Diethyl 7,8-dibromo-4,11-dioxo-11b,11c-dihydro-5H,10H-2-oxa-3a,4a,10a,11a-tetraazabenz[f]indeno[2,1,7,7a-ija]azulene-11b,11c-dicarboxylate

The title compound, C20H20Br2N4O7, is an intermediate for molecular clips. The seven- and six-membered rings have chair conformations, while the five-membered rings adopt envelope conformations. In the crystal structure, weak C—H⋯O and C—H⋯Br interactions link the molecules into a three-dimensional network. The ethoxy and ethyl groups are disordered over two orientations, with occupancy ratios of 0.735 (16):0.265 (16) and 0.51 (2):0.49 (2), respectively.


Comment
Diethoxycarbonyl glycoluril bearing a range of electron withdrawing functional groups on its convex face is an important building block for both molecular and supramolecular chemistry (Burnett et al., 2003). The title compound derived from diethoxycarbonyl glycoluril is an important intermediate for methylene-bridged glycoluril dimers, and we report herein its crystal structure.
In the crystal structure, weak C-H···O and C-H···Br interactions link the molecules into a three-dimensional network (Fig.   2), in which they may be effective in the stabilization of the structure.

Experimental
The title compound was synthesized according to a literature method (Wu et al., 2002). Crystals suitable for X-ray analysis were obtained by slow evaporation of a dichloride methane solution at 283 K.

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 Rfactors(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. 118.0 (14) O4-C12-C11 110.7 (4) C16-O6-C17 126.8 (7) O4'-C12-C11 107.0 (6) C16-O6-C17' 106.6 (6) O4-C13-C14 106.4 (5) C20-O7-