Evidence of Cu super(I)/Cu super(II) Redox Process by X-ray Absorption and EPR Spectroscopy: Direct Synthesis of Dihydrofurans from beta -Ketocarbonyl Derivatives and Olefins

• Published in: Chemistry : a European journal Vol. 21; no. 52; pp. 18925 - 18929
• Main Authors: Yi, Hong, Liao, Zhixiong, Zhang, Guanghui, Zhang, Guoting, Fan, Chao, Zhang, Xu, Bunel, Emilio E, Pao, Chih-Wen, Lee, Jyh-Fu, Lei, Aiwen
• Format: Journal Article
• Language: English
• Published: 01.12.2015
• Subjects: Absorption; Derivatives; Electron paramagnetic resonance; Olefins; Peroxides; Reduction; Spectroscopy; X-rays
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201503822

The Cu super(I)/Cu super(II) and Cu super(I)/Cu super(III) catalytic cycles have been subject to intense debate in the field of copper-catalyzed oxidative coupling reactions. A mechanistic study on the Cu super(I)/Cu super(II) redox process, by X-ray absorption (XAS) and electron paramagnetic resonance (EPR) spectroscopies, has elucidated the reduction mechanism of Cu super(II) to Cu super(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 super(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. The direct reduction of Cu super(II) to Cu super(I) and the oxidative nature of the Cu super(I) species in the reaction have been studied by X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy. This single-electron redox process is applicable to the copper-catalyzed oxidative cyclization of beta -ketocarbonyl derivatives to dihydrofurans. DTBP=di-tert-butyl peroxide