Pyrazine-2,3-dicarbonitriles substituted with maleimide derivatives

Article abstract of DOI:10.1007/s10593-007-0183-x

Syntheses and spectroscopic characteristics are reported for eight pyrazine-2,3-dicarbonitriles substituted with maleimide residue in addition to phenyl, 2-thienyl, or 2-furyl substituent.

Full text of DOI:10.1007/s10593-007-0183-x

Chemistry of Heterocyclic Compounds, Vol. 43, No. 9, 2007
PYRAZINE-2,3-DICARBONITRILES
SUBSTITUTED WITH MALEIMIDE
DERIVATIVES
E. H. Mørkved
Syntheses and spectroscopic characteristics are reported for eight pyrazine-2,3-dicarbonitriles
substituted with maleimide residue in addition to phenyl, 2-thienyl, or 2-furyl substituent.
Keywords: 2-furyl, maleimide, pyrazine-2,3-dicarbonitrile, 2-thienyl, zinc azaphthalocyanine.
Pyrazine-2,3-dicarbonitrile may be used for preparation of azaphthalocyanines (AzaPcs) or, more accurately,
tetrapyrazinoporphyrazines [1]. Substituents in positions 5 and 6 of pyrazine-2,3-dicarbonitrile may affect, for
instance, solubility and UV-vis absorption of the target AzaPcs. However, as compared to phthalocyanines, there is
limited knowledge of substituent effects on AzaPcs.
Previously we have prepared metal, i.e., Cu, Ni, Mg, and Zn, complexes of AzaPcs with sulphanyl, oxo,
or amino substituents [2-4]. We observed the exchange of both oxo and some sulphanyl substituents with
nucleophiles during cyclotetramerizations, whereas amino substituents caused slow cyclizations due to a strong
electron donation by nitrogen. Maleimide substituents are not expected to cause either of the mentioned problems,
but two maleimide substituents in adjacent positions at the pyrazine ring would certainly induce a steric strain.
Therefore, we decided to test a combination of one maleimide substituent and either one phenyl, 2-thienyl, or
2-furyl substituent. The two unsaturated substituents at the pyrazine ring are expected to cause the chromophoric
system extension of a target AzaPc.
Compounds 1a–c, viz., 5-chloro-6-phenylpyrazine-2,3-dicarbonitrile (1a), 5-chloro-6-(2-thienyl)pyrazine-
2,3-dicarbonitrile (1b), and 5-chloro-6-(2-furyl)pyrazine-2,3-dicarbonitrile (1c) are known [5]. We used
compounds 1 for the preparation of compounds 2–4, which are shown below.
The dimethylmaleimide substituent of compounds 2 was used as a reference for maleimide, but is
expected to give somewhat better solubility in organic solvents. The introduction of sulfur in conjugation with the
maleimide carbonyl groups of compounds 3 is expected to induce interesting electronic effects on the maleimide
chromophoric system. Many years ago the diimino derivative of 5,6-dihydro-1,4-dithiin- 2,3-dicarboximide was
found to be a reactive monomer for the reactions of porphyrazines [6]. More recently, the same monomer was
used to prepare mixed porphyrazines [7]. The electronic spectra of these compounds were found to have an
additional absorption band at 525-595 nm due to the n→n* excitation of the n-electrons on sulfur. As for
compounds 4, our original intention was to introduce two thiomorpholine substituents into
3,4-dichloromaleimide. However, other researchers have pointed out that only one amino substituent will be
introduced into 3,4-dichloromaleimide [8]. We decided to use monosubstituted thiomorpholinyl maleimide, since
the electronic effects of this group might be of interest as well.
__________________________________________________________________________________________
Norwegian University of Science and Technology, Department of Chemistry, N-7491 Trondheim,
Norway; e-mail: eva.morkved@chem.ntnu.no. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9,
pp. 1409-1414, September, 2007. Original article submitted September 12, 2006
0009-3122/07/4309-1197©2007 Springer Science+Business Media, Inc.
1197

R
N
CN
CN
N
N
O
R
CN
CN
N
Me
Cl
N
O
Me
1
2a–c
R
CN
CN
N
R
CN
CN
N
N
O
O
N
N
N
Cl
S
O
O
S
N
S
3a–c
4a,b
1–4 a R = Ph, b R = 2-thienyl, c R = 2-furyl
For preparations of compounds 2–4 from 1, the maleimide anions were prepared. We have chosen the
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) salts due to their good solubility, except for one reaction of compound 1c
where the dimethylmaleimide DBU salt caused extensive decomposition. Therefore, the potassium salt of
dimethylmaleimide was used to prepare 2c. However, compounds 2 were obtained in merely 20% yields, and
consequently will be of little interest for further reactions.
Compounds 3 and 4 are yellow fluorescent powders, and the UV-vis absorptions of the thienyl and furyl derivatives
are found at λmax 365 nm, whereas the phenyl derivatives show broad absorptions with shoulders from 410 to
approximately 300 nm.
Cyclotetramerizations of compounds 3 and 4 with zinc(II) acetate and quinoline gave ZnAzaPcs with λmax 655
nm for phenyl-substituted compounds, and at 675 nm for the thienyl- or furyl-substituted macrocycles. The low
solubilities of these compounds made purification difficult, and only the macrocyclic products 5a and 5b from the 2-
thienyl-substituted monomers 3b and 4b are reported. These products are mixtures of four constitutional isomers due
to unsymmetrical monomers. The elemental analyses for compounds 5a and 5b are unsatisfactory, with too high zinc
level and low values for both sulfur and nitrogen.
We have reported syntheses and spectroscopic analyses of compounds 2–4, pyrazine-2,3-dicarbonitriles,
which are substituted with one maleimide derivative in addition to phenyl-, 2-thienyl-, or 2-furyl substituents. These
compounds are not well suited for the intended purpose, i.e., preparation of ZnAzaPcs. Two zinc complexes 5a–b
were prepared from cyclotetramerizations of compounds 3b and 4b, but purification and separation of the expected
product isomers was not successful due to low solubility in organic solvents. However, compounds 2–4 are well
characterised and might find some alternative use.
EXPERIMENTAL
EI mass spectra of compounds 1–4 were obtained on a Finnigan MAT 95XL spectrometer at 70 eV electron
1
energy and 1.0 mA electron current. IR spectra were obtained on a Nicolet 20-SXC FT IR spectrometer in KBr. H
and 13C NMR spectra were recorded on a Bruker Avance DPX 400 NMR spectrometer at 399 and 100 MHz,
respectively, in CDCl3 (compounds 1a–c, 2a,b, 4a,b) and (CD3)2CO (compounds 2c, 3a–c). UV-vis spectra were
1198

obtained on a Cary 50 UV-vis spectrophotometer in DCM (compounds 2–4) and pyridine (compounds 5a,b). Melting
points were obtained on a Büchi 530 melting point apparatus and are uncorrected. Microanalyses were performed by
Analytische Laboratorien GmbH, Lindlar, Germany. The analytical samples were dried at 50°C/HV prior to analyses.
Merck Kieselgel 60F 254 was used for TLC and Merck silica 63-200: was used for column chromatography.
Compounds 1a–c were prepared similarly to [5].
Compounds 1 (General Method). A mixture of equimolar amounts of diaminomaleonitrile and
phenylglyoxylic acid, 2-thienylglyoxylic acid, or 2-furylglyoxylic acid, dissolved in water, were stirred at ambient
temperature for 1-2 h. The crude hydroxypyrazines, which were obtained in 70-90% yields, were heated with
phosphorus oxychloride and pyridine at mp 90°C for 2 h, poured on ice, extracted with DCM, and chromatographed
on silica with dichloromethane.
1
5-Chloro-6-phenylpyrazine-2,3-dicarbonitrile (1a). Yield 64%; mp 138-139°C (mp 139-141°C [5]). H
NMR spectrum, δ, ppm: 7.60 (3H, s); 7.93 (2H, s). 13C NMR spectrum, δ, ppm: 112.48 (CN), 112.81 (CN), 129.38,
130.47, 132.79, 129.95, 131.27 (C-2, pyrazine), 133.30 (C-3, pyrazine), 150.62 (C-5, pyrazine), 157.35 (C-6,
pyrazine).
5-Chloro-6-(2-thienyl)pyrazine-2,3-dicarbonitrile (1b). Yield 61%; mp 124-125°C (mp 115-117°C [5]). 1H
NMR spectrum, δ, ppm (J, Hz): 7.29 (1H, dd, J34 = 4, J45 = 5, H-4, thiophene); 7.86 (1H, dd, J45 = 5, J35 = 1, H-5);
8.47 (1H, dd, J34 = 4, J35 = 1, H-3). 13C NMR spectrum, δ, ppm: 112.32 (CN), 112.39 (CN), 127.25, 129.69, 130.64
(C-4, thiophene), 135.25 (C-5), 136.51 (C-3), 146.28, 149.93.
5-Chloro-6-(2-furyl)pyrazine-2,3-dicarbonitrile (1c). Yield 80%; mp 121-122°C (mp 118–119°C [5]).
1H NMR spectrum, δ, ppm (J, Hz): 6.57 (1H, dd, J34 = 3.7, J45 = 1.7, H-4, furan); 7.67 (1H, d, J34 = 3.7, H-3);
13
7.68 (1H, dd, J45 = 1.7, J35 = 0.6, H-5). C NMR spectrum, δ, ppm: 112.12 (CN), 112.24 (CN), 113.84, 121.96,
127.22, 130.76, 145.07, 145.68, 146.58, 149.04.
Compounds 2. Dimethylmaleimide and its DBU and Potassium Salts. Dimethylmaleimide was
prepared from dimethylmaleic anhydride and ammonium acetate [9], mp 110-114°C.
The reaction of equimolar amounts of dimethylmaleimide and DBU in acetone gave an oil upon removal of
the solvent. Trituration with diethyl ether and hexane gave a white powder (54%), mp 69-71°C.
The reaction of equimolar amounts of dimethylmaleimide and potassium t-butoxide in methanol gave a white powder
(58%), mp >300°C.
Compounds 2a,b were prepared from acetone solutions of the DBU-imide salt and compound 1a or 1b.
Acetone was removed from the dark blue reaction mixture, and the residue was chromatographed on silica with DCM.
Compound 2c was prepared from the potassium-imide salt, the phase transfer catalyst ''Aliquat'' and compound 1c
dissolved in DCM.
5-(3,4-Dimethyl-2,5-dioxopyrrolin-1-yl)-6-phenylpyrazine-2,3-dicarbonitrile (2a). A white powder; yield
20%; mp 158-160°C. IR spectrum, ν, cm-1: 2237 (w, CN), 1715 (s, C=O), 1397 (s), 1415, 1339, 1290, 1074, 1008,
1
13
814, 764, 729, 709, 694. H NMR spectrum, δ, ppm: 2.02 (6H, s); 7.55 (5H, m). C NMR spectrum, δ, ppm: 9.31,
112.44 (CN), 112.77 (CN), 128.17, 129.53, 130.23, 131.98, 132.14, 133.78, 139.78, 142.59, 156.44, 168.36. Mass
spectrum, m/z (Irel, %): 329 [M] (100), 330 (21.1). Found, M: 329.0913. C18H11N5O2. Calculated, M: 329.0913.
5-(3,4-Dimethyl-2,5-dioxopyrrolin-1-yl)-6-(2-thienyl)pyrazine-2,3-dicarbonitrile
(2b).
A
yellow
fluorescent powder; yield 21%, mp 172-173°C. IR spectrum, ν, cm-1: 2235 (w, CN), 1731 (s, C=O), 1711 (s, C=O),
1
1524, 1414 (s), 1387 (s), 1353, 1330, 1278, 1073, 856, 792, 730. UV-vis, λmax, nm (ε): 365 (23 000). H NMR
spectrum, δ, ppm (J, Hz): 2.13 (6H, s); 7.19 (1H, dd, J34 = 4, J = 5, H-4, thiophene); 7.69 (1H, dd, J45 = 5, J35 = 1,
13
H-5); 7.91 (1H, dd, J34 = 4, J35 = 1, H-3). C NMR spectrum, δ, ppm: 112.35 (CN), 112.49 (CN), 128.24, 129.39,
132.37, 133.45, 134.73, 135.25, 139.72, 140.26, 150.43, 168.74. Mass spectrum, m/z (Irel, %): 335 [M] (100), 336
(16.0), 337 (5.4). Found, M: 335.0478. C16H9N5O2S. Calculated, M: 335.0477.
5-(3,4-Dimethyl-2,5-dioxopyrrolin-1-yl)-6-(2-furyl)pyrazine-2,3-dicarbonitrile (2c). Yield 20%, mp
210-212°C. IR spectrum, ν, cm–1: 2238 (w, CN), 1732 (s, C=O), 1708 (s, C=O), 1575, 1527, 1465 (s), 1432 (s),
1199

1300, 1086, 1009, 795, 723, 706. UV-vis, λmax, nm (ε): 365 (19 000). 1H NMR spectrum, δ, ppm (J, Hz): 2.10 (6H, s);
6.76 (1H, dd, J34 = 3.7, J45 = 1.8, H-4, furan); 7.59 (1H, m, H-3); 7.88 (1H, m, H-5). 13C NMR spectrum, δ, ppm: 8.13,
113.23 (CN), 113.36 (CN), 113.62, 119.10, 128.98, 132.86, 138.27, 139.38, 144.38, 148.04, 148.57. Mass spectrum,
m/z (Irel, %) 319 [M] (100), 320 (17.7), 321 (2.2). Found, M: 319.0701. C16H9N5O3 Calculated, M: 319.0705.
Compounds 3. 5,6-Dihydro-1,4-dithiin-2,3-dicarboximide and its DBU Salt. Dichloromaleimide was
prepared by heating dichloromaleic anhydride and urea in acetic acid for 10 min. Yield 56%; mp 172–174°C (mp
173-174°C [10]). A solution of dichloromaleimide (1.66 g, 10 mmol) and ethane-1,2-dithiol (0.94 g, 10 mmol) in
DMF (10 ml) was heated at mp 170-180°C for 1.5 h. The solvent was removed under reduced pressure and the
residue was treated with DCM and water. 5,6-Dihydro-1,4-dithiin-2,3-dicarboximide, a yellow powder, insoluble
in both phases, was obtained. Yield 1.1 g (59%); mp 190-205°C (mp 217°C [6]). 1H NMR spectrum, (CDCl3), δ,
ppm: 3.33 (4H, s). 5,6-Dihydro-1,4-dithiin-2,3-dicarboximide (1.1 g, 5.9 mmol) and DBU (0.9 g, 6 mmol) were
stirred in acetone (30 ml) at ambient temperature for 1 h. Most of the solvent was removed under reduced
pressure, diethyl ether was added, and the product was filtered off. Yield 1.9 g (95%), mp 138-144°C (dec).
Compounds 3 (General procedure). Compounds 1 were stirred with an equimolar amount of the DBU-salt
of 5,6-dihydro-1,4-dithiin-2,3-dicarboximide in acetone at ambient temperature for 1 h. The crude products were
chromatographed on silica with DCM.
5-(4,7-Dioxo-4,5,6,7-tetrahydro-1,4-dithiino[2,3-c]pyrrol-2-yl)-6-phenylpyrazine-2,3-dicarbonitrile
(3a). A yellow fluorescent powder; yield 64%, mp 325°C (dec). IR spectrum, ν, cm-1: 2241 (w, CN), 1713 (s, C=O),
1542, 1396 (s), 1336, 1289, 1203, 1137, 1091, 1066, 982, 921, 855, 783, 699 (s). UV-vis, λmax, nm (ε): 420 (6 000),
352 sh (11 000), 323 sh (15 000), 285 (20 000). 1H NMR spectrum, δ, ppm: 3.63 (4H, s); 7.69 (3H, m); 7.88 (2H, m).
13C NMR spectrum, δ, ppm: 26.23, 113.41 (CN), 128.01, 129.20, 131.34, 132.39, 134.15, 142.0, 156.0, 163.10. Mass
spectrum, m/z (Irel, %): 391 [M] (100), 392 (21.9), 393 (11.7). Found, M; 391.0187. C18H9N5O2S2 Calculated,
M: 391.0198.
5-(4,7-Dioxo-4,5,6,7-tetrahydro-1,4-dithiino[2,3-c]pyrrol-2-yl)-6-(2-thienyl)pyrazine-2,3-dicarbonitrile
(3b). Yield 70%; mp 286-290°C (dec). IR spectrum, ν, cm-1: 2238 (w, CN), 1717 (s, C=O), 1546, 1525 (s), 1420 (s),
1387 (s), 1325, 1198 (s), 1127, 1061, 918, 846, 730 (s), 696, 670. UV-vis, λmax, nm (ε): 437 sh (5 000), 365 (20 000).
1H NMR spectrum, δ, ppm (J, Hz): 3.51 (4H, s); 7.30 (1H, dd, J45 = 5, J34 = 4, H-4, thiophene); 7.99 (1H, dd, J34 = 4,
J35 = 1.1 , H-3); 8.08 (1H, d, J35 = 1.1, H-5). 13C NMR spectrum, δ, ppm: 26.21, 113.50 (CN), 113.62 (CN), 128.92,
129.98, 132.78, 132.96, 133.22, 135.40, 135.46, 137.41, 148.22, 163.72. Mass spectrum, m/z (Irel, %): 397 [M] (100),
398 (17.4), 399 (14.4), 400 (2.6). Found, M: 396.9759. C17H7N5O2S3. Calculated, M: 396.9762.
5-(4,7-Dioxo-4,5,6,7-tetrahydro-1,4-dithiino[2,3-c]pyrrol-2-yl)-6-(2-furyl)pyrazine-2,3-dicarbonitrile
(3c). Yield 57%; mp 270°C (dec). IR spectrum, ν, cm–1: 2235 (w, CN), 1714 (s, C=O), 1574, 1523, 1464, 1394 (s),
1332, 1203 (s), 1016, 894, 857, 775 (s), 730 (s), 698. UV-vis, λmax, nm (ε): 350 (17 000). 1H NMR spectrum, δ, ppm:
3.71 (4H, s); 6.93 (1H, dd, J34 = 3.7, J45 = .7, H-4, furan); 7.76 (1H, dd, J34 = 3.7, J35 = 0.8, H-3); 8.07 (1H, dd,
J45 = 1.8, J35 = 0.8, H-5). 13C NMR spectrum, δ, ppm: 26.3, 113.7 (CN), 119.2, 132.4, 148.6, 163.7 (CO). Mass
spectrum, m/z (Irel, %); 381 [M] (100), 382 (17.7), 383 (9.5). Found, M: 380.9983. C16H7N5O3S2 Calculated,
M: 380.9990.
Compounds 4. 2-Chloro-3-(thiomorpholin-4-yl)maleimide. A solution of 2,3-dichlo-romaleimide (1.66
g, 10 mmol), thiomorpholine (2.1 g, 20 mmol), and triethylamine (2.2 g, 22 mmol) in acetone (40 ml) was left at
ambient temperature for 1 week. Triethylammonium chloride was removed by filtration, the solvent was removed
from the filtrate, and the residue was triturated with diethyl ether. An orange powder; yield 1.91 g (91%); mp
1
180-185°C. H NMR spectrum, δ, ppm: 2.78 (4H, s); 4.17 (4H, s). 13C NMR spectrum, δ, ppm: 28.02, 50.89,
141.41, 165.29, 165.54. Mass spectrum, m/z (Irel, %): 232 [M] (100), 233 (11.2), 234 (35.2). Found, M: 232.0067.
C8H9ClN2O2S. Calculated, M: 232.0073.
The DBU-salt of 2-chloro-3-(thiomorpholin-4-yl)maleimide was prepared in acetone and precipitated with
diethyl ether. Yield 91%; mp 100-109°C.
1200

Compounds 4 were prepared from compounds 1 and DBU-salt of 2-chloro-3-(thiomorpholin-4-yl)maleimide
by the same general procedure as for compounds 3.
5-[(3-Chloro-2,5-dioxo-4-(thiomorpholin-4-yl)pyrrolin-1-yl]-6-phenylpyrazine-2,3-dicarbonitrile (4a). A
yellow fluorescent powder; yield 73%; mp 183-185°C. IR spectrum, ν, cm-1: 2236 (w, CN), 1723 (s, C=O), 1621 (s),
1418 (s), 1394 (s), 1338, 1292, 1250, 1215, 952, 816, 755, 730, 703, 689. UV-vis, λmax, nm (ε): 412 sh (8 000), 363 sh
(11 000), 320 (16 000). 1H NMR spectrum, δ, ppm: 2.74 (4H, s); 4.12 (4H, s); 7.56 (5H, m). 13C NMR spectrum, δ,
ppm: 28.07, 51.36, 97.56, 112.11 (CN), 112.45 (CN), 127.94, 129.40, 129.97, 131.80, 133.43, 141.50, 156.16, 162.21,
162.32. Mass spectrum, m/z (Irel, %) 436 [M] (100), 437 (24.5), 438 (37.5). 439 (9.0). Found, M: 436.0497.
C20H13ClN6O2S. Calculated, M: 436.0509.
5-[(3-Chloro-2,5-dioxo-4-(thiomorpholin-4-yl)pyrrolin-1-yl]-6-(2-thienyl)pyrazine-2,3-di-carbonitrile
(4b). A yellow fluorescent powder; yield 62%; mp 207-208°C (dec). IR spectrum, ν, cm-1: 2235 (w, CN), 1720 (s,
C=O), 1614 (s), 1414 (s), 1393, 1350, 1219, 952, 815, 725 (s). UV-vis, λmax, nm (ε): 365 (25 000). 1H NMR spectrum,
δ, ppm (J, Hz): 2.85 (4H, m); 4.27 (4H, m); 7.25 (1H, dd, J45 = 5, J34 = 4, H-4, thiophene); 7.75 (1H, dd, J45 = 5, J35 =
1, H-5); 7.98 (1H, dd, J34 = 4, J35 = 1, H-3). 13C NMR spectrum, δ, ppm: 28.17, 51.45, 97.96, 112.19 (CN), 112.34
(CN), 128.07, 129.42, 132.49, 133.57, 134.84, 135.00, 138.79, 142.02, 150.37, 162.58, 163.05. Mass spectrum, m/z
(Irel, %): 406 (11.7), 407 [M–Cl] (19.2), 408 (17.6), 442 [M] (27.2), 443 (6.2), 444 (11.6). Found, M: 442.0063.
C18H11ClN6O2S2 Calculated, M: 442.0074.
Unsymmetrically substituted zinc azaphthalocyanines 5. Compounds 5 were obtained from heating the
dicarbonitriles 3b or 4b with Zn(II) acetate and freshly distilled quinoline under a nitrogen blanket at 170-180°C for
10–15 min. The crude products were repeatedly triturated and washed with methanol, water, and acetone until
colorless filtrates.
Tetrakis{(4,7-dioxo-4,5,6,7-tetrahydro-1,4-dithiino[2,3-c]pyrrol-2-yl)}tetrakis(2-thienyl)octaazaphthalo-
cyaninatozinc(II) (5a). A dark-green powder; yield 97%. UV-vis, λmax, nm (ε): 675 (119 000), 610 (29 000), 385
(95 000). Found, %: C 44.67; H 2.27; N 16.07; S 19.00; Zn 6.08. C64H28N20O8S12Zn. Calculated, %: C 46.44; H 1.71;
N 16.92; S 23.25; Zn 3.95.
Tetrakis[3-chloro-2,5-dioxo-4-(thiomorpholin-4-yl)pyrrolin-1-yl]tetrakis(2-thienyl)octaazaphthalo-
cyaninatozinc(II) (5b). A dark powder; yield 85%. UV-vis, λmax, nm (ε): 675 (142 000), 610 (40 000), 390 (126 000).
Found, %: C 46.24; H 3.21; Cl 5.92; N 17.73; S 10.62; Zn 5.78. C72H44Cl4N24O8S8Zn. Calculated, %: C 47.08; H 2.41;
Cl 7.72; N 18.30; S 13.96; Zn 3.56. TOF-SIMS (Ar+): A solution of 5b in CHCl3 was prepared on a clean Ag-
substrate. Molecular ion cluster centered at 1837 amu corresponding to C72H45Cl4N24O8S8Zn, [M + H]+ was observed.
Additional ion at [M–H]– was found.
The author would like to thank Dr. Helge Kjøsen, NTNU, for discussions and the EIMS spectrometry.
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