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

The synthesis and single-crystal X-ray structure of a substituted quinoxaline compound is described.

Abstract

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.

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 sp ³-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 ▸).

Figure 1.

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

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

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[F 2 > 2σ(F 2)], wR(F 2), S	0.047, 0.137, 1.10
No. of reflections	4742
No. of parameters	236
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.62, −0.58

Computer programs: CrysAlis PRO (Rigaku OD, 2023 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL (Sheldrick, 2015b ▸) and OLEX2 (Dolomanov et al., 2009 ▸).

Supplementary Material

CCDC reference: 2285764

Additional supporting information: crystallographic information; 3D view; checkCIF report

full crystallographic data

Crystal data

C20H16Cl2N4	F(000) = 792
Mr = 383.27	Dx = 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

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	Rint = 0.112
Detector resolution: 10.0000 pixels mm-1	θmax = 30.8°, θmin = 2.4°
ω scans	h = −12→10
Absorption correction: multi-scan (CrysalisPro; Rigaku OD, 2019)	k = −28→26
Tmin = 0.576, Tmax = 1.000	l = −14→13
29036 measured reflections

Refinement

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(Fo2) + (0.0676P)2 + 0.7299P] where P = (Fo2 + 2Fc2)/3
S = 1.10	(Δ/σ)max = 0.001
4742 reflections	Δρmax = 0.62 e Å−3
236 parameters	Δρmin = −0.58 e Å−3
0 restraints

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
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 (Ų)

	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)

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)

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

Funding Statement

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