4-(4-Bromophenyl)-7,7-dimethyl-2-methylamino-3-nitro-7,8-dihydro-4H-chromen-5(6H)-one including an unknown solvate

In the title compound, C18H19BrN2O4, the chromene unit is not quite planar (r.m.s. deviation = 0.199 Å), with the methyl C atoms lying 0.027 (4) and 1.929 (4) Å from the mean plane of the chromene unit. The six-membered carbocyclic ring of the chromene moiety adopts an envelope conformation, with the dimethyl-substituted C atom as the flap. The methylamine and nitro groups are slightly twisted from the chromene moiety, with C—N—C—O and O—N—C—C torsion angles of 2.7 (4) and −0.4 (4)°, respectively. The dihedral angle between the mean plane of the chromene unit and the benzene ring is 85.61 (13)°. An intramolecular N—H⋯O hydrogen bond generates an S(6) ring motif, which stabilizes the molecular conformation. In the crystal, molecules are linked via N—H⋯O hydrogen bonds, forming hexagonal rings lying parallel to the ab plane. A region of disordered electron density, most probably disordered ethanol solvent molecules, occupying voids of ca 432 Å3 for an electron count of 158, was treated using the SQUEEZE routine in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155]. Their formula mass and unit-cell characteristics were not taken into account during refinement.


Comment
Chromene constitutes the basic backbone of various types of polyphenols and is widely found in natural alkaloids, tocopherols, flavonoids and anthocyanins. Natural and synthetic chromene derivatives possess important biological activities such as antitumor, antispasmolytic, antivascular, anticancer, anti-HIV, estrogenic and herbicidal activity. They also plays an important role in the production of highly effective fluorescent dyes for synthetic fibers, daylight fluorescent pigments and electrophotographic and electroluminescent devices (Thomas et al., 2013).
The title compound, Fig. 1, consists of a chromene unit connected to a bromophenyl ring at C7, a nitro group at C8, a methyl amine group at C9, an oxygen atom at C12 and a dimethyl group at C14. The mean plane of the chromene unit (O2/C7-C15) is almost normal to the benzene ring (C1-C6), with a dihedral angle of 85.61 (13)°. The mean plane of the chromene unit makes dihedral angles of 7.25 (21) and 2.89 (21)° with the nitro and methylamine groups, respectively.
The crystal packing is stabilized by intermolecular N-H···O hydrogen bonds forming hexagonal rings centered about a threefold rotation axis and lying parallel to the ab plane ( Fig. 2 and Table 1). The amide N1 atom is involved in both intra and intermolecular hydrogen bonding, having a bifurcated character (Table 1).
Finally, the products were recrystallized from EtOH yielding block-like colourless crystals.

Refinement
The NH H atom was located in a difference Fourier map and freely refined. The C-bound H atoms were placed in idealized positions and allowed to ride on the parent atoms: C-H = 0.93 -0.97 Å with U iso (H)= 1.5 U eq (C-methyl) and = 1.2U eq (C) for other H atoms. A region of disordered electron density, most probably disordered ethanol solvent molecules, occupying voids of ca 432 Å 3 for an electron count of 158, was treated using the SQUEEZE routine in PLATON [Spek (2009). Acta Cryst. D65,[148][149][150][151][152][153][154][155]. The formula mass and unit-cell characteristics were not taken into account during refinement.

Figure 1
A view of the molecular structure of the title molecule, with atom labelling. Displacement ellipsoids drawn at the 30% probability level. The intramolecular N-H···O hydrogen bond is shown as a dashed line (see Table 1 for details).   Table 1 for details; H atoms not involved in hydrogen bonding have been omitted for clarity).

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.

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