Crystal structure of 3-amino-5,5-dimethyl-2-[(E)-2-nitroethenyl]cyclohex-2-en-1-one

The asymmetric unit of the title compound contains two independent molecules with similar conformations, the cyclohexene rings adopting the same envelope conformation. In the crystal, adjacent molecules are connected via N—H⋯O hydrogen bonds and weak C—H⋯O interactions, forming supramolecular layers parallel to (01).


Chemical context
sec-Nitrodienamines appear to be potentially useful synthons in organic synthesis due to the enaminic, dienic and 'pushpull' character of these molecules (Koike et al., 2000). Several methods are available for the synthesis of nitrodienamines, which include the reaction of acetaldehydes with 1-dimethylamino-2-nitroethylen followed by treatment with amines (Severin et al., 1971), the reaction of aminoacrolein with dimethylamine and subsequent treatment of the vinylamidinium salt with nitromethane (Takeuchi et al., 1988) and nitroalkenylation reactions of 2-methylindolines with nitroenamines (Attanasi et al., 2006). Previously, we found that alpha-nitro acetaldehyde undergoes an unusual condensation with aldehydes and ammonium acetate to afford 3,5-dinitro-1,2-dihydropyridines (Vigante et al., 1993). Afterwards, the synthesis of N-substituted 1,2-dihydropyridines by heterocyclic annulation reaction of secnitrodienamines with acetaldehyde was reported (Koike et al., 1999). As part of our studies of synthetic pathways to fused 1,2-dihydropyridines, the title compound was synthesized and we report herein on its molecular and crystal structure.

Structural commentary
The asymmetric unit of the title compound ( Fig. 1) contains two independent molecules (A and B) having coincident geometry. The bond lengths in the molecules are close to standard values. The cyclohexene rings adopt an envelope conformation, with flap atoms C3A and C3B lying 0.658 (3) and 0.668 (3) Å from the mean planes formed by the remaining atoms in molecules A and B, respectively.

Figure 2
The crystal packing of the title compound showing sheets parallel to (101).

Refinement
Hydrogens on the amino group were located in a difference Fourier map and freely refined. The C-bound hydrogen atoms were positioned geometrically with C-H distances ranging from 0.93 to 0.97 Å and refined as riding on their parent atoms with U iso (H) = 1.5U eq (C) for methyl groups and U iso (H) = 1.2U eq (C) for other H atoms. The reflection whose intensity was affected by the beamstop was removed from the final refinement. Crystal data, data collection and structure refinement details are summarized in Table 2. Data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR2011 (Burla et al., 2012); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009) and publCIF (Westrip, 2010).

3-Amino-5,5-dimethyl-2-[(E)-2-nitroethenyl]cyclohex-2-en-1-one
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 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.