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.

Related literature

For a similar crystal structure, 2,6-diphenyl-1,4-dithiine, see: Piao et al. (2004). For background to 1,4-dithiine derivatives, see: Kobayashi & Gajurel (1986); Scott et al. (2000). For the synthesis of a similar compound, see: Nakayama et al. (1984). For standard bond lengths, see: Allen et al. (1987).

Experimental

Crystal data

• C₁₈H₁₆O₂S₂

• M_r = 328.43

• Orthorhombic, P n m a

• a = 10.1330 (11) Å

• b = 27.318 (3) Å

• c = 5.5402 (6) Å

• V = 1533.6 (3) ų

• Z = 4

• Mo Kα radiation

• μ = 0.35 mm⁻¹

• T = 293 K

• 0.21 × 0.18 × 0.09 mm

Data collection

• Bruker SMART CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2001) T_min = 0.121, T_max = 1.000

• 8513 measured reflections

• 1541 independent reflections

• 1258 reflections with I > 2σ(I)

• R_int = 0.043

Refinement

• R[F² > 2σ(F²)] = 0.038

• wR(F²) = 0.102

• S = 1.04

• 1541 reflections

• 104 parameters

• H-atom parameters constrained

• Δρ_max = 0.29 e Å⁻³

• Δρ_min = −0.16 e Å⁻³

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.

Supporting information

S1. Comment

1,4-Dithiine derivatives are very important intermediates in organic synthesis and can be used as versatile building blocks for a variety of chemical purposes (Kobayashi & Gajurel, 1986). In addition, some 1,4-dithiine derivatives have exhibited good biological activities, For example, Scott et al. showed that 2,3-dihydro-2-phenyl-1,4-dithiin-1,1,4,4-tetroxide could be used as nonpeptide antagonist of the human Galanin hGAL-1 receptor (Scott et al., 2000). Unfortunately, there are very few acceptable methods to prepare 1,4-dithiine compounds thus far, and, in most cases, a successful protocol must use bis(arylethanonyl) sulfides compounds as precursors. Herein we report a new synthetic approaches and crystal structure of 2,6-bis(4-methoxyphenyl)-1,4-dithiine.

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.

Related literature

For a similar crystal structure, 2,6-diphenyl-1,4-dithiine, see: Piao et al. (2004). For background to 1,4-dithiine derivatives, see: Kobayashi & Gajurel (1986); Scott et al. (2000). For the synthesis of a similar compound, see: Nakayama et al. (1984). For standard bond lengths, see: Allen et al. (1987).

S2. 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, Na₂S·9H₂O (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 Na₂SO₄, and filtered. The solvent was evaporated in vacuo, and the residue was chromatographed (SiO₂; eluent, ether/dichloromethane, 4: 1) to give 93 mg of compound I (85%) as a yellow solid: mp 401–403 K; ¹H NMR (400 MHz, CDCl₃): δ = 3.83 (s, 6H; OCH₃), 6.42 (s, 2H; CH), 6.89(d, J = 8.8 Hz, 4H; Ar—H), 7.58 (d, J = 8.8 Hz, 4H; Ar—H); ¹³C NMR (100 MHz, CDCl₃): δ = 55.50 (OCH₃), 114.07 (CH), 116.40 (CH), 128.45 (CH), 129.83 (C), 139.52 (C), 160.10 (C); IR (KBr): ν = 3020, 2959, 2914, 1607, 1508, 1457, 1258, 1191, 832 cm^-1; MS (EI): m/z (%): 328.2 (M⁺, 100), 313.1 (43); HRMS (EI): m/z Calcd for C₁₈H₁₆O₂S₂ 328.0584, Found 328.0586.

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.

S3. 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 methyl)] using a riding model, with aromatic C—H = 0.93 Å, methyl C—H = 0.96 Å.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. Structural unit of the title molecule with atom labelling scheme and 50% probability displacement ellipsoids. Symmetry code to generate the entire molecule:x,-y+1/2,z.
	Fig. 2. Crystal packing reveals a columns of molecules held together by van der Waals interactions, only.

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

Crystal data

C18H16O2S2	F(000) = 688
Mr = 328.43	Dx = 1.422 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 1658 reflections
a = 10.1330 (11) Å	θ = 7.5–53.8°
b = 27.318 (3) Å	µ = 0.35 mm^−1
c = 5.5402 (6) Å	T = 293 K
V = 1533.6 (3) Å^3	Prismatic, yellow
Z = 4	0.21 × 0.18 × 0.09 mm

Data collection

Bruker SMART CCD area-detector diffractometer	1541 independent reflections
Radiation source: fine-focus sealed tube	1258 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.043
phi and ω scans	θmax = 26.0°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Bruker, 2001)	h = −12→12
Tmin = 0.121, Tmax = 1.000	k = −33→32
8513 measured reflections	l = −5→6

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.102	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0554P)^2 + 0.3159P] where P = (Fo^2 + 2Fc^2)/3
1541 reflections	(Δ/σ)max < 0.001
104 parameters	Δρmax = 0.29 e Å^−3
0 restraints	Δρmin = −0.16 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.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
S1	0.49280 (7)	0.2500	0.16602 (12)	0.0352 (2)
S2	0.70856 (7)	0.2500	−0.24173 (15)	0.0423 (2)
O1	0.14361 (14)	0.45648 (5)	0.0468 (3)	0.0484 (4)
C1	0.60102 (19)	0.29896 (6)	−0.2021 (4)	0.0364 (5)
H1	0.6115	0.3262	−0.3011	0.044*
C2	0.50486 (19)	0.29989 (6)	−0.0393 (3)	0.0307 (4)
C3	0.40701 (18)	0.33990 (6)	−0.0143 (3)	0.0296 (4)
C4	0.3199 (2)	0.34206 (7)	0.1786 (4)	0.0364 (5)
H4	0.3213	0.3172	0.2931	0.044*
C5	0.2311 (2)	0.38017 (7)	0.2059 (3)	0.0372 (5)
H5	0.1746	0.3808	0.3381	0.045*
C6	0.22660 (19)	0.41714 (7)	0.0376 (3)	0.0352 (5)
C7	0.31115 (19)	0.41530 (7)	−0.1595 (4)	0.0395 (5)
H7	0.3083	0.4399	−0.2753	0.047*
C8	0.3984 (2)	0.37754 (7)	−0.1841 (4)	0.0371 (5)
H8	0.4537	0.3769	−0.3180	0.044*
C9	0.0549 (2)	0.45883 (8)	0.2462 (5)	0.0556 (6)
H9A	0.0005	0.4301	0.2479	0.083*
H9B	0.0002	0.4874	0.2311	0.083*
H9C	0.1043	0.4606	0.3938	0.083*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0430 (4)	0.0328 (4)	0.0297 (4)	0.000	−0.0017 (3)	0.000
S2	0.0266 (4)	0.0405 (4)	0.0599 (5)	0.000	0.0101 (3)	0.000
O1	0.0487 (9)	0.0401 (8)	0.0563 (10)	0.0129 (7)	0.0112 (7)	0.0073 (7)
C1	0.0326 (10)	0.0306 (9)	0.0459 (12)	−0.0035 (8)	0.0042 (9)	0.0016 (8)
C2	0.0304 (9)	0.0287 (9)	0.0332 (11)	−0.0063 (8)	−0.0021 (8)	−0.0015 (7)
C3	0.0290 (10)	0.0274 (9)	0.0324 (10)	−0.0058 (8)	−0.0013 (8)	−0.0028 (7)
C4	0.0416 (11)	0.0314 (9)	0.0361 (11)	−0.0007 (8)	0.0067 (8)	0.0043 (8)
C5	0.0397 (11)	0.0362 (10)	0.0357 (11)	0.0002 (9)	0.0093 (9)	0.0000 (8)
C6	0.0333 (10)	0.0305 (10)	0.0420 (11)	−0.0001 (8)	−0.0015 (9)	−0.0015 (8)
C7	0.0421 (11)	0.0382 (10)	0.0381 (11)	0.0000 (9)	0.0019 (9)	0.0095 (9)
C8	0.0383 (11)	0.0397 (10)	0.0331 (11)	0.0004 (9)	0.0062 (8)	0.0030 (8)
C9	0.0548 (14)	0.0493 (13)	0.0627 (15)	0.0180 (11)	0.0168 (12)	0.0019 (12)

Geometric parameters (Å, º)

S1—C2	1.7795 (18)	C4—C5	1.384 (3)
S1—C2^i	1.7795 (18)	C4—H4	0.9300
S2—C1	1.7391 (19)	C5—C6	1.375 (3)
S2—C1^i	1.7391 (19)	C5—H5	0.9300
O1—C6	1.365 (2)	C6—C7	1.389 (3)
O1—C9	1.426 (3)	C7—C8	1.365 (3)
C1—C2	1.328 (3)	C7—H7	0.9300
C1—H1	0.9300	C8—H8	0.9300
C2—C3	1.482 (3)	C9—H9A	0.9600
C3—C4	1.387 (3)	C9—H9B	0.9600
C3—C8	1.397 (3)	C9—H9C	0.9600
C2—S1—C2^i	99.97 (12)	C4—C5—H5	120.0
C1—S2—C1^i	100.54 (13)	O1—C6—C5	124.98 (18)
C6—O1—C9	116.92 (16)	O1—C6—C7	115.96 (17)
C2—C1—S2	124.07 (15)	C5—C6—C7	119.06 (18)
C2—C1—H1	118.0	C8—C7—C6	120.36 (18)
S2—C1—H1	118.0	C8—C7—H7	119.8
C1—C2—C3	124.65 (16)	C6—C7—H7	119.8
C1—C2—S1	118.03 (15)	C7—C8—C3	121.97 (18)
C3—C2—S1	117.32 (14)	C7—C8—H8	119.0
C4—C3—C8	116.60 (17)	C3—C8—H8	119.0
C4—C3—C2	121.94 (16)	O1—C9—H9A	109.5
C8—C3—C2	121.46 (16)	O1—C9—H9B	109.5
C5—C4—C3	121.98 (17)	H9A—C9—H9B	109.5
C5—C4—H4	119.0	O1—C9—H9C	109.5
C3—C4—H4	119.0	H9A—C9—H9C	109.5
C6—C5—C4	120.00 (18)	H9B—C9—H9C	109.5
C6—C5—H5	120.0
C1^i—S2—C1—C2	39.0 (2)	C3—C4—C5—C6	0.6 (3)
S2—C1—C2—C3	−175.75 (14)	C9—O1—C6—C5	−0.4 (3)
S2—C1—C2—S1	4.9 (2)	C9—O1—C6—C7	179.31 (19)
C2^i—S1—C2—C1	−48.1 (2)	C4—C5—C6—O1	−179.75 (18)
C2^i—S1—C2—C3	132.49 (11)	C4—C5—C6—C7	0.6 (3)
C1—C2—C3—C4	−171.26 (19)	O1—C6—C7—C8	179.64 (18)
S1—C2—C3—C4	8.1 (2)	C5—C6—C7—C8	−0.7 (3)
C1—C2—C3—C8	8.5 (3)	C6—C7—C8—C3	−0.5 (3)
S1—C2—C3—C8	−172.18 (14)	C4—C3—C8—C7	1.6 (3)
C8—C3—C4—C5	−1.7 (3)	C2—C3—C8—C7	−178.16 (18)
C2—C3—C4—C5	178.07 (17)

Symmetry code: (i) x, −y+1/2, z.