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

The complete molecule of the title compound, C31H42N2O6, is generated by crystallographic twofold symmetry, with one C atom lying on the axis. The dihedral angle between the aromatic rings is 57.03 (6)°. The central heterocyclic ring adopts a half-chair conformation. The molecular conformation is stabilized by two intramolecular O—H⋯N hydrogen bonds with the N atoms of the heterocyclic ring as the acceptors. In the crystal, molecules are linked into chains along the c axis by non-classical C—H⋯O hydrogen bonds.

The complete molecule of the title compound, C 31 H 42 N 2 O 6 , is generated by crystallographic twofold symmetry, with one C atom lying on the axis. The dihedral angle between the aromatic rings is 57.03 (6) . The central heterocyclic ring adopts a half-chair conformation. The molecular conformation is stabilized by two intramolecular O-HÁ Á ÁN hydrogen bonds with the N atoms of the heterocyclic ring as the acceptors. In the crystal, molecules are linked into chains along the c axis by non-classical C-HÁ Á ÁO hydrogen bonds.

Related literature
For related structures, see: Rivera et al. (2010Rivera et al. ( , 2011Giordano et al. (1999);Feng & Grant (2006). For background to this work see: Koll et al. (2001);Filarowski et al. (2004).  Table 1 Hydrogen-bond geometry (Å , ).  3,3a,4,5,6,7, electron-withdrawing effect of chlorine atom. However, the distortion in the aromatic ring in these Mannich bases, leads to a conclusion indicating that the effect of halogen atoms seems to be no meaningful which can be explained on the basis of the presence of conjugative electron-release from lone pairs of halogen atom. To avoid the conjugation effect of halogen to aromatic ring we synthesized the title compound (I) which is a racemic Mannich base with a non-halogen electron withdrawing group in para position. The molecular structure and atom-numbering scheme for (I) are shown in Fig. 1. The X-ray diffraction analysis shows the existence of two intramolecular hydrogen bonding interactions between the hydroxy H atom and the amine groups in the heterocyclic ring (table 1) In comparison with the crystal packing of butylparaben, there are not head-to-tail hydrogen bonding interactions inside the chains that involve the O-H group as donor and the carbonyl O atom as acceptor (Giordano et al. 1999;Feng & Grant, 2006), there are non-classical hydrogen bonds C5-H5a··· O1 (table 1) which link neighboring helps stabilize the packing along c axis (Fig. 2).

Experimental
A solution of (2R,7R,11S,16S)-1,8,10,17-tetraazapentacyclo [8.8.1.1 8,\17 .0 2,7 .0 11,16 ] icosane (276 mg, 1.00 mmol) in dioxane (3 ml) and water (4 ml), previously prepared following described procedures, was added dropwise in a dioxane solution (3 ml) containing two equivalents of n-butyl 4-hydroxybenzoate (388 mg, 2.00 mmol) in a two-necked round-bottomed flask. The mixture was refluxed for about 12 h and then the solvent was evaporated under reduced pressure until a sticky 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. = 414-416 K). Single crystals of racemic (I) were grown from a chloroform solution by slow evaporation of the solvent at room temperature over a period of about 2 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 C atoms were kept in ideal positions with C-H distance 0.96 Å during the refinement.
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.