1,3-Bis(3-tert-butyl-2-hydroxy-5-methoxybenzyl)hexahydropyrimidin-5-ol monohydrate

The asymmetric unit of the title compound, C28H42N2O5·H2O, consists of one half of the organic molecule and one half-molecule of water, both of which are located on a mirror plane which passes through the central C atoms and the hydroxyl group of the heterocyclic system. The hydroxyl group at the central ring is disordered over two equally occupied positions. The six-membered ring adopts a chair conformation, and the 2-hydroxybenzyl substituents occupy the sterically preferred equatorial positions. The aromatic rings make dihedral angles of 75.57 (9)° with the mean plane of the heterocyclic ring. The dihedral angle between the two aromatic rings is 19.18 (10)°. The molecular structure features two intramolecular phenolic O—H⋯N hydrogen bonds with graph-set motif S(6). In the crystal, molecules are connected via O—H⋯O hydrogen bonds into zigzag chains running along the a-axis direction.

The asymmetric unit of the title compound, C 28 H 42 N 2 O 5 ÁH 2 O, consists of one half of the organic molecule and one halfmolecule of water, both of which are located on a mirror plane which passes through the central C atoms and the hydroxyl group of the heterocyclic system. The hydroxyl group at the central ring is disordered over two equally occupied positions. The six-membered ring adopts a chair conformation, and the 2-hydroxybenzyl substituents occupy the sterically preferred equatorial positions. The aromatic rings make dihedral angles of 75.57 (9) with the mean plane of the heterocyclic ring. The dihedral angle between the two aromatic rings is 19.18 (10) . The molecular structure features two intramolecular phenolic O-HÁ Á ÁN hydrogen bonds with graph-set motif S(6). In the crystal, molecules are connected via O-HÁ Á ÁO hydrogen bonds into zigzag chains running along the a-axis direction.

Experimental
We acknowledge the Direcció n de Investigaciones, Sede Bogotá (DIB) de la Universidad Nacional de Colombia, for financial support of this work.

Comment
Recently our group reported a protocol for the synthesis of a series of 2,2′-(dihydropyrimidine-1,3(2H,4H)-diyldimethanediyl)diphenols via a Mannich-type reaction (Rivera et al., 2013). As an extension of these studies, in this paper we describe the synthesis and crystal structure of the title compound, 1,3-bis(3-tert-butyl-2-hydroxy-5-methoxybenzyl)hexahydropyrimidin-5-ol, C 28 H 42 N 2 O 5 , as a monohydrate. The molecular structure and atom-numbering scheme for the title compound are shown in Fig. 1. The asymmetric unit contains one half-organic molecule and one half water molecule, which are both located on a mirror plane which passes through the central C atoms and the hydroxyl group of the heterocyclic system. In Fig. 1, atoms without labels were generated by the symmetry operator x, 1/2 -y, z. The 1,3diazinane ring of the title compound adopts a chair conformation with a diequatorial substitution with puckering parameters Q, θ and φ of 0.594 (2) Å, 2.23 (19)°, 60 (4)° (Cremer & Pople, 1975). The aromatic rings make dihedral angles of 75.57 (9)° with the mean plane of the heterocyclic ring. The benzyl groups are located in a 1,3-diequatorial syn arrangement in the heterocyclic ring with a dihedral angle between the planes containing the aromatic rings of 19.18 (10)°. In the molecule of the title compound ( Fig. 1), bond lengths (Allen et al., 1987) and angles are normal and comparable to those observed in related structures namely 4,4′,6,6′-tetra-tert-butyl-2,2′-[1,3-diazinane-1,3diylbis(methylene)]diphenol 0.25-hydrate (Zhang et al., 2012) and 6,6′-di-tert-butyl-4,4′-dimethoxy-2,2′-[1,3diazinane-1,3-diylbis(methylene)]-diphenol 0.19-hydrate (Rivera et al., 2012). The crystal structure shows two intramolecular O-H···N(1,3-diazinane) hydrogen bonds with graph-set motif S(6) (Bernstein et al., 1995) (Table 1), where the N···O distance [N1···O1, 2.671 (2) Å] is shorter in comparison with the values observed in the related structure (Zhang et al. 2012). In contrast to the 4′,6′-di-tert-butyl analog, the title compound was found to be more similar to the other related structure (Rivera et al., 2012), indicating that the methoxy substituent slightly influences the strength of the intermolecular hydrogen bonds in these compounds. In the crystal, hydroxyl groups of the 1,3-diazinane ring are linked to water molecules via O-H···O hydrogen bonds, leading to a two-molecule aggregate where the water-O accepts these interactions. These are linked into a zigzag chain along the a axis via O-H···O interactions between the water molecules and the phenolic-O atoms. (Fig. 2 and Table 1).

Experimental
The title compound was prepared as follows: In a 50 ml round bottom flask equipped with a magnetic stir bar, 1 equiv. of 1,3-diamino-2-propanol, 3 equiv. of paraformaldehyde, and 2 equiv. of 2-tert-butyl-4-methoxyphenol were combined with 15 ml of methanol. Upon completion of the addition, the reaction mixture was stirred under reflux for 36 h. Then the reflux was stopped, the solvent was removed on a rotary evaporator under vacuum and the residue obtained (Anal. calcd.

Refinement
H atoms bonded to C were positioned geometrically, with C-H = 0.95-0.99 Å and constrained to ride on their parent atoms, with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms. The non disordered hydroxyl H atoms were refined isotropically, but the disordered ones were refined with U iso (H) = 1.5U eq (O). The water H atoms were geometrically positioned with O-H = 0.84 Å and constrained to ride on their parent atom with U iso (H) = 1.5U eq (O).

Figure 1
The molecular structure of the title compound, Displacement ellipsoids are drawn at the 50% probability level. Hydrogen