2,2-Dimethyl-5-(2-nitro­benzyl­idene)-1,3-dioxane-4,6-dione

The asymmetric unit of the title compound, C₁₃H₁₁NO₆, contains two mol­ecules in both of which the six-membered 1,3-dioxane-4,6-dione ring shows a screw-boat conformation. The dihedral angles between the best planes through the six-membered rings are 47.8 (2) and 49.8 (2)°. In the crystal, C—H...O inter­actions link the mol­ecules, building a supramolecular sheet parallel to the c axis.

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].

Second monoclinic form of (E)-3-(4-fluoro­phen­yl)-1-phenyl­prop-2-en-1-one

The unit-cell dimensions and space group of the second monoclinic polymorph of the title compound, C₁₅H₁₁FO, differ from those of the previously reported form [Jing (2009). Acta Cryst. E65, o2515]. The title compound shows an E conformation of the C=C bond with the 4-fluoro­phenyl group opposite to the benzoyl group. The torsion angle of between the planes of the 4-fluoro­phenyl and benzoyl groups is 10.53 (6)°. In the crystal, weak C—H...O and C—H...F inter­actions form a cross-linked packing motif, building sheets parallel to (-102).