Studies On Visible-light-promoted Eosin Y Catalyzed Pinacol Coupling Of α-keto Esters And Hydrosilylation Of Carbon-Carbon Unsaturated Bonds

In recent decade,visible-light-driven photochemical reactions are experencing an unprecedented period of rapid development.The core mechanism of these reactions is highly depended on proper photo catalysts,which can be excited to an excited state by visible light irradiation.The resulting highly reactive chemical species further induce the conversion of the substrates to free radical intermediates through exchanging electrons or energy with the substrates and initiate the chemical reactions.The commonly used visible light photo catalysts,which have been reported so far,can be classified into two categories,transition metal catalysts and organic catalysts.The former,such as[Ru(bpy)3]Cl2,has been widely used and showed excellent catalytic performance.However,these catalysts are mostly bipyridyl complexes with heavy metals(such as Ru,Ir,etc.)as their central atoms,exhibiting the disadvantages of high cost and potential toxicity,and therefore greatly limit their industrialization.In contrast,organic photo catalysts,which are cheap,easy to obtain,low or even none-toxic,are more favorable for a practical process.Eosin Y,for example,is currently used in various types of visible-light-promoted reactions and exhibits excellent catalytic properties.Its catalytic performance is comparable to[Ru(bpy)3]Cl2,but is over one-hundred times cheaper.Furthermore,Eosin Y,which has been widely applied as a pigment intocosmetics,also exhibits low or none-toxicity.Based on these advantages of Eosin Y,our group wishs to explore several new visible-light-promoted reactions and further develop more efficient and practically useful synthetic methods.The main contents of this Ph.D.thesis include:Using organic dye Eosin Y as the photo catalyst,we successfully developed a method for preparing 2,3-dialkyl tartaric acid derivatives through the visible-light-promoted pinacol coupling of a-keto esters,and a visible-light-promoted metal-free hydrosilylation reaction of alkenes and alkynes.The visible-light-promoted pinacol coupling:We successfully prepared a variety of 2,3-dialkyl tartaric acid derivatives through the newly developed visible-light-promoted pinacol coupling reaction.With the relevant control experiments,it is proposed that the ketyl radical might be generated by a mechanism of proton cooperative electron transfer(PCET).The representative compounds could be prepared by gram-scale reactions,and the optically pure enantiomers were prepared by classic chirality resolution.The visible-light-promoted hydrosilylation of alkenes:A novel visible light-promoted hydrosilylation reaction of alkenes has been studied and developed.Meanwhile,the compatibility of olefins with different types of substitutions and electronic effects on the reactions were investigated,as well as the regio-selectivity of complex olefin substrates.Finally,this method was applied and examined in the structural modification of several natural products and drug molecules.The visible-light-promoted hydrosilylation of alkynes:A new entrance has been discovered to generate silicon radicals for hydrosilylation of alkynes.The evidences of relevant control and mechanistic experiments indicate that the reaction is initiated preferentially by a single electron transfer(SET)between hydrosilane and excited Eosin Y,and a photoredox mechanism is preferred.The corresponding alkenylsilanes were provided with high regio-and stereo-selectivities in the reactions of various terminal and internal alkynes.The above visible-light-promoted reactions are novel,high efficient and good functional group tolerant by using cheaply available organic photo catalysts.Simple and convenient experimental operation also shows great practical application value and high industrialization potential.