8-Methoxy-3-methyl-3,4-dihydro-2H-1,3-benzoxazine

The title compound, C10H13NO2, crystallizes with two crystallographically independent molecules of similar geometry in the asymmetric unit; the six-membered oxazine rings adopts a half-chair conformation. Neither hydrogen bonds nor π–π interactions are observed in the crystal structure.

The title compound, C 10 H 13 NO 2 , crystallizes with two crystallographically independent molecules of similar geometry in the asymmetric unit; the six-membered oxazine rings adopts a half-chair conformation. Neither hydrogen bonds norinteractions are observed in the crystal structure.

Comment
Benzo[e][1,3]oxazines, which are synthesized by an amine, a phenolic compound and formaldehyde via Mannich reaction (Holly & Cope, 1944), are a useful class of heterocyclic compounds. They can be cured via thermal ring-opening polymerization to construct a novel class of thermosetting resins called polybenzoxazins (Ning & Ishida, 1994).
The asymmetric unit of the title compound consists of two crystallographically independent molecules of similar geometry ( Fig. 1). In both molecules the six-membered oxazine rings adopt a half-chair conformation, with atoms N1, C1 and N1′ hydrogen bonding or π-π stacking interactions are observed.

Experimental
Methylamine (40 wt% in water; 3.9 g, 0.05 mol), formaldehyde (37% wt in water; 8.1 g, 0.1 mol), 4-methoxyphenol (6.2 g, 0.05 mol) and 1, 4-dioxine (50 ml) were added to a 250 ml flask equipped with a condenser. The mixture was stirred at 90 °C for 5 h. After condensed by rotary evaporator, a yellowish-brown viscous liquid was obtained and set at room temperature for a few hours. After washing several times with methanol, a yellowish powder was precipitated. Anhydrous ether was used to dissolve the powder, and colourless crystals suitable for X-ray diffraction analysis were obtained by slow evoporation of the solvent.

Refinement
All H atoms were refined using a riding model approximation, with C-H = 0.93-0.97 Å and with U iso (H) = 1.2 U eq (C) or 1.5 U eq (C) for methyl H atoms.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.