Visible-Light-Driven and Nickel (II) Catalyzed Csp-S Cross Coupling to Synthesize Sulfonyl Acetylene via Sulfonylation of Brominated Alkynes

Herein, a visible-light-driven and nickel (II) catalyzed Csp-S radical cross coupling reaction to prepare sulfonyl acetylenes via phenylsulfinyl is reported. The reaction conditions are established as the combination of (PhSO2Na) (0.1 mmol, 1.0 equiv.), 2-bromoethynyl-tri(propan-2-yl)silane (0.15 mmol, 1.5 equiv.), 9-fluorenone (0.02 mmol, 0.2 equiv.), NiCl2•DME (0.02 mmol, 0.2 equiv.), dtbbpy (0.025 mmol, 0.25 equiv.) in CH3CN (2.0 mL, 0.05 M) and exposed to a 23 W white LEDs under a nitrogen atmosphere with yields up to 94%. Both substrates bearing electron-rich groups and electron-poor groups can provide desired sulfonyl acetylenes. The substrate scope evaluation demonstrates the broad compatibility of this method with various substrates. Extensive studies, including control experiments and radical scavenger experiments showed that the reaction involves radical species. 8 triazole compounds were also successfully prepared via Rh(I) catalyzed “Click Reaction” with obtained sulfonyl acetylene products. The reaction is initiated with formation of benzenesulfonyl radicals under oxidation of the excited-state photosensitizer 9-fluorenone. Simultaneously, a radical addition reaction between brominated yne and Ni (0) through oxidation addition occurs, which subsequently produces Intermediate product Int-6 via oxidation addition with benzenesulfonyl radicals. Reduction elimination of intermediate Int-6 results in the final coupling product 3a.