6,8-Di­chloro-3-(pyridin-2-yl)-2-[1-(pyridin-2-yl)eth­yl]-1,2-di­hydro­quinoxaline

Malan, F.P.; Mansour, A.M.; Manicum, A.-L.E.

doi:10.1107/S241431462300665X

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 8| Part 8| August 2023| x230665

https://doi.org/10.1107/S241431462300665X

Open

access

6,8-Dichloro-3-(pyridin-2-yl)-2-[1-(pyridin-2-yl)ethyl]-1,2-dihydroquinoxaline

Frederick P. Malan,^a Ahmed M. Mansour ^b and Amanda-Lee E. Manicum ^c ^*

^aDepartment of Chemistry, University of Pretoria, 0002, Pretoria, South Africa, ^bDepartment of Chemistry, Faculty of Science, Cairo University, Gamma Street, Giza, Cairo 12613, Egypt, and ^cDepartment of Chemistry, Tshwane, University of Technology, 0001, Pretoria, South Africa
^*Correspondence e-mail: ManicumAE@tut.ac.za

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 29 June 2023; accepted 31 July 2023; online 4 August 2023)

This article is part of a collection of articles to commemorate the founding of the African Crystallographic Association and the 75th anniversary of the IUCr.

The crystal structure of the racemic title compound, C₂₀H₁₆C_l2N₄ is described, where the formation of a di-substituted 6,8-dichloro quinoxaline, containing two stereogenic centres, is confirmed.

Keywords: crystal structure; quinoxaline derivative; chiral compound.

CCDC reference: 2285764

Structure description

The family of functionalized quinoxaline compounds is an important class of heterocyclic compounds because of their synthetic utility and electroluminescent properties, as well as the different biological properties they have been found to exhibit (Pereira et al., 2015 ). The gradually expanding library of active compounds has lead to a growing interest into their solid- and solution-state characterization, including single-crystal X-ray diffraction. As part of our studies in this area, we now describe the synthesis and structure of the title compound, C₂₀H₁₆C_l2N₄.

The compound crystallizes in the monoclinic space group P2₁/c with Z = 4. The asymmetric unit (Fig. 1) contains one molecule, featuring the 6,8-dichloroquinoxaline-based skeleton with two pyridyl-based substituents attached to positions 2 and 3 (atoms C1 and C2, respectively). The compound contains two chiral centres, namely atoms C3 and C14: in the arbitrarily chosen asymmetric unit, these both have an R configuration, but crystal symmetry generates a racemic mixture. The quinoxalinyl ring system and the 2-pyridyl groups are close to co-planar [N3—C9—C1—N1 = −179.61 (14), C8—N1—C1—C9 = 175.17 (13)°], with the third picolyl-containing substituent more notably rotated out of plane [C1—C2—C14—C16 = −166.73 (12)°] with respect to the quinoxalinyl group. In the quinoxaline moiety, partial saturation on C2 (position 3) occurs and C2 is sp³-hybridized with bond angles of 113.58 (12)° (N2—C2—C14), 108.58 (12)° (N2—C2—C1) and 112.34 (12)° (C1—C2—C14). This leads C2 to be displaced by 0.383 (3) Å from the quinoxalinyl mean plane. Bonds lengths supporting the partially saturated character include: 1.290 (2) Å (N1—C1), 1.522 (2) Å (C1—C2), 1.4586 (19) Å (C2—N2) and 1.550 (2) Å (C2—C14). The remaining C—C, C—Cl, and C—N bond lengths and angles agree well with similar pyridyl-containing quinoxaline systems (Wang et al., 2015 ). A weak bifurcated intramolecular N—H⋯(N,Cl) hydrogen bond occurs (Table 1).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H2⋯Cl1	0.88	2.64	2.9941 (13)	105
N2—H2⋯N4	0.88	2.50	2.815 (2)	102

Figure 1
Perspective view of the molecular structure of the title compound showing displacement ellipsoids at the 50% probability level.

In the crystal, the compound packs as layers that extend down the c-axis interlinked by weak C—H⋯N hydrogen-bonding interactions (Fig. 2). No aromatic π–π stacking interactions were observed.

Figure 2
Packing viewed along the a-axis direction. Hydrogen-bonding interactions are indicated by means of cyan lines.

Synthesis and crystallization

Picolylamine (1 mmol), 2-methyl-2-(2-pyridyl)ethylamine (1 mmol) and 3,5-dichlorocyclohexan-1,2-dione (1 mmol) were added to a round-bottom flask with methanol (20 ml). The resulting solution was carefully heated to 50°C for approximately 2 h. The yellow solution was left to crystallize, after which yellow crystals of the title compound (which in this case represents the major product) were obtained.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The highest calculated residual electron density is 0.62 e Å⁻³ at 0.91 Å from N2.

Table 2
Experimental details

Crystal data
Chemical formula	C₂₀H₁₆Cl₂N₄
M_r	383.27
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	150
a, b, c (Å)	8.4245 (3), 20.7040 (6), 10.2055 (3)
β (°)	96.448 (3)
V (Å³)	1768.79 (10)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.38
Crystal size (mm)	0.27 × 0.19 × 0.09

Data collection
Diffractometer	XtaLAB Synergy R, DW system, HyPix
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku OD, 2019)
T_min, T_max	0.576, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	29036, 4742, 3981
R_int	0.112
(sin θ/λ)_max (Å⁻¹)	0.719

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.047, 0.137, 1.10
No. of reflections	4742
No. of parameters	236
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.62, −0.58
Computer programs: CrysAlis PRO (Rigaku OD, 2023 $[Rigaku OD (2023). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]$ ), SHELXT (Sheldrick, 2015a ), SHELXL (Sheldrick, 2015b ) and OLEX2 (Dolomanov et al., 2009 ).

Structural data

CCDC reference: 2285764

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S241431462300665X/hb4436sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S241431462300665X/hb4436Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S241431462300665X/hb4436Isup3.cdx

Supporting information file. DOI: https://doi.org/10.1107/S241431462300665X/hb4436Isup4.cml

checkCIF report

Computing details top

Data collection: CrysAlis PRO 1.171.42.89a (Rigaku OD, 2023); cell refinement: CrysAlis PRO 1.171.42.89a (Rigaku OD, 2023); data reduction: CrysAlis PRO 1.171.42.89a (Rigaku OD, 2023); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: Olex2 (Dolomanov et al., 2009); software used to prepare material for publication: Olex2 (Dolomanov et al., 2009).

6,8-Dichloro-3-(pyridin-2-yl)-2-[1-(pyridin-2-yl)ethyl]-1,2-dihydroquinoxaline top

Crystal data top

C₂₀H₁₆Cl₂N₄	F(000) = 792
M_r = 383.27	D_x = 1.439 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.4245 (3) Å	Cell parameters from 18589 reflections
b = 20.7040 (6) Å	θ = 2.6–31.0°
c = 10.2055 (3) Å	µ = 0.38 mm⁻¹
β = 96.448 (3)°	T = 150 K
V = 1768.79 (10) Å³	Blade, yellow
Z = 4	0.27 × 0.19 × 0.09 mm

Data collection top

XtaLAB Synergy R, DW system, HyPix diffractometer	4742 independent reflections
Radiation source: Rotating-anode X-ray tube, Rigaku (Mo) X-ray Source	3981 reflections with I > 2σ(I)
Mirror monochromator	R_int = 0.112
Detector resolution: 10.0000 pixels mm^-1	θ_max = 30.8°, θ_min = 2.4°
ω scans	h = −12→10
Absorption correction: multi-scan (CrysalisPro; Rigaku OD, 2019)	k = −28→26
T_min = 0.576, T_max = 1.000	l = −14→13
29036 measured reflections

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.047	H-atom parameters constrained
wR(F²) = 0.137	w = 1/[σ²(F_o²) + (0.0676P)² + 0.7299P] where P = (F_o² + 2F_c²)/3
S = 1.10	(Δ/σ)_max = 0.001
4742 reflections	Δρ_max = 0.62 e Å⁻³
236 parameters	Δρ_min = −0.58 e Å⁻³
0 restraints

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. All H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Cl2	1.12383 (5)	0.09926 (2)	0.40380 (4)	0.02882 (13)
Cl1	0.83348 (6)	0.03634 (2)	0.83287 (5)	0.03650 (15)
N1	0.81871 (15)	0.26674 (6)	0.64452 (13)	0.0189 (3)
N2	0.73638 (16)	0.17552 (6)	0.82624 (13)	0.0201 (3)
H2	0.7411	0.1527	0.8994	0.024*
N3	0.59274 (18)	0.36766 (7)	0.83720 (15)	0.0261 (3)
N4	0.45284 (17)	0.14108 (7)	0.93078 (16)	0.0279 (3)
C16	0.37494 (18)	0.18777 (7)	0.85957 (15)	0.0179 (3)
C8	0.85917 (17)	0.20116 (7)	0.63224 (15)	0.0181 (3)
C3	0.81853 (18)	0.15560 (7)	0.72517 (15)	0.0187 (3)
C9	0.69244 (18)	0.35242 (7)	0.74782 (15)	0.0189 (3)
C1	0.72267 (17)	0.28236 (7)	0.72928 (15)	0.0175 (3)
C2	0.64108 (17)	0.23446 (7)	0.81296 (14)	0.0169 (3)
H2A	0.6423	0.2536	0.9030	0.020*
C6	1.00485 (19)	0.12035 (8)	0.52627 (16)	0.0215 (3)
C14	0.46394 (18)	0.22276 (7)	0.75909 (15)	0.0190 (3)
H14	0.4123	0.2659	0.7422	0.023*
C7	0.95056 (18)	0.18329 (8)	0.53247 (15)	0.0205 (3)
H7	0.9755	0.2141	0.4690	0.025*
C10	0.76783 (19)	0.39916 (8)	0.67700 (17)	0.0224 (3)
H10	0.8372	0.3868	0.6142	0.027*
C5	0.96985 (19)	0.07447 (8)	0.61717 (16)	0.0236 (3)
H5	1.0082	0.0315	0.6126	0.028*
C4	0.8772 (2)	0.09267 (8)	0.71550 (17)	0.0230 (3)
C17	0.2167 (2)	0.20287 (8)	0.87252 (19)	0.0271 (4)
H17	0.1635	0.2360	0.8203	0.033*
C19	0.2179 (2)	0.12117 (8)	1.03820 (18)	0.0263 (3)
H19	0.1672	0.0977	1.1018	0.032*
C20	0.3742 (2)	0.10886 (9)	1.01806 (19)	0.0300 (4)
H20	0.4295	0.0757	1.0688	0.036*
C11	0.7391 (2)	0.46377 (8)	0.70050 (19)	0.0288 (4)
H11	0.7886	0.4965	0.6541	0.035*
C12	0.6367 (2)	0.47994 (9)	0.7931 (2)	0.0325 (4)
H12	0.6154	0.5238	0.8118	0.039*
C13	0.5664 (2)	0.43017 (9)	0.8576 (2)	0.0330 (4)
H13	0.4954	0.4414	0.9199	0.040*
C18	0.1374 (2)	0.16896 (9)	0.9625 (2)	0.0305 (4)
H18	0.0290	0.1784	0.9722	0.037*
C15	0.4450 (2)	0.18517 (10)	0.62926 (16)	0.0290 (4)
H15A	0.4889	0.1416	0.6441	0.044*
H15B	0.5026	0.2076	0.5644	0.044*
H15C	0.3315	0.1822	0.5961	0.044*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cl2	0.0285 (2)	0.0321 (2)	0.0284 (2)	0.00069 (15)	0.01460 (17)	−0.00866 (15)
Cl1	0.0531 (3)	0.0222 (2)	0.0386 (3)	0.00890 (18)	0.0247 (2)	0.00922 (17)
N1	0.0183 (6)	0.0205 (6)	0.0189 (6)	0.0000 (5)	0.0063 (5)	0.0003 (5)
N2	0.0214 (6)	0.0216 (6)	0.0188 (6)	0.0054 (5)	0.0087 (5)	0.0045 (5)
N3	0.0305 (7)	0.0215 (7)	0.0287 (7)	0.0010 (5)	0.0135 (6)	−0.0030 (5)
N4	0.0194 (7)	0.0333 (8)	0.0324 (8)	0.0030 (6)	0.0085 (6)	0.0137 (6)
C16	0.0175 (7)	0.0186 (7)	0.0182 (7)	−0.0023 (5)	0.0043 (5)	0.0000 (5)
C8	0.0163 (7)	0.0203 (7)	0.0184 (7)	0.0002 (5)	0.0054 (5)	−0.0002 (5)
C3	0.0170 (7)	0.0207 (7)	0.0192 (7)	0.0010 (5)	0.0054 (6)	0.0005 (5)
C9	0.0180 (7)	0.0188 (7)	0.0205 (7)	−0.0004 (5)	0.0044 (6)	−0.0006 (5)
C1	0.0159 (7)	0.0192 (7)	0.0179 (7)	−0.0007 (5)	0.0040 (5)	0.0012 (5)
C2	0.0168 (7)	0.0176 (7)	0.0172 (7)	0.0008 (5)	0.0056 (5)	0.0006 (5)
C6	0.0195 (7)	0.0256 (8)	0.0206 (7)	0.0008 (6)	0.0074 (6)	−0.0066 (6)
C14	0.0163 (7)	0.0217 (7)	0.0196 (7)	0.0002 (5)	0.0047 (5)	0.0053 (6)
C7	0.0209 (7)	0.0226 (8)	0.0190 (7)	−0.0017 (6)	0.0071 (6)	−0.0016 (6)
C10	0.0205 (7)	0.0220 (8)	0.0254 (8)	−0.0009 (6)	0.0062 (6)	0.0017 (6)
C5	0.0241 (8)	0.0208 (8)	0.0266 (8)	0.0031 (6)	0.0059 (6)	−0.0035 (6)
C4	0.0249 (8)	0.0204 (7)	0.0248 (8)	0.0014 (6)	0.0085 (6)	0.0018 (6)
C17	0.0213 (8)	0.0252 (8)	0.0368 (9)	0.0047 (6)	0.0116 (7)	0.0079 (7)
C19	0.0277 (8)	0.0256 (8)	0.0276 (8)	−0.0060 (6)	0.0120 (7)	0.0010 (6)
C20	0.0239 (8)	0.0332 (9)	0.0337 (9)	0.0010 (7)	0.0068 (7)	0.0146 (7)
C11	0.0287 (9)	0.0221 (8)	0.0361 (9)	−0.0044 (6)	0.0056 (7)	0.0010 (7)
C12	0.0383 (10)	0.0196 (8)	0.0407 (10)	0.0001 (7)	0.0093 (8)	−0.0041 (7)
C13	0.0409 (10)	0.0247 (9)	0.0363 (10)	0.0023 (7)	0.0177 (8)	−0.0053 (7)
C18	0.0231 (8)	0.0275 (9)	0.0442 (10)	0.0020 (6)	0.0176 (7)	0.0059 (7)
C15	0.0264 (8)	0.0428 (10)	0.0181 (7)	−0.0098 (7)	0.0033 (6)	−0.0003 (7)

Geometric parameters (Å, º) top

Cl2—C6	1.7432 (16)	C9—C1	1.488 (2)
Cl1—C4	1.7406 (17)	C9—C10	1.402 (2)
N1—C8	1.409 (2)	C1—C2	1.522 (2)
N1—C1	1.290 (2)	C2—C14	1.550 (2)
N2—C3	1.3687 (19)	C6—C7	1.385 (2)
N2—C2	1.4586 (19)	C6—C5	1.382 (2)
N3—C9	1.345 (2)	C14—C15	1.529 (2)
N3—C13	1.333 (2)	C10—C11	1.385 (2)
N4—C16	1.336 (2)	C5—C4	1.391 (2)
N4—C20	1.346 (2)	C17—C18	1.385 (2)
C16—C14	1.520 (2)	C19—C20	1.379 (2)
C16—C17	1.390 (2)	C19—C18	1.385 (3)
C8—C3	1.407 (2)	C11—C12	1.390 (3)
C8—C7	1.394 (2)	C12—C13	1.391 (3)
C3—C4	1.401 (2)

C1—N1—C8	118.51 (13)	C1—C2—C14	112.34 (12)
C3—N2—C2	120.11 (13)	C7—C6—Cl2	119.20 (13)
C13—N3—C9	117.45 (15)	C5—C6—Cl2	119.49 (12)
C16—N4—C20	118.06 (14)	C5—C6—C7	121.29 (14)
N4—C16—C14	117.53 (13)	C16—C14—C2	111.30 (12)
N4—C16—C17	121.91 (15)	C16—C14—C15	109.31 (13)
C17—C16—C14	120.53 (14)	C15—C14—C2	112.90 (13)
C3—C8—N1	120.43 (13)	C6—C7—C8	119.71 (15)
C7—C8—N1	118.68 (14)	C11—C10—C9	118.64 (16)
C7—C8—C3	120.70 (14)	C6—C5—C4	118.51 (15)
N2—C3—C8	119.20 (14)	C3—C4—Cl1	118.10 (12)
N2—C3—C4	123.06 (14)	C5—C4—Cl1	119.63 (12)
C4—C3—C8	117.49 (14)	C5—C4—C3	122.26 (15)
N3—C9—C1	116.33 (14)	C18—C17—C16	119.20 (15)
N3—C9—C10	122.77 (15)	C20—C19—C18	117.70 (16)
C10—C9—C1	120.88 (14)	N4—C20—C19	123.81 (16)
N1—C1—C9	117.29 (14)	C10—C11—C12	118.95 (17)
N1—C1—C2	124.72 (13)	C11—C12—C13	118.25 (17)
C9—C1—C2	117.98 (13)	N3—C13—C12	123.93 (17)
N2—C2—C1	108.58 (12)	C19—C18—C17	119.30 (16)
N2—C2—C14	113.58 (12)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···Cl1	0.88	2.64	2.9941 (13)	105
N2—H2···N4	0.88	2.50	2.815 (2)	102

Acknowledgements

We would like to acknowledge the National Research Foundation, University of Pretoria and the Tshwane University of Technology for funding and institutional support provided.

Funding information

Funding for this research was provided by: National Research Foundation (grant No. 138280 to FPM; grant No. 129468 to ALEM).

References

Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341. Web of Science CrossRef CAS IUCr Journals Google Scholar
Pereira, J. A., Pessoa, A. M., Cordeiro, M. N. D. S., Fernandes, R., Prudêncio, C., Noronha, J. P. & Vieira, M. (2015). Eur. J. Med. Chem. 97, 664–672. Web of Science CrossRef CAS PubMed Google Scholar
Rigaku OD (2023). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England. Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Wang, X.-M., Chen, S. R.-Q., Fan, R. Q., Zhang, F.-Q. & Yang, Y.-L. (2015). Dalton Trans. 44, 8107–8125. Web of Science CSD CrossRef CAS PubMed Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.