Visible Light Photoredox Catalyzed Fluoalklation And C-H Functionalization Of Aldehyde Hydrazones

Visible light photoredox catalysis,which relies the single electron transfer between excited photocatalyst and substrate,can realize the conversion of light energy to chemical energy.Most photoredox reactions proceed under room temperature and light source is typically household light bulb,LEDS or sunlight.In addition,the photocatalyst is often employed at low loadings(less than 1.0 mol%).In general,visible light photoredox catalysis already become a green,efficient and low energy consumption synthetic strategy and will promote the development of clean chemical industry.Organic fluorine chemistry has become a hot research area due to the wide application of fluorine compounds in medicine,materials and other fields.The core research project in this field is the development of mild and efficient methodology for the introduction of fluorine group into taget compounds.We successfully developed a series of visible light photoredox catalyzed trifluormethylation and difluoroalkylation reactions under mild conditions.Aldehyde hydrazone is a category of important compound which is easily synthesized from aldehyde and hydrazine and has found a wide application in organic chemisty.We aim to develop new methods for the synthesis of functionalized hydrazones.By amine radical polar crossover strategy and directing group strategy,we realized the photoredox-neutral difluoroalkylation,oxidative phosphonation of aldehyde hydrazones and Rh(?)catalyzed oxidative double C-H cross coupling.Part ?:We developed the first visible-light photoredox catalyzed carbotrifluoromethylation of alkenes with Togni reagent as CF3 source.The easily available arylacryamides can undergo a cascade radical addition/cyclization,providing a variety of CF3-containing quaternary oxindoles.Part ?:We realized the visible-light-induced decarboxylative trifluoromethylation of?,?-unsaturated carboxylic acids.Corresponding trifluoromethylated alkenes were obtained in moderate to high yields with excellent functional group tolerance at ambient temperature.Preliminary mechanistic analyses suggest this novel reaction proceeds with a novel radical-type mechanism.Part ?:We developed the carbofluoroalkylation of allylic alcohols through visible light promoted radical 1,2-aryl migration.It provides an efficient method for the synthesis of functionalized difluoro 1,5-dicarbonyl compounds and ?-trifluoromethyl ketones.Part ?:We developed the visible-light photoredox-catalyzed C-H difluoroalkylation of aldehyde hydrazone for the first time.This reaction comprises a new way to synthesize substituted hydrazone.The salient features of this reaction include extremely mild conditions,wide substrate scope and one pot synthesis.Mechanistic analysis and theoretical calculations indicate this reaction is enabled by a novel aminyl radical-polar crossover mechanism,with aminyl radical being oxidized into corresponding aminy cation through a single electron transfer(SET)process.Part V:We demonstrated a practical procedure for the C-H bond phosphonation of aldehyde N,N-dialkylhydrazones.It provides a novel approach to the synthesis of functionalized a-iminophosphine oxides.In addition,this reaction offers a new protocol for C-P bond formation which is based on the aminyl radical-polar crossover process.Part VI:Intramolecular directing group strategy has been successfully applied in the C(aldehyde)-H functionalization of aldehyde hydrazones for the first time.The highly functionaiized 1H-indazoles could be directly accessed via the Rh(?)-catalyzed oxidative C-H/C-H cross coupling.Mechanism experiments and DFT calculations suggest the distinctive Rh(III)-catalyzed C-H/C-H cross coupling reaction undergo a cascade C(aryl)-H bond metalation,C(aldhyde)-H bond insertion and reductive eliminlation process.