Crystal structure of the cage derivative pentacyclo[5.4.0.02,6.03,10.05,9]undeca-8,11-dione ethylene dithioketal

The pentacycloundecane cage derivative exhibits unusual Csp 3—Csp 3 single bond lengths ranging from 1.495 (3) to 1.581 (2) and strained bond angles as small as 89.29 (12) and as large as 115.11 (11)°.


Chemical context
Caged molecules have found utility in various fields of science such as medicine, high energy materials and complex natural product synthesis. The high symmetry, rigid geometry and inherent strain present in these molecules make them theoretically interesting and synthetically challenging molecular frames (Marchand, 1989;Mehta et al., 1997).
The presence of C-S bonds in (2) reveals the loss of coupling of one sp 2 carbon atom in the parent diketone (1). The distance between the carbons C10 and C9 bearing dithioketal ring is found to be considerably longer [1.533 (2) Å ] than the carbons C1 and C2 [1.507 (2) Å ] bearing the carbonyl group.

Synthesis and crystallization
Preparation of compound (2): To a stirred suspension of dione (1) (630 mg, 3.6 mmol) in dry benzene (20 mL) was added 1,2ethanedithiol (1 mL) and p-toluenesulfonic acid (PTSA) (20 mg). The reaction mixture was refluxed and the water generated was removed with the aid of a Dean-Stark apparatus for 1 h. The progress of the reaction was monitored by TLC and at the conclusion of the reaction, the mixture was extracted with ethyl acetate (20 mL Â 4). Yellow crystals were isolated when the solvent was allowed to evaporate (926 mg, 100%). The 1 H NMR and 13 C spectra were compared with literature reports and found to be identical. M.p. 382-383 K (literature m.p. 369-371 K; Majerski & Veljkovik, 1998).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. C-bound H atoms were positioned geometrically with C-H = 1.00 Å , and refined as rinding with U iso (H) = 1.2U eq (C). ORTEP diagrams of (2) showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.   (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Special details
Experimental. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. Melting points were recorded on Labhosp or Veego melting point apparatus and are uncorrected. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > 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.