Visible-light Photoredox Synthesis Of Internal Alkynes

In organic chemistry,chemists were devoted to the study of new chemical reactions and synthesis methods.Synthesis of transition metal catalyzed cross-coupling C-C,C-N,C-O,C-S bond are very important chemical reactions.These reactions had high temperature?80-135??and need suitable ligand,which lead to increased response costs.With developing of the research,the visible light catalysis has been considered as a highly activated catalyst system.Visible-light photoredox synthetic strategy was using renewable energy irradiated metal complexes or organic dyes excited single electron transfer.These reactions had mild conditions with fewer side effects and less cost savings.Internal alkyne intermediates are important building blocks,and they are widely used in synthesis of antibiotics,antimycotics,polymers,optical or electronic materials,and liquid crystals.The traditional method for synthesis of internal alkynes is through palladium/copper co-catalyzed Sonogashira couplings of terminal alkynes with aryl halides,and the corresponding C?sp²?–C?sp?bonds are constructed.The protocol shows high efficiency with tolerance of functional groups.However,diversity of the synthesized products is limited by using this strategy.In this thesis,we report visible-light photoredox decarboxylative coupling of tert-alkyl N-phthalimidoyl oxalate derivatives with 1-?2-?arylsulfonyl?ethynyl?benzenes leading to internal alkynes containing quaternary carbons,and the corresponding results are as follows:We have developed a novel and efficient method for visible-light photoredox synthesis of internal alkynes containing quaternary carbons.The protocol used[Ru?bpy?₃]Cl₂ as the visible-light catalysts,Hantzsch ester as the reductant,the readily available N-phthalimidoyl oxalates of tert-alcohols and1-?2-?arylsulfonyl?ethynyl?benzenes as the starting materials,and the reactions were performed well at room temperature with good tolerance of functional groups.Various novel internal alkynes were prepared by using the present method,but it is difficult to make them in the previous methods.The corresponding mechanism was explored well.Therefore,the development of this method enriches synthesis of internal alkynes,and we believe that it will be of wide applications in some fields.