Fluorine-containing quinoline and quinoxaline styryl derivatives: Synthesis and photophysical properties

Article abstract of DOI:10.1007/s11172-011-0148-1

(E)-2-Styryl-substituted 6,7-difluoroquinolines and quinoxalines were synthesized by the condensation of the corresponding 2-methylbenzazines with aromatic aldehydes. Photoluminescence of the synthesized 6,7-difluoro-2- styrylbenzazines was studied.

Full text of DOI:10.1007/s11172-011-0148-1

Russian Chemical Bulletin, International Edition, Vol. 60, No. 5, pp. 942—947, May, 2011
942
Fluorineꢀcontaining quinoline and quinoxaline styryl derivatives:
synthesis and photophysical properties
E. V. Nosova,a T. V. Trashakhova,a V. S. Ustyugov,a N. N. Mochul´skaya,a
M. S. Valova,b G. N. Lipunova,b and V. N. Charushinb
aUral Federal University named after the First President of Russia B. N. El´tsyn,
19 ul. Mira, 620002 Ekaterinburg, Russian Federation.
Eꢀmail: emily74@rambler.ru
bI. Ya. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences,
22 ul. S. Kovalevskoi, 620219 Ekaterinburg, Russian Federation.
Eꢀmail: lipunova@ios.uran.ru
(E)ꢀ2ꢀStyrylꢀsubstituted 6,7ꢀdifluoroquinolines and quinoxalines were synthesized by the
condensation of the corresponding 2ꢀmethylbenzazines with aromatic aldehydes. Photoluminesꢀ
cence of the synthesized 6,7ꢀdifluoroꢀ2ꢀstyrylbenzazines was studied.
Key words: styrylbenzazines, photoluminescence, 6,7ꢀdifluoroquinaldine, 6,7ꢀdifluoroꢀ
quinolineꢀ4ꢀcarboxylic acid.
Fluorescent styryl dyes and metallochelates are imꢀ
matic aldehydes. Only one fluorineꢀcontaining styrylquinꢀ
oline derivative, viz., 3ꢀ[2ꢀ(6,7ꢀdifluoroquinolinꢀ2ꢀyl)ꢀ
vinyl]benzaldehyde, was described as an intermediate for
the preparation of leukotriene antagonist LTD4.12 The
condensation of 6,7ꢀdifluoroquinaldine 2b with benzaldeꢀ
hyde, pꢀnitrobenzaldehyde, and pꢀmethoxybenzaldehyde
on heating in glacial acetic acid in the presence of sodium
acetate for 12 h afforded new (E)ꢀ2ꢀ(arylvinyl)ꢀ6,7ꢀdiꢀ
fluoroquinolines 3а—с (Scheme 1). The 1Н NMR spectra
of quinolines 3 are characterized by doublets of the fragment
СН=СН in regions of 7.22—7.63 and 7.73—7.90 ppm
with the spinꢀspin coupling constant (SSCC) 16.2—16.6 Hz,
which indicates its (E)ꢀconfiguration along with signals of
protons of the difluoroquinoline fragment and aryl residue.
Polymer materials with the nonlinear optical properꢀ
ties were obtained from the 2ꢀstyryl derivatives of quinoꢀ
lineꢀ4ꢀcarboxylic acid.13 The fluorescence properties of
push—pool systems based on 4ꢀtrifluoromethylquinoline
were described.14 The photoluminescence spectra of
2ꢀstyrylquinolineꢀ4ꢀcarboxylic acids were not studied, and
data on syntheses of the fluorinated analogs are lacking in
the literature. In order to obtain 6,7ꢀdifluorine analogs of
2ꢀstyrylquinazolinones, we developed the synthetic apꢀ
proach to 6,7ꢀdifluoroꢀ2ꢀstyrylquinolines 6а—с (Scheme 2).
The Pfitzinger reaction of isatin 4 with acetone in the
presence of potassium hydroxide affords 6,7ꢀdifluoroꢀ2ꢀ
methylquinolineꢀ4ꢀcarboxylic acid 5, and the reaction
conditions are analogous to those described for the nonꢀ
fluorinated analog.15 The condensation of 5 with aromatic
aldehydes in acetic acid in the presence of sodium acetate
on reflux for 7—12 h resulted in the formation of styryl
portant electroluminescent organic materials.1 The luminoꢀ
phore structure includes πꢀdeficient heterocyclic fragments
(quinoline, quinoxaline, and others), which opens prosꢀ
pects for the construction of materials of the electronꢀ
transporting layer.2 Tris(8ꢀhydroxyquinolinato)aluminum
is an excellent electroluminescent and electronꢀtransportꢀ
ing material.3
Interest in zinc complexes of 2ꢀstyrylꢀ8ꢀhydroxyquinoꢀ
line has increased in the recent time, since they are recꢀ
ommended themselves as materials for monolayer organic
lightꢀemitting diodes.4 The study of a correlation between
the solvent polarity and the maximum of emission of
4ꢀdimethylaminoꢀ2ꢀ(E)ꢀstyrylꢀ(6ꢀchloroquinoline) made
it possible to recommend it as a biosensor.5 Search for
photoluminescent materials in the series of styrylbenzꢀ
azines is topical, which is indicated by the study of the
photophysical characteristics of 2ꢀstyryl derivatives of
3Hꢀquinazolinꢀ4ꢀones.6 Since fluorinated poly(pꢀphenyleneꢀ
vinylene) exceeds polyphenylvinylene in electron conducꢀ
tivity,7,8 the study of the photophysical characteristics of
fluorineꢀcontaining styrylbenzazines seems promising.
We chose fluorineꢀcontaining styryl derivatives of such
πꢀdeficient heterocycles as quinoline and quinoxaline as
objects of investigation, because the nonꢀfluorinated anaꢀ
logs demonstrated considerable luminescence properties
and the introduction of fluorine atoms can enhance the
solubility in organic solvents, which is important for the
production of electronic devices.
Several publications9—11 are devoted to the search for
optimal conditions of quinaldine condensation with aroꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 920—925, May, 2011.
1066ꢀ5285/11/6005ꢀ942 © 2011 Springer Science+Business Media, Inc.

Fluorinated styrylquinolines and quinoxalines
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 5, May, 2011
943
isonitrosoacetone was described,16 and we proposed to use
pyruvic aldehyde for cyclocondensation. The synthesis of
nonꢀfluorinated analog 9c and the photophysical behavior
of (E)ꢀ2ꢀstyrylquinoxaline conformers were described.17,18
The condensation of methylquinoxaline 8 with aromatic
aldehydes on reflux in glacial MeCOOH in the presence of
sodium acetate for 6—12 h gave new (Е)ꢀ2ꢀ(arylvinyl)ꢀ
6,7ꢀdifluoroquinoxalines 9а—с (Scheme 3). The 1Н NMR
spectra of quinoxalines 9 are characterized by doublets
of the fragment СН=СН in regions of 7.31—7.76 and
Scheme 1
3
7.92—8.10 ppm with the J = 16.3—16.6 Hz along with
signals of protons of the difluoroquinoxaline fragment and
the aryl residue.
2ꢀThienylvinyl derivatives of 8ꢀacetoxyquinoline were
described as promising materials for πꢀconjugated oligoꢀ
mers applied in organic lightꢀemitting diodes, being doꢀ
norꢀacceptor conjugated systems suitable for film prepaꢀ
ration.19 The synthesis of 2ꢀ(2ꢀthienyl)vinyl derivatives
10a—c was achieved by reflux of 2b, 5, and 8 with
thiopheneꢀ2ꢀcarbaldehyde and sodium acetate in acetic
acid for 12—36 h in 26—55% yields (Scheme 4). Strucꢀ
1
tures 10a—c were confirmed by the H NMR and mass
spectral data.
2ꢀStyryl derivatives 3—10 are characterized by the
longꢀwavelength absorption band at 348—376 nm in the
electronic spectra (Table 1). The introduction of a strong
electronꢀwithdrawing (R = NO2) or electronꢀreleasing
group (R = OMe) into the pꢀposition of the aryl fragment
results in the bathochromic shift of the longꢀwavelength
absorption band by 8—11 nm.
i. Chloranil, butanol.
3: R = H (a), NO2 (b), OMe (c)
The synthesized styrylquinolines and styrylquinoxaꢀ
lines exhibit photoluminescence in an acetonitrile soluꢀ
tion with the emission maximum at 399—569 nm (see
Table 1). The elongation of the conjugation chain due to
the variation of substituent R shifts the emission band to
a longerꢀwavelength region and results in the transition
from blue to green or yellowꢀorange fluorescence regardꢀ
less of the electronic character of the introduced group.
However, the value of shift for the nitrophenyl derivatives
(3b, 6b, 9b) is higher than that for the methoxy derivatives
(3c, 6c, 9c). The nitro derivative of the quinoxaline series
9b has the maximum Stokes shift (200 nm, see Table 1).
derivatives 6а—с; the reaction duration is maximum for
the formation of methoxy derivative 6с because of the
lower reactivity of 4ꢀmethoxybenzaldehyde in the conꢀ
densation reactions. The characteristic doublets of proꢀ
tons of the СН=СН fragment with the coupling constants
1
3J = 16.2—16.3 Hz appear in the Н NMR spectrum at
7.30—7.71 and 7.79—7.96 ppm.
6,7ꢀDifluoroꢀ2ꢀstyrylquinoxalines 8 are other analogs
of 6,7ꢀdifluoroꢀ2ꢀstyrylquinolines containing the electronꢀ
withdrawing group in position 4. The synthesis of comꢀ
pounds 8 from 4,5ꢀdifluoroꢀоꢀphenylenediamine and
Scheme 2
6: R = H (a), NO2 (b), OMe (c)

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Nosova et al.
Scheme 3
9: R = H (a), NO2 (b), OMe (c)
Scheme 4
The quantum yields of compounds 3—10 (Table 1) lie
in the same ranges as those for similar in structure 3ꢀstyryl
derivatives of quinoxaninꢀ2ꢀones (0.04—0.09, and a high
value of 0.18—0.20 was obtained only for the compound
containing the dimethylamino group).20 As a whole, rather
low luminescence intensity of the styryl derivatives of
heterocycles in solutions is related to the occurrence of
(E)ꢀ(Z)ꢀisomerization.21,22 In films or in the solid state
the quantum yield can increase by several orders of
magnitude.
The results of this study suggests that the properties
can be tuned by the variation of the styryldiazine strucꢀ
ture. Styrylquinolines and styrylquinoxalines containing
the nitro or methoxy group in the styryl fragment are promꢀ
ising for the further deepened study of the photophysical
properties in various aggregation states.
10: X = CH (a), C—COOH (b), N (c)
At the same time, the photoluminescence intensity of the
methoxy derivatives is considerably higher than that of the
phenyl and nitrophenyl derivatives, the highest value of
quantum yield was obtained for compound 9с (0.186, see
Table 1). The replacement of the phenyl fragment by
thiophene (compounds 10a—c) results in the red shift in
the emission spectra with a decrease in the fluorescence
intensity.
Experimental
1
Н NMR spectra in DMSOꢀd6 were recorded on a Bruker
DRXꢀ400 spectrometer with a working frequency of 400.13 MHz,
and chemical shifts were measured relative to SiMe4.
Mass spectra were recorded on a MicrOTOFꢀQ II mass specꢀ
trometer (Bruker Daltonics, Bremen, Germany) equipped with
an electrospray ionization source, a sixꢀport valve, and a kd
Table 1. Data on the absorption and photoluminescence spectra of styrylbenzazines 3, 6, 9, and 10
abs
fl
Comꢀ
pound
Х
Ar (Het)
λ
λ
*
Stokes
shift/nm
Quantum
yield
max
nm
3a
3b
3c
6а
6b
6c
9а
9b
9c
СН
СН
CH
С—СOOH
С—СOOH
С—СOOH
N
N
N
Ph
348, 335
356
356
352, 340
359
360
365, 353
369
376
360
363
399
483
451
430
495
484
425
569
493
439
476
479
51
127
95
0.0100
0.0003
0.0240
0.0590
0.0002
0.0860
0.0500
0.0002
0.1860
0.0040
0.0180
0.0160
4ꢀNO2C6H4
4ꢀOMeC6H4
Ph
4ꢀNO2C6H4
4ꢀOMeC6H4
Ph
4ꢀNO2C6H4
4ꢀOMeC6H4
2ꢀthienyl
2ꢀthienyl
2ꢀthienyl
78
136
124
60
200
117
79
10a
10b
10c
СН
С—СOOH
N
113
101
378
* Excitation in the region of the longꢀwavelength absorption band.

Fluorinated styrylquinolines and quinoxalines
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 5, May, 2011
945
Scientific device of direct injection (flow rate 180 μL h–1). The
mass spectrometer was controlled by the micrOTOFcontrol
2.3 patch 1 and HyStar 3.2 program software (Bruker Daltonics).
The nominal resolution of the instrument was 17 500. The mass
spectrometer worked in the positive ionization mode in the mass
range m/z = 50—800 Da. The voltage on the capillary of the
ionization source was 4500 V, and the voltage potential at the
outlet from the glass capillary was 166 V. The pressure of the
spraying gas was 0.8 bar, and the flow rate of the drying gas was
4 L min–1. The temperature of the gas heater was 250 °С. The
averaging was 3, and the value of summation was 5000, which
corresponds to one spectrum per 1 s. The time of ion transit was
70 μs, and the radio frequency of the hexafield was 100 Vpp. The
external calibration of the instrument was carried out by six points
before each detection. The peaks of lithium formate clusters
were used as reference points upon the introduction into the
instrument of a LiOH solution (10 mmol L–1) in a propanꢀ2ꢀ
ol—0.2% aqueous solution of formic acid (1 : 1 vol/vol) mixture.
Absorption spectra were recorded using a Shimadzu
UVꢀ2401PC spectrophotometer (Japan) in an acetonitrile soluꢀ
tion. Luminescence spectra were measured on a Cary Eclipse
spectrofluorimeter (Varian, USA) in an acetonitrile solution with
a concentration of ∼5•10–6 mol L–1. The relative quantum yield
was determined by a known procedure23 using quinine bisulfate
as a standard (ϕ = 0.546). Melting points were determined on
a Stuart SMP3 instrument. The reaction course was monitored
using thin layer chromatography on silica gel.
(100%). Found (%): C, 76.35; H, 4.11; N, 5.26. С17H11F2N.
Calculated (%): C, 76.40; H, 4.15; N, 5.24.
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀ[2ꢀ(4ꢀmethoxyphenyl)vinyl]quinoline (3c).
The yield was 31%, m.p. 160—162 °С. 1Н NMR (DMSOꢀd6), δ:
3
3.83 (s, 3 Н, ОСН3); 6.94 (d, 2 Н, Н(3´), Н(5´), J = 8.7 Hz);
3
7.22 (d, 1 Н, СН=, J = 16.3 Hz); 7.61 (d, 2 Н, Н(2´), Н(6´),
3J = 8.7 Hz); 7.73 (d, 1 Н, СН=, 3J = 16.2 Hz); 7.74 (d, 1 Н, Н(3),
3J = 8.6 Hz); 7.77 (dd, 1 Н, Н(5) or Н(8), 3J = 11.7 Hz, 4J = 7.9 Hz);
7.83 (dd, 1 Н, Н(8) or Н(5), 3J = 10.7 Hz, 4J = 8.9 Hz); 8.24
3
(d, 1 Н, Н(4), J = 8.6 Hz). MS, m/z (Irel (%)): 298 [M + H]+
(100%). Found (%): C, 72.69; H, 4.38; N, 4.75. С18H13F2NО.
Calculated (%): C, 72.72; H, 4.41; N, 4.71.
6,7ꢀDifluoroꢀ2ꢀmethylquinolineꢀ4ꢀcarboxylic acid (5). A soluꢀ
tion of potassium hydroxide (5.5 g, 98 mmol) in water (11 mL)
was added to difluoroisatin 4 (2.25 g, 12.3 mmol). The mixture
was stirred for 5 min at 25 °С, after which the mixture turned
green and became viscous. Acetone (18 mL, 24.5 mmol) was
added to the contents of the flask, and the flask was heated for
6 h at 90 °С. After the reaction mixture was cooled down, neuꢀ
tralization was carried out to pH 5—6 by the addition of 10%
hydrochloric acid, and the precipitate that formed was filtered
off. The yield was 2.3 g (79%), m.p. 228—230 °С. 1Н NMR
(DMSOꢀd6), δ: 2.72 (s, 3 Н, СН3); 7.82 (dd, 1 Н, Н(8) or Н(5),
4
3J = 11.4 Hz, J = 8.1 Hz); 7.90 (s, 1 Н, Н(3)); 8.71 (dd, 1 Н,
Н(5) or Н(8), 3J = 12.8 Hz, 4J = 9.1 Hz); 13.7 (br.s, 1 Н,
COOH). MS, m/z (Irel (%)): 224 [M + H]+ (100%). Found (%):
C, 59.24; H, 3.19; N, 6.24. С11H7F2NО2. Calculated (%):
C, 59.20; H, 3.16; N, 6.28.
6,7ꢀDifluoroꢀ2ꢀmethylquinoline (2a), difluoroisatin 4, and
diamine 7 were synthesized by known procedures (see Refs 12,
24, and 25).
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀstyrylquinolineꢀ4ꢀcarboxylic acid (6а).
Anhydrous sodium acetate (0.1 g) and benzaldehyde (0.4 mL,
3.8 mmol) were added to a solution of quinolinecarboxylic acid 5
(0.2 g, 0.89 mmol) in glacial acetic acid (5 mL). The reaction
mixture was refluxed for 7 h, and the precipitate that formed
after cooling was filtered off and washed with ethanol. The yield
was 0.2 g (72%), m.p. 268—270 °С. 1Н NMR (DMSOꢀd6), δ:
7.33 (m, 1 Н, Ph); 7.41 (m, 2 Н, Ph); 7.43 (d, 1 Н, СН=,
3J = 16.3 Hz); 7.68 (m, 2 Н, Ph); 7.83 (d, 1 Н, СН=, 3J = 16.3 Hz);
7.88 (dd, 1 Н, Н(8) or Н(5), 3J = 11.3 Hz, 4J = 8.1 Hz); 8.28
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀ[2ꢀ(4ꢀnitrophenyl)vinyl]quinoline (3b).
A 2 М solution of Na2CO3 (10 mL) was added to a suspension
of 6,7ꢀdifluoroꢀ2ꢀmethylquinoline hydrochloride 2a (0.3 g,
2.1 mmol) in water (10 mL), the mixture was stirred for 5 min,
and the colorless precipitate of base 2b that formed was filtered
off and dried. Then methylquinoxaline 2b was dissolved in glaꢀ
cial acetic acid (20 mL), sodium acetate (0.1 g) and pꢀnitrobenzꢀ
aldehyde (0.5 g, 3.3 mmol) were added, and the reaction mixture
was refluxed for 12 h. After cooling the solution was concentratꢀ
ed by evaporation to dryness and washed with water and then
with ethanol. The yield was 0.4 g (45%), m.p. 200—202 °С.
1Н NMR (DMSOꢀd6), δ: 7.63 (d, 1 Н, СН=, 3J = 16.2 Hz); 7.82
(dd, 1 Н, Н(5) or Н(8), 3J = 11.6 Hz, 4J = 7.9 Hz); 7.85 (d, 1 Н,
3
(s, 1 Н, Н(3)); 8.72 (dd, 1 Н, Н(5) or Н(8), J = 12.8 Hz, 4J =
= 9.1 Hz); 13.0—14.0 (br.s, 1 Н, COOH). MS, m/z (Irel (%)):
312 [M + H]+ (100%). Found (%): C, 69.50; H, 3.61; N, 4.46.
С18H11F2NO2. Calculated (%): C, 69.45; H, 3.56; N, 4.50.
Quinoline derivatives 6b,c were synthesized similarly. For
the synthesis of 6c, the duration of the reaction was elongated to
12 h and recrystallization from ethanol was used.
3
3
Н(3), J = 8.5 Hz); 7.89 (dd, 1 Н, Н(8) or Н(5), J = 11.4 Hz,
4J = 9.3 Hz); 7.90 (d, 1 Н, СН=, J = 16.2 Hz); 7.94 and 8.25
3
(both d, 2 Н each, Н(2´), Н(3´), Н(5´), Н(6´), 3J = 8.6 Hz);
8.34 (d, 1 Н, Н(4), 3J = 8.5 Hz). MS, m/z (Irel (%)): 313 [M + H]+
(100%). Found (%): C, 65.35; H, 3.19; N, 9.02. С17H10F2N2O2.
Calculated (%): C, 65.39; H, 3.23; N, 8.97.
Compounds 3а,c were synthesized similarly. To isolate comꢀ
pound 3c, after the reaction mixture was evaporated, water
(10 mL) was added to the residue, the product was extracted with
methylene chloride, and the precipitate formed after the partial
evaporation of the extragent was filtered off and washed with
hexane.
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀ[2ꢀ(4ꢀnitrophenyl)vinyl]quinolineꢀ4ꢀcarbꢀ
oxylic acid (6b). The yield was 78%, m.p. 276—278 °С. 1Н NMR,
δ: 7.71 (d, 1 Н, СН=, 3J = 16.3 Hz); 7.91 (dd, 1 Н, Н(8) or Н(5),
3J = 11.2 Hz, J = 8.2 Hz); 7.96 (d, 1 Н, СН=, J = 16.3 Hz);
7.97 and 8.25 (both d, 2 Н each, Н(2´), Н(3´), H(5´), H(6´),
3J = 8.8 Hz); 8.35 (s, 1 Н, Н(3)); 8.75 (dd, 1 Н, Н(5) or Н(8),
3J = 12.7 Hz, 4J = 9.1 Hz); 13.5—14.5 (br.s, 1 Н, COOH). MS,
m/z (Irel (%)): 357 [M + H]+ (100%). Found (%): C, 60.70;
H, 2.85; N, 7.82. С18H10F2N2O4. Calculated (%): C, 60.68;
H, 2.83; N, 7.86.
4
3
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀstyrylquinoline (3а). The yield was 0.2 g
(36%), m.p. 140—142 °С. 1Н (DMSOꢀd6), δ: 7.32 (m, 1 Н, Ph);
7.37 (d, 1 Н, СН=, 3J = 16.6 Hz); 7.40 (m, 2 Н, Ph); 7.67 (m, 2 Н,
Ph); 7.77 (d, 1 Н, Н(3), 3J = 8.6 Hz); 7.78 (d, 1 Н, СН=,
3J = 16.6 Hz); 7.83 and 7.86 (both m, 2 Н each, Н(5), Н(8));
8.28 (d, 1 Н, Н(4), 3J = 8.6 Hz). MS, m/z (Irel (%)): 268 [M + H]+
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀ[2ꢀ(4ꢀmethoxyphenyl)vinyl]quinolineꢀ4ꢀ
carboxylic acid (6с). The yield was 49%, m.p. 278—280 °С.
1Н NMR (DMSOꢀd6), δ: 6.95 (d, 2 Н, Н(3´), H(5´), 3J = 8.6 Hz);
3
7.30 (d, 1 Н, СН=, J = 16.2 Hz); 7.64 (d, 2 Н, Н(2´), H(6´),
3J = 8.6 Hz); 7.79 (d, 1 Н, СН=, 3J = 16.3 Hz); 7.86 (dd, 1 Н,
3
4
Н(8) or Н(5), J = 11.3 Hz, J = 8.2 Hz); 8.25 (s, 1 Н, Н(3));

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Nosova et al.
8.71 (dd, 1 Н, Н(5) or Н(8), 3J = 12.6 Hz, 4J = 9.2 Hz);
13.0—14.0 (br.s, 1 Н, COOH). MS, m/z (Irel (%)): 342 [M + H]+
(100%). Found (%): C, 66.91; H, 3.86; N, 4.05. С19H13F2NO3.
Calculated (%): C, 66.86; H, 3.84; N, 4.10.
6,7ꢀDifluoroꢀ2ꢀmethylquinoxaline (8). A 35% aqueous soluꢀ
tion of methylglyoxal (pyruvic aldehyde) (1.07 g, 5.2 mmol) was
added to a solution of 2ꢀaminoꢀ4,5ꢀdifluoroaniline (0.75 g,
5.2 mmol). The reaction mixture was stored for 1.5 h at 80 °С.
The precipitate of quinoxaline formed after cooling was filtered
off. The yield was 0.8 g (85%). According to the melting point
and spectral characteristics, the product is identical to that deꢀ
scribed earlier.16
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀ[2ꢀ(4ꢀnitrophenyl)vinyl]quinoxaline (9b).
Anhydrous sodium acetate (0.15 g) and pꢀnitrobenzaldehyde (0.6 g,
4 mmol) were added to a solution of 6,7ꢀdifluoroꢀ2ꢀmethylquiꢀ
noxaline 8 (0.3 g, 1.65 mmol) in glacial acetic acid (20 mL). The
reaction mixture was refluxed for 6 h and after cooling concenꢀ
trated to 0.5 volume. The precipitate that formed was filtered
off, washed with water (50 mL) and then with ethanol (15 mL)
(to separate aldehyde excess), and recrystallized from ethanol.
The yield was 0.23 g (45%), m.p. 210—212 °С. 1Н NMR
(DMSOꢀd6), δ: 7.76 (d, 1 Н, СН=, 3J = 16.4 Hz); 7.95 (dd, 1 Н,
Н(5) or Н(8), 3J = 10.9 Hz, 4J = 8.4 Hz); 7.98 (dd, 1 Н, Н(8) or
Н(5), 3J = 11.2 Hz, 4J = 7.6 Hz); 8.00 and 8.28 (both d, 2 Н
each, Н(2´), Н(3´), H(5´), H(6´), 3J = 8.8 Hz); 8.10 (d, 1 Н,
СН=, 3J = 16.4 Hz); 9.25 (s, 1 Н, Н(3)). MS, m/z (Irel (%)): 314
[M + H]+ (100%). Found (%): C, 61.30; H, 2.86; N, 13.44.
С16H9F2N3O2. Calculated (%): C, 61.35; H, 2.90; N, 13.41.
Compounds 9а,с were synthesized similarly, and the reacꢀ
tion duration was 12 h. To isolate compound 9с, after evaporaꢀ
tion of the reaction mixture, water (10 mL) was added to the
residue, and the product was extracted with methylene chloride.
The precipitate that formed after the partial evaporation of the
extragent was filtered off and washed with hexane.
(dd, 1 Н, Н(8) or Н(5), 3J = 10.8 Hz, 4J = 8.9 Hz); 7.96 (d, 1 Н,
СН=, 3J = 16.0 Hz); 8.26 (d, 1 Н, Н(4), 3J = 8.6 Hz). MS,
m/z (Irel (%)): 274 [M + H]+ (100%). Found (%): C, 65.88;
H, 3.27; N, 5.14. С15H9F2NS. Calculated (%): C 65.92; H 3.32;
N 5.12.
Compounds 10b,с were synthesized similarly. To obtain 10с,
the reaction duration was elongated to 36 h.
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀ(2ꢀthienyl)vinylquinolineꢀ4ꢀcarboxylic
acid (10b). The yield was 51%, m.p. 240—242 °С. 1Н NMR
(DMSOꢀd6), δ: 7.09 (dd, 1 Н, Н(4´), 3J = 4.9 Hz, 3J = 3.3 Hz);
7.15 (d, 1 Н, СН=, 3J = 16.0 Hz); 7.37 (d, 1 Н, Н(5´), 3J = 3.3 Hz);
3
7.47 (d, 1 Н, Н(3´), J = 4.9 Hz); 7.85 (dd, 1 Н, Н(8) or Н(5),
4
3
3J = 11.2 Hz, J = 8.2 Hz); 8.02 (d, 1 Н, СН=, J = 16.0 Hz);
3
8.23 (s, 1 Н, Н(3)); 8.72 (dd, 1 Н, Н(5) or Н(8), J = 12.7 Hz,
4J = 9.6 Hz); 13.0—14.0 (br.s, 1 Н, COOH). MS, m/z (Irel (%)):
318 [M + H]+ (100%). Found (%): C, 60.60; H, 2.91; N, 4.38.
С16H9F2NO2S. Calculated (%): C, 60.56; H, 2.86; N, 4.41.
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀ(2ꢀthienyl)vinylquinoxaline (10с). The
yield was 55%, m.p. 139—141 °С. 1Н NMR (DMSOꢀd6), δ: 7.12
3
(dd, 1 Н, Н(4´), J = 5.0 Hz, 3J = 3.6 Hz); 7.18 (d, 1 Н, СН=,
3
3J = 16.0 Hz); 7.42 (d, 1 Н, Н(5´), J = 3.6 Hz); 7.54 (d, 1 Н,
Н(3´), 3J = 5.0 Hz); 7.87 (dd, 1 Н, Н(8) or Н(5), 3J = 11.0 Hz,
4J = 8.4 Hz); 7.93 (dd, 1 Н, Н(5) or Н(8), 3J = 10.8 Hz, 4J = 8.4 Hz);
8.15 (d, 1 Н, СН=, 3J = 16.0 Hz); 9.14 (s, 1 Н, Н(3)). MS,
m/z (Irel (%)): 275 [M + H]+ (100%). Found (%): C, 61.27;
H, 2.90; N, 10.24. С14H8F2N2S. Calculated (%): C, 61.31;
H, 2.94; N, 10.21.
This work was financially supported by the Ministry of
Education and Science of the Russian Federation (State
Contract No. 02.740.11.0260), the Council on Grants at
the President of the Russian Federation (Program for Supꢀ
port of Leading Scientific Schools of the Russian Federaꢀ
tion, Grant NShꢀ65261.2010.3), and the Russian Founꢀ
dation for Basic Research (Project No. 11ꢀ03ꢀ00718).
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀstyrylquinoxaline (9а). The yield was
1
29%, m.p. 153—155 °С. Н (DMSOꢀd6), δ: 7.36 (m, 1 Н, Ph);
7.43 (m, 2 Н, Ph); 7.47 (d, 1 Н, СН=, 3J = 16.6 Hz); 7.70 (m, 2 Н,
4
Ph); 7.90 (dd, 1 Н, Н(5) or Н(8), 3J = 11.0 Hz, J = 8.5 Hz);
References
7.94 (dd, 1 Н, Н(8) or Н(5), 3J = 10.5 Hz, 4J = 8.0 Hz); 7.97
(d, 1 Н, СН=, 3J = 16.6 Hz); 9.19 (s, 1 Н, Н(3)). MS, m/z (Irel (%)):
269 [M + H]+ (100%). Found (%): C, 71.68; H, 3.80; N, 10.39.
С16H10F2N2. Calculated (%): C, 71.64; H, 3.76; N, 10.44.
(E)ꢀ6,7ꢀDifluoroꢀ2ꢀ[2ꢀ(4ꢀmethoxyphenyl)vinyl]quinoxaline
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(9с). The yield was 25%, m.p. 238—240 °С. Н (DMSOꢀd6), δ:
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(E)ꢀ6,7ꢀDifluoroꢀ2ꢀ(2ꢀthienyl)vinylquinoline (10а). Anꢀ
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Received February 1, 2011;
in revised form March 17, 2011