4-(4-Bromophenyl)-2-methylamino-3-nitro-5,6,7,8-tetrahydro-4H-chromen-5-one

In the title compound, C16H15BrN2O4, the six-membered carbocyclic ring of the chromene moiety adopts an envelope conformation with the disordered methylene C atom as the flap. The pyran ring is almost orthogonal to the chlorophenyl ring, making a dihedral angle of 87.11 (12)°. The amine-group N atom deviates significantly from the pyran ring [0.238 (3) Å]. The molecular structure is stabilized by an intramolecular N—H⋯O hydrogen bond, which generates an S(6) ring motif. In the crystal, molecules are linked via C—H⋯O hydrogen bonds, which generate C(8) chains running parallel to the b axis. The chains are linked by C—H⋯π interactions. The methylene-group C atom of the chromene system that is disordered, along with its attached H atoms and the H atoms on the two adjacent C atoms, has an occupancy ratio of 0.791 (7):0.209 (7).

The mean planes of the nitro and methylamine groups are almost co-planar with the pyran ring, with dihedral angles of 4.66 (20) and 3.87 (19) °, respectively. The mean plane of six membered carbocyclic ring (C8-C10/C11-C13) makes a dihedral angle of 86.50 (14) ° with the chlorophenyl ring, which shows that they too are almost perpendicular to each other.
The six membered carbocyclic ring (C8-C10/C11-C13) of the chromene moiety adopts an envelope conformation on C11 atom which deviates by 0.302 (4) Å out of the mean plane formed by the remaining ring atoms. The amine group nitrogen atom N2 deviates by -0.2382 (25) Å from the pyran ring. The bromine atom Br1 deviates from the phenyl ring (C1-C6) by 0.0953 (4) Å. The title compound exhibits structural similarities with a related structure (Sun et al., 2012).
In the crystal, molecules are linked via C-H···O hydrogen bonds, which generate C(8) chains running parallel to the b axis (Bernstein et al.,1995); see Table 1 and Fig. 2. The crystal structure is further stabilized by C-H···π interactions (Table 1).

Experimental
A solution of the 4-bromobenzaldehyde (0.18 g, 1.0 mmol), cyclic 1,3-dicarbonyl compound (1.0 mmol), NMSM (0.15 g, 1.0 mmol) and piperidine (0.2 equiv) in EtOH (2 ml) was stirred for 3.5 hrs. After the reaction was complete, as indicated by TLC, the product was filtered and washed with EtOH (2 ml) to remove excess base and other impurities. Single crystals suitable for X-ray diffraction were prepared by slow evaporation of a solution of the title compound in ethanol at room temperature.

Refinement
The H atoms were localed from difference electron density maps and their distances were geometrically constrained. The amine group H atoms were constrained: N-H = 0.90 (1) Å with U iso (H) = 1.2U eq (N). The C-bound H atoms were treated as riding atoms: C-H = 0.93, 0.97, 0.96 and 0.98 Å for CH(aromatic), methylene, methine and methyl H atoms, respectively, with U iso (H) = k × U eq (C) where k = 1.5 for methyl H atoms and = 1.2 for other H atoms. The rotation angles for the methyl groups were optimized by least squares. The bond distances of the disordered components of atom C11 were restrained using standard similarity restraint SADI [SHELXL97, Sheldrick, 2008] with s.u. of 0.01 Å. The atomic displacement parameters of the major and minor components were made equal using the constraint EADP.

Computing details
Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009   The molecular structure of the title molecule, with atom labelling. Displacement ellipsoids are drawn at 30% probability level. The intramolecular hydrogen bond, which generates an S(6) ring motif, is shown as a dashed line.  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.