2-p-Toluoyl­quinoxaline

The title compound, C₁₆H₁₂N₂O, consists of planar quinoxaline and tolyl moieties linked by a carbonyl group. The carbonyl group is nearly coplanar with the tolyl ring but is inclined at an angle of 34.9 (1)° to the quinoxaline ring. Intermolecular hydrogen bonds stabilize the packing of the mol­ecules in the unit cell.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.043
• wR factor = 0.127
• Data-to-parameter ratio = 19.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Quinoxaline heterocycles have attracted much attention owing to their natural occurance (Dell et al., 1975) and biological activities (Kher et al., 1995). Many quinoxaline derivatives display unusual solid-tumor selectivity against multidrug-resistant cancer cells (Gao et al., 1999). The synthetic utility and pharmacological importance of these compounds have prompted us to synthesize and characterize novel quinoxaline derivatives (Banerjee et al., 2001). During the synthesis of a di-p-tosyl-1,2,3,4-tetrahydroquinoxaline, (II), via a palladium–copper catalized reaction, an unexpected product, namely 2-p-toluoylquinoxaline, (III), was obtained in good yield. The X-ray structure analysis of (III) was undertaken in order to establish the regio- and stereospecificities of the reaction.

The title molecule (Fig. 1) consists of essentially planar quinoxaline and tolyl moieties [the maximum deviation of an in-plane atom from the least-squares plane through the ring atom is 0.032 (1) Å for C2] linked by a carbonyl group. The dihedral angle between the two planar aromatic parts, C1—C8/N1/N2 and C10—C16, is 50.96 (3)°. The carbonyl group is almost coplanar with the tolyl ring [O1—C9—C10—C11 15.5 (2)°] but it is inclined at an angle of 34.9 (1)° to the quinoxaline ring. As a result, the π conjugation between the carbonyl group and the tolyl ring is more effective than that for the carbonyl and quinoxaline moieties. This is also reflected in the slight shortening of the C9—C10 bond length [1.489 (2) Å] compared to the C1—C9 distance [1.511 (2) Å]. Other bond distances and angles are comparable to those reported for similar structures (Degen & Bolte, 1999; Fang et al., 2001).

In addition to van der Waals forces, the packing of the molecules in the unit cell is governed by weak C—H···O and C—H···N hydrogen bonds (Table 2).

S2. Experimental

A mixture of N-[(3-p-toluoyl)prop-2-ynyl]-N,N'-1,2-phenylenedi-p-tosylamide, (I) (1 mmol) (Mukhopadhyay & Kundu 2000), anhydrous potassium carbonate (2 mmol) and cuprous iodide (10 mol%) in DMF (5 ml) was heated at 373 K for 24 h. After usual work-up and purification by column chromatography on neutral alumina (10% ethyl acetate in petroleum ether, b.p. 333–353 K, as eluent), 2-p-toluoylquinoxaline, (III), was obtained (m.p. 352 K). Single crystals of (III) suitable for X-ray analysis were obtained by slow crystallization from a chloroform–petroleum ether solution. Elemental analysis, calculated for C₁₆H₁₂N₂O: C 77.41, H 4.83, N 11.29%; found: C 77.07, H 5.00, N 10.95%.

S3. Refinement

The structure was solved by direct method using MULTAN88 (Debaerdemaeker et al., 1988). The H atoms were refined using a riding model and their isotropic displacement parameters were set to 1.2 times (1.5 times for CH₃ groups) the equivalent displacement parameters of their parent atoms.

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SAINT (Siemens, 1996); program(s) used to solve structure: MULTAN88 (Debaerdemaeker et al., 1988); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ZORTEP (Zsolnai, 1995); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. ZORTEP (Zsolnai, 1995) view (50% probability level) of the molecule of (III).

2-p-Toluoylquinoxaline

Crystal data

C16H12N2O	Dx = 1.343 Mg m^−3
Mr = 248.28	Melting point: 352 K
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.5973 (2) Å	Cell parameters from 918 reflections
b = 18.5701 (5) Å	θ = 5.1–31.0°
c = 11.8195 (3) Å	µ = 0.09 mm^−1
β = 91.304 (1)°	T = 293 K
V = 1228.23 (6) Å^3	Block, yellow
Z = 4	0.55 × 0.50 × 0.30 mm
F(000) = 520

Data collection

Bruker SMART-CCD diffractometer	2864 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.028
Graphite monochromator	θmax = 29.8°, θmin = 2.0°
ω scans	h = −7→7
9672 measured reflections	k = −25→25
3352 independent reflections	l = −16→12

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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.127	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0718P)^2 + 0.3457P] where P = (Fo^2 + 2Fc^2)/3
3352 reflections	(Δ/σ)max < 0.001
173 parameters	Δρmax = 0.38 e Å^−3
0 restraints	Δρmin = −0.20 e Å^−3

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

	x	y	z	Uiso*/Ueq
C1	0.54873 (19)	0.10498 (6)	0.32676 (9)	0.0213 (2)
C2	0.7436 (2)	0.11743 (6)	0.40448 (9)	0.0242 (2)
H2	0.7533	0.0903	0.4706	0.029*
C3	0.88349 (19)	0.20556 (6)	0.28875 (9)	0.0218 (2)
C4	1.0553 (2)	0.25902 (6)	0.26404 (10)	0.0258 (2)
H4	1.1864	0.2660	0.3125	0.031*
C5	1.0279 (2)	0.30045 (6)	0.16832 (11)	0.0267 (2)
H5	1.1418	0.3352	0.1521	0.032*
C6	0.8281 (2)	0.29083 (6)	0.09410 (10)	0.0257 (2)
H6	0.8102	0.3200	0.0306	0.031*
C7	0.6606 (2)	0.23874 (6)	0.11514 (10)	0.0240 (2)
H7	0.5306	0.2325	0.0657	0.029*
C8	0.68630 (19)	0.19441 (6)	0.21254 (9)	0.0209 (2)
C9	0.36090 (19)	0.05080 (6)	0.35914 (9)	0.0217 (2)
C10	0.24081 (19)	0.00467 (6)	0.27194 (9)	0.0217 (2)
C11	0.0300 (2)	−0.03092 (6)	0.30103 (10)	0.0244 (2)
H11	−0.0319	−0.0247	0.3727	0.029*
C12	−0.0864 (2)	−0.07541 (6)	0.22341 (10)	0.0265 (2)
H12	−0.2271	−0.0982	0.2436	0.032*
C13	0.0036 (2)	−0.08666 (6)	0.11529 (10)	0.0256 (2)
C14	0.2162 (2)	−0.05232 (6)	0.08758 (10)	0.0272 (2)
H14	0.2805	−0.0599	0.0167	0.033*
C15	0.3335 (2)	−0.00682 (6)	0.16428 (10)	0.0252 (2)
H15	0.4740	0.0160	0.1440	0.030*
C16	−0.1266 (2)	−0.13512 (7)	0.03226 (12)	0.0335 (3)
H16A	−0.2955	−0.1269	0.0365	0.050*
H16B	−0.0922	−0.1845	0.0504	0.050*
H16C	−0.0751	−0.1248	−0.0430	0.050*
N1	0.51987 (16)	0.14197 (5)	0.23203 (8)	0.0222 (2)
N2	0.91001 (18)	0.16581 (5)	0.38602 (8)	0.0255 (2)
O1	0.31123 (15)	0.04652 (4)	0.45927 (7)	0.0268 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0228 (5)	0.0198 (5)	0.0212 (5)	0.0020 (4)	0.0011 (4)	0.0005 (4)
C2	0.0281 (5)	0.0236 (5)	0.0209 (5)	0.0029 (4)	−0.0029 (4)	0.0016 (4)
C3	0.0219 (5)	0.0200 (5)	0.0236 (5)	0.0024 (4)	−0.0014 (4)	−0.0018 (4)
C4	0.0220 (5)	0.0241 (5)	0.0313 (6)	−0.0007 (4)	−0.0027 (4)	−0.0028 (4)
C5	0.0257 (5)	0.0213 (5)	0.0331 (6)	−0.0029 (4)	0.0029 (4)	−0.0007 (4)
C6	0.0299 (6)	0.0211 (5)	0.0262 (5)	−0.0001 (4)	0.0022 (4)	0.0026 (4)
C7	0.0256 (5)	0.0231 (5)	0.0232 (5)	−0.0002 (4)	−0.0024 (4)	0.0027 (4)
C8	0.0218 (5)	0.0198 (5)	0.0210 (5)	0.0009 (4)	−0.0006 (4)	−0.0003 (4)
C9	0.0219 (5)	0.0202 (5)	0.0231 (5)	0.0038 (4)	0.0015 (4)	0.0036 (4)
C10	0.0220 (5)	0.0198 (5)	0.0235 (5)	0.0019 (4)	0.0021 (4)	0.0031 (4)
C11	0.0243 (5)	0.0236 (5)	0.0254 (5)	0.0015 (4)	0.0052 (4)	0.0041 (4)
C12	0.0227 (5)	0.0240 (5)	0.0329 (6)	−0.0013 (4)	0.0036 (4)	0.0045 (4)
C13	0.0259 (5)	0.0206 (5)	0.0302 (6)	0.0015 (4)	−0.0012 (4)	0.0013 (4)
C14	0.0287 (6)	0.0287 (6)	0.0245 (5)	−0.0008 (4)	0.0045 (4)	−0.0012 (4)
C15	0.0234 (5)	0.0267 (5)	0.0257 (5)	−0.0022 (4)	0.0050 (4)	0.0016 (4)
C16	0.0330 (6)	0.0287 (6)	0.0387 (7)	−0.0025 (5)	−0.0028 (5)	−0.0052 (5)
N1	0.0222 (4)	0.0220 (4)	0.0223 (4)	0.0002 (3)	−0.0010 (3)	0.0019 (3)
N2	0.0268 (5)	0.0248 (5)	0.0246 (5)	0.0020 (4)	−0.0052 (4)	0.0003 (3)
O1	0.0313 (4)	0.0274 (4)	0.0219 (4)	0.0028 (3)	0.0038 (3)	0.0031 (3)

Geometric parameters (Å, º)

C1—N1	1.3203 (14)	C9—O1	1.2243 (14)
C1—C2	1.4290 (15)	C9—C10	1.4888 (15)
C1—C9	1.5108 (15)	C10—C11	1.4019 (15)
C2—N2	1.3158 (15)	C10—C15	1.4015 (15)
C2—H2	0.9300	C11—C12	1.3864 (17)
C3—N2	1.3714 (14)	C11—H11	0.9300
C3—C4	1.4173 (15)	C12—C13	1.4000 (17)
C3—C8	1.4238 (15)	C12—H12	0.9300
C4—C5	1.3739 (17)	C13—C14	1.3954 (16)
C4—H4	0.9300	C13—C16	1.5071 (17)
C5—C6	1.4169 (17)	C14—C15	1.3930 (16)
C5—H5	0.9300	C14—H14	0.9300
C6—C7	1.3739 (15)	C15—H15	0.9300
C6—H6	0.9300	C16—H16A	0.9600
C7—C8	1.4200 (15)	C16—H16B	0.9600
C7—H7	0.9300	C16—H16C	0.9600
C8—N1	1.3707 (14)
N1—C1—C2	122.54 (10)	C11—C10—C15	118.82 (10)
N1—C1—C9	119.27 (9)	C11—C10—C9	118.08 (10)
C2—C1—C9	118.06 (9)	C15—C10—C9	123.06 (10)
N2—C2—C1	122.46 (10)	C12—C11—C10	120.29 (10)
N2—C2—H2	118.8	C12—C11—H11	119.9
C1—C2—H2	118.8	C10—C11—H11	119.9
N2—C3—C4	119.26 (10)	C11—C12—C13	121.29 (10)
N2—C3—C8	121.31 (10)	C11—C12—H12	119.4
C4—C3—C8	119.44 (10)	C13—C12—H12	119.4
C5—C4—C3	119.89 (10)	C14—C13—C12	118.20 (11)
C5—C4—H4	120.1	C14—C13—C16	121.48 (11)
C3—C4—H4	120.1	C12—C13—C16	120.31 (11)
C4—C5—C6	120.72 (10)	C15—C14—C13	121.10 (11)
C4—C5—H5	119.6	C15—C14—H14	119.5
C6—C5—H5	119.6	C13—C14—H14	119.5
C7—C6—C5	120.62 (10)	C14—C15—C10	120.28 (10)
C7—C6—H6	119.7	C14—C15—H15	119.9
C5—C6—H6	119.7	C10—C15—H15	119.9
C6—C7—C8	119.85 (10)	C13—C16—H16A	109.5
C6—C7—H7	120.1	C13—C16—H16B	109.5
C8—C7—H7	120.1	H16A—C16—H16B	109.5
N1—C8—C7	119.43 (9)	C13—C16—H16C	109.5
N1—C8—C3	121.13 (9)	H16A—C16—H16C	109.5
C7—C8—C3	119.44 (10)	H16B—C16—H16C	109.5
O1—C9—C10	121.53 (10)	C1—N1—C8	116.21 (9)
O1—C9—C1	117.57 (10)	C2—N2—C3	116.30 (9)
C10—C9—C1	120.91 (9)
N1—C1—C2—N2	−1.16 (18)	O1—C9—C10—C15	−161.99 (11)
C9—C1—C2—N2	−176.92 (10)	C1—C9—C10—C15	18.22 (15)
N2—C3—C4—C5	−178.41 (10)	C15—C10—C11—C12	−1.35 (16)
C8—C3—C4—C5	1.28 (16)	C9—C10—C11—C12	−178.96 (10)
C3—C4—C5—C6	0.54 (17)	C10—C11—C12—C13	0.75 (17)
C4—C5—C6—C7	−1.45 (18)	C11—C12—C13—C14	0.60 (17)
C5—C6—C7—C8	0.48 (17)	C11—C12—C13—C16	−179.83 (11)
C6—C7—C8—N1	−179.15 (10)	C12—C13—C14—C15	−1.35 (17)
C6—C7—C8—C3	1.35 (16)	C16—C13—C14—C15	179.08 (11)
N2—C3—C8—N1	−2.03 (16)	C13—C14—C15—C10	0.76 (18)
C4—C3—C8—N1	178.28 (10)	C11—C10—C15—C14	0.60 (16)
N2—C3—C8—C7	177.46 (10)	C9—C10—C15—C14	178.09 (10)
C4—C3—C8—C7	−2.22 (16)	C2—C1—N1—C8	−1.02 (16)
N1—C1—C9—O1	−141.01 (11)	C9—C1—N1—C8	174.69 (9)
C2—C1—C9—O1	34.89 (14)	C7—C8—N1—C1	−176.97 (10)
N1—C1—C9—C10	38.78 (14)	C3—C8—N1—C1	2.52 (15)
C2—C1—C9—C10	−145.31 (10)	C1—C2—N2—C3	1.69 (16)
O1—C9—C10—C11	15.52 (15)	C4—C3—N2—C2	179.53 (10)
C1—C9—C10—C11	−164.27 (10)	C8—C3—N2—C2	−0.16 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2···O1^i	0.93	2.70	3.4611 (14)	140
C6—H6···N2^ii	0.93	2.80	3.4515 (15)	128
C7—H7···N2^ii	0.93	2.91	3.5027 (14)	123
C6—H6···O1^iii	0.93	2.62	3.4155 (14)	144
C11—H11···O1^iv	0.93	2.59	3.4650 (14)	158

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