Studies On Visible-Light-Induction [3+2] Oxidative Cyclization Of Ketene Dithioacetals And Alkynes

In recent years,visible light promoted transformations have flourished in the fields of organic chemistry and materials chemistry.Visible-light-induced redox reactions can usually be carried out under very mild conditions,providing clean,cheap energy and a green catalytic system for organic synthesis.With the aid of photosensitizers,the substrates could be easily activated to active radical cations without additional oxidants.Visible light-induced free radical-type organic chemical conversion has broad research prospects.Functionalized ketene dithioacetals is an important class of organic synthons.The double bond is highly polarized due to the push-pull electronic effect of the attached alkylthio group and the electron withdrawing group.The unique structure characteristics of ketene dithioacetals and its easy preparation advantages make it widely used in the fields of organic synthesis,medicine,pesticides,materials,especially in the synthesis of heterocyclic compounds.Literature research shows that there are few examples of radical cation reactions of ketene dithioacetals,and only a few of them are carried out via radical cationic intermediates under electrochemical conditions.This thesis studies a visible light-induced [3+2] oxidative cyclization reaction with ketene dithioacetals acted as a novel thiovinyl 1,3-dipole via radical cationic intermediates.A series of poly-substituted thiophenes were prepared regioselectively with up to 98% yields.It was known that thiophene and its derivatives are significant five-membered heterocyclic compounds,and are the key structural units commonly found in natural products and medicines.Herein,under the induction of visible light,the reaction proceeded under very mild transition metal-free conditions without the use of acids,bases or additional oxidants.A variety of poly-substituted thiophenes can be obtained efficiently and in high yields,providing a novel,green synthetic strategy for the synthesis of poly-substituted thiophenes.This reaction is readily extended to a gram-scale production and can be applied to the modification of alkynyl-containing natural products and the synthesis of fused thiophenes.The detailed mechanism studies clarified that ketene dithioacetals is a practical thiovinyl1,3-dipole,which is expected to be widely used in the synthesis of various important heterocyclic compounds.