Reaction of 3-alkynylquinoxaline-2-carbonitriles with sodium azide: An experimental and theoretical study

Article abstract of DOI:10.1007/s10593-013-1373-3

The reaction of 3-alkynylquinoxaline-2-carbonitriles with sodium azide in DMF at 60 C leads to the formation of 4,5-disubstituted 2H-1,2,3-triazoles in 38-82% yields. The analogous reaction in toluene in the presence of AlCl ₃ takes place as a tandem process involving 1,3-dipolar cycloaddition of the azide ion to the nitrile group followed by 6-endo-digonal cyclization with the formation of 5-aryl-tetrazolo[1′,5′:1,3]pyrido[3,4-b] quinoxalines.

Full text of DOI:10.1007/s10593-013-1373-3

Chemistry of Heterocyclic Compounds, Vol. 49, No. 9, December, 2013 (Russian Original Vol. 49, No. 9, September, 2013)
REACTION OF 3-ALKYNYLQUINOXALINE-2-CARBO-
NITRILES WITH SODIUM AZIDE: AN EXPERIMENTAL AND
THEORETICAL STUDY
A. S. Tyaglivy1, D. V. Steglenko1, and A. V. Gulevskaya1*
The reaction of 3-alkynylquinoxaline-2-carbonitriles with sodium azide in DMF at 60°C leads to the
formation of 4,5-disubstituted 2H-1,2,3-triazoles in 38-82% yields. The analogous reaction in toluene in
the presence of AlCl3 takes place as a tandem process involving 1,3-dipolar cycloaddition of the azide
ion to the nitrile group followed by 6-endo-digonal cyclization with the formation of 5-aryl-
tetrazolo[1′,5′:1,3]pyrido[3,4-b]quinoxalines.
Keywords:
3-alkynylquinoxaline-3-carbonitriles,
5-aryltetrazolo[1',5':1,2]pyrido[3,4-b]quinoxalines,
2H-1,2,3-triazoles, 1,3-dipolar cycloaddition, tandem process.
The quinoxaline ring serves as the structural base of a multitude of biologically active compounds [1-6],
including some antibiotics [7]. Quinoxaline derivatives, including condensed derivatives, frequently exhibit
photo- and electroluminescent characteristics [8, 9] and are regarded as a promising class of compounds for the
creation of organic light-emitting diodes and optoelectronic devises [10, 11]. The development of new methods
for the synthesis of quinoxalines is therefore an extremely important task.
In recent years, acetylene derivatives have been used more and more often in the synthesis of
heterocycles [12]. However, in spite of the effectiveness of this approach there are few examples of its using in
the synthesis of quinoxaline derivatives [13-19]. One of them is found by us tandem cyclization of condenced
_______
*To whom correspondence should be addressed, e-mail: agulevskaya@sfedu.ru.
1Southern Federal University, 7 Zorge St., Rostov-on-the-Don 344090, Russia.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1346-1355, September, 2013.
Original article submitted August 27, 2013.
0009-3122/13/4909-1255©2013 Springer Science+Business Media New York
1255

2,3-dialkynylpyrazines (quinoxalines and pteridines) 1 to [1,2,3]triazolo[1',5':1,2]pyrido[3,4-b]pyrazines 3 in
the presence of sodium azide [20]. The reaction mechanism includes 1,3-dipolar cycloaddition of the azide ion
to one of the C≡C bonds and intramolecular N-nucleophilic attack by the formed triazolyl anion 2 at the
adjacent triple bond, leading to the formation of the pyridine ring. The first stage of this transformation is a
quite rare example of cycloaddition of an azide anion with an internal alkyne [21-24]. As a rule such reaction
requires prolonged heating and gives moderate yields of the products. However, the cyclization represented in
the scheme above takes place under surprisingly mild conditions and give good yields of the products.
The aim of the present work was to investigate the reaction of 3-alkynylquinoxaline-2-carbonitriles 4
with sodium azide. Compounds 4 are unique hetero analogs of 2,3-dialkynylquinoxalines 1, and their reaction
with sodium azide can theoretically proceed through one of the paths indicated in the scheme below and lead to
the polynuclear derivatives of quinoxaline 5 or 6. Path A presupposes initial cycloaddition of the azide anion to
the nitrile group followed by 6-endo-digonal (6-endo-dig) cyclization. Path B involves the intermediate
formation of 1,2,3-triazoles and subsequent attack at the nitrile group.
N
N
N
N
N
N
N
N
N
N
Path А
N
N
6-endo-dig
R
N
+
R
N
N
NaN3
5
NH
N
N
N
+
N
N
N
N
R
Path B
5-exo-dig
4
N
N
N
N
R
R
6
The starting 3-alkynylquinoxaline-3-carbonitriles 4a-e were obtained through the coupling of 3-chloro-
quinoxaline-2-carbonitriles with terminal alkynes by the previously described method [25].
We found that 3-(5-phenyl-2H-1,2,3-triazol-4-yl)quinoxaline-2-carbonitrile (7a) is formed exclusively
in 82% yield when a mixture of 3-(phenylethynyl)quinoxaline-2-carbonitrile (4a) is stirred for 24 h with a
1.5-fold excess of sodium azide in DMF at 55-56°C. The reaction of the quinoxalines 4b,c with NaN3 takes
place similarly, i.e., the substituent in the aryl fragment at the C≡C bond does not have an appreciable effect on
the cycloaddition. However, the reaction of compounds 4d,e with alkyl or alkenyl substituents at the C≡C bond
requires heating up to 80°C and provides the corresponding triazoles 7d,e in 38-50% yields.
The structure of compounds 7 was established on the basis of spectral and mass-spectrometric data.
Their IR spectra contain characteristic absorption bands of the C≡N (2235-2250 cm-1) and N–H (3177-3278 cm-1)
bonds. In the 13C NMR spectra of the triazoles 7a-e, the signals typical of the carbon atoms of C≡C bonds at
80-100 ppm are absent. This indicates that the azide is added to the C≡C bond of the initial compound 4. In the
1H NMR spectra of the triazoles 7 the signal of the N–H proton is observed at 12.1-12.4 ppm (CDCl3) or
15.5-16.0 ppm (DMSO-d6). In the mass spectra of all the compounds 7 except the triazole 7c the peak of the
molecular ion is the most intense.
Attempts to convert the triazoles 7 into the tetracyclic compounds 6 were unsuccessful; compounds 7a-c
remained unchanged even after prolonged heating with K2CO3 in DMF.
1256

It is known that the 1,3-dipolar cycloaddition of the azide ion at the nitrile group is facilitated by the use
of Lewis acids [26]. In order to direct the transformation along path A we performed the reaction of
3-(phenylethynyl)quinoxaline-2-carbonitrile (4a) with sodium azide in DMF in the presence of Zn(OAc)2
(5 equiv.). When the reaction mixture was heated to 80°C for 120 h 5-phenyltetrazolo[1',5':1,2]pyrido[3,4-b]-
quinoxaline (5a) was formed in 30% yield. Replacement of the Zn(OAc)2 with zinc bromide led to a slight
decrease in the yield of the product, even less effective additive proved to be the NH4Cl/LiCl (10 equiv.)
mixture; it is only provided compound 5a in 10% yield.
Replacement of the DMF with the low-polarity toluene might accelerate the transformation of the nitrile
into the tetrazole [26]. We found that the reaction of 3-(phenylethynyl)quinoxaline-2-carbonitrile (4a) with
sodium azide (3 equiv.) in toluene in the presence of AlCl3 (1.5 equiv.) at 60°C for 24 h lead to the formation of
compound 5a in 42% yield. The reaction of 3-(p-tolylethynyl)quinoxaline-2-carbonitrile (4b) with NaN3 under
the same conditions gave the tetrazole 5b in 40% yield. Compound 4d did not react with sodium azide under
these conditions, and with the carbonitriles 4c,e as starting compounds tarring of the reaction mixture was
observed.
The proposed structure 5 is indicated by the following facts. The IR spectra of compounds 5a,b do not
1
contain absorption bands of the triple bonds or the N─H bond. The H NMR spectra are characterized by a
singlet at 7.8 ppm, corresponding to the H-6 proton. The 13C NMR spectra of the tetrazoles 5a,b do not contain
signals in the region of 80-100 ppm typical of the carbon atoms of C≡C bonds. The mass spectra of compounds
5a,b contain molecular-ion peaks with 8-11% intensity, and the strongest in both cases is the [M-N2]+ peak. The
molecular structure of the tetrazole 5b was established unambiguously by X-ray structural analysis (Fig. 1).
Fig. 1. A general view of the molecule of tetrazole 6b with the atoms represented by thermal vibration ellipsoids
of 50% probability.
1257

TABLE 1. Full and Relative Electronic Energies (Ezpe and ∆E) and Gibbs
Free Energies (G298.15 and ∆G298.15) of the Calculated Structures
Е,
kcal/mol
Structure
Ezpe, au
G298.15, au
ΔG298.15, kcal/mol
-817.15553
-164.20200
-981.37978
-981.34781
-981.43779
-981.41218
-981.43058
-981.35655
-981.39000
-981.37256
-981.39272
-981.38255
-981.49150
—
—
-164.21656
-817.20056
-981.43024
-981.39596
-981.48501
-981.45700
-981.47462
-981.40604
-981.43554
-981.42146
-981.44182
-981.43066
-981.53867
—
—
4а
N3

-14.0
6.1
-8.2
PRC
TS 1А
1А
13.3
-42.6
-25.0
-36.1
7.0
-50.4
-34.3
-45.8
0.6
TS 2A
2А
TS 1B
2B
-20.4
-9.4
-11.6
-2.7
TS 1C
1С
-22.1
-15.7
-84.1
-15.5
-8.5
TS 2С
3С
-76.3
For the better understanding of the reaction mechanism between 3-alkynylquinoxaline-2-carbonitriles 4
and sodium azide, DFT calculations were performed with the M05-2X functional [27] in the 6-31+G(d,p) basis
set [28-30] using the Gaussian 03 software package [31]. According to the calculations in the gas phase,
3-(phenylethynyl)quinoxaline-2-carbonitrile (4a) and the azide ion form a fairly stable pre-reaction π-complex
(PRC), the stabilization energy of which amounts to ~14.0 kcal/mol (Fig. 2, Table 1). Addition of the azide ion
to the C≡N bond takes place as a concerted process with an activation energy of 20.1 kcal/mol. The structure of
the transition state TS 1A has clearly defined asymmetry (С···N 1.612, N···N 2.385 Å). The transfer of charge
from the nucleophile to the electrophile, estimated by NBO analysis [32], amounts to 0.51 e. The energy gain in
the transition from the PRC to the cyclic adduct 1A amounts to 36.4 kcal/mol. The subsequent 6-endo-dig
cyclization (1A ⇄ TS 2A ⇄ 2A) requires an activation energy of 16.1 kcal/mol. However, this process is
energetically unfavorable (endothermic), and the destabilization energy amounts to 4.6 kcal/mol.
The addition of the azide ion to the C≡C bond can start with attack both at the C(α) atom and at the C(β)
atom. In the first case the process is concerted and results in 5-exo-dig cyclization with the formation of
cyclopentaquinoxaline (PRC ⇄ TS 1B ⇄ 1B). The required activation energy amounts to 14.6 kcal/mol. The
structure of the transition state TS 1B has clearly defined asymmetry (C(α)···N 1.881, C(β)···N 3.145 Å), and
the calculated charge transfer is 0.47 e.
The addition of the azide ion at the C(β) atom of the C≡C bond takes place in two kinetic stages with
the formation of the metastable intermediate 1C at the first of them. The activation energy in this case amounts
to only 4.6 kcal/mol, and the energy gain is 8.1 kcal/mol. The low kinetic stability of the intermediate 1C favors
its rapid cyclization through the transition state TS 2C with a barrier of 6.4 kcal/mol to the corresponding cyclic
adduct 2C. The total energy gain in the transition from the PRC to the cyclic adduct 2C amounts to
70.1 kcal/mol. Thus, the reaction path PRC ⇄ TS 1C ⇄ 1C ⇄ TS 2C ⇄ 2C is greatly preferred both kinetically
and thermodynamically. Such regioselectivity is also explained well in terms of frontier molecular orbital
theory. Thus the HOMO of the nucleophile (the azide ion) and the LUMO of the electrophile (compound 4a)
have close energy values (-1.454 and -2.035 eV, respectively), which in the Pearson classification corresponds to
soft base–soft acid interaction. Therefore, the regioselectivity of nucleophilic attack will be determined by the
contribution from the atomic orbitals of the electrophile LUMO. Analysis of the contributions from the respective
AOs, calculated by the AM1 method, shows that the largest value corresponds to the pz-orbital of the C(β) atom:
0.005 and 0.011 for the carbon and nitrogen atoms of the C≡N group and 0.169 and 0.290 for the C(α) and C(β)
atoms of the C≡C bond. The data from the calculations clearly agree fully with the experimental data.
1258

1259

We have thus established that, unlike 2,3-dialkynylquinoxalines, 3-alkynylquinoxaline-2-carbonitriles
exhibit dual reactivity toward sodium azide. In the absence of the Lewis acid the reaction develops as
1,3-dipolar cycloaddition of the azide ion at the C≡C bond of the initial molecule, leading to the selective
formation of 4,5-disubstituted 2H-1,2,3-triazole. The Lewis acid initiates a tandem process involving
cycloaddition of the azide ion at the C≡N group and subsequent 6-endo-digonal cyclization with the formation
of 5-aryl-tetrazolo[1',5':1,2]pyrido[3,4-b]quinoxaline.
EXPERIMENTAL
The IR spectra were recorded on a FT FSM-1202 spectrometer in Nujol. The UV spectra were recorded on
1
13
a Varian Cary 50 Probe spectrometer in MeCN. The Н and С NMR spectra were recored on a Bruker DPX-
250 spectrometer (250 и 62.9 MHz, respectively) with ТМS as internal standard. The mass spectra were
recorded on a Finnigan MAT INCOS 50 mass spectrometer with direct sample introduction and accelerating
voltage of 70 eV. Elemental analysis was carried out following the Pregl–Dumas method. The melting points
were determined in glass capillaries on a Stuart SMP30 apparatus.
Geometry optimization of the molecular structures corresponding to the stationary points on the PES
has been performed by analytical calculation of the gradients according to the Berny algorithm. The nature of
the stationary points was established by analysis of the force constant matrix (Hessian). With the presence of
one and only one imaginary frequency the structure was referred to the transition state, and with its absence it
was assigned to the energy minimum. Zero-point vibration energies and the corresponding thermodynamic
corrections were calculated in harmonic approximation. The minimum-energy reaction path connecting the two
minima through the corresponding saddle point was calculated by the gradient descent algorithm [33]. The
initial direction of the gradient line was set by displacement along the transition vector of the corresponding
transition state.
3-(5-Phenyl-2H-1,2,3-triazol-4-yl)quinoxaline-2-carbonitrile (7а). A mixture of 3-(phenylethynyl)-
quinoxaline-2-carbonitrile (4а) [25] (0.128 g, 0.50 mmol) and NaN3 (0.050 g, 0.77 mmol) in DMF (3 ml) was
stirred for 24 h at 55-60°С. A saturated NH4Cl solution (70 ml) was added to the reaction mixture followed by
extraction with CHCl3 (330 ml). The solvent was removed from the extract on a rotary evaporator, and the
residue was separated by chromatography on SiO2 with CHCl3 as eluent; the fraction with Rf 0.2-0.3 was
collected. The product was recrystallized from MeOH. Yield 0.122 g (82%), colorless crystals, mp >180°С
(decomp.). IR spectrum, , cm-1: 2235 (СN), 3202 (N–H). UV spectrum, max, nm (log ): 246 (4.51), 341
1
(3.65). Н NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.34-7.40 (3Н, m, H Ph); 7.67-7.71 (2Н, m, H Ph);
7.87-7.97 (2Н, m, Н-6,7); 8.08-8.12 (1Н, m) and 8.19-8.23 (1Н, m, Н-5,8); 12.28 (1Н, br. s, NH). 13C NMR
spectrum (CDCl3), δ, ppm: 116.2; 128.8; 129.0; 129.5; 129.8; 129.9; 130.0; 132.4; 134.1; 139.0; 141.2; 142.2;
145.1; 147.3; 163.5. Mass spectrum, m/z (Irel, %): 298 [M]+ (100), 272 [M-СN]+ (96), 243 [M-HСN-N2]+ (39),
217 (34), 190 (18), 115 (16), 102 (17), 89 (17), 77 (29). Found, %: C 68.29; H 3.54; N 28.03. C17H10N6.
Calculated, %: C 68.45; H 3.38; N 28.17.
3-[5-(p-Tolyl)-2H-1,2,3-triazol-4-yl)]quinoxaline-2-carbonitrile (7b) was obtained from 3-[(p-tolyl)-
ethynyl]quinoxaline-2-carbonitrile (4b) [25] analogously to compound 7а. Yield 0.125 g (80%), colorless
crystals, mp >172°С (decomp., МеОН). IR spectrum, , cm-1: 2249 (СN), 3200 (N–H). UV spectrum, max, nm
(log ): 247 (4.55), 342 (3.63). 1Н NMR spectrum (CDCl3), δ, ppm (J, Hz): 2.36 (3Н, s, CH3); 7.18 (2Н, d, J = 7.9,
H Ar); 7.57 (2Н, d, J = 7.9, H Ar); 7.88-7.98 (2Н, m, Н-6,7); 8.11-8.23 (2Н, m, Н-5,8); 12.42 (1Н, br. s, NH).
13C NMR spectrum (CDCl3), δ, ppm: 21.8; 116.2; 126.4; 128.8; 129.8; 130.0; 130.1; 132.4; 134.0; 139.3; 139.8;
141.3; 142.2; 145.3; 147.2; 163.3. Mass spectrum, m/z (Irel, %): 312 [M]+ (100), 286 [M-СN]+ (88), 257
[M-HСN-N2]+ (33), 231 (27), 128 (13), 102 (26), 77 (26). Found, %: C 69.06; H 3.98; N 27.09. C18H12N6.
Calculated, %: C 69.22; H 3.87; N 26.91.
1260

3-[5-(4-Nitrophenyl)-2H-1,2,3-triazol-4-yl)]quinoxaline-2-carbonitrile (7с) was obtained from 3-[(4-
nitrophenyl)ethynyl]quinoxaline-2-carbonitrile (4с) [25] analogously to compound 7а. Yield 0.130 g (76%),
colorless crystals, mp >276°С (decomp., МеОН). IR spectrum, , cm-1: 2250 (СN), 3177 (N–H). UV spectrum,
1

max, nm (log ): 250 (4.44), 298 (4.06), 347 (sh, 3.71). Н NMR spectrum (CDCl3), δ, ppm (J, Hz): 8.04-8.09
(5Н, m, Н Ar); 8.26-8.29 (3Н, m, Н Ar); 16.05 (1Н, br. s, NH). 13C NMR spectrum (CDCl3), δ, ppm: 117.2;
124.4; 129.8; 130.0; 130.1; 130.5; 133.4; 135.1; 140.2; 141.1; 141.2; 141.8; 146.6; 146.7; 148.3. Mass spectrum,
m/z (Irel, %): 343 [M]+ (44), 317 [M-СN]+ (100), 296 [M-HNO2]+ (45), 268 (51), 243 (75), 230 (17), 215 (51),
204 (11), 190 (65), 177 (11), 164 (17), 140 (17), 114 (13), 102 (20), 76 (25). Found, %: C 59.33; H 2.47; N 28.66.
C17H9N7O2. Calculated, %: C 59.48; H 2.64; N 28.56.
3-(5-Octyl-2H-1,2,3-triazol-4-yl)quinoxaline-2-carbonitrile (7d) was obtained from 3-(dec-1-ynyl)-
quinoxaline-2-carbonitrile (4d) [25] analogously to compound 7а at 80°С. Yield 0.084 g (50%), colorless
crystals, mp 124-126°С (МеОН). IR spectrum, , cm-1: 2249 (СN), 3217 (N–H). UV spectrum, max, nm (log
): 246 (4.44), 269 (sh, 4.24), 352 (3.66). 1Н NMR spectrum (CDCl3), δ, ppm (J, Hz): 0.88 (3Н, t, J = 7.0, CH3);
1.23-1.50 (10Н, m, СH2СH2(СH2)5CH3); 1.76-1.88 (2Н, m, СH2СH2(СH2)5CH3); 3.23 (2Н, t, J = 7.7,
СH2СH2(СH2)5CH3); 7.90-8.03 (2Н, m, Н-6,7); 8.17-8.25 (2Н, m, Н-5,8); 12.15 (1Н, br. s, NH). 13C NMR
spectrum (CDCl3), δ, ppm: 14.8; 22.9; 28.9; 29.1; 29.4; 29.5; 29.6; 32.0; 117.4; 128.3; 128.4; 129.6; 130.0;
132.6; 134.9; 139.1; 140.4; 142.0; 147.1. Mass spectrum, m/z (Irel, %): 334 [M]+ (100), 277 [M-С4H9]+ (4), 263
[M-С5H11]+ (6), 249 [M-С6H13]+ (11), 236 [M-С7H14]+ (11), 102 (5). Found, %: C 68.07; H 6.81; N 25.00.
C19H22N6. Calculated, %: C 68.24; H 6.63; N 25.13.
3-[5-(Cyclohex-1-enyl)-2H-1,2,3-triazol-4-yl)quinoxaline-2-carbonitrile (7e) was obtained from
3-[(cyclohex-1-enyl)ethynyl]quinoxaline-2-carbonitrile (4е) [25] analogously to compound 7а at 80°С. Yield
0.057 g (38%), colorless crystals, mp 199-201°С (МеОН). IR spectrum, , cm-1: 2242 (СN), 3278 (N–H). UV
1
spectrum, max, nm (log ): 247 (4.45), 269 (sh., 4.06), 346 (3.61). Н NMR spectrum (DMSO-d6), δ, ppm (J,
Hz): 1.61-1.72 (4Н, m, 2СH2); 2.08-2.20 (2Н, m, СH2); 2.35-2.45 (2Н, m, СH2); 6.10-6.30 (1H, m, =СН); 8.05-
8.17 (2Н, m, Н-6,7); 8.21-8.31 (2Н, m, Н-5,8); 15.51 (1Н, br. s, NH). 13C NMR spectrum (DMSO-d6), δ, ppm:
21.4; 22.2; 25.3; 26.9; 116.4; 129.0; 129.3; 129.5; 131.3; 131.6; 132.6; 134.5; 137.6; 140.1; 141.6; 147.1;
147.2. Mass spectrum, m/z (Irel, %): 302 [M]+ (100), 273 [M-С2H5]+ (64), 259 [M-С3H7]+ (11), 245 [M-С4H9]+
(30), 232 [M-С5H10]+ (10), 219 [M-С6H11]+ (15), 129 (9), 102 (26), 77 (17). Found, %: C 67.41; H 4.59;
N 27.94. C17H14N6. Calculated, %: C 67.54; H 4.67; N 27.80.
5-Phenyltetrazolo[1',5':1,2]pyrido[3,4-b]quinoxaline (5а). A mixture of 3-(phenylethynyl)quinoxaline-
2-carbonitrile (4а) [25] (0.128 g, 0.5 mmol), NaN3 (0.098 g, 1.5 mmol), and anhydrous AlCl3 (0.100 g,
0.75 mmol) in dry toluene (5 ml) was stirred for 24 h at 60°С. A saturated NH4Cl solution (70 ml) was added to
the reaction mixture followed by extraction with CHCl3 (330 ml). The solvent was removed from the extract
on a rotary evaporator, and the residue was separated by chromatography on SiO2 with CHCl3 as eluent; the
fraction with Rf 0.3-0.4 was collected. The product was recrystallized from MeOH. Yield 0.062 g (42%),
colorless crystals, mp >230°С (decomp.). UV spectrum, max, nm (log ): 265 (4.45), 304 (sh, 3.97), 377 (3.95),
396 (sh, 3.90). 1Н NMR spectrum (CDCl3), δ, ppm: 7.63-7.66 (3Н, m, H Ph); 7.82 (1Н, s, Н-6); 7.95-8.12 (4Н,
m, Н-9,10, H Ph); 8.29-8.33 (1Н, m, Н-8); 8.51-8.56 (1Н, m, Н-11). 13C NMR spectrum (CDCl3), δ, ppm:
116.9; 129.5; 129.8; 130.0; 130.6; 131.0; 131.9; 132.6; 133.4; 133.6; 140.4; 143.4; 144.4; 145.5; 149.4. Mass
spectrum, m/z (Irel, %): 298 [M]+ (8), 270 [MN2]+ (100), 243 (12), 167 (12), 142 (21), 135 (21), 116 (12), 102
(73), 90 (15), 77 (58). Found, %: C 68.61; H 3.49; N 27.99. C17H10N6. Calculated, %: %: C 68.45; H 3.38;
N 28.17.
5-(p-Tolyl)tetrazolo[1',5':1,2]pyrido[3,4-b]quinoxaline (5b) was obtained from 3-[(p-tolyl)ethynyl]-
quinoxaline-2-carbonitrile (4b) [25] analogously to compound 5а. Yield 0.062 g (40%), colorless crystals,
mp >250°С (decomp., МеОН). UV spectrum, max, nm (log ): 265 (4.31), 309 (sh, 3.88), 383 (3.83), 402 (sh,
1
3.80). Н NMR spectrum (CDCl3), δ, ppm (J, Hz): 2.50 (3Н, s, CH3); 7.44 (2Н, d, J = 7.8, H Ar); 7.78 (1Н, s,
Н-6); 7.95-8.04 (4Н, m, Н-9,10, H Ar); 8.28-8.32 (1Н, m, Н-8); 8.51-8.56 (1Н, m, Н-11). 13C NMR spectrum
(CF3COOD), δ, ppm: 19.1; 105.9; 119.9; 123.6; 129.0; 129.3; 130.5; 131.9; 132.7; 133.9; 134.4; 140.1; 144.0;
1261

145.8; 146.6; 147.1. Mass spectrum, m/z (Irel, %): 312 [M]+ (11), 284 [M-N2]+ (100), 142 (17), 115 (23), 102 (17),
91 (10), 76 (9). Found, %: C 69.34; H 4.03; N 26.77. C18H12N6. Calculated, %: C 69.22; H 3.87; N 26.91.
X-ray structure investigation of compound 5b monocrystal was carried out at 100 K on a Bruker
APEX II, ССD area detector diffractometer, МоKα radiation,  0.71073 Å, -scanning. The crystal of
compound 5b (C18H12N6, М 312.34) was orthorhombic, space group Aba2; а 18.0728(11), b 22.1373(15),
c 7.1640(4) Å, V 2866.2(3) Å3, Z 8, dcalc 1.448 g/cm3,  0.093 mm-1, F(000) 1296. The structure was solved by
the direct method and full-matrix least-squares refinement in anisotropic approximation using Bruker SHELXTL
software. The complete crystallographic information has been deposited at the Cambridge Crystallographic Data
Center (deposit CCDC 955007).
The work was carried out with financial support from the Russian Foundation for Basic Research (grant
No. 11-03-00079).
The authors thank Z. A. Starikova* (Institute of Organoelement Compounds, Russian Academy of
Sciences, Moscow) for carrying out the X-ray structural investigation.
_______
*Deceased
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