6-(Het)aryl-[1,2,5]oxadiazolo[3,4-b]pyrazines
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 6, June, 2018
1081
115.6, 68.5, 31.5, 29.0, 25.6, 22.6, 14.0. Found (%): C, 64.29;
H, 6.20; N, 18.63. C16H18N4O2 (298.35). Calculated (%):
C, 64.41; H, 6.08; N, 18.78.
which can be used as sensory elements for nitroaromatic
compounds.
5-(4-Nitrophenyl)-[1,2,5]oxadiazolo[3,4-b]pyrazine (4c).
The yield was 1.57 g (75%), a yellow powder. M.p. 151—152 °С.
1H NMR (DMSO-d6), δ: 9.87 (s, 1 H, Hpyrazine); 8.64 (d, 2 H,
Harom, J = 8.9 Hz); 8.47 (d, 2 H, Harom, J = 8.9 Hz). 13C NMR
(DMSO-d6), δ: 158.3, 155.8, 152.2, 151.6, 149.7, 139.8, 130.4,
124.2. Found (%): C, 49.53; H, 2.04; N, 28.84. C10H5N5O3
(243.18). Calculated (%): C, 49.39; H, 2.07; N, 28.80.
Synthesis of 9-ethyl-3-{6-aryl-[1,2,5]oxadiazolo[3,4-b]-
pyrazin-5-yl}-9H-carbazole derivatives (6b,c) (general procedure).
The reagent BF3•Et2O (62 μL, 0.5 mmol) was added to a mixture
of 5-aryl-[1,2,5]oxadiazolo[3,4-b]pyrazine (4b or 4c) (0.5 mmol)
and 9-ethyl-9Н-carbazole (98 mg, 0.5 mmol) in acetоnitrile
(4 mL) with stirring. The mixture was stirred for 12 h at room
temperature. The solvent was evaporated at reduced pressure,
the residue was treated with aqueous Na2CO3, filtered, washed
with Н2О, and dried in air. Recrystallization of the resulting
powder gave the target SNH-products 6b or 6c.
Experimental
Compounds 6a and 6d were synthesized earlier according to
a similar procedure in 44 and 56% yields, respectively.19
1Н and 13C NMR spectra were recorded on a Bruker
AVANCEIII-500 spectrometer (500 and 126 МHz) in СDCl3 or
DMSO-d6, using TMS as an internal standard. Elemental
analysis was carried out on a Perkin–Elmer PE-2400 automated
analyzer. Melting points were determined on a Boetius hot-stage
and were not corrected.
Reaction progress and purity of products were monitored by
TLC on Sorbfil plates, visualizing under UV light.
UV spectra were recorded on a UV-2401 PC spectrometer
(Shimadzu) for solutions of compounds in acetоnitrile with
a concentration of 10–5 mol L–1. Excitation and emission spec-
tra were recorded on a Hitachi F-7000 spectrofluorimeter at room
temperature.
9-Ethyl-3-[6-(4-hexyloxyphenyl-[1,2,5]oxadiazolo[3,4-b]-
pyrazin-5-yl]-9H-carbazole (6b). The yield was 103 mg (42%),
a red powder. M.p. 155 °С. 1H NMR (DMSO-d6), δ: 8.45 (d,
1 H, Harom, J = 1.3 Hz); 8.11 (d, 1 H, Harom, J = 7.7 Hz); 7.67
(d, 1 H, Harom, J = 8.2 Hz); 7.59 (d, 1 H, Harom, J = 8.7 Hz);
7.51 (dd, 2 H, Harom, J = 11.0 Hz, J = 4.7 Hz); 7.47 (d, 2 H,
To measure emission in the solid state, the sample of the test
compound (~1 mg) was dissolved in acetone (1 mL). The result-
ing suspension was applied to quartz glass in the form of a thin-
nest film. Then, the sample was placed in a cuvette compartment
to record the fluorescence spectrum.
X-ray diffraction studies were performed on a Xcalibur 3
automatic four-circle diffractometer with a CCD detector
using the standard procedure (λMoК, graphite monochromator,
ω/2θ-scan technique in 1° steps, 295(2) K). The structure was
solved and refined using the SHELXTL24 software package by
the full-matrix least squares method with respect to F2.
Nonhydrogen atoms were included in the model in the anisotro-
pic approximation. Hydrogen atoms were localized using the
electron density distribution maps and included in the refinement
in the isotropic approximation by the riding model with depen-
dent thermal parameters. The results of X-ray diffraction studies
were deposited with the Cambridge Crystallographic Data Center
as cif-files (CCDC 1581898 for compound 6b). These materials
cam.ac.uk/data_request/cif.
Harom, J = 8.7 Hz); 7.25 (m, 1 H, Harom); 6.91 (d, 2 H, Harom
,
J = 8.8 Hz); 4.47 (q, 2 H, CH2, J = 7.0 Hz); 3.97 (t, 2 H, CH2,
J = 6.5 Hz); 1.71—1.63 (m, 2 H, CH2); 1.40—1.31 (m, 5 H,
Haliph); 1.29—1.22 (m, 4 H, (CH2)2); 0.85 (t, 3 H, CH3, J =
= 6.7 Hz). 13C NMR (DMSO-d6), δ: 164.5, 164.0, 161.2, 152.0,
141.3, 140.6, 132.4, 130.6, 128.7, 128.6, 126.9, 123.4, 122.6, 122.3,
120.9, 120.2, 114.5, 110.2, 108.9, 68.2, 37.7, 31.4, 28.9, 25.5, 22.4,
14.3, 14.2. Found (%): C, 73.40; H, 5.99; N, 14.03. C30H29N5O2
(491.60). Calculated (%): C, 73.30; H, 5.95; N, 14.25.
9-Ethyl-3-[6-(4-nitrophenyl)-[1,2,5]oxadiazolo[3,4-b]pyr-
azin-5-yl]-9H-carbazole (6c). The yield was 148 mg (68%),
a dark red powder. M.p. 246—248 °С (decomp.). 1H NMR
(DMSO-d6), δ: 8.44 (s, 1 H, Harom); 8.25 (d, 2 H, Harom, J =
= 8.5 Hz); 8.11 (d, 1 H, Harom, J = 7.7 Hz); 7.78 (d, 2 H, Harom
J = 8.2 Hz); 7.66 (d, 1 H, Harom, J = 8.1 Hz); 7.57 (d, 1 H, Harom
J = 8.6 Hz); 7.50 (t, 1 H, Harom, J = 7.6 Hz); 7.44 (d, 1 H, Harom
,
,
,
Synthesis of 5-(4-R-phenyl)-[1,2,5]oxadiazolo[3,4-b]-
pyrazines (4b and 4c) (general procedure). A mixture of 4-substi-
tuted acetоphenone 1b (or 1c) (10 mmol) and selenium dioxide
(1.1 g, 10 mmol) in a solution of 1,4-dioxane (15 mL) and water
(1 mL) was refluxed for 12 h. Selenium was filtered off, washed
with 1,4-dioxane (5 mL). The solvent was evaporated at reduced
pressure. The residue was dissolved in a mixture of ethanol
(5 mL) and acetic acid (5 mL), 3,4-diaminofurazan (3) (1.0 g,
10 mmol) was added, and the resulting mixture was refluxed for
1 h and cooled to room temperature. A precipitate formed was
filtered, washed with ethanol, and dried in air. Compounds 4b
(4c) were obtained as crystalline powders.
J = 8.4 Hz); 7.24 (t, 1H, Harom, J = 7.4 Hz); 4.44 (q, 2 H, CH2,
J = 6.7 Hz); 1.30 (t, 3 H, CH3, J = 7.0 Hz). 13C NMR
(DMSO-d6), δ: 163.4, 162.9, 151.8, 151.2, 148.1, 144.3, 140.9,
140.1, 131.2, 128.3, 127.0, 126.5, 123.3, 123.2, 122.0, 121.9, 120.4,
119.8, 109.7, 108.6, 37.2, 13.6. Found (%): C, 65.94; H, 3.79;
N, 19.20. C24H16N6O3 (436.43). Calculated (%): C, 66.05;
H, 3.70; N, 19.26.
Preparation of a sensor element based on fluorophores 6a—d
for Nitroscan instrument. A dry, undyed, nonwoven industrial
spunlace fabric (70% wood pulp, 30% polypropylene) manufac-
tured by Kunshan Yichen Clean Material Co. (China) was used as
a porous substrate for the sensor. A piece of the nonwoven fabric
(50 mm in diameter) was immersed in a solution of each of the
fluorophores 6a—d with a concentration of 1.0•10–3 mol L–1 for
5 min. Then, the nonwoven fabric with the immobilized fluoro-
phore was removed from the solution and dried for 30 min at
70—80 °С. The sensory material thus obtained was placed in a
cartridge. The assembled sensor was used in the Nitroscan device.23
5-(4-Hexyloxyphenyl)-[1,2,5]oxadiazolo[3,4-b]pyrazine (4b).
The yield was 1.29 g (62%), a yellow powder. M.p. 75 °С. 1H
NMR (CDCl3), δ: 9.39 (s, 1 H, Hpyrazine); 8.25 (d, 2 H, Harom
,
J = 8.8 Hz); 7.08 (d, 2 H, Harom, J = 8.8 Hz); 4.08 (t, 2 H, CH2,
J = 6.5 Hz); 1.87—1.82 (m, 2 H, CH2); 1.50—1.36 (m, 2 H, CH2);
1.37 (d, 4 H, (CH2)2, J = 3.2 Hz); 0.93 (m, 3 H, CH3). 13C NMR
(DMSO-d6), δ: 163.6, 158.0, 153.0, 152.3, 151.2, 130.7, 126.4,