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Transition-Metal-Free C–C, C–O, and C–N Cross-Couplings Enabled by Light

Liu, Wenbo, Li, Jianbin, Querard, Pierre, Li, Chao-Jun
Journal of the American Chemical Society 2019 v.141 no.16 pp. 6755-6764
Lewis acids, acetone, air, alcohols, bromides, catalysts, cations, chemical bonding, fluorescence emission spectroscopy, ligands, nitriles, organoiodine compounds, potassium
Transition-metal-catalyzed cross-couplings to construct C–C, C–O, and C–N bonds have revolutionized chemical science. Despite great achievements, these metal catalysts also raise certain issues including their high cost, requirement of specialized ligands, sensitivity to air and moisture, and so-called “transition-metal-residue issue”. Complementary strategy, which does not rely on the well-established oxidative addition, transmetalation, and reductive elimination mechanistic paradigm, would potentially eliminate all of these metal-related issues. Herein, we show that aryl triflates can be coupled with potassium aryl trifluoroborates, aliphatic alcohols, and nitriles without the assistance of metal catalysts empowered by photoenergy. Control experiments reveal that among all common aryl electrophiles only aryl triflates are competent in these couplings whereas aryl iodides and bromides cannot serve as the coupling partners. DFT calculation reveals that once converted to the aryl radical cation, aryl triflate would be more favorable to ipso substitution. Fluorescence spectroscopy and cyclic voltammetry investigations suggest that the interaction between excited acetone and aryl triflate is essential to these couplings. The results in this report are anticipated to provide new opportunities to perform cross-couplings.