Iminoxyl radicals vs. tert-butylperoxyl radical in competitive oxidative C–O coupling with β-dicarbonyl compounds. Oxime ether formation prevails over Kharasch peroxidation |
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Authors: | I B Krylov S A Paveliev N S Shumakova M A Syroeshkin B N Shelimov G I Nikishin A O Terent'ev |
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Institution: | N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, 47 Leninsky Prosp., Moscow 119991 Russian Federation, |
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Abstract: | Oxidative coupling of oxime and β-dicarbonyl compounds dominates in a β-dicarbonyl compound/oxime/Cu(ii)/t-BuOOH system; in the absence of oxime, oxidative coupling of t-BuOOH and a β-dicarbonyl compound (Kharasch peroxidation) takes place. The proposed conditions for oxidative coupling of oximes with dicarbonyl compounds require only catalytic amounts of copper salt and t-BuOOH serves as a terminal oxidant. The C–O coupling reaction proceeds via the formation of tert-butoxyl, tert-butylperoxyl and iminoxyl radicals. Apparently, tert-butylperoxyl radicals oxidize oxime into iminoxyl radical faster than they react with β-dicarbonyl compounds forming the Kharasch peroxidation product. Iminoxyl radicals are responsible for the formation of the target C–O coupling products; the yields are up to 77%.The Kharasch peroxidation system Cu(ii)cat./t-BuOOH, the source of t-BuOO˙ radicals, can be switched to generate iminoxyl radicals by adding various oximes. |
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