4,4-Dichlorotricyclo[5.4.0.03,5]undeca-7,9,11-triene

The title compound, C11H10Cl2, is a useful intermediate for the synthesis of 1H-cyclopropa[b]naphthalene. Strain in the molecule is evidenced by the fact that the cyclohexane ring is essentially planar and nearly coplanar with the benzene ring [dihedral angle 1.87 (18)°], and the cyclopropyl ring is almost perpendicular to the cyclohexane ring [dihedral angle 70.99 (12)°]. The molecules are loosely connected into one-dimensional chains by intermolecular Cl⋯Cl interactions with a distance of 3.571 (1) Å. The centroid-to-centroid distance between stacked benzene rings is ca 5.89 Å, indicating that no π–π stacking exists in the crystal structure.

The title compound, C 11 H 10 Cl 2 , is a useful intermediate for the synthesis of 1H-cyclopropa [b]naphthalene. Strain in the molecule is evidenced by the fact that the cyclohexane ring is essentially planar and nearly coplanar with the benzene ring [dihedral angle 1.87 (18) ], and the cyclopropyl ring is almost perpendicular to the cyclohexane ring [dihedral angle 70.99 (12) ]. The molecules are loosely connected into onedimensional chains by intermolecular ClÁ Á ÁCl interactions with a distance of 3.571 (1) Å . The centroid-to-centroid distance between stacked benzene rings is ca 5.89 Å , indicating that nostacking exists in the crystal structure.

Related literature
For related literature, see: Browne et al. (1974); Halton (2003 Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and publCIF (Westrip, 2008). naphthalene, which is a highly strained but readily accessible molecule that has been used as a building block in organic synthesis. It can undergo a variety of reactions because relief of ring strain provides a potent thermodynamic driving force for the reactions (Halton, 2003). Strain in (I) is evidenced by the fact that the cyclohexane ring is essentialy planar (Fig. 1) and nearly coplanar with the benzene ring with a dihedral angle of 1.87 (18)° and that the cyclopropyl ring is almost perpendicular to cyclohexane ring with a dihedral angle of 70.99 (12)°. The molecules pack to form one-dimensional chains connected by intermolecular Cl···Cl interactions with distance of 3.571 (1) Å (Fig. 2). The centroid to centroid distance between stacked benzene rings is ca 5.89 Å, which is very long indicating that no π-π stacking exists in the crystal.

Experimental
Following the general procedure of Browne et al. (1974) a mixture of 1,4-dihydronaphthalene (15g, 0.115 mol), 7 ml of diethylene glycol dimethyl, and 10 ml of tetrachloroethylene was stirred magnetically and brought to 115°C, and sodium trichloroacetate (25 g, 0.144 mol) was added in 1 g portions over a period of 1 h. The mixture was stirred and maintained near boiling (115-120°C) during the addition and for an additional half hour. After separating, washing, and drying the organic phase, concentration in vacuum afforded a brown oil which was distilled to give 7,7-dichlorobenzobicyclo[4.1.0]hept-3-ene

Refinement
H atoms were positioned geometrically and treated as riding, with C-H bond lengths constrained to 0.93 (aromatic CH), 0.97 Å (methylene CH2) and with U iso (H) = 1.2Ueq (carrier aromatic C and methylene C). Fig. 1. The molecular structure of (I), with displacement ellipsoids drawn at the 40% probability level. H atoms are shown as spheres of arbitrary radius.

Figures
supplementary materials sup-2  about twice as large as those based on F, and R-factors based on ALL data will be even larger.