3-Hydroxy-2,2-bis(1H-pyrazol-1-yl)cyclopentanone

The title compound, C11H12N4O2, was unexpectedly obtained in the reaction of α,α′-disubstituted cyclopentanone with 1,1,3,3-tetramethoxypropane in the presence of dioxane saturated with HCl. It belongs to a previously unknown class of gem-bihetaryl ketones which may be useful for screening of new substances with biological activity. In the studied structure, the cyclopentanone moiety adopts an envelope conformation, with the hydroxy-bearing C atom as the flap [deviation from basal plane = 0.643 (3) ]. The dihedral angle between the two pyrazole rings is 80.02 (8)°. In the crystal, inversion dimers are formed via a pair of O—H...N hydrogen bonds.