Study On Photocatalyzed Radical Difluoromethylation

Organic compounds containing difluoroalkyl groups have special physiological activities and physicochemical properties.They also play important roles in medicine,pesticides and advanced functional materials.α-difluoromethyl ketones are widely used as important synthetic intermediates in the pharmaceuticals.In recent years,abundant methods for the synthesis of α-difluoromethyl ketones have been developed,but these methods need strict conditions and complicated operations.In this paper,we reported the development of a novel and effective route to synthesize a-difluoromethyl ketones under photocatalytic conditions has been achieved,providing a new and simple method for the preparation of fluorinated compounds.The reaction is carried out under visible light irradiation at room temperature using aryl enol esters as the carbonyl source,difluoromethyltriphenylphosphonium bromide as the difluoromethyl source and N-methylpyrrolidone(NMP)as the reaction solvent.The reaction system requires no additional base.The conditions are mild and easy to operate.The substrates are suitable for various aryl and heteroaryl enol esters.The main research work is as follows.Optimized conditions for the reaction are investigated by using phenyl enol esters and difluoromethyltriphenylphosphonium bromide as model substrates.With the optimized conditions in hand,we investigate the generality of this radical difluoromethylation with aryl enol esters.The results show good generality and high functional group tolerance with a maximum yield of 89%(Figure 1).Subsequently,a series of fluorescence quenching experiments,competition experiments and radical trapping experiments are performed to study the possible reaction mechanism.