3-(Nitromethyl)-3,4-dihydroquinoxalin-2(1H)-ones: synthesis and structure

Article abstract of DOI:10.1007/s10593-016-1934-3

[Figure not available: see fulltext.] Reactions of ethyl 3-nitroacrylate with o-phenylenediamine and its substituted derivatives were used for the synthesis of 3-(nitromethyl)-3,4-dihydroquinoxalin-2(1H)-ones, followed by structural characterization. Thes

Full text of DOI:10.1007/s10593-016-1934-3

DOI 10.1007/s10593-016-1934-3
Chemistry of Heterocyclic Compounds 2016, 52(8), 574–577
3
-(Nitromethyl)-3,4-dihydroquinoxalin-2(1H)-ones:
synthesis and structure
1
1
Vasilii V. Pelipko , Sergey V. Makarenko ,
1
1
Valentina M. Berestovitskaya *, Ruslan I. Baichurin
1
Herzen State Pedagogical University of Russia,
4
8 Moyka River Embankment, Saint Petersburg 191186, Russia; e-mail: kohrgpu@yandex.ru
Translated from Khimiya Geterotsiklicheskikh Soedinenii,
016, 52(8), 574–577
Submitted June 15, 2016
Accepted after revision August 8, 2016
2
Reactions of ethyl 3-nitroacrylate with о-phenylenediamine and its substituted derivatives were used for the synthesis of 3-(nitromethyl)-
3
,4-dihydroquinoxalin-2(1H)-ones, followed by structural characterization. These compounds were found to undergo elimination of
nitromethane, leading to quinoxalin-2(1H)-ones.
Keywords: 1,2-diaminobenzene, ethyl 3-nitroacrylate, 3-(nitromethyl)-3,4-dihydroquinoxalin-2(1H)-one, quinoxalin-2(1Н)-one, aza-
Michael reaction.
Quinoxaline (1,4-benzopyrazine) is an important
example of benzocondensed nitrogen-containing hetero-
The reaction of ethyl 3-nitroacrylate (1) with
о-phenylenediamines 2а–c (in 1:1.25 ratio) in anhydrous
ethyl acetate solution at room temperature was complete in
2 h and led to the formation of the respective
3-(nitromethyl)-3,4-dihydroquinoxalin-2(1Н)-ones 3a–c in
51–81% yields (Scheme 1).
This tandem reaction involved initial formation of aza-
Michael adduct A, which then underwent intramolecular
heterocyclization via an attack by the second nucleophilic
center at the ester group.
1
cycles. This heterocycle is a part of the molecular structure
2
–4
of the natural antibiotic echinomycin, as well as synthetic
antibacterial drugs: quinoxidine and dioxidine.5 The
practical applications of quinoxaline derivatives, substituted
,6
7
quinoxalin-2(1H)-ones, show even greater promise. Certain
substituted quinoxalin-2(1H)-ones have exhibited antibacte-
8
,9
8
10
rial and anti-inflammatory, as well as antidiabetic and
11
antiviral activity, including effects against HIV. Such com-
pounds are being considered as effective inhibitors of aldose
In contrast to the reactions of о-phenylenediamine (2a)
and its symmetrically substituted analogs 2b,c, the reactions
of 4-methyl- and 4-chloro-1,2-diaminobenzenes (2d,e) with
ethyl 3-nitroacrylate (1) under analogous conditions led to
the formation of two regioisomers in the ratios of 17:10
12
13
reductase and partial antagonists of γ-aminobutyric acid.
Compounds of quinoxalin-2(1H)-one series have been
7
synthesized by various methods, typically based on
о-phenylenediamine reactions with bifunctional carbonyl
1
4
1
substrates, such as acetylene dicarboxylates, α-bromo-
(3'd:3''d) and 25:10 (3'e:3''e) according to H NMR spectral
15
16,17
esters, glyoxylic acid and its esters,
as well as
data. Besides that, it was found that the synthesized
dihydroquinoxalin-2(1H)-ones 3a–e underwent elimination
of nitromethane upon refluxing in aqueous solution, as
demonstrated in the case of compounds 3a,b, which were
transformed in quantitative yields to the known quinoxalin-
2(1Н)-ones 4a,b1 under these conditions.
1
8
2
,3-epoxyaldehydes.
Representatives of nitroalkenes,
ethyl 3-alkyl-3-nitroacrylates, have also been used
successfully as substrates in reactions with о-phenylene-
diamine for the preparation of 3-(α-nitroalkyl)-3,4-dihydro-
quinoxalin-2(1Н)-ones, although these products required
6,20
1
9
additional chromatographic purification.
The structure of 3-(nitromethyl)-3,4-dihydroquinoxalin-
2(1H)-ones 3a–e was characterized by IR, UV, and one-di-
In this work, we used a reaction of the simplest unsubsti-
tuted ethyl 3-nitroacrylate with a series of о-phenylenedi-
amines to synthesize previously unknown derivatives of
1
13
1
1
mensional Н and С NMR spectra, two-dimensional Н– Н
1
1
1
13
1
13
COSY, Н– Н NOESY, H– C HMQC, and H– C
HMBC experiments, while the physicochemical characteristics
of quinoxalin-2(1Н)-ones 4a,b matched those described in
3
,4-dihydroquinoxalin-2(1Н)-one that contained 3-nitro-
methyl groups.
0
009-3122/16/52(8)-0574©2016 Springer Science+Business Media New York
574

Chemistry of Heterocyclic Compounds 2016, 52(8), 574–577
Scheme 1
R
R
NH2
R
R
NH2
H
1
NH2
R
R
N
O
H
N
CO2Et
8
5
2
3
(From3a,b)
H2O, , 1.5–9 h
R
R
O
2a–c
7
6
N
H
O2N
4
–
EtOH
N
H
N
4a,b
–
MeNO2
NO2
EtO2C
3a–c
R1
NH2
A
EtOAc
rt, 2 h
NO2
H
N
H
N
1
NH2 R1
O
O
2
d,e
+
N
H
'd,e
R1
N
H
3''d,e
–
EtOH
NO2
NO2
3
1
1
2
–4 a R = H, b R = Cl; 2, 3 c R = Me; 2d, 3'd, 3''dR = Me; 2e, 3'e, 3''e R = Cl
the literature.16, 20 IR spectra of compounds 3а–е contained
Thus, we have shown that the reaction of ethyl 3-nitro-
acrylate with 1,2-diaminobenzenes at room temperature
gave good yields of heterocyclic compounds belonging to
absorption bands due to a covalent nitro group at 1542–
–
1
1
548 (νas) and 1377–1380 cm (ν ), characteristic for
s
2
1,22
aliphatic nitro compounds,
absorption bands of amide
3-(nitromethyl)-3,4-dihydroquinoxalin-2(1H)-one
series.
–
1
carbonyl group at 1674–1679 cm , as well as a set of
absorption bands characteristic for amide and amine NH
These compounds showed a tendency to eliminate nitro-
methane, resulting in conversion to quinoxalin-2(1Н)-ones.
–
1
groups (3183–3188, 3366–3417 cm ). UV absorption
Experimental
spectra of compounds 3а–е contained long-wavelength
–1
–1
absorption maxima at 267–277 (ε 3000–4100 l·mol ·cm )
IR spectra were recorded on a Shimadzu IR Prestige-21
FT-IR spectrometer in KBr pellets. Electronic absorption
spectra were recorded on a Shimadzu UV–2401PC
spectrophotometer in DMSO solution in quartz cuvettes
–
1
–1
and 307–325 nm (ε 4300–5100 l·mol ·cm ), and were in
agreement with the data from structurally related
23–25
dihydroquinoxalinones.
1
13
1
1
1
1
An interesting structural feature of the synthesized
dihydroquinoxalinones 3a–e containing nitromethyl groups
was the presence of a chiral С-3 atom in their molecules,
(optical path length 1.01 mm). Н, С, Н– Н COSY, Н– Н
1 13 1 13
NOESY (mixing time 1 s), H– C HMQC, and H– C
HMBC NMR spectra were acquired on a Jeol ECX–400A
1
13
creating a diastereotopic difference between the CH
group protons and forming an АВС spin system with the
-СН methine proton. The signal of the latter (Н ) was
observed as a multiplet at 4.38–4.66 ppm, while the
protons of 3-CH methylene group (Н and Н ) gave
double doublets at 4.72–4.76 and 4.82–4.97 ppm
2
NO
2
instrument at 400 (for H nuclei) and 100 MHz (for
С
nuclei) in DMSO-d . The internal standards were residual
6
1
3
С
solvent protons for Н NMR spectra (δ 2.47 ppm) and
solvent carbon atoms for 13С NMR spectra (δ 40.0 ppm).
Elemental analysis was performed on a EuroVector
EA3000 CHN Dual analyzer.
2
А
В
2
3
3
(
J
АВ = 13.6–14.1, JАС = 4.2–4.7, JВС = 5.0–5.5 Hz). This
Ethyl 3-nitroacrylate was synthesized according to a
1
1
26
coupling pattern was manifested in Н– Н COSY spectra
modified literature procedure.
by the respective cross peaks, while the presence of cross
3-(Nitromethyl)-3,4-dihydroquinoxalin-2(1H)-one (3a).
A solution of ethyl 3-nitroacrylate (1) (160 mg, 1.103 mmol)
in anhydrous ethyl acetate (10 ml) was added dropwise at
room temperature to a solution of о-phenylenediamine (2а)
(149 mg, 1.379 mmol) in anhydrous ethyl acetate (10 ml),
and the reaction mixture was maintained for 2 h. After the
removal of solvent, the resinified residue was crystallized
from ethyl alcohol and the precipitate that formed was
filtered off. Yield 169 mg (74%), yellow powder, mp 165–
peaks between the Н
С
methine proton signal and the
broadened split signal at 6.06–6.74 ppm allowed to assign
the latter to the 4-NH amine proton. Such interpretation
1
1
was also supported by Н– Н NOESY spectra, which
contained additional cross peaks between the broadened
downfield singlet of 1-NH group and the signal of H-8
proton in the aromatic ring.
–
1
1
67°С (EtOH). IR spectrum, ν, cm : 1380 (s), 1542 (s, NO ),
2
1
674 (vs, C=O), 3188 (w), 3382 (w), 3417 (m, NH). UV spect-
–1
–1
1
rum, λmax, nm (ε, l×mol ×cm ): 268 (3000), 307 (4300). H
NMR spectrum, δ, ppm (J, Hz): 4.49–4.56 (1H, m, 3-CH);
2
3
2
4
.76 (1Н, dd, J = 13.8, J = 4.5) and 4.89 (1Н, dd, J = 13.8,
3
3
J = 5.2, СН
2
NO
2
); 6.32 (1H, br. d, J = 1.9, 4-NH); 6.58
3
3
(
1H, t, J = 7.5, Н-7); 6.64 (1H, d, J = 7.3, Н-5); 6.70 (1H, d,
3
3
J = 7.9, Н-8); 6.74 (1H, t, J = 7.5, Н-6); 10.51 (1Н, s, 1-NH).
13
C NMR spectrum, δ, ppm: 54.4 (С-3); 76.5 (СН
2
NO );
2
1
1
1
1
Figure 1. The main correlations in Н– Н COSY and Н– Н
NOESY NMR spectra of compounds 3a–e.
114.1 (C-5); 115.5 (C-8); 118.7 (C-7); 123.6 (C-6); 125.6
(C-8a); 133.3 (C-4a); 164.5 (C=O). Found, %: С 52.23; H 4.43;
5
75

Chemistry of Heterocyclic Compounds 2016, 52(8), 574–577
N 20.33. C
,7-Dichloro-3-(nitromethyl)-3,4-dihydroquinoxalin-
(1H)-one (3b) was obtained from 1,2-diamino-4,5-
dichlorobenzene (2b) (244 mg, 1.379 mmol) and ethyl
-nitroacrylate (1) (160 mg, 1.103 mmol) analogously to
compound 3a. Yield 154 mg (51%), yellow powder, mp
9
H
9
N
3
O
3
. Calculated, %: C 52.17; H 4.38; N 20.28.
1-NH). 13C NMR spectrum, δ, ppm: 21.2 (CH
76.5 (СН NO ); 114.6 (C-5); 115.4 (C-8); 119.2 (C-7); 123.3
3
), 54.4 (С-3);
6
2
2
2
(C-8а); 132.6 (C-6); 133.1 (C-4a); 164.3 (C=O). Found, %:
C 54.41; H 5.01; N 18.76. C10
H
11
N
3
O . Calculated, %: C
3
3
54.29; H 5.01; N 19.00.
7-Chloro-3-(nitromethyl)-3,4-dihydroquinoxalin-2(1H)-
one (3e') and 6-chloro-3-(nitromethyl)-3,4-dihydro-
quinoxalin-2(1H)-one (3e'') were obtained from 1,2-di-
amino-4-chlorobenzene (2e) (197 mg, 1.379 mmol) and
ethyl 3-nitroacrylate (1) (160 mg, 1.103 mmol) analogously
to compound 3a. Yield 162 mg (61%), brown powder, a
–
1
2
64–266°С (EtOH). IR spectrum, ν, cm : 1379 (s), 1546
(
s, NO ), 1675 (vs, C=O), 3184 (w), 3363 (m), 3380 (m),
2
–1
–1
3
397 (m, NH). UV spectrum, λmax, nm (ε, l×mol ×cm ):
1
2
77 (3400), 325 (4900). H NMR spectrum, δ, ppm (J, Hz):
2 3
4
.60–4.66 (1H, m, 3-СН); 4.77 (1Н, dd, J = 14.1, J = 4.2)
2
3
and 4.97 (1Н, dd, J = 14.1, J = 5.0, СН
2
NO
2
); 6.74 (1H,
mixture of compounds 3e' and 3e'' (25:10) with mp 182–
3
–1
br. d, J = 1.7, 4-NH); 6.80 (1H, s, Н-5); 6.82 (1H, s, Н-8);
1
185°C (CCl
1544 (s, NO
4
–MeOH, 3:2). IR spectrum, ν, cm : 1378 (s),
1
3
0.74 (1Н, s, 1-NH). C NMR spectrum, δ, ppm: 53.8
С-3); 76.7 (СН NO ); 114.4 (C-5); 116.1 (C-8); 118.9
C-7); 124.7 (C-6); 125.8 (C-8a); 133.7 (C-4a); 164.1
C=O). Found, %: C 39.29; H 2.45; N 15.46. C Cl
2
), 1675 (vs, C=O), 3184 (m), 3371 (m), 3392 (s,
–1
–1
(
(
(
2
2
NH). UV spectrum, λmax, nm (ε, l×mol ×cm ): 273 (4100), 317
1
(5100). Isomer 3e'. H NMR spectrum, δ, ppm (J, Hz):
2
9
H
7
2
N
3
O
3
.
4.54–4.61 (1H, m, 3-СН); 4.757 (1Н, dd, J = 13.9,
3
2
3
Calculated, %: C 39.15; H 2.56; N 15.22.
,7-Dimethyl-3-(nitromethyl)-3,4-dihydroquinoxalin-
(1H)-one (3с) was obtained from 1,2-diamino-4,5-di-
methylbenzene (2с) (188 mg, 1.379 mmol) and ethyl
-nitroacrylate (1) (160 mg, 1.103 mmol) analogously to
compound 3a. Yield 189 mg (73%), orange powder,
decomp. temp. 295°С (CCl –MeOH, 3:2). IR spectrum, ν,
cm : 1377 (s), 1544 (s, NO ), 1679 (vs, C=O), 3184 (m),
191 (m), 3387 (w), 3416 (m, NH). UV spectrum, λmax, nm
J = 4.4) and 4.927 (1Н, dd, J = 13.9, J = 5.0, СН
2
NO );
2
3
3
6
6.51 (1H, d, J = 1.9, 4-NH); 6.63 (1H, d, J = 8.4, Н-5); 6.71
4
3
4
2
(1H, d, J = 2.3, Н-8), 6.76 (1H, dd, J = 8.4, J = 2.3,
13
Н-6); 10.64 (1Н, br. s, 1-NH). C NMR spectrum, δ, ppm:
3
54.1 (С-3); 76.5 (СН
2
NO ); 114.8 (C-8); 115.1 (C-5); 121.6
2
(C-7); 123.0 (C-6); 126.8 (C-8а); 132.3 (C-4a); 164.5 (C=O).
1
4
Isomer 3e''. H NMR spectrum, δ, ppm (J, Hz): 4.54–4.61
–
1
2
3
2
(1H, m, 3-СН); 4.761 (1Н, dd, J = 13.9, J = 4.3) and 4.933
2 3
3
(1Н, dd, J = 13.9, J = 5.1, СН
2
NO ); 6.59 (1H, dd,
2
–
1
–1
1
3
4
4
(
ε, l×mol ×cm ): 271 (3000), 313 (4600). H NMR
spectrum, δ, ppm (J, Hz): 2.01 (3Н, s, СН ); 2.02 (3Н, s,
СН ); 4.38–4.47 (1H, m, 3-СН); 4.72 (1Н, dd, J = 13.6,
J = 8.3, J = 2.2, Н-7); 6.60 (1H, br. s, 4-NH); 6.65 (1H, d,
3
3
J = 2.2, Н-5); 6.67 (1H, d, J = 8.3, Н-8); 10.64 (1Н, br. s,
2
13
3
1-NH). C NMR spectrum, δ, ppm: 53.9 (С-3); 76.6
3
2
3
J = 4.7) and 4.82 (1Н, dd, J = 13.6, J= 5.5, СН
2
NO
2
);
(СН
2
NO ); 113.1 (C-5); 116.5 (C-8); 117.8 (C-7); 124.5
2
3
6
.06 (1H, br. d, J = 2.1 4-NH); 6.44 (1H, s, Н-5); 6.48 (1H, s,
(C-8а); 127.2 (C-6); 134.7 (C-4a); 164.1 (C=O). Found, %:
13
Н-8); 10.38 (1Н, s, 1-NH). C NMR spectrum, δ, ppm:
C 44.64; H 3.48; N 17.27. C
C 44.74; H 3.39; N 17.39.
9
H
8
ClN
3
O . Calculated, %:
3
1
(
(
9.1 (СН
3
); 19.5 (СН
3
); 54.7 (С-3); 76.4 (СН
2
NO ); 115.7
2
C-5); 116.7 (C-8); 123.5 (C-8а); 126.1 (C-7); 130.9
C-4a); 131.0 (C-6); 164.5 (C=O). Found, %: C 56.00;
Quinoxalin-2(1Н)-one (4а). A suspension of 3-nitro-
methyl)-3,4-dihydroquinoxalin-2(1Н)-one (3а) (100 mg,
0.483 mmol) in water (10 ml) was refluxed for 1.5 h by
heating a flask equipped with reflux condenser on a sand
bath. The mixture was cooled to room temperature and
maintained for 18 h, the precipitate that formed was filtered
off on a sintered glass filter. Yield 69 mg (98%), light-
H 5.63; N 17.81. C11
H 5.57; N 17.86.
H
13
N
3
O . Calculated, %: C 56.16;
3
7
-Methyl-3-(nitromethyl)-3,4-dihydroquinoxalin-2(1H)-
one (3d') and 6-methyl-3-(nitromethyl)-3,4-dihydro-
quinoxalin-2(1H)-one (3d'') were obtained from 1,2-diamino-
4
-methylbenzene (2d) (316 mg, 2.586 mmol) and ethyl
yellow crystals, mp 263–265°С (H O) (mp 268–269°С
2
16
1
3
-nitroacrylate (1) (300 mg, 2.069 mmol) analogously to
(EtOH) ). H NMR spectrum, δ, ppm (J, Hz): 7.24–7.30
(2H, m), 7.48–7.55 (1Н, m) and 7.71–7.77 (1Н, m,
Н-5,6,7,8); 8.13 (1Н, s, 3-СН); 12.40 (1Н, br. s, 1-NH).
compound 3a. Yield 372 mg (81%), yellow powder, a
mixture of compounds 3d' and 3d'' (17:10) with mp 154–
–
1
13
1
1
55°С (CCl
548 (s, NO
4
–MeOH, 3:1). IR spectrum, ν, cm : 1377 (s),
), 1676 (vs, C=O), 3183 (m), 3366 (m), 3388
C NMR spectrum, δ, ppm: 116.2; 123.8; 129.3; 131.3;
2
132.3; 132.5 (С-5,6,7,8,4а,8а); 152.1 (С-3); 155.4 (С=О).
6,7-Dichloroquinoxalin-2(1Н)-one (4b) was obtained
analogously to compound 4a from 6,7-dichloro-3-(nitro-
methyl)-3,4-dihydroquinoxalin-2(1Н)-one (3b) (100 mg,
0.362 mmol) by refluxing in water (10 ml) for 9 h. Yield
59 mg (75%), yellowish-white crystals, decomp. temp.
–
1
–1
(
(
(
s, NH). UV spectrum, λmax, nm (ε, l×mol ×cm ): 267
1
3500), 311 (4600). Isomer 3d'. H NMR spectrum, δ, ppm
J, Hz): 2.10 (3Н, s, CH
3
); 4.43–4.51 (1H, m, 3-СН); 4.74–
2
3
4
.78 (1Н, m) and 4.85 (1Н, dd, J = 13.7, J = 5.4,
3
СН
2
NO
2
); 6.15 (1H, br. d, J = 2.2, 4-NH); 6.51–6.57 (3H, m,
1
3
20
1
Н-5,6,8); 10.46 (1Н, s, 1-NH). C NMR spectrum, δ, ppm:
286°С (H O) (decomp. temp. 275°С (2-PrOH) ). H NMR
2
2
0.8 (CH
3
); 54.5 (С-3); 76.4 (СН
2
NO
2
); 114.2 (C-5); 116.0
spectrum, δ, ppm (J, Hz): 7.41 (1Н, s) and 8.02 (1Н, s,
Н-5,8); 8.18 (1Н, s, 3-СН); 12.51 (1Н, br. s, 1-NH).
(
C-8); 124.0 (C-6); 125.7 (C-8а); 127.6 (C-7); 130.9 (C-4a); 164.8
1
(
C=O). Isomer 3d''. H NMR spectrum, δ, ppm (J, Hz): 2.10
(
3H, s, CH ); 4.43–4.51 (1H, m, 3-СН); 4.70–4.74 (1Н, m)
3
2
3
and 4.86 (1Н, dd, J = 13.7, J = 5.2, СН
2
NO
2
); 6.24 (1H, br. d,
Supplementary information file containing spectral data
for the synthesized compounds is available at http://
link.springer.com/journal/10593.
3
3
4
J = 2.0, 4-NH); 6.39 (1H, dd, J = 7.8, J = 1.2, Н-7); 6.45
3
(1H, br. s, Н-5); 6.58 (1H, d, J = 7.8, Н-8); 10.43 (1Н, s,
5
76

Chemistry of Heterocyclic Compounds 2016, 52(8), 574–577
12. Sarges, R.; Lyga, J. W. J. Heterocycl. Chem. 1988, 25, 1475.
This work received financial support from the Ministry
1
1
1
1
3. Lee, L.; Murray, W. V.; Rivero, R. A. J. Org. Chem. 1997,
of Education and Science of Russian Federation, within the
6
2, 3874.
framework of baseline of the State Assignment.
4. Suschitzky, H.; Wakefield, B. J.; Whittaker, R. A. J. Chem.
Soc., Perkin Trans. 1 1975, 401.
5. Kim, Y.; Lee, M. H.; Choi, E. T.; No, E. S.; Park, Y. S.
Heterocycles 2007, 71, 5.
6. Chupakhin, O. N.; Egorov, I. N.; Rusinov, V. L.;
Slepukhin, P. A. Russ. Chem. Bull. 2010, 59, 991. [Izv. Akad.
Nauk, Ser. Khim. 2010, 970.]
References
1
. Pereira, J. A.; Pessoa, A. M.; Cordeiro, M. N. D. S.;
Fernandes, R.; Prudêncio, C.; Noronha, J. P.; Vieira, M. Eur.
J. Med. Chem. 2015, 97, 664.
. General Organic Chemistry [Russian translation]; Barton, D.;
Ollis, W. D., Eds.; Khimiya: Moscow, 1985, Vol. 8, p. 161.
. Waring, M. J.; Wakelin, L. P. G. Nature 1974, 252, 653.
. Kim, Y. B.; Kim, Y. H.; Park, J. Y.; Kim, S. K. Bioorg. Med.
Chem. Lett. 2004, 14, 541.
. Mashkovsky, M. D. Drugs [in Russian]; Novaya Volna:
Moscow, 2002, 14th ed., Vol. 2, p. 298.
. Russian Drug Directory. Encyclopedia of Medicines [in
Russian]; RLS, Moscow, 2002, 2nd ed., p. 305, 938.
. Carta, A.; Piras, S.; Loriga, G.; Paglietti, G. Mini-Rev. Med.
Chem. 2006, 6, 1179.
2
17. Carrër, A.; Brion, J.-D.; Messaoudi, S.; Alami, M. Org. Lett.
2
013, 15, 5606.
3
4
1
1
2
2
8. Murata, S.; Sugimoto, T.; Matsuura, S. Heterocycles 1987, 26, 883.
9. Ballini, R.; Gabrielli, S.; Palmieri, A. Synlett 2009, 965.
. Kazimierczuk, Z.; Pfleiderer, W. Liebigs Ann. Chem. 1982, 754.
0
5
6
7
8
9
1. Silverstein, R.; Webster, F.; Kimle, D. Spectrometric
Identification of Organic Compounds [Russian translation];
BINOM. Laboratoriya Znanii: Moscow, 2012, p. 557.
22. Pretsch, E.; Buhlmann, P.; Affolter, C. Structure
Determination of Organic Compounds. Tables of Spectral Data
[
Russian
translation]; Mir; BINOM. Laboratoriya Znanii:
. El-Sabbagh, O. I.; El-Sadek, M. E.; Lashine, S. M.; Yassin, S. H.;
El-Nabtity, S. M. Med. Chem. Res. 2009, 18, 782.
. Ajani, O. O.; Obafemi, C. A.; Ikpo, C. O.; Ogunniran, K. O.;
Nwinyi, O. C. Chem. Heterocycl. Compd. 2009, 45, 1370.
Moscow, 2006.
23. Dawson, W.; Newbold, G. T.; Spring F. S. J. Chem. Soc.
1
949, 2579.
2
4. Pflegel, P.; Wagner, G. Z. Chem. (Stuttgart, Ger.) 1968, 8, 179.
5. Marxer, A.; Salzmann, U.; Hofer F. Helv. Chim. Acta 1971,
54, 2507.
[
Khim. Geterotsikl. Soedin. 2009, 1703.]
2
1
1
0. Gupta, D.; Ghosh, N. N.; Chandra, R. Bioorg. Med. Chem.
Lett. 2005, 15, 1019.
1. Rösner, M.; Billhardt-Troughton, U.-M.; Kirsh, R.; Kleim, J.-P.;
Meichsner, C.; Riess, G.; Winkler, I. US Patent 5723461.
26. McMurry, J. E.; Musser, J. H.; Fleming, I.; Fortunak, J.;
Nübling, C. Org. Synth. 1977, 56, 65.
5
77