Direct C-H trifluoromethylation of di- and trisubstituted alkenes by photoredox catalysis

Background: Trifluoromethylated alkene scaffolds are known as useful structural motifs in pharmaceuticals and agrochemicals as well as functional organic materials. But reported synthetic methods usually require multiple synthetic steps and/ or exhibit limitation with respect to access to tri-and tetrasubstituted CF3-alkenes. Thus development of new methodologies for facile construction of C-alkenyl-CF3 bonds is highly demanded. Results: The photoredox reaction of alkenes with 5-(trifluoromethyl)dibenzo[b,d] thiophenium tetrafluoroborate, Umemoto's reagent, as a CF3 source in the presence of [Ru(bpy)(3)](2+) catalyst (bpy = 2,2 '-bipyridine) under visible light irradiation without any additive afforded CF3-substituted alkenes via direct C-alkenyl-H trifluoromethylation. 1,1-Di-and trisubstituted alkenes were applicable to this photocatalytic system, providing the corresponding multisubstituted CF3-alkenes. In addition, use of an excess amount of the CF3 source induced double C-H trifluoromethylation to afford geminal bis(trifluoromethyl) alkenes. Conclusion: A range of multisubstituted CF3-alkenes are easily accessible by photoredox-catalyzed direct C-H trifluoromethylation of alkenes under mild reaction conditions. In particular, trifluoromethylation of triphenylethene derivatives, from which synthetically valuable tetrasubstituted CF3-alkenes are obtained, have never been reported so far. Remarkably, the present facile and straightforward protocol is extended to double trifluoromethylation of alkenes.