1,3-Dicyclohexylimidazolidine-2,4,5-trione

The title compound, C15H22N2O3, has been isolated as a by-product of an oxidative cleavage of the C—C bond linking two five-membered rings of 1,3-dicyclohexyl-5-(3-oxo-2,3-dihydrobenzofuran-2-yl)imidazolidine-2,4-dione. Individual molecular units are engaged in weak C=O⋯C=O interactions [O⋯C = 2.814 (10) and 2.871 (11) Å], leading to the formation of supramolecular chains which close pack, mediated by van der Waals contacts, in the bc plane.

The title compound (3) has recently been prepared and tested against cell lines modeling amyotrophic lateral sclerosis (Xia et al., 2011), but its crystal structure remains unpublished. Following our interest on the structural features of compounds with biological activity (Fernandes et al., 2010(Fernandes et al., , 2011Loughzail et al. 2011) here we wish to report the crystal structure of (3).
The asymmetric unit comprises a whole molecule (3, Fig. 2). The two cyclohexane substituent groups appear to exhibit chair conformations and their medium planes are almost perpendicular (ca 81 and 87°) with the medium plane of the central imidazolidine ring. The crystal packing is mainly driven by the need to effectively fill the available space in conjunction with several weak interactions, namely C═O···C═O: one O2 atom interacts with two vicinal carbonyl carbon atoms (C2 and C3) of a neighboring molecule [d O···C of 2.814 (10) and 2.871 (11) Å, dashed green lines in Fig. 3]. These weak interactions contribute to the formation of a zigzag columnar arrangement of the molecular units parallel to the a axis of the unit cell.
Columns close pack in the bc plane in a typical brick-wall type fashion (Fig. 4).
supplementary materials sup-2 Experimental NMR spectra were recorded on a Bruker Avance 300 spectrometer (300.13 for 1 H and 75.47 MHz for 13 C), with CDCl 3 used as solvent. Chemical shifts (δ) are reported in p.p.m. and coupling constants (J) in Hz. The internal standard was TMS.
Unequivocal 13 C assignments have been performed with the aid of two-dimensional HSQC and HMBC experiments (delays for one bond and long-range J C/H couplings were optimized for 145 and 7 Hz, respectively).
Iodine (8.63 mg, 0.034 mmol dissolved in 1 ml of DMSO) was added to a solution of 2 (0.27 g, 0.681 mmol) in DMSO (2 ml). The reaction was refluxed in a sand bath for 30 minutes. After this period, the solution was poured into ice (5 g) and water (10 ml), leading to the formation of a yellow precipitate. The solid was collected by filtration, washed with water and dissolved in dichloromethane (30 ml). This organic solution was washed with a saturated sodium thiosulfate solution (2 × 200 ml) and finally purified by silica gel column chromatography using dichloromethane as eluent. The resulting compound was recrystallized from ethanol to give bright-yellow crystals of the title compound (Richter et al., 1984).

Refinement
Hydrogen atoms bound to carbon were placed in idealized positions with C-H = 1.00 (for methine-H) and 0.99 Å (for methylene-H). These atoms were included in the final structural model in riding-motion approximation with the isotropic thermal displacement parameters fixed at 1.2×U eq of the carbon atom to which they are attached.
The cyclohexane rings are severely affected by disorder. Attempts to model this disorder proved to be unsuccessful hence, the large electron residual density surrounding these moieties: the largest peak and hole, 0.74 and -0.42 e . Å -3 , are located at 0.92 and 0.40 Å, respectively, from the C10 atom.
In the absence of significant anomalous scattering effects, 1098 Friedel pairs were averaged in the final refinement. Fig. 1. (Top). Molecular representation of imidazolidine-2,4,5-trione (1). (Bottom). Reaction scheme to isolate the title compound (3) from 1,3-dicyclohexyl-(3-oxo-2,3-dihydrobenzofuran-2-yl)imidazolidine-2,4-dione (2).    Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.