3,3′-(Ethane-1,2-diyl)bis(3,4-dihydro-2H-1,3-benzoxazine)

The title compound, C18H20N2O2, was prepared by Mannich-type reaction of phenol, ethane-1,2-diamine and formaldehyde. The heterocyclic rings adopt half-chair conformations. The acyclic methylene groups attached to the N atoms are in an axial position. In the crystal, weak C—H⋯O hydrogen bonds link the molecules into dimers. These dimers are further connected via C—H⋯π contacts.


Comment
We have recently reported the molecular structure of two 3,3'-(ethane-1,2-diyl)bis(6-substituted-3,4-dihydro-2H-1,3-benzoxazine). The substituents in position 6 were methyl and chlorine respectively (Rivera et al., 2011(Rivera et al., , 2010. Their crystal structures established the existence of an anomeric effect in N-C-O sequence in oxazine ring. In connection with our interest in anomeric effect in benzo-fused oxazine ring, we decided it was important to establish the effect of substituent at the aromatic ring in the N-C-O moiety. Thus, we obtained the title compound (I) which has no substituent in position 6.
The molecular structure of the title compound is illustrated in Fig. 1 In the crystal weak intermolecular C-H···O contacts ( Table 1) that could be considered as weak hydrogen bonds (Desiraju & Steiner, 1999) link molecules into dimers (Fig. 2). Neighboring pair of these dimers are linked together via weaker C-H···π contacts into chains extended along the b axis ( Figure 2).

Experimental
To a stirred mixture of ethane-1,2-diamine (0.34 ml, 5 mmol) and phenol (0.94 g, 10 mmol) dissolved in dioxane (10 ml) was added dropwise an aqueous solution of formaldehyde (1.5 ml, 20 mmol). The reaction mixture was stirred for4 h. at room temperature. The resultant precipitate was collected, washed with water, dried in vacuum and recrystallized from ethanol to give title compound.

Refinement
All H atoms atoms were positioned geometrically and treated as riding on their parent atoms. The isotropic atomic displacement parameters of hydrogen atoms were evaluated as 1.2×U eq of the parent atom. As the structure contains only light atoms, the Friedel-pair reflections were merged and the Flack parameter has not been determined.  Fig. 1. A view of (I) with the numbering scheme.displacement ellipsoids are drawn at the 50% probability level. 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.