2,6-Bis(4-methoxyphenyl)-1,4-dithiine

The title molecule, C18H16O2S2, reveals crystallographic twofold rotation symmetry (with both S atoms lying on the axis) and one half-molecule defines an asymmetric unit. The dithiine ring is in a boat conformation. The aromatic ring and the C=C bond are nearly coplanar, with small torsion angles of −171.26 (19) and 8.5 (3)°. The two S—C bond lengths [1.7391 (19) and 1.7795 (18) Å] are shorter than single C—S bonds and longer than analogous C=S double bonds, which indicates a certain degree of conjugation between the lone pair on the S atom and π electrons of the C=C bond. The crystal packing only features van der Waals interactions.

The title molecule, C 18 H 16 O 2 S 2 , reveals crystallographic twofold rotation symmetry (with both S atoms lying on the axis) and one half-molecule defines an asymmetric unit. The dithiine ring is in a boat conformation. The aromatic ring and the C C bond are nearly coplanar, with small torsion angles of À171.26 (19) and 8.5 (3) . The two S-C bond lengths [1.7391 (19) and 1.7795 (18) Å ] are shorter than single C-S bonds and longer than analogous C S double bonds, which indicates a certain degree of conjugation between the lone pair on the S atom and electrons of the C C bond. The crystal packing only features van der Waals interactions.
The molecular structure of the title compound(I) (Fig. 1) exhibits a twofold rotation axes symmetry. The dithiine ring is in a boat conformation. In the crystal, dominate columns of assembled molecules, however, their separation distances are larger than 5.5402 (13) Å (Fig. 2). The bond lengths of C1-C2 in heterocyclic ring presents a characteristic of the C=C double bond. An aromatic ring and the C=C bond are nearly coplanar, with small torsion angles of -171.26 (19)° and 8.5 (3)° for C1-C2-C3-C4 and C1-C2-C3-C8,respectively ·. The two characteristic bond lengths of S1-C2 and S2 -C1 are shorter than C-S single bonds and longer than analogous C=S double bonds (Allen et al., 1987), which indicates a certain degree of conjugation between the lone pair on the sulfur atom and π electrons of the C=C bond.

Experimental
NaOEt (224 mg, 3.3 mmol) was dissolved in alcohol (10 mL), and then added to bis(4-methoxyphenylethynyl) sulfide (97.8 mg,0.33 mmol). After the mixture was stirred at room temperature for 10 min, Na 2 S·9H 2 O (159 mg, 0.66 mmol) was added. The resulting mixture was then stirred at reflux temperature for 2 h. The reaction mixture was cooled to room temperature and quenched by water and extracted with dichloromethane. The extract was then washed with brine, dried over Na 2 SO 4 , and filtered. The solvent was evaporated in vacuo, and the residue was chromatographed (SiO 2 ; eluent, ether/dichloromethane, 4: 1) to give 93 mg of compound I (85%) as a yellow solid: mp 401-403 K; 1 H NMR (400 MHz, Single crystals of (I) suitable for X-ray diffraction analysis was obtained by slow diffusion of petroleum ether into a dichloromethane solution at 298 K.

Refinement
H atoms were refined with fixed individual displacement parameters [U iso (H) = 1.2 U eq (C) and U iso (H) = 1.5 U eq (C

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. 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.