Visible-Light- and Oxygen-Promoted Direct Csp2-H Radical Difluoromethylation of Coumarins and Antifungal Activities.

An efficient general method using a clean and transition-metal-free photochemical strategy for the direct Csp2-H radical difluoromethylation of coumarins with HCF2SO2Na was developed. The visible-light-promoted strategy proceeds with 5 mol % Eosin Y under mild reaction conditions and showed excellent functional group compatibility. The control experiments illustrated that O2•- participated in this process and plays an important role in the reactions. Moreover, the representative products exhibited excellent antifungal activities in vitro. It was noted that the EC50 value of compound 3a was determined to be as low as 1.5463 μg/mL against Rhizoctorzia solani, which was better than Boscalid (EC50 = 2.9767 μg/mL).