(E)-1,2-Bis(1,2-di­methyl-3-indolizinyl)­ethene

The molecule of the title compound, C₂₂H₂₂N₂, has a center of symmetry, and two bulky indolizinyl groups are situated on opposite sides of the C=C double bond, resulting in an E configuration. The two indolizinyl groups and the C=C double bond are in the same plane, forming a fully extended conjugated system. There are π–π stacking interactions between neighboring mol­ecules related by a center of symmetry.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.050
• wR factor = 0.106
• Data-to-parameter ratio = 15.5

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Thiocarbonyl compounds are much more reactive than the corresponding carbonyl compounds because of the lower electronegativity and the special electronic structure of the S atom as compared with the O atom. Thiocarbonyl compounds can take part in diversified chemical reactions. As a result, they have found wide-ranging applications in the synthesis of cyclic compounds (Vedejs et al., 1998), natural products (Vedejs et al., 1998), organic conductors and superconductors (Parg et al., 1994). Many practical applications of thiocarbonyl compounds have also been reported (Mastalerz et al., 2001). The majority of thiocarbonyl chemistry are based on investigation with thioketones as substrate because simple thioaldehydes are unstable. However, resonance-stabilized thioaldehydes, such as 1,2-dimethyl-3-thioformylindolizine are quite stable even on long standing. We have investigated the reactions of the indolizinethioaldehyde with tributylphosphine, and found that the conversion of the indolizinethioaldehyde into the title compound, (I), is stereoselective (see Scheme). The structure of (I) is similar to that of trans-stilbene. It is expected that (I) may have great potential as antitumor agent.

The title molecule is centrosymmetric (Fig. 1 and Table 1). The two bulky indolizinyl groups are situated on opposite sides of the C═C double bond, resulting in an E configuration. The indolizine rings are coplanar with the C═C double bond, forming a large extended conjugate system. In the crystal structure, two neighbouring molecules related by center of symmetry show π–π-stacking interactions, with vertical distances of 3.269 (6) Å between the centers of the six-membered rings.

S2. Experimental

A solution of 1,2-dimethyl-3-thioformylindolizine (0.28 g, 1.5 mmol) in anhydrous THF (8 ml) was stirred at room temperature and after the air had been replaced by N₂ gas, tributylphosphine (1.1 g, 5.4 mmol) was added. The reaction mixture was maintained under reflux for 14 h until all the 1,2-dimethyl-3-thioformylindolizine disappeared (monitored by TLC). The solvent was removed in vacuo, the mixture was cooled and the title compound, (I), was collected by filtration and washed with petroleum ether. Yellow single crystals of (I) suitable for X-ray crystallographic analysis were obtained by recrystallization from petroleum ether.

S3. Refinement

The positions of all H atoms were fixed geometrically and refined as riding. The distances to H atoms were in the range 0.93–0.96 Å.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART; data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXTL (Bruker, 2000); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular structure of (I), with 50% probability displacement ellipsoids.
	Fig. 2. The packing diagram of (I), viewed down the a axis.

(E)-1,2-bis(1,2-dimethyl-3-indolizinyl)ethene

Crystal data

C22H22N2	F(000) = 336
Mr = 314.42	Dx = 1.251 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1482 reflections
a = 8.253 (2) Å	θ = 2.5–24.4°
b = 5.435 (1) Å	µ = 0.07 mm^−1
c = 19.056 (4) Å	T = 293 K
β = 102.51 (1)°	Block, yellow
V = 834.5 (3) Å^3	0.3 × 0.2 × 0.2 mm
Z = 2

Data collection

Bruker Smart APEX CCD area-detector diffractometer	1105 reflections with I > 2σ(I)
Radiation source: sealed tube	Rint = 0.060
Graphite monochromator	θmax = 25.5°, θmin = 2.2°
ϕ and ω scans	h = −8→10
4170 measured reflections	k = −6→6
1530 independent reflections	l = −23→20

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)] = 0.050	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.106	H-atom parameters constrained
S = 1.02	w = 1/[σ^2(Fo^2) + (0.02P)^2 + 0.25P] where P = (Fo^2 + 2Fc^2)/3
1530 reflections	(Δ/σ)max < 0.001
99 parameters	Δρmax = 0.27 e Å^−3
0 restraints	Δρmin = −0.31 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
C1	0.1852 (2)	0.3177 (3)	0.34019 (9)	0.0466 (3)
C2	0.0733 (2)	0.2805 (3)	0.38456 (9)	0.0457 (4)
C3	0.1295 (2)	0.0877 (4)	0.43166 (10)	0.0513 (4)
C5	0.3784 (2)	−0.1860 (4)	0.44393 (11)	0.0590 (6)
H5	0.3533	−0.2807	0.4808	0.071*
C6	0.5148 (3)	−0.2342 (4)	0.41966 (12)	0.0662 (6)
H6	0.5825	−0.3650	0.4392	0.079*
C7	0.5584 (3)	−0.0910 (4)	0.36505 (11)	0.0655 (6)
H7	0.6558	−0.1233	0.3497	0.079*
C8	0.4571 (2)	0.0944 (4)	0.33500 (10)	0.0556 (5)
H8	0.4840	0.1873	0.2982	0.067*
C9	0.3113 (2)	0.1472 (4)	0.35912 (9)	0.0466 (3)
C10	0.0679 (2)	−0.0263 (4)	0.48879 (10)	0.0513 (4)
H10	0.1324	−0.1533	0.5130	0.062*
C11	−0.0830 (2)	0.4273 (4)	0.38055 (11)	0.0609 (6)
H11A	−0.0924	0.5488	0.3433	0.091*
H11B	−0.0791	0.5074	0.4258	0.091*
H11C	−0.1772	0.3194	0.3700	0.091*
C12	0.1745 (3)	0.5079 (4)	0.28209 (10)	0.0624 (6)
H12A	0.1056	0.4473	0.2383	0.094*
H12B	0.2837	0.5415	0.2746	0.094*
H12C	0.1273	0.6564	0.2963	0.094*
N4	0.27450 (18)	0.0029 (3)	0.41486 (7)	0.0467 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0442 (7)	0.0541 (8)	0.0423 (7)	−0.0051 (6)	0.0116 (6)	0.0003 (6)
C2	0.0379 (9)	0.0517 (11)	0.0477 (10)	−0.0035 (9)	0.0098 (8)	−0.0049 (9)
C3	0.0437 (7)	0.0601 (9)	0.0531 (8)	0.0002 (7)	0.0175 (6)	0.0018 (7)
C5	0.0575 (12)	0.0663 (14)	0.0560 (11)	0.0070 (11)	0.0187 (10)	0.0114 (10)
C6	0.0564 (12)	0.0713 (15)	0.0745 (14)	0.0175 (12)	0.0223 (11)	0.0098 (12)
C7	0.0455 (11)	0.0825 (16)	0.0734 (14)	0.0055 (11)	0.0239 (11)	−0.0019 (12)
C8	0.0510 (11)	0.0674 (14)	0.0535 (11)	−0.0042 (11)	0.0229 (10)	−0.0002 (10)
C9	0.0442 (7)	0.0541 (8)	0.0423 (7)	−0.0051 (6)	0.0116 (6)	0.0003 (6)
C10	0.0437 (7)	0.0601 (9)	0.0531 (8)	0.0002 (7)	0.0175 (6)	0.0018 (7)
C11	0.0534 (11)	0.0618 (13)	0.0701 (13)	0.0112 (11)	0.0193 (10)	0.0075 (11)
C12	0.0626 (13)	0.0663 (14)	0.0601 (12)	0.0006 (11)	0.0171 (10)	0.0118 (11)
N4	0.0446 (8)	0.0530 (9)	0.0456 (8)	0.0010 (8)	0.0165 (7)	0.0029 (7)

Geometric parameters (Å, º)

C1—C9	1.382 (3)	C7—H7	0.9300
C1—C2	1.395 (2)	C8—C9	1.407 (2)
C1—C12	1.503 (2)	C8—H8	0.9300
C2—C3	1.392 (3)	C9—N4	1.405 (2)
C2—C11	1.505 (3)	C10—C10^i	1.315 (3)
C3—N4	1.383 (2)	C10—H10	0.9300
C3—C10	1.438 (2)	C11—H11A	0.9600
C5—C6	1.333 (3)	C11—H11B	0.9600
C5—N4	1.375 (2)	C11—H11C	0.9600
C5—H5	0.9300	C12—H12A	0.9600
C6—C7	1.407 (3)	C12—H12B	0.9600
C6—H6	0.9300	C12—H12C	0.9600
C7—C8	1.354 (3)
C9—C1—C2	107.73 (16)	C1—C9—N4	107.31 (15)
C9—C1—C12	125.05 (17)	C1—C9—C8	134.45 (18)
C2—C1—C12	127.22 (17)	N4—C9—C8	118.24 (17)
C3—C2—C1	109.15 (16)	C10^i—C10—C3	128.2 (3)
C3—C2—C11	126.44 (16)	C10^i—C10—H10	115.9
C1—C2—C11	124.41 (17)	C3—C10—H10	115.9
N4—C3—C2	106.60 (15)	C2—C11—H11A	109.5
N4—C3—C10	119.80 (17)	C2—C11—H11B	109.5
C2—C3—C10	133.60 (17)	H11A—C11—H11B	109.5
C6—C5—N4	120.49 (19)	C2—C11—H11C	109.5
C6—C5—H5	119.8	H11A—C11—H11C	109.5
N4—C5—H5	119.8	H11B—C11—H11C	109.5
C5—C6—C7	121.2 (2)	C1—C12—H12A	109.5
C5—C6—H6	119.4	C1—C12—H12B	109.5
C7—C6—H6	119.4	H12A—C12—H12B	109.5
C8—C7—C6	119.42 (18)	C1—C12—H12C	109.5
C8—C7—H7	120.3	H12A—C12—H12C	109.5
C6—C7—H7	120.3	H12B—C12—H12C	109.5
C7—C8—C9	120.44 (19)	C5—N4—C3	130.62 (16)
C7—C8—H8	119.8	C5—N4—C9	120.19 (15)
C9—C8—H8	119.8	C3—N4—C9	109.18 (15)
C9—C1—C2—C3	0.4 (2)	C7—C8—C9—C1	−179.7 (2)
C12—C1—C2—C3	−179.38 (18)	C7—C8—C9—N4	0.0 (3)
C9—C1—C2—C11	−179.25 (18)	N4—C3—C10—C10^i	−178.7 (2)
C12—C1—C2—C11	1.0 (3)	C2—C3—C10—C10^i	1.2 (4)
C1—C2—C3—N4	−1.4 (2)	C6—C5—N4—C3	−179.1 (2)
C11—C2—C3—N4	178.23 (18)	C6—C5—N4—C9	0.0 (3)
C1—C2—C3—C10	178.8 (2)	C2—C3—N4—C5	−178.94 (18)
C11—C2—C3—C10	−1.6 (4)	C10—C3—N4—C5	0.9 (3)
N4—C5—C6—C7	1.4 (3)	C2—C3—N4—C9	1.9 (2)
C5—C6—C7—C8	−2.1 (3)	C10—C3—N4—C9	−178.28 (16)
C6—C7—C8—C9	1.4 (3)	C1—C9—N4—C5	179.05 (17)
C2—C1—C9—N4	0.8 (2)	C8—C9—N4—C5	−0.7 (3)
C12—C1—C9—N4	−179.47 (16)	C1—C9—N4—C3	−1.7 (2)
C2—C1—C9—C8	−179.5 (2)	C8—C9—N4—C3	178.57 (17)
C12—C1—C9—C8	0.2 (3)

Symmetry code: (i) −x, −y, −z+1.