Di-n-propyl 4,4′-dihydroxy-3,3′-{[(3aRS,7aRS)-2,3,3a,4,5,6,7,7a-octahydro-1H-benzimidazole-1,3-diyl]bis(methylene)}dibenzoate

The title compound, C29H38N2O6, was prepared as model for studying intramolecular hydrogen-bonding interactions. Molecules of the title compound are located on a crystallographic twofold rotation axis, which passes through the C atom linked to the two N atoms on the imidazolidine ring. The molecular structure shows the existence of two intramolecular O—H⋯N hydrogen-bonding interactions between the two N atoms of the imidazolidine moiety and the hydroxy groups in the aromatic rings. The crystal structure shows the strain of ring fusion in the perhydrobenzimidazole moiety according to the endocyclic bond angles and the torsion angles, which evidence a puckering of the cyclohexane ring with respect to normal tetrahedral bond angles in an ideal chair conformation.

The title compound, C 29 H 38 N 2 O 6 , was prepared as model for studying intramolecular hydrogen-bonding interactions. Molecules of the title compound are located on a crystallographic twofold rotation axis, which passes through the C atom linked to the two N atoms on the imidazolidine ring. The molecular structure shows the existence of two intramolecular O-HÁ Á ÁN hydrogen-bonding interactions between the two N atoms of the imidazolidine moiety and the hydroxy groups in the aromatic rings. The crystal structure shows the strain of ring fusion in the perhydrobenzimidazole moiety according to the endocyclic bond angles and the torsion angles, which evidence a puckering of the cyclohexane ring with respect to normal tetrahedral bond angles in an ideal chair conformation.

Comment
Hydrogen bonding involving phenols has been the subject of extensive experimental and theoretical studies because hydrogen-bonding interactions of phenol itself can be regarded as a prototype to understand the attraction between the lone pair of the amine nitrogen atom and the phenolic hydroxyl proton. (Lu et al. 2006). Continuing our studies on the synthesis and structural analysis of Mannich bases derived from phenols, the title compound, (I), was obtained from n-propyl-4-hydroxy-  (Geise, et al. 1971). These values suggest a constraint of the cyclohexane ring, which is minimized by an increasing of the C3-C4-C4 i bond angle [113.4 (1)°]. The imidazolidine moiety has a half-chair conformation (C2) with intraanular bond angles ranging from 105.1 (1)° to 106.6 (1)° which are shorter respect the tetrahedrical normal bond angles, indicating that the heterocyclic ring is also strained. This conformation is adopted
The reaction mixture was treated with chloroform by discontinuous liquid-liquid extraction (5 × 20 ml). The combined extracts were concentrated under reduced pressure until a residue appeared. The product was purified by chromatography on a silica column, and subjected to gradient elution with benzene:ethyl acetate (yield 19%, m.p. = 449-450 K).Single crystals of racemic (I) were grown from a CHCl 3 :MeOH solution by slow evaporation of the solvent at room temperature over a period of about two weeks.
supplementary materials sup-2 Refinement All hydrogen atoms were discernible in difference Fourier maps and could be refined to reasonable geometry. According to common practice H atoms bonded to C atoms were kept in ideal positions with C-H distance 0.96 Å during the refinement.
The methyl H atoms were allowed to rotate freely about the adjacent C-C bonds. The hydroxyl H atoms were found in difference Fourier maps and their coordinates were refined freely. All H atoms were refined with thermal displacement coefficients U iso (H) set to 1.5Ueq(C, O) for methyl and hydroxyl groups and to to 1.2Ueq(C) for the CH-and CH2-groups. Fig. 1. A view of (I). Displacement ellipsoids are drawn at the 50% probability level.

Special details
Refinement. The refinement was carried out against all reflections. The conventional R-factor is always based on F. The goodness of fit as well as the weighted R-factor are based on F and F 2 for refinement carried out on F and F 2 , respectively. The threshold expression is used only for calculating R-factors etc. and it is not relevant to the choice of reflections for refinement.
The program used for refinement, Jana2006, uses the weighting scheme based on the experimental expectations, see _refine_ls_weighting_details, that does not force S to be one. Therefore the values of S are usually larger than the ones from the SHELX program.