4-(3,4-Dimethyl-5-phenyl-1,3-oxazolidin-2-yl)-2-methoxyphenol

In the title compound, C18H21NO3, the oxazolidine ring adopts an envelope conformation with the N atom at the flap position. The two benzene rings make dihedral angles of 74.27 (14) and 73.26 (15)° with the mean plane through the oxazolidine ring. In the crystal structure, O—H⋯O and C—H⋯O hydrogen bonds connect adjacent molecules into chains along [010] incorporating R 2 2(8) loops and further stabilization is provided by weak intermolecular C—H⋯π interactions.

In the title compound, C 18 H 21 NO 3 , the oxazolidine ring adopts an envelope conformation with the N atom at the flap position. The two benzene rings make dihedral angles of 74.27 (14) and 73.26 (15) with the mean plane through the oxazolidine ring. In the crystal structure, O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds connect adjacent molecules into chains along [010] incorporating R 2 2 (8) loops and further stabilization is provided by weak intermolecular C-HÁ Á Á interactions.
The title oxazolidine compound contains two aromatic phenyl rings bridged by an oxazolidine ring (Fig. 1). The oxazolidine ring with atom sequence C7/N1/C8/C9/O3 adopts an envolope conformation, with puckering parameters of Q = 0.421 (3) Å and φ = 73.7 (3)°. The N1 atom is at the envelope flap position and it deviates from the least-square plane through the remaining four atoms by 0.634 (2) Å. The mean plane through the oxazolidine ring inclines at dihedral angles of 74.27 (14) and 73.26 (15)°, respectively, with the C1-C6 and C10-C15 phenyl rings. The bond lengths (Allen et al., 1987) and angles are within normal ranges and consistent to a closely related oxazolidine structure (Duffy et al., 2004).

Experimental
An anhydrous methanol solution of 4-hydroxy-3-methoxy-benzyldehyde (1.52 g, 10 mmol) was added to an anhydrous methanol solution of 2-methylamino-1-phenylpropan-1-ol (1.65 g, 10 mmol) and the reaction mixture was refluxed and stirred at 350 K for 8 h. The product was isolated and recrystallized from methanol and dried in vacuo to give colourless blocks of (I) in 80 % yield, which were washed three times with ethyl acetate and dried in a vacuum desiccator using CaCl 2 .

Refinement
Atom H1O1 was located from difference Fourier map and allowed to refine freely [O1-H1O1 = 0.92 (3) Å]. All other H atoms were placed in their calculated positions, with C-H = 0.93 -0.98 Å, and refined using a riding model, with U iso = 1.2 or 1.5 U eq (C). A rotating group model was used for the methyl groups. Fig. 1. The molecular structure of (I) showing 30% probability displacement ellipsoids for non-H atoms.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 120.0 (1)K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.