Abstract

The Cu-I/Cu-II and Cu-I/Cu-III catalytic cycles have been subject to intense debate in the field of copper-catalyzed oxidative coupling reactions. A mechanistic study on the Cu-I/Cu-II redox process, by X-ray absorption (XAS) and electron paramagnetic resonance (EPR) spectroscopies, has elucidated the reduction mechanism of Cu-II to Cu-I by 1,3-diketone and detailed investigation revealed that the halide ion is important for the reduction process. The oxidative nature of the thereby-formed Cu-I has also been studied by XAS and EPR spectroscopy. This mechanistic information is applicable to the copper-catalyzed oxidative cyclization of beta-ketocarbonyl derivatives to dihydrofurans. This protocol provides an ideal route to highly substituted dihydrofuran rings from easily available 1,3-dicarbonyls and olefins.