Investigation On Transition Metal-Catalyzed Alkyne Transformation For The Synthesis Of Sulfur/Selenium-Containing Compounds

Alkynes are compounds with unsaturated carbon-carbon triple bonds,which are important precursors of organic synthesis.They can participate in a variety of chemical transformations to construct diverse organic compounds.On the other hand,transition metal-catalyzed reactions involving alkynes have been an important field of organic synthesis,which provides an important strategy for the preparation of complex organic molecules with advantages of mild reaction conditions,high catalytic efficiency and good functional group tolerance.Both sulfur and selenium are chalcogen elements,and they are in the VIA group of the periodic table and have similar chemical properties.Sulfur/selenium-containing compounds including thiophenes,thiazoles,thiochromones,thiols,sulfones,sulfonamides,selenophenes,benzoselenophenes and selenoamides,are widely applied in the fields of pharmaceuticals,pesticides,new organic photoelectric materials etc.In view of the great utility and enormous potential of sulfur/selenium-containing compounds,the synthesis and transformation of sulfur/selenium-containing compounds have always attracted the attention of chemists.In this regard,it is of vital importance and practical significance to explore more methods for the construction of sulfur/selenium-containing compounds through transition metal catalysis.Based on our long-term interest in the transformations of alkynes through transition metal catalysis,we have developed novel strategies for the efficient and selective construction of sulfur/selenium-containing compounds with the participation of alkynes under palladium or copper catalysis.The details are as follows:(i)A novel copper-catalyzed intermolecular[2+2+1]coupling cyclization reaction with two terminal alkynes and selenium for the synthesis of 2,5-disubstituted selenophenes has been developed.One C(sp~2)-C(sp~2)bond and two C(sp~2)-Se bonds are formed simultaneously with available terminal alkynes and non-toxic,odorless and stable selenium by using inexpensive copper as catalyst.Terminal aromatic alkynes,terminal aliphatic alkynes and terminal heterocyclic alkynes are all compatible with the transformation to construct diversified selenophene,which shows broad substrate scope and good functional group tolerance of the reaction.(ii)A palladium-catalyzed regio-and stereoselective three-component cascade reaction of alkynyl sulfones,alkenes and metal chloride under mild reaction conditions for the synthesis of(E)-(β)-chloro-tetrasubstituted vinyl sulfone via chloroalkylation of alkyne.The reaction features broad substrate scope and good functional group tolerance.A wide range of alkenes are compatible with this reaction,including acrylic ester,styrene,acrylamide and acrylonitrile.The method can be scaled up to gram scale,which are beneficial for the further decorations of the desired products.