Application Of COFs In Photoinduced C-Arylation And Construction Of A Nitrogen-Sulfur Bond

Covalent organic framworks(COFs)is a new crystalline material with ordered porous structure formed by reversible polymerization of C,O,N and other light elements through covalent bond and thermodynamic control.In recent years,it has been widely reported for its applications in gas storage and separation,polyphase catalysis,energy storage materials and photoelectric materials.Currently,the application of COFs materials in the field of photocatalytic synthesis mainly focuses on some simple redox reactions,so it is of great significance to develop the application of COFs in other chemical reactions.Herein,carbon arylation and N-S bond oxidation were studied by using two-dimension covalent organic frame material(2D-COFs)as heterogeneous photosensitizer under visible light promotion.The main research results are as follows:(1)A series of 1,3-dicarbonyl compounds were synthesized by using 2D-COFs as photosensitive agent and using aryl halides and 1,3-dicarbonyl compounds as substrates under transition-metal-free and visible light promoted conditions.At the same time,a photoinduced single electron transfer mechanism is proposed,which is different from the double electron transfer mechanism using transition metals(such as Pd,Ni,Cu,etc.)to catalyze carbon arylation by oxidative addition and reductive elimination.(2)Base on the study of photoinduced Hurtley reaction above,the isocoumarin derivatives were synthesized by using o-halobenzoamide and 1,3-dicarbonyl compounds at room temperature,under transition-metal-free and visible light promoted conditions.The Hurtley couplinged product was first produced,and then the target product was synthesized by retro-Claisen deacylation and an intramolecular lactonization with loss of an amine.This method avoids use transition-metal.The reaction mechanism is a free radical mechanism of single electron transfer(3)Under 2D-COFs-sensitized,visible light promoted and transition-metal-free conditions,with o-halobenzoic acid and terminal alkynes as substrates,through the electrophile addition of carboxyl and alkynes and the selective synthesis of 3-phenyl isocummarin compounds by the Heck reaction inside the molecule.This method presents a new reaction process,so it has excellent regional selectivity and avoids the generation of five-membered ring by-products.(4)Employing a two-dimensional covalent organic framework as the reusable solar photosensitizer,the sunlight-driven aerobic oxidative construction of a nitrogen-sulfur bond has been achieved.3,5 Disubstituted 1,2,4-thiadiazoles are smoothly prepared in water by using this procedure.Furthermore,a radical mechanism with a sunlight-promoted single electron transfer(SET)process is proposed for this transformation.