Dimethyl 5-acetyl-1-hy-droxy-4-methyl-1H-pyrrole-2,3-di-carboxyl-ate, an oxidation-resistant N-hy-droxy-pyrrole.

The title compound, C11H13NO6, exhibits an intra-molecular O-H⋯O=C hydrogen bond between the N-hydroxyl H atom and carbonyl O atom of the neighboring acetyl group. This finding contradicts a previously published model in which the hydrogen bond was postulated to occur with the neighboring carbomethoxy group. This relatively strong hydrogen bond [O-H⋯O: D = 2.5583†(11)†à and θ = 152°] may underlie the resistance of the title compound to oxidation into the corresponding nitroxide.