Photocatalytic Decarboxylative Acylation Of 2-phenylquinoxalines

Quinoxaline and its derivatives are an important class of nitrogen-containing heterocycles displaying various biologial activities including anti-cancer,anti-depressant,anti-HIV and anti-tumor activities.In addition,quinoxaline derivatives have been also applied for pesticide,dyes,electron luminescent materials,organic semiconductors and other fields.Thus,the development of the functionalizations of quinoxalines to construct quinoxaline derivatives with structural diversity will be of great significance to their application studies.In recent years,it is noteworthy that visible light photocatalysis has been applied in various organic reactions due to the environmentally benign characteristics.Photocatalytic organic reactions have been developed and become a hot spot of research in organic chemistry because of its great catalytic efficiency.Benzoylformic acid as the novel decarboxylative coupling reagent was reacted with many substrates.The decarboxylative coupling reactions provide powerful methods for the construction of C-C and C-Y?Y=N,O,P etc.?bonds with high reactivity.Therefore,the introduction of photocatalysis may provide new opportunities for the development of decarboxylative coupling reactions.Based on our previous research interest in the nitrogen-containing heterocycles,in this paper,2-phenylquinoxaline was used as the substrate,and benzoylformic acid was used as the decarboxylative acylating reagent to realize the decarboxylative acylation of 2-phenylquinoxalines via visible light photocatalysis.The effects of the solvents,additives,acylating reagents,reaction time and the photocatalyst on the reaction were discussed.The results demonstrated that the reaction proceeded smoothly in the presence of Ir?ppy?2?dtbbpy?PF6?2 mol%?with K₂S₂O₈?3 equiv?,Ag₂CO₃?20 mol%?and CH₃COOH?2 equiv?in CH₃CN/H₂O?2 m L,0.5/1.5,v/v?for 12 h at rt providing the target product in 92% yield.A series of target products were synthesized under the optimized conditions.In addition,the reaction mechanism was also explored preliminarily and a radical process was involved in the reaction.The reaction system provides a new approach to the acylation of 2-phenylquinoxalines by the photocatalystic strategy and more reaction examples for the photocatalystic organic reactions.