Visible Light-catalyzed Difunctionalization Of Alkynes

Alkynes belong to one of the fundamental functional groups which could be underwent diversity functionalizations due to its particular reaction activities.The molecular orbital of carbon-carbon triple bond is composed of one ? bond and two ?bonds.Therefore,the development of the functionalizations of alkynes will provide unlimited possibilities for exploring novel reactions.Up to now,significant progress has been achieved in the field of transition-metal catalyzed functionalization of alkynes such as hydroarylation,carbonarylation,carbonoxygenation,alkenylation and cyclization of alkynes.However,the existed transformations of alkynes generally suffer from poor atom-economy,heavy metal pollution,and harsh reaction conditions,etc.To address these challenges,developing green transformation of alkynes is therefore highly desirable.In these regards,visible light-mediated chemical photoredox catalysis provides a conceptually related valuable method which could enable previously inaccessible transformations under mild reaction conditions.1.Photocatalyzed Formal Carbooxygenation of Terminal AlkynesA visible light-catalyzed carbooxygenation of N-arylsulfonylamido alkynes with molecular oxygen has been developed,in which the benzothiazine ring and aldehyde unit could be synchronously assembled through an intramolecular formal carbooxygenation process.The reactive functional group of aldehyde renders this reaction highly valuable for further constructing structurally complex benzothiazines.This transformation features a visible-light-induced and metal-free carbooxygenation strategy by employing air as “oxygen” sources at room temperature.Control experiments including Stern-Volmer fluorescence quenching analysis,H/D exchange,radical trapping reaction and 18O-labelling experiments demonstrated the reaction mechanism involved in homolysis of Ph SSPh and the followed radical cyclization.2.Photocatalyzed Cycloaromatization of Vinylsilanes with ArylsulfonylazidesSilahydrocarbons are often encountered in pharmaceuticals and material chemistry.Compared with all-carbon parent compounds,Si-element generally endows the corresponding hydrocarbons with unique biological activity and physical-chemical properties,which are mainly determined by the different covalent radius and electronegativity of silicon from carbon.The photoredox-catalyzed cycloaromatization of ortho-alkynylaryl vinylsilanes and arylsulfonyl azides has been developed to furnish naphthyl-fused benzosilole skeletons via cascade S-N/C-S bond cleavages and alphasilyl radical Smiles rearrangement.These silaarenes show promising potential in luminescent materials.Based on radical trapping reactions,determination of the triplet energies of catalysts and substrates,Stern-Volmer fluorescence quenching experiment,cyclic voltammetry experiments and density functional theory(DFT)calculations,a possible mechanism involved ?-silyl radical Smiles rearrangement was proposed.3.Photocatalyzed Coupling-Cyclization of ortho-Alkynylaryl Vinyl ethers with Arylsulfonyl AzidesSulfone-containing benzofurans commonly appear as pivotal core units in many natural products and material molecules.Introducing a sulfonyl moiety into organic molecules is an important chemical process due to that a sulfone unit could leverage versatile biological activities and photophysical properties of pharmaceuticals and advanced materials.A visible light-catalyzed coupling-cyclization of vinyl ethers with arylsulfonyl azides has been explored to assemble C3-exocyclic C=C bond/C2-alkylsulfone-tethered benzofuran skeletons,in which solvent system plays a key role in leveraging different reaction pathways including carbosulfonylation and [2+2+3]cyclization.A wide scope of vinyl ethers and sulfonyl azides are well-tolerated in this coupling-cyclization with good to excellent reaction conversions.Mechanism studies demonstrated that nitrene radicals and sulfonyl radical play key roles in triggering this transformation.