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Paper | Special issue | Vol 99, No. 2, 2019, pp.906-918
Published online, 12th December, 2018
DOI: 10.3987/COM-18-S(F)58
Mechanistic Insight into Catalytic Aerobic Chemoselective α-Oxidation of Acylpyrazoles

Seiya Taninokuchi, Ryo Yazaki,* and Takashi Ohshima*

*Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan


Mechanistic studies on catalytic aerobic chemoselective α-oxidation of acylpyrazoles, including control experiments, kinetic isotope effect experiments, and radical clock experiments, are described. The key to promoting the reaction was the in-situ generation of a copper(II) peroxo complex, which serves as a Lewis acid/Brønsted base cooperative catalyst for efficient enolization. The present catalysis was applicable to late-stage α-oxidation of functionalized acylpyrazoles. A preliminary diastereoselective reaction using readily available chiral acylpyrazoles demonstrated that the present catalysis provided access to optically active α-hydroxy acid derivatives.