1-Isopropyl-4,7-dimethyl-2,8-dinitronaphthalene

The title compound, C15H16N2O4, was synthesized from a mixture of α-himachalene (2-methylene-6,6,9-trimethylbicyclo[5.4.O1,7]undec-8-ene) and β-himachalene (2,6,6,9-tetramethylbicyclo[5.4.01,7]undeca-1,8-diene) which were isolated from an oil of the Atlas cedar (Cedrus atlantica). The asymmetric unit contains two independent molecules. In each of the two molecules, two O atoms of one nitro group are disordered over two sets of sites with site-occupancy factors of 0.636 (5):0.364 (5) and 0.832 (5):0.168 (5). The crystal structure features weak C—H⋯O hydrogen bonds.


D-HÁ
Data collection: CrysAlis PRO (Agilent, 2010); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 1999 The bicyclic sesquiterpenes α-and β-himachalene are the main constituents of the essential oil of the Atlas cedar (Cedrus atlantica) (Joseph & Dev, 1968;Plattier & Teisseire, 1974). The reactivity of these sesquiterpenes and its derivatives has been studied extensively by our team in order to prepare new products having biological proprieties (Lassaba et al., 1998;Chekroun et al., 2000;El Jamili et al., 2002;Sbai et al., 2002;Dakir et al., 2004). Indeed, these compounds were tested, using the food poisoning technique, for their potential antifungal activity against the phytopathogen Botrytis cinerea (Daoubi et al., 2004). The catalytic dehydrogenation of the mixture of α-and β-himachalene by 5% of palladium on carbon(10%) gives, with good yield, the aryl-himachalene (Daunis et al., 1981). Treatement of the latter by a mixture of nitric acid and sulfuric acid, gives the title compound with a yield of 20%. The structure of this new product was confirmed by its crystal structure. The molecular structure of (I) is shown in Fig. 1. The asymmetric unit contains two molecules of 1-isopropyl-4,7-dimethyl-2,8-dinitro-naphthalene. The naphthalene ring systems are approximately planar with r.s.d.deviations of 0.087 (2) and 0.090 (2) A°. The bond lengths and angles are within normal ranges in both molecules. In the crystal structure, the two molecules are not parallel but have a dihedral angle of 1.54 (7)°. The crystal structure is stabilized by intermolecular C-H···O hydrogen bonds, which link the molecules into chains parallel to the c axis ( Fig. 2, Table 1).

Experimental
In a reactor of 250 ml equipped with a magnetic stirrer and a dropping funnel, we introduct 60 ml of dichloromethane, 3 ml of nitric acid and 5 ml of concentrated sulfuric acid. After cooling, added dropwise through the dropping funnel 6 g (30 mmol) of aryl-himachalene dissolved in 30 ml of dichloromethane. The reaction mixture was stirred for 4 h, then added 50 ml of water ice and extracted with dichloromethane. The organic layers were combined, washed five times with 4O ml with water and dried over sodium sulfate and then concentrated under vacuum. The residue was subjected to chromatography on a column of silica gel with hexane-ethyl acetate (98/2) as eluent, to obtain 1.7 g (6 mmol) of the title compound which was recrystallized in ethyl acetate.

Figure 1
Molecular structure of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms are represented as small spheres of arbitrary radii.

Figure 2
Partial packing view showing the C-H···O interactions (dashed lines) and the formation of a chain parallel to the a axis.
H atoms not involved in hydrogen bonding have been omitted for clarity.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.19 e Å −3 Δρ min = −0.26 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.