Synthesis of isomeric (E)-[4-(dimethylamino)phenyl]-vinylquinoxalines – precursors for a new class of nonlinear optical chromophores

Article abstract of DOI:10.1007/s10593-017-2084-y

[Figure not available: see fulltext.] Methods are presented for the preparation of isomeric (Е)-3-, (Е)-6-, (Е)-7-[4-(dimethylamino)phenylethenyl]quinoxalin-2-ones and 2-phenylquinoxalines – compounds of “donor–π-bridge” type, which serve as precursors for new nonlinear optical chromophores with potentially high first hyperpolarizability values. The introduction of dimethylanilinoethenyl moiety at position 3 of the quinoxaline system was achieved in good yields by fusion of 3-methyl derivatives with 4-(dimethylamino)benzaldehyde at 220°С in the presence of catalytic amounts of acetic anhydride and pyridine during the synthesis of 3-(dimethylaminophenylethenyl)quinoxalin-2-ones or as a result of condensation of these reactants by the action of 20 М sodium hydroxide solution in the presence of Aliquat 336 during the synthesis of 3-(dimethylaminophenylethenyl)-2-phenylquinoxalines. The introduction of dimethylanilinoethenyl moiety at positions 6 and 7 was achieved by Heck reaction of p-dimethylaminovinylbenzene with 6- or 7-bromoquinoxalines in the presence of palladium acetate. The structures of isomeric 6-bromo- and 7-bromo-3-methyl derivatives of quinoxalines were confirmed by X-ray diffraction analysis.

Full text of DOI:10.1007/s10593-017-2084-y

DOI 10.1007/s10593-017-2084-y
Chemistry of Heterocyclic Compounds 2017, 53(5), 504–510
Synthesis of isomeric (E)-[4-(dimethylamino)phenyl]-
vinylquinoxalines – precursors for a new class
of nonlinear optical chromophores
Sirina M. Sharipova1, Alina A. Gilmutdinova1, Dmitry B. Krivolapov1,
Zilya R. Khisametdinova2, Olga N. Kataeva1, Alexey A. Kalinin1*
1 A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of the Russian Academy of Sciences,
8 Akademika Arbuzova St., Kazan 420088, Russia; е-mail: kalinin@iopc.ru
2 A. M. Butlerov Institute of Chemistry, Kazan Federal University,
18 Kremlevskaya St., Kazan 420008, Russia; е-mail: zika0527@mail.ru
Submitted December 27, 2016
Accepted January 28, 2017
Translated from Khimiya Geterotsiklicheskikh Soedinenii,
2017, 53(5), 504–510
Methods are presented for the preparation of isomeric (Е)-3-, (Е)-6-, (Е)-7-[4-(dimethylamino)phenylethenyl]quinoxalin-2-ones and
2-phenylquinoxalines – compounds of ''donor–π-bridge'' type, which serve as precursors for new nonlinear optical chromophores with
potentially high first hyperpolarizability values. The introduction of dimethylanilinoethenyl moiety at position 3 of the quinoxaline
system was achieved in good yields by fusion of 3-methyl derivatives with 4-(dimethylamino)benzaldehyde at 220°С in the presence of
catalytic amounts of acetic anhydride and pyridine during the synthesis of 3-(dimethylaminophenylethenyl)quinoxalin-2-ones or as a
result of condensation of these reactants by the action of 20 М sodium hydroxide solution in the presence of Aliquat 336 during the
synthesis of 3-(dimethylaminophenylethenyl)-2-phenylquinoxalines. The introduction of dimethylanilinoethenyl moiety at positions 6
and 7 was achieved by Heck reaction of p-dimethylaminovinylbenzene with 6- or 7-bromoquinoxalines in the presence of palladium
acetate. The structures of isomeric 6-bromo- and 7-bromo-3-methyl derivatives of quinoxalines were confirmed by X-ray diffraction
analysis.
Keywords: (Е)-[4-(dimethylamino)phenyl]ethenylquinoxalines, first hyperpolarizability, nonlinear optical chromophores, X-ray
diffraction analysis.
Synthesis of new chromophores with high values of first
hyperpolarizability, the molecular characteristic of non-
linear optical (NLO) chromophores, provides the
foundation for the creation of NLO materials, which find
use in the design of devices for information storage and fast
processing.1 Wide application of heterocyclic compounds
for the synthesis of NLO chromophores started in the last
decade of the 20th century. Heterocyclic moieties can be
included in one, two, or all three components of such
chromophores – the donor and acceptor and the π-bridge.
The main attention of researchers has been focused on
chromophores with one2 or several3 thiophene rings within
the π-bridge. One of the new directions in this field is the
synthesis and characterization of NLO effects in
chromophores with fused heterocyclic moieties, such as
thienothiophene,4 carbazole,5 and phenothiazine,5 in the
structure of π-bridge as well as in the donor6 and acceptor.7
Recently we predicted theoretically8 that the
replacement of thiophene in the FTC chromophore9 (one of
the best NLO chromophores, Fig. 1) with a quinoxaline
moiety (compounds 1 and 2, Fig. 2) should result in
increased first hyperpolarizability values.
The quinoxaline ring system is a part of compounds with
valuable biological properties;10 its derivatives11–14 serve as
initial compounds for the preparation of other heterocycles
that may contain quinoxaline12 or other moieties,13 as well
Figure 1. The structure of FTC chromophore.
0009-3122/17/53(05)-0504©2017 Springer Science+Business Media New York
504

Chemistry of Heterocyclic Compounds 2017, 53(5), 504–510
Me
NMe2
NMe2
O
CN
CN
Me
N
N
NC
O
CN
NC
NC
N
O
N
O
Et
Et
Me
Me
1
2
Me2N
Me
Me
O
CN
CN
Me
N
N
N
N
NC
O
NC
NC
CN
Ph
Ph
3
4
Me
Me2N
Figure 2. Chromophores 1–4 with divinylquinoxaline π-bridge.
as for the synthesis of macrocycles,14 but have not yet been
applied in the synthesis of effective NLO chromophores.
In the current work, we present a method for the
preparation of isomeric (Е)-[4-(dimethylamino)phenyl]-
ethenylquinoxalines, which can be used for the synthesis of
new, effective NLO chromophores with quinoxalinone
(compounds 1 and 2) or 2-phenylquinoxaline (compounds
3 and 4) moieties in the π-bridges (Fig. 2). Despite the
structural similarity of all compounds 1–4, compounds 3
and 4 differ from compounds 1 and 2 by the presence of a
bulky phenyl substituent, which can function as an
isolating group, decreasing the aggregation of
chromophores in the material15 and thus enabling higher
NLO activity of such material.
1Н NMR spectra provided some clues for the assignment
of isomeric products formed as a result of these reactions.
The examples of various quinoxalinone derivatives12,14b
have shown that their spectra contain characteristic
downfield signals of the Н-5 proton belonging to the
quinoxalinone moiety, and therefore, due to the presence of
a substituent at the aromatic ring, these isomers can be
identified by their spin-spin coupling constants. Thus, the
1
isomer showing Н NMR spectrum with the most down-
field signal being a doublet with J = 8.9 Hz at 7.65 ppm
was identified as compound 8, while the isomer with a
doublet at 7.83 ppm with J = 2.1 Hz as the most downfield
1H NMR signal was identified as compound 7. The
A highly successful strategy for the synthesis of NLO
chromophores is the construction of π-conjugated system
within the precursor of the electron-donating fragment by
linking it with the precursor of π-bridge, followed by
modification and introduction of the acceptor as the last
step. The introduction of electron-donating dimethylaniline
moiety in the structure of quinoxaline derivatives,
depending on the regioposition of its addition, was based
on either the Heck raction – addition through vinyl group
to the carbon atom at position 6 or 7 of quinoxaline system,
or Knoevenagel condensation – addition to the carbon atom
at position 3. In order to emply these approaches,
derivatives of 6- and 7-bromo-3-methylquinoxalines were
obtained. Condensation of ethyl pyruvate with 4-bromo-1,2-
benzenediamine allowed to synthesize 6- and 7-bromo-
3-methylquinoxalin-2-ones 5 and 6, which were further
subjected to alkylation with propyl iodide in the presence
of KOH in order to increase the solubility of the new
precursors for π-bridge – N-propyl derivatives 7 and 8
(Scheme 1). The condensation of 4-bromo-1,2-benzenedi-
amine with 1-phenylpropane-1,2-dione provided access to
phenylquinoxalines 9, 10. Compounds 7–10 were readily
soluble in organic solvents. Isomers 7 and 8, in contrast to
isomers 9 and 10, had practically the same Rf values,
complicating their separation by column chromatography.
Nevertheless, the use of a longer column eventually
allowed to chromatographically isolate isomer 7. The
isomeric mixture that was enriched with compound 8 was
separated by several recrystallization steps using hexane.
Scheme 1
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Chemistry of Heterocyclic Compounds 2017, 53(5), 504–510
Figure 3. The molecular structures of bromoquinoxalines 7–10 with atoms represented by thermal vibration ellipsoids of 50%
probability.
following assumption can be made for the other isomeric
donating substituents, can lead to a further decrease in the
yield of their reactions with 4-(dimethylamino)-
benzaldehyde. Indeed, 4-(dimethylamino)benzaldehyde
doesn't react with compound 8 at 200 and 165°С in the
presence of piperidine, while the reaction according to the
published method16e – heating of the starting compounds in
acetic anhydride in the presence of pyridine, provided the
target product 12 in 15% yield. In order to increase yields
of compounds 11 and 12, we performed the reaction of
compounds 7 and 8 with 4-(dimethylamino)benzaldehyde
under the following conditions: fusion at 225°С in open
test tube in the presence of catalytic amounts of acetic
anhydride and pyridine (Scheme 2). These experimental
conditions allowed to increase the yields of compounds 11
and 12 up to 60–70%.
1
pair of compounds 9 and 10: the isomer with H NMR
signal of the ortho protons of phenyl group at a lower field
and the signal of methyl group at a higher field corresponds
to compound 10. Then the isomer showing the signal of
ortho protons of phenyl group at higher field, and the signal
of methyl group at lower field coresponds to isomer 9.
The structures of compounds 7–10 were established by
X-ray diffraction analysis (Fig. 3). The asymmetric part of
the unit cell in the crystal of compound 8 contained three
independent molecules that differed by the conformation of
propyl substituents. Analogously, the crystal of compound
9 contained two independent molecules that differed by the
orientation of the phenyl group. Our assumptions about the
1
structure of these compounds, based on Н NMR spectral
data, were in complete agreement with the X-ray
diffraction analysis results for these crystals. Isomers 5 and
6, 9 and 10 were formed in approximately equal ratios
This experimental procedure was found to be ineffective
for the synthesis of quinoxalines 13 and 14. The formation
of these compounds occurred with considerably lower
yields, and further increase of temperature resulted in
1
(according to the Н NMR data), with a small excess (3–
5%) of compounds 6 and 9.
resinification of the reaction mixture. In a recent article,17
a
The methyl group in π-electron-deficient heterocycles,
which is linked to the carbon atom of the endocyclic imine
group, had enhanced reactivity and readily underwent
Knoevenagel condensation with aldehydes. The synthesis
of 3-styrylquinoxalin-2(1Н)-ones was achieved with such
methods as fusion of the starting reagents or reaction in
acetic anhydride. The first method with the reaction
temperature reaching 180°С provided yields above 90% in
the case of benzaldehyde and its halo and nitro
derivatives,16а while in the case of 4-(dimethylamino)-
benzaldehyde the reaction at 200°С allowed to achieve
85% yield.16b At the same time, fusion in the presence of
piperidine allowed to decrease the temperature to 165°С,
leading to the target product in 70% yield.16c The use of
acetic anhydride as solvent provided 46% yield of the
target product in the case of benzaldehyde and merely 12%
yield in the case of 4-(dimethylamino)phenylbenz-
aldehyde.16d The use of acetic anhydride with catalytic
amounts of pyridine has been described for the synthesis of
trans-arylquinoxalinonylethylenes, but the starting aldehydes
in that case were 2-nitrobenzaldehyde and 5-chloro-2-nitro-
benzaldehyde, instead of 4-(dimethylamino)benzaldehyde.16e
According to literature data, the replacement of
benzaldehyde or nitrobenzaldehyde with the less reactive
4-(dimethylamino)benzaldehyde resulted in a lower yield
of the target product. The probably diminished reactivity of
methyl group in 6- and 7-bromo-3-methyl-1-propyl-
quinoxalin-2-ones, caused by the presence of two electron-
procedure was proposed for the condensation of
methylazines with aldehydes upon heating in aqueous
20 М NaOH solution in the presence of Aliquat 336. This
procedure was found to be effective also for the conden-
sation of phenylquinoxalines 9, 10 with 4-(dimethylamino)
benzaldehyde, leading to the formation of compounds 13
and 14 in 77 and 70% yields, respectively (Scheme 2). It
should be noted that the method described above was, in
turn, less effective for the preparation of quinoxalinones 11
and 12 due to resinification and partial hydrolysis.
The introduction of 4-(dimethylamino)phenylethenyl
moiety at position 6 or 7 of the quinoxaline ring system
was achieved by using the Heck reaction between
compounds 7–10 and 4-(dimethylamino)vinylbenzene,
obtained by Wittig reaction from 4-(dimethylamino)phenyl-
benzaldehyde and methyltriphenylphosphonium bromide.18
The Heck reaction proceeded in DMF in the presence of
Pd(OAc)2, tri(о-tolyl)phosphine, and NEt3 (Scheme 2).
(Dimethylamino)phenylethenylquinoxalines 11–18 were
isolated as trans-isomers, as evidenced by the presence of
1
two H NMR doublet signals of the ethene protons with a
spin-spin coupling constant of ~16 Hz. When changing
from 3-dimethylaminophenylvinyl derivatives 11–14 to
6- and 7-dimethylaminophenylvinyl derivatives 15–18, a
hypsochromic shift of the UV absorption maximum was
observed (see Experimental); the powder color was in the
range from red (compounds 11–14) to orange (compounds
16–18) and yellow (compound 15).
506

Chemistry of Heterocyclic Compounds 2017, 53(5), 504–510
Scheme 2
Thus, we have proposed methods for the synthesis of
oxalin-2(1Н)-one (8). A mixture of compounds 5 and 6
(5.4 g, 23 mmol) and solid potassium hydroxide (2.5 g,
45 mmol) were added to dioxane (30 ml). The reaction
mixture was stirred for 5 min at 100°С, cooled, treated with
a solution of PrI (4.6 g, 27 mmol) in dioxane (5 ml), stirred
for 6 h at 100°С, cooled, poured into water, and extracted
with CH2Cl2. The organic layer was washed with water,
dried over anhydrous MgSO4, and CH2Cl2 was removed at
reduced pressure. The residue was separated by column
chromatography (eluting with a gradient from petroleum
ether to a 3:1 mixture of petroleum ether – EtOAc) and
purified by recrystallization from petroleum ether. The
chromatographic separation first yielded a mixture of
compounds 7 and 8, enriched in isomer 8, which was
separated by several recrystallization steps. Isomer 7 was
isolated at the end of the chromatographic separation.
various (E)-[4-(dimethylamino)phenyl]ethenylquinoxalines –
precursors for new nonlinear optical chromophores, which
showed high first hyperpolarizability values.
Experimental
IR spectra were recorded on a Bruker Vector 22 FT-IR
1
spectrometer in KBr pellets. Н and 13С NMR spectra of
compounds 9, 15–17 were acquired on a Bruker Avance
1
600 instrument (600 and 150 MHz, respectively). Н and
13С NMR spectra of the other compounds were acquired on
a Bruker Avance 400 instrument (400 and 100 MHz,
respectively). Chemical shifts were experimentally
determined relative to the respective signals of deuterated
solvents and are reported on δ scale. The solvents were:
acetone-d6 (2.05 and 29.8 ppm, respectively, compounds
15, 16) and CDCl3 (7.26 and 77.0 ppm, respectively, the
rest of the compounds). UV spectra were recorded on a
PerkinElmer Lambda-35 UV/Vis spectrometer in CH2Cl2
solution. Mass spectra (MALDI TOF) were recorded on a
Bruker Daltonics Ultraflex III mass spectrometer by using
p-nitroaniline as matrix. Elemental analysis was performed
on a Euro EA 3000 CHNS–analyzer, while halogens were
determined according to the Schöniger method. Melting
points were determined on a Boetius hot stage. The
reaction progress and the purity of the obtained compounds
were controlled by TLC on Sorbfil UV-254 plates with
visualization under UV light.
Isomer 7. Yield 2.1 g (31%), white powder, mp 102–
104°C. Rf 0.43 (petroleum ether – EtOAc, 4:1). IR spect-
rum, ν, cm–1: 3280, 3232, 3083, 2961, 2931, 2874, 1643,
1592, 1558, 1478, 1464, 1420, 1381, 1337, 1313, 1281,
1
1244, 1190, 1149, 1120, 1021, 897, 878, 815. H NMR
spectrum, δ, ppm (J, Hz): 0.98 (3H, t, J = 7.4, CH3); 1.67–
1.75 (2Н, m, CH2); 2.51 (3H, s, CH3); 4.10 (2Н, t, J = 7.8,
NCH2); 7.08 (1Н, d, J = 8.9, Н-8); 7.49 (1Н, dd, J = 2.1,
J = 8.9, Н-7); 7.83 (1Н, d, J = 2.1, Н-5). 13C NMR
spectrum, δ, ppm: 11.8; 20.6; 21.5; 43.8; 115.0; 115.6;
115.7; 132.0; 132.1; 133.7; 154.4; 159.8. Found, %: C 51.13;
H 4.53; N 9.99; Br 28.79. C12H13BrN2O. Calculated, %:
C 51.26; H 4.66; N 9.96; Br 28.42.
Preparation of 6-bromo-3-methylquinoxalin-2(1Н)-
one (5) and 7-bromo-3-methylquinoxalin-2(1Н)-one (6).
A solution of ethyl pyruvate (3.1 g, 27 mmol) in EtOH
(5 ml) was added to a solution of 4-bromo-1,2-diamino-
benzene (5.0 g, 27 mmol) in EtOH (30 ml). The reaction
mixture was stirred for 6 h (precipitate formed after 5 min)
and left overnight. The crystals that formed were filtered
off and washed with EtOH. The isolated product (5.20 g)
was a mixture of isomers. The filtrate was evaporated, and
the residue was washed with EtOH, resulting in 0.53 g of
isomeric mixture. The precipitates were combined, the
obtained mixture of isomers was used without separation in
the next reaction.
Isomer 8. Yield 3.0 g (47%), white powder, mp 96–98°C.
Rf 0.43 (petroleum ether – EtOAc, 4:1). IR spectrum, ν, cm–1:
3295, 3245, 3110, 3024, 2967, 2936, 2876, 1653, 1596,
1557, 1481, 1469, 1453, 1437, 1391, 1371, 1349, 1335,
1304, 1286, 1226, 1192, 1119, 1086, 1062, 1016, 986, 947.
1H NMR spectrum, δ, ppm (J, Hz): 1.06 (3H, t, J = 7.4,
CH3); 1.72–1.82 (2Н, m, CH2); 2.57 (3H, s, CH3); 4.15 (2Н,
t, J = 7.8, NCH2); 7.39–7.44 (2Н, m, Н-6,8); 7.65 (1Н, d,
J = 8.9, Н-5). 13C NMR spectrum, δ, ppm: 11.3; 20.5; 21.5;
43.9; 116.6; 123.4; 126.6; 130.9; 131.7; 133.6; 154.5; 158.8.
Found, %: C 51.17; H 4.58; N 9.89; Br 28.61. C12H13BrN2O.
Calculated, %: C 51.26; H 4.66; N 9.96; Br 28.42.
Preparation of 6-bromo-3-methyl-1-propylquin-
oxalin-2(1H)-one (7) and 7-bromo-3-methyl-1-propylquin-
Preparation of 6-bromo-3-methyl-2-phenylquin-
oxaline (9) and 6-bromo-2-methyl-3-phenylquinoxaline
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Chemistry of Heterocyclic Compounds 2017, 53(5), 504–510
(10). A solution of 1-phenylpropane-1,2-dione (7.9 g,
Н-8); 7.39 (1Н, dd, J = 8.3, J = 1.9, Н-6); 7.53 (1Н, d,
J = 16.0, –СН=); 7.57 (2Н, d, J = 8.8, Н Ar); 7.66 (1Н, d,
J = 8.3, Н-5); 8.07 (1Н, d, J = 16.0, –СН=). 13C NMR
spectrum, δ, ppm: 11.4; 20.6; 40.2; 44.0; 112.0; 116.4; 116.8;
122.4; 124.6; 126.7; 130.0; 130.8; 132.8; 132.9; 139.3; 151.3;
153.2; 154.7. Mass spectrum, m/z (Irel, %): 412 [М(79Br)+Н]+,
414 [М(81Br)+Н]+.
53 mmol) was added to a solution of 4-bromo-1,2-
benzenediamine (10.0 g, 54 mmol) in EtOH (10 ml), the
mixture was stirred for 6 h (precipitate formed after 5 min)
and left overnight. The crystals that formed were filtered
off and washed with EtOH. The product (14.1 g) was a
mixture of isomers. The filtrate was evaporated, giving a
mixture of isomers (1.3 g). The precipitates were
combined, the isomers were separated by column
chromatography (eluting with a gradient from petroleum
ether to a 30:1 mixture of petroleum ether – EtOAc) and
then by recrystallization from petroleum ether.
6-Bromo-3{(E)-[4-(dimethylamino)phenyl]ethenyl}-
2-phenylquinoxaline (13). Yield 0.13 g (29%) (method I),
0.33 g (77%) (method II), red powder, mp 165–167°C.
Rf 0.67 (petroleum ether – EtOAc, 4:1). UV spectrum, λmax, nm:
454. IR spectrum, ν, cm–1: 2893, 2805, 1605, 1519, 1431,
1392, 1363, 1328, 1273, 1236, 1183, 1149, 1128, 1053,
Isomer 9. Yield 5.5 g (35%), white powder, mp 93–95°C
(mp 100–102°C24). Rf 0.65 (petroleum ether – EtOAc, 4:1).
Isomer 10. Yield 5.9 g (37%), white powder, mp 105–
107°С (mp 100–102°C24). Rf 0.52.
Preparation of bromo-3-[(E)-4-(dimethylamino)-
phenylethenyl]quinoxalines 11–14 (General method).
Method I. Methylquinoxaline 7–10 (1 mmol) and
4-(dimethylamino)benzaldehyde (1 mmol) were mixed in
an open test tube, then Ac2O (2 drops) and pyridine
(1 drop) were added. The reaction mixture was fused for
1.5 h at 220°С, cooled, and purified by silica gel column
chromatography (eluent petroleum ether – EtOAc, gradient
from 100:1 to 20:1).
Method II. A mixture of methylquinoxaline 9, 10
(1 mmol) and 4-(dimethylamino)benzaldehyde (1 mmol)
was treated with 20 М NaOH (15 ml) and Aliquat 336
(1 drop). The reaction mixture was heated for 15 h at 100°С,
cooled, the solid precipitate was washed with water, dried,
and purified by silica gel column chromatography (eluent
petroleum ether – EtOAc, gradient from 100:1 to 20:1).
6-Bromo-3-{(E)-[4-(dimethylamino)phenyl]ethenyl}-
1-propylquinoxalin-2(1Н)-one (11) was obtained according
to method I. Yield 0.28 g (68%), red powder, mp 170–172°C.
Rf 0.44 (petroleum ether – EtOAc, 4:1). UV spectrum, λmax, nm:
464. IR spectrum, ν, cm–1: 2928, 2799, 1652, 1598, 1565,
1514, 1475, 1429, 1359, 1312, 1248, 1223, 1179, 1165,
1113, 1094, 977, 943, 919, 866, 800, 782. 1H NMR
spectrum, δ, ppm (J, Hz): 1.08 (3H, t, J = 7.5, CH3); 1.77–
1.87 (2Н, m, CH2); 3.06 (6H, s, 2CH3); 4.23 (2Н, t, J = 7.7,
NCH2); 6.73 (2Н, d, J = 8.8, H Ar); 7.14 (1Н, d, J = 8.9,
Н-8); 7.53 (1Н, dd, J = 2.2, J = 8.9, Н-7); 7.57 (1Н, d,
J = 16.0, –СН=); 7.61 (2Н, d, J = 8.8, H Ar); 8.00 (1Н, d,
J = 2.2, Н-5); 8.10 (1Н, d, J = 16.0, –СН=). 13C NMR
spectrum, δ, ppm: 11.4; 20.6; 40.2; 44.0; 112.0; 114.9;
116.0; 116.7; 124.5; 129.8; 131.0; 131.1; 131.9; 135.0;
139.7; 151.4; 154.1; 154.7. Mass spectrum, m/z (Irel, %): 412
[М(79Br)+Н]+, 414 [М(81Br)+Н]+.
1
1013, 974, 944, 873, 805, 697. H NMR spectrum, δ, ppm
(J, Hz): 3.00 (6H, s, 2CH3); 6.68 (2Н, d, J = 8.9, H Ar);
7.15 (1Н, d, J = 15.5, –СН=); 7.42 (2Н, d, J = 8.8, H Ar);
7.52–7.58 (3Н, m, Н Ph); 7.69–7.75 (2Н, m, H Ph, Н-7);
7.92 (1Н, d, J = 8.9, Н-8); 8.01 (1Н, d, J = 15.5, –СН=);
8.27 (1Н, d, J = 2.1, Н-5). 13C NMR spectrum, δ, ppm:
40.2; 112.0; 119.1; 123.6; 124.5; 128.6; 129.1; 129.2; 129.6;
130.4; 130.9; 132.1; 138.0; 138.5; 139.6; 142.4; 150.6;
151.1; 154.5. Mass spectrum, m/z: 430 [М(79Br)+Н]+,
432 [М(81Br)+Н]+.
7-Bromo-3-{(E)-[4-(dimethylamino)phenyl]ethenyl}-
2-phenylquinoxaline (14). Yield 25% (method I), 70%
(method II), red powder, mp 163–165°C. Rf 0.70
(petroleum ether – EtOAc, 4:1). UV spectrum, λmax, nm:
456. IR spectrum, ν, cm–1: 3059, 2888, 2797, 1600, 1520,
1433, 1391, 1361, 1330, 1303, 1234, 1185, 1149, 1121,
1
1051, 1014, 969, 946, 935, 878, 827, 788, 767. H NMR
spectrum, δ, ppm (J, Hz): 3.00 (6H, s, 2CH3); 6.68 (2Н, d,
J = 8.8, H Ar); 7.15 (1Н, d, J = 15.5, –СН=); 7.42 (2Н, d,
J = 8.8, H Ar); 7.51–7.58 (3Н, m, Н Ph); 7.71–7.75 (2Н, m,
H Ph); 7.78 (1Н, dd, J = 8.9, J = 2.2, Н-6); 7.94 (1Н, d,
J = 8.9, Н-5); 8.01 (1Н, d, J = 15.5, –СН=); 8.24 (1Н, d,
J = 2.2, Н-8). 13C NMR spectrum, δ, ppm: 40.2; 112.2;
119.3; 122.3; 124.6; 128.6; 129.1; 129.2; 129.6; 129.9; 131.4;
133.2; 137.6; 138.4; 140.6; 141.4; 150.2; 151.1; 154.9. Mass
spectrum, m/z: 430 [М(79Br)+Н]+, 432 [М(81Br)+Н]+.
Preparation of (Е)-[4-(dimethylamino)phenyl]ethenyl-
3-methylquinoxalines 15–18 (General method). A mixture
of the appropriate bromoquinoxaline 7–10 (1 mmol),
N,N-dimethyl-4-vinylaniline (0.15 g, 1 mmol), tri(о-tolyl)-
phosphine (3 mg, 0.01 mmol), Pd(OAc)2 (1 mg, 0.005 mmol),
Et3N (25 mg, 0.25 mmol), and anhydrous DMF (1 ml) was
stirred for 24 h at 100°С. The reaction mixture was cooled,
poured into water, and extracted with CH2Cl2. The organic
layer was separated, washed with water, dried over
anhydrous MgSO4, filtered, the solvent was removed at
reduced pressure, and the residue was purified by silica gel
column chromatography (eluent petroleum ether – EtOAc,
gradient from 100:1 to 10:1).
6-{(E)-[4-(Dimethylamino)phenyl]ethenyl}-3-methyl-
1-propylquinoxalin-2(1Н)-one (15). Yield 0.17 g (50%),
yellow powder, mp 160–162°C. Rf 0.22 (petroleum ether –
EtOAc, 4:1). UV spectrum, λmax, nm: 363. IR spectrum,
ν, cm–1: 2961, 2875, 2801, 1659, 1607, 1558, 1522, 1495,
1443, 1351, 1285, 1250, 1219, 1195, 1162, 1120, 1061,
1002, 964, 896, 854, 817. 1H NMR spectrum, δ, ppm (J, Hz):
7-Bromo-3-{(E)-[4-(dimethylamino)phenyl]ethenyl}-
1-propylquinoxalin-2(1Н)-one (12) was obtained according
to the method I. Yield 0.25 g (61%), red powder, mp 176–177°C.
Rf 0.46 (petroleum ether – EtOAc, 4:1). UV spectrum, λmax, nm:
462. IR spectrum, ν, cm–1: 2961, 2877, 2804, 1652, 1595,
1561, 1526, 1508, 1475, 1434, 1365, 1326, 1295, 1228,
1
1165, 1109, 1077, 1035, 1001, 979, 947, 817. H NMR
spectrum, δ, ppm (J, Hz): 1.07 (3H, t, J = 7.4, CH3); 1.75–
1.85 (2Н, m, CH2); 3.02 (6H, s, 2CH3); 4.19 (2Н, t, J = 7.8,
NCH2); 6.70 (2Н, d, J = 8.8, H Ar), 7.38 (1Н, d, J = 1.9,
508

Chemistry of Heterocyclic Compounds 2017, 53(5), 504–510
1.03 (3H, t, J = 7.4, CH3); 1.57–1.63 (2Н, m, CH2); 2.48
diffractometer using MoKα radiation (λ 0.71073 Å) at
room temperature. Crystals suitable for X-ray diffraction
analysis were obtained by recrystallization of compounds
from hexane. Compound 7: rhombic syngony, space group
Pca2. Compound 8: monoclinic syngony, space group P21/c.
Compound 9: monoclinic syngony, space group C2/c.
Compound 10: rhombic syngony, space group Pbca. The
following software was used: APEX219 (data acquisition),
SAINT20 (data processing), SADABS Version 2.1021
(accounting for absorption), SHELXS22 (solving of
structures), SHELXL22 (refinement of structures by the least
squares method). The structures were visualized by using
the Mercury 3.0 program.23 The positions and temperature
parameters of non-hydrogen atoms were refined in
anisotropic approximation. Hydrogen atom positions were
calculated geometrically and refined according to the
"rider" model. The complete X-ray diffraction data sets for
compounds 7–10 were deposited at the Cambridge
Crystallographic Data Center (deposits CCDC 1523877,
CCDC 1523876, CCDC 1523879, CCDC 1523878,
respectively).
(3H, s, CH3); 3.00 (6H, s, 2CH3); 4.23 (2Н, t, J = 7.7,
NCH2); 6.76 (2Н, d, J = 8.5, H Ar); 7.06 (1Н, d, J = 16.2,
–СН=); 7.20 (1Н, d, J = 16.2, –СН=); 7.47 (2Н, d, J = 8.5,
Н Ar); 7.48 (1Н, d, J = 8.1, Н-8); 7.74 (1Н, dd, J = 8.3,
J = 1.4, Н-7); 7.84 (1Н, d, J = 1.4, Н-5). 13C NMR spectrum,
δ, ppm (J, Hz): 11.5; 21.4; 21.6; 40.5; 44.1; 113.2; 115.2;
123.3; 126.4; 127.1; 128.0; 128.5; 130.0; 132.3; 134.0;
134.6; 151.4; 155.2; 159.1. Mass spectrum m/z: 348 [М+Н]+.
7-{(E)-[4-(Dimethylamino)phenyl]ethenyl}-3-methyl-
1-propylquinoxalin-2(1Н)-one (16). Yield 0.21 g (61%),
orange powder, mp 164–165°C. Rf 0.24 (petroleum ether –
EtOAc, 4:1). UV spectrum, λmax, nm: 402. IR spectrum,
ν, cm–1: 3019, 2959, 2929, 2874, 2802, 1652, 1599, 1557,
1522, 1495, 1445, 1355, 1285, 1219, 1190, 1164, 1117,
1062, 1002, 962, 948, 892, 816. 1H NMR spectrum, δ, ppm
(J, Hz): 1.03 (3H, t, J = 7.5, CH3); 1.76–1.82 (2Н, m, CH2);
2.44 (3H, s, CH3); 2.99 (6H, s, 2CH3); 4.29 (2Н, t, J = 7.7,
NCH2); 6.75 (2Н, d, J = 8.8, H Ar); 7.13 (1Н, d, J = 16.3,
–СН=); 7.30 (1Н, d, J = 16.3, –СН=); 7.47 (2Н, d, J = 8.8,
Н Ar); 7.55 (1Н, dd, J = 8.3, J = 1.4, Н-6); 7.56 (1Н, s,
Н-8); 7.66 (1Н, d, J = 8.7, Н-5). 13C NMR spectrum,
δ, ppm: 11.6; 21.4; 21.5; 40.4; 43.9; 112.3; 113.2; 121.2;
126.0; 126.9; 128.8; 130.4; 132.1; 132.7; 134.1; 140.9;
151.6; 155.6; 157.4. Mass spectrum, m/z: 348 [М+Н]+.
The work was performed with financial support from the
Russian Science Foundation (grant 16-13-10215).
6-{(E)-[4-(Dimethylamino)phenyl]ethenyl}-3-methyl-
2-phenylquinoxaline (17). Yield 0.18 g (48%), orange
powder, mp 155–157°C. Rf 0.33 (petroleum ether – EtOAc,
4:1). UV spectrum, λmax, nm: 414. IR spectrum, ν, cm–1: 3060,
3017, 2923, 2850, 2803, 1601, 1555, 1521, 1486, 1443,
1347, 1271, 1229, 1180, 1166, 1061, 1006, 995, 949, 911,
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