Radical fluoroalkylation of aryl alkenes with fluorinated sulfones by visible-light photoredox catalysis

Abstract

The incorporation of fluorine atoms or fluorinated moieties into organic molecules can often lead to significant changes of their physical, chemical, or biological properties. Consequently, fluorinated organic molecules are widely used in areas of pharmaceuticals, agrochemicals and materials. Traditional approaches for the incorporation of fluorinated moieties into organic molecules include nucleophilic, electrophilic, and radical pathways. Among them, radical fluoroalkylations under visible-light photoredox catalysis have attracted much attention because of the mild reaction conditions and broad functionalgroup tolerance. In our previous work, the radical fluoroalkylation of isocyanides with fluorinated sulfones as the fluoroalkyl radical precursors via Rf-SO2Ar bond cleavage has been achieved under visible-light photoredox catalysis (Rong, J. et al. Angew. Chem., Int. Ed. 2016, 55, 2743). Herein, as a logical extension of our previous research, we report the radical fluoroalkylation of aryl alkenes with fluorinated sulfones as the practical fluoroalkyl radical precursors under visible-light photoredox catalysis. Various fluoroalkyl radicals, including trifluoromethyl (CF3), difluoromethyl (HCF2), 1,1-difluoroethyl (CH3CF2) and (phenyl)difluoromethyl (PhCF2) radicals, can be incorporated into styrene derivatives via this method, delivering the oxyfluoroalkylation products in 46%~93% yields. Typical procedures for this reaction are given as follows: to a Schlenk tube were added 2-vinylnaphthalene (1a) (0.20 mmol, 30.8 mg, 1.0 equiv.), trifluoromethyl 2-benzo[d]thiazolyl sulfone (2b) (0.24 mmol, 64.1 mg, 1.2 equiv.), fac-Ir(ppy)3(2.7 mg, 0.004 mmol, 2 mol%), H2O (0.5 mL), and acetone (4.5 mL) sequentially. The resulting mixture was degassed with a freeze-pump-thaw procedure (3 times) and irradiated by a 6 W blue LED for 12 h. After the reaction completed, the mixture was extracted with Et2O and dried over anhydrous MgSO4. The organic solvent was removed under reduced pressure and the residue was purified by column chromatography on silica gel by using a 10:1 (V/V) mixture of petroleum ether/EtOAc as an eluent to provide the hydroxytrifluoromethylation product 3a (31.2 mg, 65% yield).