Divergence between Organometallic and Single-Electron Transfer Mechanisms in Copper(II)-Mediated Aerobic C–H Oxidation

Suess, A. M.; Ertem, M. Z.; Cramer, C. J.; Stahl, S. S.
J. Am. Chem. Soc. 2013, 135, 9797 (doi:10.1021/ja4026424).

Copper(II)-mediated C–H oxidation is the subject of extensive interest in synthetic chemistry, but the mechanisms of many of these reactions are poorly understood. Here, we observe different products from Cu^II-mediated oxidation of N-(8-quinolinyl)benzamide, depending on the reaction conditions. Under basic conditions, the benzamide group undergoes directed C–H methoxylation or chlorination. Under acidic conditions, the quinoline group undergoes non-directed chlorination. Experimental and computational mechanistic studies implicate an organometallic C–H activation/functionalization mechanism under the former conditions and a single-electron transfer mechanism under the latter conditions. This rare observation of divergent, condition-dependent mechanisms for oxidation of a single substrate provides a valuable foundation for understanding Cu^II-mediated C–H oxidation reactions.