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 Calkenyl-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 Calkenyl-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.