3,6-Dibromo-7-ethylamino-4-methyl-2H-chromen-2-one

In title compound, C12H11Br2NO2, the coumarin ring system is almost planar, the two rings being inclined to one another by 1.40 (15)°. There are two short intramolecular interactions (N—H⋯Br and C—H⋯Br) involving the Br atoms. In the crystal, molecules stack along the a-axis direction via π–π interactions; the centroid–centroid distances vary from 3.6484 (19) to 3.7942 (19) Å.


Comment
The title compound is used as an important intermediate to synthesis fluorescent tracers, for example, it has been recognized as an effective protein tracer (Belluti et al., 2010). Herein we report on the crystal structure of the title compound, which is illustrated in Fig. 1. The coumarin ring system is almost planar with a dihedral angle involving rings (O2,C1-C5) and (C4-C9) of only 1.40 (2) °. This is normal for such coumarin compounds (Kruszynski et al., 2005). The bromine atoms are involved in short Br···H interactions (Table 1).

Experimental
The title compound was prepared by the method reported by (Belluti et al., 2010). To a suspension of 4-methyl-7-N,N-diethylamino coumarin (5 mmol, 1.61 g) and bromosuccinimide (6 mmol, 1.06 g) in carbon tetrachloride (50 ml), a catalytic amount of benzoyl peroxide was added. The reaction mixture was refluxed for 8 h, then the succinimide produced during the reaction was filtered off. The resulting mixture was washed with water, dried and the solvent was removed under reduced pressure. The pale yellow product obtained was recrystallized from ethanol, yielding colourless block-like crystals of the title compound on evaporating the solvent slowly at room temperature for about 5 days.

Refinement
The NH H-atom was located in a difference electron-density map and was freely refined. The C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.93, 0.97 and 0.96 Å for CH, CH 2 and CH 3 H-atoms, respectively, with U iso (H) = k × U eq (parent C-atom), where k = 1.5 for CH 3 H-atoms and = 1.2 for other H-atoms.  The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. The short Br···H interactions are shown as dashed lines.

Figure 2
A view along the a axis of the crystal packing of the title compound. The short Br···H interactions are shown as dashed lines.

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 Br1 0.93608 (