2,5-Dichloro-2,5-dihydro­thio­phene 1-oxide: determinaton of the complete stereochemistry

The title five-membered heterocycle, C₄H₄Cl₂OS, adopts an envelope conformation with the S atom at the tip of the flap. All three ring substituents, viz. the sulfoxide O atom and the two Cl atoms, are cis to each other. The two C atoms α to the sulfoxide group are also bonded to chlorine. The electron-withdrawing chlorine substituents give rise to weak C—H...O hydrogen bonds with the sulfoxide O atom of a symmetry-related mol­ecule [H...O = 2.44 (2) and 2.61 (2) Å, C...O = 3.143 (3) and 3.302 (2) Å and C—H...O = 129.9 (19) and 135.1 (19)°]. There is also a possible weak C—H...Cl inter­action. Chains of mol­ecules held together by these weak inter­actions run parallel to the a axis.

S1. Comment

Several decades ago, Kergomard & Vincent (1967) reported the synthesis of 2,5-dichloro-2,5-dihydrothiophene 1-oxide, (I) (stereochemistry not shown), from the reaction of thiophene and sodium hypochlorite. Also isolated were monochlorothiophenes and dichlorothiophenes. The preparation of sulfoxide (I) was also described in a patent (Kergomard & Thiolliere, 1965) and its use as an inhibitor of spore formation of mushrooms was claimed. In addition, the authors stated that the double bond is only slightly reactive towards peracetic acid and displays no reaction with chlorine or bromine. The narrow melting point range, reported by Kergomard & Vincent (1967) simply as 385 K, indicated that a single isomer was formed of the three possible shown in the scheme. Additional evidence that sulfoxide (I) is a single isomer was provided by a ¹³C NMR spectrum (obtained by us) that had just two signals, one at 130.96 p.p.m. (the sp² hybridized C atoms) and the other at 69.92 p.p.m. (the sp³ hybridized C atoms). From the ¹H NMR spectrum of (I), Kergomard & Vincent (1967) concluded that the two Cl substituents were cis to one another, which meant that the stereochemistry could be that of either (Ia) or (Ib).

Haynes & Placek (1981), who extended the experimental efforts of Zawaski (1978), attempted to oxidize the sulfoxide to the sulfone using hydrogen peroxide in the presence of zirconium tetrachloride with diglyme as the solvent. The only product isolated was (E,E)-1,4-dichloro-1,3-butadiene, (II). Assuming that the sulfoxide was converted to the sulfone, a retro Diels–Alder reaction following the Woodward–Hoffman rules would produce the single diene if the Cl substituents were cis to one another. Thus, formation of (E,E)-1,4-dichloro-1,3-butadiene is further indirect evidence that the two Cl substituents are indeed cis to one another.

The unanswered question was the stereo relationship of the O atom to the two Cl substituents. To confirm the stereochemistry indicated by the above observations, and to establish with certainty all aspects of the stereochemistry of sulfoxide (I), a sample was crystallized from chloroform, the solvent used by Kergomard & Vincent (1967).

The crystal structure of (I) reveals that the stereochemistry is that of (Ib), with the two Cl atoms and the O atom all cis to each other, as shown in the displacement ellipsoid plot in Fig. 1. The five-membered ring itself adopts an envelope conformation; the four C atoms are almost coplanar [torsion angle −0.3 (3)°], with the S atom at the tip of the flap.

One interesting aspect of the packing in the crystal of (I), as shown in Fig. 2, is the weak C—H··· O hydrogen bonding involving atoms C2, C5 and the sulfoxide O atom. Apparently, the electron-withdrawing atoms Cl2 and Cl5 bonded to C2 and C5 promote a positive charge on H2 and H5. Although the H···O distances shown in Table 2 are longer than those in O—H···O hydrogen bonds, they are typical of distances observed for similar weak hydrogen bonds (Desiraju & Steiner, 1999). As has been observed for other weak hydrogen bonds (Glusker, 1998), the C—H···O bond angle deviates significantly from 180°. The packing diagram in Fig. 2 shows the possibility that there may actually be a bifurcated or three-center C2—H2···(O,Cl2) hydrogen bond. The H2···Cl2 distance is 2.90 Å and C2···Cl2 is 3.67 Å, with the C2—H2···Cl angle being 144.2°. The H2 atom is only 0.23 Å from the plane formed by atoms C2, O and Cl2; this tendency toward planarity is characteristic of atoms that participate in a three-center interaction (Desiraju & Steiner, 1999). The molecules held together by these weak interactions form chains parallel to the a axis.

S2. Experimental

The title compound was prepared following the procedure described by Kergomard & Vincent (1967). Crystallization from chloroform produced colorless hexagonal plates of (I) suitable for X-ray diffraction.

S3. Refinement

Two low-angle reflections (106 and 204) were omitted from the refinement. Idealized positions for atoms H3 and H4 were calculated at 0.93 Å from atoms C3 and C4, respectively, with U_iso(H) = 1.2U_eq(C). Because they participate in a weak hydrogen bond, the positions of atoms H2 and H5 were refined, with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 2003); cell refinement: SMART; data reduction: SHELXTL (Sheldrick, 1997b); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: ORTEP-3 (Farrugia, 1997), Mercury (Bruno et al., 2002) and SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of the molecule of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A packing diagram for (I), with the weak C—H···O bonds to the sulfoxide O atom indicated by dotted lines. A very weak interaction between atoms H2 and Cl2 is also indicated by dotted lines. [Symmetry codes: (i) 1/2 − x, y − 1/2, z); (ii) 1/2 + x, 1/2 − y, 1 − z.]
	Fig. 3. Please provide missing caption.

2,5-Dichloro-2,5-dihydrothiophene 1-oxide

Crystal data

C4H4Cl2OS	F(000) = 688
Mr = 171.03	Dx = 1.749 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 9966 reflections
a = 10.1041 (4) Å	θ = 2.3–28.3°
b = 7.2210 (3) Å	µ = 1.21 mm^−1
c = 17.8026 (7) Å	T = 294 K
V = 1298.91 (9) Å^3	Plate, colorless
Z = 8	0.70 × 0.46 × 0.18 mm

Data collection

Bruker SMART CCD area-detector diffractometer	1606 independent reflections
Radiation source: fine-focus sealed tube	1429 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
ϕ and ω scans	θmax = 28.3°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 2001)	h = −13→13
Tmin = 0.632, Tmax = 0.804	k = −9→9
9966 measured reflections	l = −23→23

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)] = 0.032	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.089	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0444P)^2 + 0.801P] where P = (Fo^2 + 2Fc^2)/3
1606 reflections	(Δ/σ)max = 0.002
79 parameters	Δρmax = 0.57 e Å^−3
0 restraints	Δρmin = −0.46 e Å^−3

Special details

Experimental. Diffraction data were obtained on a Bruker SMART CCD system and refined with Bruker SMART software (Bruker, 2003). The phase problem was solved by direct methods in SHELXTL (Sheldrick, 1997b).

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
S	0.40496 (5)	0.19880 (7)	0.45559 (2)	0.04045 (15)
O	0.29208 (13)	0.3283 (2)	0.46124 (8)	0.0492 (4)
C2	0.4018 (2)	0.0732 (3)	0.36541 (11)	0.0450 (4)
H2	0.362 (2)	−0.038 (4)	0.3709 (12)	0.054*
Cl2	0.30374 (5)	0.18980 (8)	0.29703 (3)	0.05251 (17)
C3	0.5446 (2)	0.0642 (3)	0.34445 (13)	0.0573 (6)
H3	0.5774	−0.0248	0.3116	0.069*
C4	0.6213 (2)	0.1900 (4)	0.37542 (12)	0.0565 (6)
H4	0.7117	0.1949	0.3658	0.068*
C5	0.55593 (18)	0.3234 (3)	0.42629 (11)	0.0446 (4)
H5	0.602 (2)	0.352 (4)	0.4716 (13)	0.054*
Cl5	0.51474 (6)	0.53555 (8)	0.38047 (3)	0.05672 (18)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S	0.0387 (2)	0.0514 (3)	0.0313 (2)	0.00534 (17)	0.00597 (16)	0.00755 (17)
O	0.0378 (7)	0.0646 (9)	0.0452 (7)	0.0092 (6)	0.0078 (5)	−0.0026 (6)
C2	0.0511 (11)	0.0411 (9)	0.0428 (10)	−0.0005 (8)	0.0049 (8)	0.0013 (8)
Cl2	0.0512 (3)	0.0662 (3)	0.0401 (3)	−0.0039 (2)	−0.00417 (19)	−0.0030 (2)
C3	0.0602 (13)	0.0629 (13)	0.0488 (11)	0.0227 (11)	0.0137 (10)	−0.0005 (10)
C4	0.0354 (9)	0.0840 (17)	0.0501 (12)	0.0141 (10)	0.0075 (8)	0.0044 (11)
C5	0.0316 (8)	0.0643 (12)	0.0379 (9)	0.0009 (8)	−0.0027 (7)	0.0051 (8)
Cl5	0.0582 (3)	0.0567 (3)	0.0553 (3)	−0.0141 (2)	−0.0059 (2)	0.0087 (2)

Geometric parameters (Å, º)

S—O	1.4781 (14)	C3—C4	1.315 (4)
S—C2	1.844 (2)	C3—H3	0.9300
S—C5	1.846 (2)	C4—C5	1.477 (3)
C2—C3	1.492 (3)	C4—H4	0.9300
C2—Cl2	1.781 (2)	C5—Cl5	1.785 (2)
C2—H2	0.91 (3)	C5—H5	0.96 (2)
O—S—C2	110.92 (9)	C2—C3—H3	122.1
O—S—C5	110.40 (9)	C3—C4—C5	116.38 (19)
C2—S—C5	90.46 (9)	C3—C4—H4	121.8
C3—C2—Cl2	112.81 (15)	C5—C4—H4	121.8
C3—C2—S	102.85 (15)	C4—C5—Cl5	112.54 (14)
Cl2—C2—S	111.84 (11)	C4—C5—S	102.99 (16)
C3—C2—H2	114.9 (16)	Cl5—C5—S	110.78 (10)
Cl2—C2—H2	104.2 (15)	C4—C5—H5	115.9 (15)
S—C2—H2	110.5 (14)	Cl5—C5—H5	108.4 (15)
C4—C3—C2	115.76 (19)	S—C5—H5	105.9 (15)
C4—C3—H3	122.1
O—S—C2—C3	141.37 (14)	C3—C4—C5—Cl5	−96.5 (2)
C5—S—C2—C3	29.27 (15)	C3—C4—C5—S	22.8 (2)
O—S—C2—Cl2	20.05 (14)	O—S—C5—C4	−142.06 (13)
C5—S—C2—Cl2	−92.05 (12)	C2—S—C5—C4	−29.48 (14)
Cl2—C2—C3—C4	98.2 (2)	O—S—C5—Cl5	−21.51 (14)
S—C2—C3—C4	−22.4 (2)	C2—S—C5—Cl5	91.07 (12)
C2—C3—C4—C5	−0.3 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2···O^i	0.91 (3)	2.44 (2)	3.143 (3)	135.1 (19)
C5—H5···O^ii	0.96 (2)	2.61 (2)	3.302 (2)	129.9 (19)

Symmetry codes: (i) −x+1/2, y−1/2, z; (ii) x+1/2, −y+1/2, −z+1.