Iminoxyl radicals vs. tert -butylperoxyl radical in competitive oxidative C-O coupling with β-dicarbonyl compounds. Oxime ether formation prevails over Kharasch peroxidation.

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%.