Covalent Organic Frameworks Catalyzed Visible-Light-Driven Three-Component Reactions For The Synthesis Of Trifluoroalkyl And Trifluoroalkenyl Quinoxalin-2(1H)-One Derivatives

Visible-light-driven multicomponent reaction aims to use visible light energy to drive three or more reactants to form a single complex product in one step.Due to its capabilities in applying renewable energy,step economy,simplicity,and reaction efficiency,it has been a powerful tool for synthesizing high-value-added organic molecules.Photoactive covalent organic frameworks(COFs)possess extended π-conjugated frameworks and excellent visible-light absorption,exhibiting a bright application future in photochemistry.Moreover,distinguished from other photocatalysts,they offer an enticing alternative because of their high stability,considerable BET surface area,and expediently adjustable photoelectric properties.Photoactive COF has become a novel heterogeneous photocatalyst for visible-light-driven organic transformations.In this thesis,based on the intensive investigation of visible-light-driven three-component reactions and the successful synthesis of photoactive 2D-COFs,we have developed a sustainable and practical protocol for applying a photoactive 2D-COF(2D-COF-5)into the visible-lightdriven three-component C3 trifluoroalkylation and trifluoroalkenylation of quinoxalin-2(1H)-one derivatives.A wide range of C3 trifluoroalkyl and trifluoroalkenyl quinoxalin-2(1H)-one derivatives were produced in satisfied yields.The excellent stability and photoactivity of 2D-COF-5 allow for the easy recycling of photocatalysts and the efficient synthesis of target molecules on a gram scale.The reaction mechanism and the stability of 2D-COF-5 in organic reactions were also investigated.The main contents are summarized as follows:(1)According to the previously reported procedure,a covalent organic framework(2D-COF-5)was successfully synthesized with [2,2’-bipyridine]-5,5’-dicarbaldehyde and 4,4’,4’’,4’’’-(1,9-dihydropyrene-1,3,6,8-tetrayl)tetraaniline via the solvothermal reaction.Its structure and micro appearance were characterized,and its photoactivity and stability were evaluated.The results show that it is capable of serving as a heterogeneous photocatalyst for visible-light-driven organic transformations.(2)2D-COF-5 was then applied into the visible-light-driven three-component C3 trifluoroalkylation and trifluoroalkenylation of quinoxalin-2(1H)-one derivatives.With the optimal reaction conditions,diverse C3 trifluoroalkyl and trifluoroalkenyl quinoxalin-2(1H)-one derivatives were obtained efficiently.This reaction features the application of visible light,good functional group tolerance,external stoichiometric oxidant-free,and excellent step economy.(3)The photocatalyst was easily recycled in multi-runs because of the inherent heterogeneous nature and excellent stability of 2D-COF-5.The model reaction was conducted on a gram-scale,delivering the target molecule in good yield.We then compared the structure and micro appearance of the 2D-COF-5 in recycling,and the results confirmed that its structure and photoactivity were maintained in the recycling.(4)Based on the above results,the existing state of oxygen in the air and its reaction mode with photocatalyst was investigated by the radical-capture experiment.Then the relationship between different substrates and reaction yields was disclosed by several control experiments.Finally,a possible mechanism for this three-component reaction was proposed.