Synthesis Of Allylic Ketones And Allylic Sulfones By Photoredox/Cobalt Co-catalysis

The allyl compounds are well understood and often encountered in flavor and fragrance industries,pharmaceuticals,supra-molecular assemblies,and synthetic bioactive natural products.And for the formation of allyl compounds,high temperature,sacrificial oxidants,toxic metal reagents are usually required.However,these harsh reaction conditions will result in the stoichiometric amounts of chemical waste,low efficiency and environmental pollution.These doesn’t fit with the idea of green chemistry.Therefore,it’s important to develop a highly efficient and selective allylation reaction under mild conditions in organic synthesis.Recently,visible-light catalysis reaction as a complementary strategy has been received extensive attention by chemists.Due to the simple,mild reaction conditions and environmentally friendly character,it is gradually developing into a powerful synthesis tool and has been continuously applied in the synthesis of high value-added organic chemicals.In view of the common problems existing in the traditional allylation reactions,we try to develop a mild,green and efficient synthesis method of allyl compounds to avoid the many shortcomings caused by the harsh reaction conditions such as high temperature and high pressure,external oxidant and the use of precious metals.Therefore,we successfully achieved the preparation of allylic ketones and allylic sulfones with highly selective under mild and green reaction conditions by combining visible-light catalysis with cheap transition metal catalysis.My research results are as follows:1.Allylic ketones are the important building blocks for the synthesis of bioactive compounds in the pharmaceutical industry.Therefore,the construction of allylic ketones has attracted much attention from synthetic chemists.In this part,through the photoredox/cobaloxime co-catalysis at room temperature,degassed with nitrogen,under visible-light irradiation,we used methyl acrylate compounds as allyl source,phenyl glyoxylic acids as the source of benzoyl radicals,2,6-lutidine as the base to synthesize allylic ketones.It should be pointed out that when the cobaloxime catalyst was removed in the reaction,only the alkyl ketone 1,4-dicarbonyl compound was formed.The proposed reaction mechanisms were as follows:Under visible light catalysis,the excited*4-Cz IPN was reductively quenched by the anion ofα-keto acids,leading to a benzoyl radical with CO₂ extrusion.Benzoyl radical added to the double bond of ethyl methacrylate and generated a new alkyl radical species,which could be captured by Co（Ⅱ）to form a transient Co（Ⅲ）–C intermediate.The cleavage of Co–C and subsequentb-H elimination resulted in the final allylic ketone product and Co（Ⅲ）–H.Next,Co（Ⅲ）-H could react with protons to release H₂,thus finishing the cobalt catalytic cycle.However,in the absence of cobalt catalyst,the new alkyl radicals could be directly reduced and react with hydrogen to form the alkylation product—1,4-dicarbonyl compound.In a word,different with traditional synthesis methods,this strategy had the following advantages:simple operation,environmental-friendly,low cost and good functional group tolerance.In addition,this strategy was suitable for gram-scale reactions.2.On the basis of the above work,we try to apply similar catalytic strategies to explore the possibility of synthesizing allylic sulfones.Allylic sulfone compounds are important sulfur-containing compounds,which have good chemical and biological activity due to their allyl structure adjacent to sulfonyl group.Here,we used benzene sulfonyl hydrazine as the source of sulfonyl radical,Cs₂CO₃ as base and eosin Y as visible-light catalyst to generate sulfonyl radical at room temperature,degassed with nitrogen and under visible-light irradiation.Sulfonyl radical added to the double bond ofα-methyl styrene to generate new alkyl radicals,which were captured by Co（Ⅱ）to form a transient Co（Ⅲ）-C intermediate.Furtherb-H elimination resulted in the final allylic sulfones product.In a word,our reaction conditions of the catalytic system were green,mild,simple,efficient and without substrate pre-functionalization.