Hidden Reactivity of Barbituric and Meldrum's Acids: Atom-Efficient Free-Radical C-O Coupling with N -Hydroxy Compounds

The reactivity of CH-acidic and structurally related enol-containing heterocycles towards N -oxyl radicals is disclosed. Traditionally, these substrates have been considered as reactants for ionic transformations. Highly selective and efficient N -oxyl radical mediated C-O coupling of substituted barbituric or Meldrum's acids with N -hydroxy compounds (N -hydroxyimides, hydroxamic acids, oximes, and N -hydroxybenzotriazole) was achieved using inexpensive manganese-containing salts as oxidants. Metal-free C-O coupling was demonstrated using diacetyliminoxyl as both the oxidant (hydrogen-atom acceptor) and the coupling partner.

Automated summary

The reactivity of CH-acidic and structurally related enol-containing heterocycles towards N-oxyl radicals was investigated, showing high affinity between these substrates. Highly selective and efficient N-oxyl radical mediated C-O coupling of substituted barbituric or Meldrum's acids with N-hydroxy compounds was achieved using inexpensive manganese-containing salts as oxidants. Metal-free C-O coupling was demonstrated using diacetyliminoxyl as both the oxidant and the coupling partner.