Visible-light induced trifluoromethylation of internal olefinic C-H bonds through photoredox catalysis

An approach for direct trifluoromethylation of internal olefins of α-oxoketene dithioacetals has been achieved by using Ru(bpy)₃Cl₂as photocatalyst and Togni's reagent as trifluoromethylating agent under irradiation with visible light. Under a nitrogen atmosphere, a mixture of α-oxoketene dithioacetal (0.1 mmol), Togni's reagent (0.15 mmol), Ru(bpy)₃Cl₂(0.005 mmol), and Na₂CO₃(0.3 mmol) in DMSO (1 mL) was stirred at room temperature for 72 h under 5 W Blue LEDS, which led to the trifluoromethylated products in 40%~90% yield. This protocol provides an efficient and easy access to prepare trifluoromethylated dithioalkyl α-oxoketene acetals under mild conditions, and is highlighted by its operational simplicity and avoiding using toxic reagent. Furthermore, the gram-scale reaction of 1a suggested the potential application of this protocol in organic synthesis.