CdS QDs Catalyzed Photoinduced Decarboxylation Difluoroalkylation Of Cinnamic Acids

Allyl group are widely present in drug molecules,and the introduction of a fluorine-containing group into the vinylic site can significantly increase the biological activity of the parent compound,providing potential for drug molecular modification.The traditional method uses transition metal catalysis to introduce a difluoroalkyl group into the unsaturated C-C bond to construct an allyl difluoroalkyl structure,and has obtained rich research results.However,there are still some shortcomings,such as:transition metals are expensive,complicated to prepare,highly toxic,unable to be used in large-scale industrial applications,and do not conform to the concept of green chemistry.In recent years,photocatalytic reactions have attracted extensive attention due to their advantages such as green energy conservation.Therefore,it is of great significance to develop new photocatalytic introduction of difluoroalkyl groups.In this paper,we reported decarboxylative difluoroalkylation ofα,β-unsaturated carboxylic acids catalyzed by cadmium sulfide quantum dots.The paper studies the introduction of cinnamic acid and ethyl bromodifluoroacetate into the difluoroalkyl group by decarboxylation coupling.Using 4-methylcinnamic acid and ethyl bromodifluoroacetate as substrates for the model reaction,we screened the catalyst,material ratio,reaction temperature and reaction time to obtain optimal conditions.The optimization reaction condition is:0.1 mmol 4-methylcinnamic acid,0.2mmol ethyl bromodifluoroacetate,2 mol%CdS QDs,0.2 mmol BI-OH,0.2 mmol iPr₂NEt,V_DCE:V_H2O=1:1,under argon protection,the reaction was irradiated with 15 W white light at room temperature for 12 h.Based on the optimal conditions,we studied the range of substrates for the reaction.The results show that the reaction system has good adaptability to the aromatic hydrocarbon acid having a methyl group,a methoxy group,an ethoxy group,a halogen group,a boronic acid group,a cyano group and a sterically hindered tert-butyl substituent.The yield is 52%⁸0%,and the E/Z selectivity is mostly99:1.Based on the results of free radical verification experiments and previous literature,we propose a single electron transfer（SET）free radical mechanism process.Finally,we performed an amplification experiment with a yield of 45%.In summary,we have developed a new method for decarboxylative difluoroalkylation ofα,β-unsaturated carboxylic acids catalyzed by CdS QDs.The method is carried out under light at room temperature,the reaction conditions are mild,the substrate range is wide and the E/Z selectivity is good.