Visible Light Photoredox Catalyzed Deoxygenative Functionalization Of Carboxylic Acids

Visible light is safe,inexpensive,abundant,renewable natural resource.Using visible light as an energy source,the photoredox catalysts exhibit special catalytic performance,which has injected new vitality into organic synthetic chemistry.In the past few years,visible light photoredox catalysis has been greatly developed,and a series of novel and valuable chemical reactions have been gradually developed.Mild reaction conditions and extensive substrate scope make visible light photoredox catalysis more and more popular among chemists.Using photoredox catalysts,sustainable light energy is converted into chemical energy.The reaction substrate is activated by single electron transfer or energy transfer to form high activity reaction intermediates such as free radicals,radical ions,and triplet substrates,which are involved in subsequent transformation.Visible light photoredox catalysis have become effective methods for constructing carbon-carbon and carbon-heteroatom bonds.Carboxylic acids are inexpensive,readily available,and abundant starting materials.Further functionalization of carboxylic acids is of great value in synthetic applications.However,at present,the activation mode for carboxylic acid via photoredox catalysis is still very simple,which also limits the substrate scope and reaction type.Acyl radicals are also important organic intermediates in organic synthesis.However,there are few studies on acyl radicals compared to alkyl radicals.The method of generating acyl free radicals is also very limited.It is of great significance to further explore different types of acyl radical reactions by developing various photocatalytic modes and introducing new catalytic concepts.Part Ⅰ:A hydroacylation reaction of alkenes has been achieved employing readily available carboxylic acids as acyl sources and hydrosilanes as a hydrogen source via photoredox catalysis.The combination of both single electron transfer and hydrogen-atom transfer steps has dramatically expanded new applications of carboxylic acids in organic synthesis.Part Ⅱ:The direct reduction of carboxylic acids to aldehydes with hydrosilane was acthieved through visible light photoredox catalysis.The combination of both single electron transfer and hydrogen atom transfer steps offer a novel and convenient approach to selective reduction of carboxylic acids to aldehydes.The method also features mild conditions,high yields,broad substrate scope,and good functional group tolerance,such as alkyne,ester,ketone,amide and amine groups.Part Ⅲ:We achieved the first direct deoxygenative ketone synthesis in aqueous solutioin from readily available aromatic car’boxylic acids and alkenes,affording a wide array of structurally diverse ketones in moderate to good yields.The sustainable visible-light photoredox catalysis used enables direct deoxygenation of acids as an acyl source with triphenylphosphine and represents a new conceptual perspective on activation.Part Ⅳ:We report a general,practical and scalable means of preparing deuterated aldehydes from aromatic and aliphatic carboxylic acids with D2O as an inexpensive deuterium source.The use of Ph3P as an O-atom transfer reagent can facilitate the deoxygenation of aromatic acids while Ph2POEt is a better O-atom transfer reagent for aliphatic acids.Highly precise deoxygcnation of complex carboxylic acids allows this protocol promising for late-stage deoxygenative deuteration of natural product derivatives and pharmaceutical chemicals.