Visible-Light-Promoted Decarboxylative Cyclization And Alkylation Of N-Arylglycines

Visible light is an inexpensive,abundant,renewable and pollution-free energy source.In recent years,due to the unremitting efforts of scientific researchers,visible-light photocatalysis has made great breakthroughs in the field of organic synthesis and has truly developed into a practical strategy for organic synthesis.As an important building block in organic synthesis,N-aryl glycine has the advantages of inexpensive,readily available,non-toxic,and stable to air and humidity.In the photochemical reactions,amino acids can release carbon dioxide in situ to form corresponding aminomethyl radicals or imine active intermediates,and then cross-couple with various coupling reagents with high efficiency and high selectivity to construct a variety of nitrogen-containing organic compounds.The visible-light promoted decarboxylative coupling reaction of α-amino acid derivatives is a promising synthesis strategy for the preparation of nitrogenous compounds.In this thesis,the decarboxylation cyclization and alkylation reactions involving N-arylglycines were studied using photochemical synthesis strategy,mainly including:（1）Through systematic research,a new method for decarboxylative cyclization of N-aryl glycines with β-nitrostyrenes promoted by visible light was established,and a series of monosubstituted 3-arylquinolines were specifically synthesized.Using commercially available photocatalyst Ir[dF（CF₃）ppy]₂（dtbbpy）PF₆,the reactions proceeded smoothly under visible light irradiation and air conditions at room temperature.A range of N-arylglycines and β-nitrostyrenes converted into the corrspounding 3-arylquinolines in moderate to good yields.This method has the advantages of easily available raw materials,no need for additional oxidants as well as acids or bases,mild reaction conditions and simple operation,providing a novel,green and mild way for the synthesis of 3-arylquinolines.（2）Through systematic research,a new strategy for decarboxylative alkylation of N-aryl glycines with electron-deficient olefins promoted by visible light was developed.Using commercially available photocatalyst Ru（bpy）₃Cl₂,the reactions proceeded smoothly under visible light irradiation and inert gas atmosphere at room temperature,and the target products were obtained in moderate to good yields for a range of N-arylglycines and electron-deficient olefins.This method has mild reaction conditions and a short reaction time（10 min～4 h）.It is worth noting that there is a significant difference in the reaction effect of some substrates in aerobic and inert gas atmosphere.After comprehensive comparison,it was found that some substrates can afford the target product with high yield in both aerobic and anaerobic atmospheres,while some substrates that hardly react in air atmospheres can get satisfactory results in inert gas atmospheres.Through the preliminary study of the mechanism,it is speculated that the reduction potential of the free radical intermediates may be the key factor to determine the priority of the main reaction or the competitive reaction with oxygen participation.