7-Nitro-1,2,3,4-tetrahydronaphthalene-1-spiro-2′-(1,3-dithiane)

In the title compound, C13H15NO2S2, the nitro group is coplanar with the benzene ring to which it is attached, forming a dihedral angle of 1.07 (14)°. The dithiane ring adopts a chair conformation. In the crystal structure, molecules are linked through C—H⋯O and C—H⋯π [C⋯Cg = 3.7164 (15) Å] interactions. The crystal studied was an inversion twin with an 0.134 (5):0.866 (5) domain ratio.

In the title compound, C 13 H 15 NO 2 S 2 , the nitro group is coplanar with the benzene ring to which it is attached, forming a dihedral angle of 1.07 (14) . The dithiane ring adopts a chair conformation. In the crystal structure, molecules are linked through C-HÁ Á ÁO and C-HÁ Á Á [CÁ Á ÁCg = 3.7164 (15) Å ] interactions. The crystal studied was an inversion twin with an 0.134 (5):0.866 (5) domain ratio.

Comment
The protection of carbonyl groups to produce dithioketals is now commonly used as an important synthetic technique in the preparation of many organic compounds, including multi-functional complex molecules (Goswami & Maity 2008;Fun et al., 2009). Herein, we report the synthesis of the title compound, (I), from 5-nitro-3,4-dihydro-2H-naphthalen-1-one using boron trifluoride etherate as the catalyst.
After completion of the reaction, NaHCO 3 solution was added carefully to neutralize the mixture at room temperature. This was then extracted with dichloromethane. The organic layer was dried (anhydrous Na 2 SO 4 ) and the solvent removed under reduced pressure. The crude product was purified by column chromatography using silica gel with 10 % ethyl acetate in petroleum ether as eluant to afford (I) (670 mg, 92 %) as a colourless crystalline solid along with other thiane derivatives.

Refinement
All hydrogen atoms were positioned geometrically and refined in the riding model approximation with C-H = 0.93-0.97 Å, and with U iso (H) = 1.2 U eq (C). The structure was twinned with a refined BASF ratio of 0.134 (5):0.866 (5). Fig. 1. The molecular structure of (I), showing 50% probability displacement ellipsoids and the atomic numbering.

Special details
Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment.
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.