Crystal structure of (1S,2R,6R,7R,8S,12S)-4,10,17-triphenyl-15-thia-4,10-diaza-penta-cyclo[5.5.5.0(1,16).0(2,6).0(8,12)]hepta-deca-13,16-diene-3,5,9,11-tetrone p-xylene hemisolvate.

The title tetrone compound, C32H22N2O4S· 0.5C8H10, is the major product (50% yield) of an attempted Diels-Alder reaction of 2-(α-styr-yl)thio-phene with N-phenyl-male-imide (2 equivalents) in toluene. Recrystallization of the resulting powder from p-xylene gave the title hemisolvate; the p-xylene mol-ecule is located about an inversion center. In the crystal, the primary tetrone contacts are between a carbonyl O atom and the four flagpole H atoms of the bi-cyclo-[2.2.2]octene core, forming chains along [001].


Chemical context
The title compound, (3), is the first reported double-Diels-Alder adduct obtained from a one-pot reaction of a 2-vinylthiophene ( Fig. 1). This methodology may have use in the synthesis of novel ligands, zeolites, or polyamides.
Mechanism: Mechanisms proposed for double adducts (7) (Lovely et al., 2007) and (8) (Noland et al., 1993) suggest a ISSN 1600-5368 Diels-Alder reaction (Fig. 3), with loss of H 2 by an unknown pathway, and then a second cycloaddition. Noland et al. (1993) observed that formation of (8) was accelerated by exposure to oxygen, and aromatization to (9) was favored over (8) in acid. Brewer & Elix (1975a) reported a double adduct (10) and a hydroperoxy intermediate thereof; they proposed loss of H 2 in an autoxidation followed by elimination of H 2 O 2 , a pathway that fits both observations made by the Noland group. The crystal structures of (3) and the hydroperoxide (11) (Noland et al., 2014), and preliminary HRMS and 1 H NMR evidence that (12) is an intermediate to (3), all support the mechanism proposed by Brewer & Elix (1975a).

Figure 1
The molecular structure of compound (3), with atom labelling (nonlabelled atoms in the p-xylene solvent molecule are related to the labelled atoms by inversion symmetry). Displacement ellipsoids are drawn at the 50% probability level.

Supramolecular features
In the crystal of (3), the carbonyl atom O5 forms weak hydrogen bonds with the endo face of the bicyclo[2.

Figure 6
The crystal packing of compound (3)   A view along the c axis of the crystal packing of compound (3). p-Xylene molecules and inversion-related pairs (O11Á Á ÁH14) of molecules occupy alternating layers about inversion centers.

Refinement
Crystal data, data collection, and structure refinement details are summarized in Table 2. C-bound H atoms were placed in calculated positions and refined as riding atoms, with C-H = 0.0.95-0.98 Å and with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms.  program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXTL2008 (Sheldrick, 2008), enCIFer (Allen et al., 2004) and publCIF (Westrip, 2010). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.38 e Å −3 Δρ min = −0.36 e Å −3 Special details 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.