Copper-Catalyzed Vinylogous Aerobic Oxidation of Unsaturated Compounds with Air.

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.