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Copper-Catalyzed Vinylogous Aerobic Oxidation of Unsaturated Compounds with Air

Zhang, Hai-Jun, Schuppe, Alexander W., Pan, Shi-Tao, Chen, Jin-Xiang, Wang, Bo-Ran, Newhouse, Timothy R., Yin, Liang
Journal of the American Chemical Society 2018 v.140 no.15 pp. 5300-5310
air, aldehydes, amides, catalysts, copper, esters, ketones, ligands, moieties, nitriles, oxidation, regioselectivity
A mild and operationally simple copper-catalyzed vinylogous aerobic oxidation of β,γ- and α,β-unsaturated esters is described. This method features good yields, broad substrate scope, excellent chemo- and regioselectivity, and good functional group tolerance. This method is additionally capable of oxidizing β,γ- and α,β-unsaturated aldehydes, ketones, amides, nitriles, and sulfones. Furthermore, the present catalytic system is suitable for bisvinylogous and trisvinylogous oxidation. Tetramethylguanidine (TMG) was found to be crucial in its role as a base, but we also speculate that it serves as a ligand to copper(II) triflate to produce the active copper(II) catalyst. Mechanistic experiments conducted suggest a plausible reaction pathway via an allylcopper(II) species. Finally, the breadth of scope and power of this methodology are demonstrated through its application to complex natural product substrates.