3-Hy-droxy-2,2-bis-(1H-pyrazol-1-yl)-cyclo-penta-none.

The title compound, C(11)H(12)N(4)O(2), was unexpectedly obtained in the reaction of α,α'-disubstituted cyclo-penta-none with 1,1,3,3-tetra-meth-oxy-propane 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 cyclo-penta-none moiety adopts an envelope conformation, with the hy-droxy-bearing C atom as the flap [deviation from basal plane = 0.643 (3) Å]. 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.