Evidence of CuI/CuII Redox Process by X-ray Absorption and EPR Spectroscopy: Direct Synthesis of Dihydrofurans from β-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: Weinheim WILEY-VCH Verlag 21.12.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Absorption; Alkenes; Chemical reactions; Chemistry; Copper; Diketones; Electron paramagnetic resonance; Electron spin resonance; homogeneous catalysis; oxidative coupling; redox chemistry; Reduction; Spectroscopy; Spectrum analysis; X-ray absorption spectroscopy
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201503822

The CuI/CuII and CuI/CuIII catalytic cycles have been subject to intense debate in the field of copper‐catalyzed oxidative coupling reactions. A mechanistic study on the CuI/CuII redox process, by X‐ray absorption (XAS) and electron paramagnetic resonance (EPR) spectroscopies, has elucidated the reduction mechanism of CuII to CuI 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 CuI has also been studied by XAS and EPR spectroscopy. This mechanistic information is applicable to the copper‐catalyzed oxidative cyclization of β‐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 CuII to CuI and the oxidative nature of the CuI 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 β‐ketocarbonyl derivatives to dihydrofurans. DTBP=di‐tert‐butyl peroxide