meso-4,4′-Dimethoxy-2,2′-{[(3aR,7aS)-2,3,3a,4,5,6,7,7a-octahydro-1H-benzimidazole-1,3-diyl]bis(methylene)}diphenol

The title compound, C23H30N2O4, a di-Mannich base derived from 4-methoxyphenol and cis-1,2-diaminecyclohexane, has a perhydrobenzimidazolidine nucleus, in which the cyclohexane ring adopts a chair conformation and the heterocyclic ring has a half-chair conformation with a C—N—C—C torsion angles of −48.14 (15) and −14.57 (16)°. The mean plane of the heterocycle makes dihedral angles of 86.29 (6) and 78.92 (6)° with the pendant benzene rings. The molecular structure of the title compound shows the presence of two interactions between the N atoms of the imidazolidine ring and the hydroxyl groups through intramolecular O—H⋯N hydrogen bonds with graph-set motif S(6). The unobserved lone pairs of the N atoms are presumed to be disposed in a syn conformation, being only the second example of an exception to the typical ‘rabbit-ears’ effect in 1,2-diamines.

The title compound, C 23 H 30 N 2 O 4 , a di-Mannich base derived from 4-methoxyphenol and cis-1,2-diaminecyclohexane, has a perhydrobenzimidazolidine nucleus, in which the cyclohexane ring adopts a chair conformation and the heterocyclic ring has a half-chair conformation with a C-N-C-C torsion angles of À48.14 (15) and À14.57 (16) . The mean plane of the heterocycle makes dihedral angles of 86.29 (6) and 78.92 (6) with the pendant benzene rings. The molecular structure of the title compound shows the presence of two interactions between the N atoms of the imidazolidine ring and the hydroxyl groups through intramolecular O-HÁ Á ÁN hydrogen bonds with graph-set motif S(6). The unobserved lone pairs of the N atoms are presumed to be disposed in a syn conformation, being only the second example of an exception to the typical 'rabbit-ears' effect in 1,2-diamines.
(methylene)}diphenol (Rivera et al., 2013a), one exception of the "rabbit-ears effect" (Hutchins et al., 1968). Here we report the synthesis and crystal structure of the title compound (I).
The molecular structure and atom-numbering scheme for (I) are shown in Fig. 1. The bond lengths are close to normal (Allen et al., 1987). The crystal structure of (I) shows two intramolecular hydrogen bonds with graph-set motif S(6) (Bernstein et al., 1995) (Table 1), where the N···H distances and the N···O distances are shorter (by about 0.06 Å and 0.03 Å, respectively) than the observed values in a related structure (Rivera, et al. 2013a). These results suggest that the electronic character of the< i>para substituent in the aromatic rings does not significantly influence the strength of the intermolecular hydrogen bonds in these compounds.
The cyclohexane ring adopts a chair conformation where the endocyclic C-C-C bond angles are distorted from the normal tetrahedral bond angles in a chair conformation (Geise et al., 1971), since these values are in the range of 110.29 (15)° to 114.50 (14)°. The imidazolidine ring adopts a half chair conformation (Van den Enden & Geise, 1981), where the nitrogen lone pairs are oriented in a syn disposition and the benzyl groups are located in 1,3-diequatorial positions.
The dihedral angle between the aromatic rings is 49.19 (52) °. The C3-C8 and C6-C4 bonds are the longest and the C10-C12 and C19-C22 bond are the shortest in the aromatic rings.

Experimental
A solution of p-methoxyphenol (2.00 mmol) in dioxane (3 ml) was added dropwise to a stirred solution of (2S,7R,11S,16R)-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). The mixture was stirred for 15 min at room temperature and then water (4 ml) was added. The mixture was heated at 313 K during 30 h. After cooling to room temperature, the solvent was removed in vacuo and the crude product was purified by chromatography on a silica column and subjected to gradient elution with light petroleum ether: ethyl acetate (yield 45%, M.p. = 405-406 K). Single crystals of (I) were grown from a CHCl 3 solution by slow evaporation of the solvent at room temperature over a period of about 2 weeks.

Refinement
The hydroxyl hydrogen atoms were found in difference Fourier maps and their coordinates were refined with a distance restraint d(O-H) = 0.926 Å with σ 0.01. All other H atoms atoms were kept in the geometrically correct positions with C -H distance 0.96 A. The isotropic atomic displacement parameters of hydrogen atoms were evaluated as 1.2×U eq of the parent atom.

diyl]bis(methylene)}diphenol
Crystal data C 23 H 30 N 2 O 4 M r = 398.5 Orthorhombic, P2 1 2 1 2 1 Hall symbol: P 2ac 2ab a = 6.4135 (3)  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.