4-Hy­droxy-1,1′-bis­[(S)-1-phenyl­eth­yl]-5,5′,6,6′-tetra­hydro-3,4′-bipyridine-2,2′(1H,1′H)-dione

The title bis-piperidine, C₂₆H₂₈N₂O₃, was unexpectedly obtained via a dimerization mechanism promoted by acetic acid when performing the Dieckmann cyclization of a chiral amido ester. The S,S configuration was assigned by reference to the enanti­omerically pure starting material. In the mol­ecule, two core heterocycles are linked by a σ bond. One ring includes a keto–enol group, while the other presents an enone functionality. Both rings present a conformation inter­mediate between envelope and screw-boat, and the dihedral angle between the mean planes passing through the rings [48.9 (1)°] is large enough to avoid hindrance between ring substituents. The enol tautomeric form in one ring favors the formation of strong inter­molecular O—H...O=C hydrogen bonds. The resulting one-dimensional supra­molecular structure features single-stranded helices running along the 2₁ screw axis parallel to [100].