Metal-free visible-light-enabled vicinal trifluoromethyl dithiolation of unactivated alkenes

The difunctionalization of alkenes involving a trifluoromethylthio group (SCF3) for the conversion of versatile and readily available olefins into structurally more complex molecules has been successfully studied. However, the disproportionate dithiolation of alkenes is unknown. Herein, a transition-metal-free protocol is presented for the vicinal trifluoromethylthio–thiolation of unactivated alkenes via a radical process under mild conditions with a broad substrate scope and excellent tolerance.


I. General methods
All reactions were performed in flame-dried glassware with equipped with a magnetic stirring bar and sealed with a rubber septum. The solvents were distilled by standard methods. Reagents were obtained from commercial suppliers and were used without further purification unless otherwise noted. Silica gel column chromatography was carried out using silica gel 60 (230-400 mesh). Analytical thin layer chromatography (TLC) was done using silica gel (silica gel 60 F254). TLC plates were analyzed by exposure to ultraviolet (UV) light. NMR experiments were performed using a Bruker AVANCE III-400 or 500 spectrometer and carried out in deuterochloroform (CDCl 3 ) 1

Procedure for the synthesis of N-(trifluoromethylthio)phthalimide (3)[6]
Under argon, dried CH 3 CN (40 mL) was added to a mixture of Nbromophthalimide (5.2 g, 23 mmol), AgSCF 3 (6.25 g, 30 mmol) in a 100 mL round-bottomed flask. The mixture was stirred at room temperature for 3 h and then the solvent was evacuated under rotary evaporator. Before filtering the residue through a short plug of Celite, CH 2 Cl 2 (20 mL) was added. Then, the filter residue was evacuated again under reduced pressure to obtain the target compound as a white solid (5.3 g, 93%). N- [b] Crude yields were determined by 19 F NMR using trifluoromethoxybenzene as internal standard. [b] Crude yields were determined by 19 F NMR using trifluoromethoxybenzene as internal standard. [a] All reactions were carried out with 1a (0.1 mmol, 1 equiv), 2a, 3, K 2 HPO 4 (10 mol %), photocatalyst 4CzIPN (2 mol %) in DMSO (1.0 mL) at rt under Ar and 10 W blue LEDs.
[b] Crude yields were determined by 19 F NMR using trifluoromethoxybenzene as internal standard.

General procedure
Under argon, 4CzIPN (2 mol %) and N-(trifluoromethylthio)phthalimide (3, 1.5 equiv), 1a (0.2 mmol, 1 equiv), 2a (0.2 mmol, 1 equiv), and K 2 HPO 4 (10 mol %) were dissolved in dried DMSO (2 mL) at room temperature. After that, the tube was exposed to 10 W blue LEDs and the mixture was stirred at room temperature for about 24 h until the reaction was completed as monitored by TLC analysis. Then, the reaction solution was poured into 10 mL of water. The aqueous phase was extracted with EA (3 × 15 mL). The combined organic phases were washed with 15 mL of water and 15 mL of brine. After drying over Na 2 SO 4 and removal of the solvent in vacuo, the crude products were directly purified by flash chromatography on silica gel to give the desired product. S7

V. Mechanistic investigations
The GC-MS of the reaction mixture S8