Dipropyl 4,8-dioxo-1H,5H-2,6-dioxa-3a,4a,7a,8a-tetraazacyclopenta[def]fluorene-8b,8c-dicarboxylate

The title compound, C16H22N4O8, is a glycoluril derivative with two propoxycarbonyl substituents on the convex face of the glycoluril system. The dihedral angle between the five-membered rings in the glycoluril unit is 72.70 (2)°. The oxadiazinane six-membered ring displays a normal chair conformation. One of the propyl groups is disordered over two positions with site occupancies of 0.557 (7) and 0.443 (7). Intermolecular C—H⋯O hydrogen bonds are effective in the stabilization of the crystal structure.

The title compound, C 16 H 22 N 4 O 8 , is a glycoluril derivative with two propoxycarbonyl substituents on the convex face of the glycoluril system. The dihedral angle between the fivemembered rings in the glycoluril unit is 72.70 (2) . The oxadiazinane six-membered ring displays a normal chair conformation. One of the propyl groups is disordered over two positions with site occupancies of 0.557 (7) and 0.443 (7). Intermolecular C-HÁ Á ÁO hydrogen bonds are effective in the stabilization of the crystal structure.

Comment
Glycolurils are a topic of numerous reports; these compounds are of use in supramolecular chemistry as building blocks for molecular clips  and molecular capsules (Rebek, 1999). The derivatives of glycoluril have been employed in many applications, including polymer cross-linking, explosives and combinational chemistry (Witt et al., 2000). The widespread interest in glycolurils has led to a variety of crystal structures reported for a number of its derivatives. Here we report the structure of the title glycoluril derivative, (I) (Fig. 1), which is an important intermediate for the preparation glycoluril receptors (Wu et al., 2002) and in which the bond lengths and angles present no unusual features and are similar to those found in other similar compounds (Gao & Sun, 2007;She & Xi, 2007;Li et al., 2007).
The oxadiazinane six-membered ring displays a normal chair conformation. The weak intermolecular C-H···O hydrogen bonds cause the formation of a three-dimensional network structure (Fig. 2).

Experimental
The title compound was synthesized according to the procedure reported (Isaacs et al., 1999). Crystals appropriate for X-ray data collection were obtained by slow evaporation of a dichloromethane solution at 283 K.

Refinement
All H atoms were positioned geometrically, with C-H = 0.97 and 0.96 Å for methylene and methyl groups, respectively, and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). One of the propyl groups is disordered over two positions and the final occupancies refined to 0.557 (7) and 0.443 (7). C15-C16 and C15'-C16' bond lengths were restrained to be 1.54 (1) Å, and C14-C15 and C14'-C15' to be 1.45 (1) Å. Same displacement parameters were used for atoms C15 and C15', and for atoms C16 and C16'. In the absence of significant anomalous scattering effects, Friedel pairs have been merged.    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 > 2sigma(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 )