bonds to form new C-centered radicals,which are then oxydated into carbonyl.?-Functionalized carbonyl derivatives are obtained as the products.Based on this mechanism,the reaction of aryl alkene in the oxygen with aryl diazonium salt as the aryl radical precursor was explored.The reaction proceeded smoothly and led to 1,2-diarylated ethanone as the product with the yield up to 90%.Then,the reaction of alkyne was also tested.P-centered radical was generated via single-electron oxidation,and was then reacted with alkyne and oxygen to give ?-ketophosphine oxide with the yield ranging from 64%to 94%.Only 0.5 mol%rhodamine B,an organic dye,was utilized as the photocatalyst.Next,photoredox catalyzed trifluoromethylation and trifluoromethylthiolation with inexpensive and shelf-stable fluorochemicals were studied.The single-electron reduction of CF3SO2Cl by the excited state of photocatalyst would produce trifluoromethyl radical,which is highly reactive for trifluoromethylation.Aryl alkynoates underwent visible-light-mediated trifluoromethylation with trifluoromethyl radical,5-exo cyclization,and 1,2-ester migration to give trifluoromethylated coumarines.The photoreaction conducted on a gram scale obtained the desired product in 72%yield,demonstrating the preparative utility of this chemistry.The photocatalytic trfluoromethylthiolation was further studied.CF3SCl,generated in situ by the reaction of CF3SO2Na,triphenylphosphine,and N-chlorophthalimide,could be reduced to trifluoromethylthio radical via SET and reacted with indoles to yield the C-3 trifluoromethylated products.Eosin Y was employed as the photocatalyst and gave up to 93%yield in 6 h.Finally,photoredox catalysis conducted in solely water was researched.A transition-metal-free aqueous photocatalytic system was developed using Triton X-100 as the surfactant and eosin B,an organic dye,as the photocatalyst.Both are commercially available and cheap.The photocatalytic arylation of heteroarenes and enol acetates with anilines nitrosated in situ,along with[4+2]benzannulation could all be enabled by this system at room temperature without any organic solvents or additives within 2-3 h.An amphiphile-attached photocatalyst was designed that undergoes self-aggregation in water into nanomicelles.These nanoparticles provide not only the source of the photocatalyst,but also the lipophilic cores of tailor-made micellar arrays for Ir-based photoredox catalysis to take place.Sulfonylation of both alkenes and enol acetates with sulfonyl chlorides could be enabled by this system.Both the aqueous medium and the precious metal catalyst could be recycled several times without removal from the reaction vessel,resulting in a net usage of iridium at the ppm level.The photocatalytic difunctionalization of alkenes or alkynes under aroebic conditions,the photoredox catalyzed trifluomethylation and trifluoromethylthiolation,photoredox catalysis in water were discosed.These results establish the foundation for developing environmental-benign,energy-saving and sustainable photoredox catalytic system. |
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