2-( Adamantan-1-yl )-5-methylbenzo [ d ]-[ 1 , 3 ] oxazin-4-one

The title compound, (I), has a planar benzo[d][1,3]oxazin-4one heterocycle that lies on a crystallographic mirror plane. The molecular structure of (I) is shown in Fig. 1 and selected bond distances and angles are given in Table 1. Within the oxazin-4-one group the C O and C N double bonds are clearly localized, but of the two formally single CÐO bonds, O2ÐC2 is signi®cantly shorter than O2ÐC1. The bicyclic heterocycle is planar despite the unfavourable steric interaction between the 5-methyl and 4-carbonyl groups, but the planarity allows -stacking of these groups in the direction of the b axis (Fig. 2), with an inter-layer distance of 3.3662 (4) AÊ (Table 2). The widened bond angles of 128.39 (12), 121.75 (11) and 123.51 (12) for O1ÐC1ÐC4, C1ÐC4ÐC5 and C4Ð C5ÐC9, respectively, still result in a short O1 C9 distance of 2.838 (2) AÊ .

At 150 K, the benzo[d] [1,3]oxazin-4-one heterocycle in the title compound, C 19 H 21 NO 2 , lies on a crystallographic mirror plane. This group is planar despite the resulting unfavourable steric interaction between the proximal 5-methyl and 4carbonyl groups.

Comment
The title compound, (I), has a planar benzo [d] [1,3]oxazin-4one heterocycle that lies on a crystallographic mirror plane. The molecular structure of (I) is shown in Fig. 1 and selected bond distances and angles are given in Table 1. Within the oxazin-4-one group the C O and C N double bonds are clearly localized, but of the two formally single CÐO bonds, O2ÐC2 is signi®cantly shorter than O2ÐC1. The bicyclic heterocycle is planar despite the unfavourable steric interaction between the 5-methyl and 4-carbonyl groups, but the planarity allows %-stacking of these groups in the direction of the b axis (Fig. 2), with an inter-layer distance of 3.3662 (4) A Ê ( Table 2). The widened bond angles of 128.39 (12), 121.75 (11) and 123.51 (12) for O1ÐC1ÐC4, C1ÐC4ÐC5 and C4Ð C5ÐC9, respectively, still result in a short O1Á Á ÁC9 distance of 2.838 (2) A Ê .

Figure 1
View of the molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are represented by spheres of arbitrary size. Only one orientation of the disordered methyl group is shown.   Contact distances (A Ê ).
All H atoms were initially located in a difference Fourier map. The methyl H atoms were constrained to an ideal geometry with a CÐH distance of 0.98 A Ê , but the group was allowed to rotate freely about its XÐC bond. In its ®nal position, the methyl group is not bisected exactly by the mirror plane and hence is disordered 50:50 about the mirror plane. All other H atoms were placed in geometrically idealized positions, with CÐH distances of 0.95±1.00 A Ê . U iso (H) values were set at 1.2U eq (C) for all of the H atoms.

Figure 2
Packing diagram for (I), viewed down the b axis. Only one orientation for the disordered methyl group is shown. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.49 e Å −3 Δρ min = −0.37 e Å −3 Extinction correction: SHELXL97, Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.032 (7) sup-2 Special details Experimental. The crystal was mounted under the perfluoro-polyether PFO-XR75 (Lancaster Synthesis). A total of 160 frames (2 minute exposure) were collected (phi/omega: 35/90-160, 120/90-180, delta-omega = 1 °.) 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (