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.
Key words
radicals - oxidative coupling - NHPI - barbituric acids - Meldrum’s acids
