5-Amino-3-ethoxy-1,8,8-trimethyl-2-azabicyclo[2.2.2]octa-2,5-diene-4,6-dicarbonitrile

The title 2-azabicyclo[2.2.2]octa-2,5-diene derivative, C14H18N4O, crystallized out with two independent molecules with similar conformations in the asymmetric unit. In each molecule, the three six-membered rings adopt boat conformations. The molecules exist in the enamine form. In the crystal, molecules are linked by N—H⋯O and N—H⋯N hydrogen bonds into a two-dimensional network parallel to the ab plane.

The title 2-azabicyclo[2.2.2]octa-2,5-diene derivative, C 14 H 18 N 4 O, crystallized out with two independent molecules with similar conformations in the asymmetric unit. In each molecule, the three six-membered rings adopt boat conformations. The molecules exist in the enamine form. In the crystal, molecules are linked by N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds into a two-dimensional network parallel to the ab plane.
The asymmetric of the title compound contains two crystallographic independent molecules A and B with similar conformation but differences in bond angles (Fig. 1). In both molecules A and B, the three six-membered rings are in boat conformation (Cremer & Pople, 1975). The molecules exist in the enamine form as indicated by the two H atoms  et al., 1987) and are comparable with those reported for a related structure (Nakano & Igarashi, 1987).
In the crystal packing ( Fig. 2), the molecules are linked by intermolecular N-H···N and N-H···O hydrogen bonds (Table 1) into two dimensional networks parallel to the ab plane.

Experimental
The title compound was obtained by the condensation reaction of malononitrile (1.5 mmol) with acetone (20 ml) in the presence of freshly prepared sodium ethoxide (1.0 mmol of sodium in 20 ml of ethanol). The mixture was continuously stirred at room temperature until a precipitate was formed. The resulting solid was filtered. Colourless block-shaped single crystals of the title compound suitable for X-ray structure determination were recrystalized from acetone/methanol (1:1 v/v) by the slow evaporation of the solvent at room temperature after several days.

Refinement
Amino H atoms were located in a Fourier difference map and isotropically refined. The remaining H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C-H) = 0.99 Å for CH 2 and 0.98 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups.

Figure 1
The molecular structure of the title compound, showing 40% probability displacement ellipsoids.  The crystal packing of the title compound viewed along the b axis, showing the two-dimensional networks. Only H atoms involved in hydrogen bonds (dashed lines) are shown.  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.