Fused polycyclic nitrogen-containing heterocycles: IX. Oxidative fusion of imidazole ring to 3-benzoylquinoxalin-2-ones

Article abstract of DOI:10.1023/B:RUJO.0000045201.90930.ff

3-α-Chlorobenzyl- and 3-benzoylquinoxalin-2-ones react with benzylamine in DMSO to give intermediate 3-(α-benzyliminobenzylidene) quinoxalin-2-one which is capable of existing in several tautomeric forms. The subsequent oxidative cyclocondensation leads to imidazo[1,5-a]quinoxalin-4-one. This new procedure for building up imidazo[1,5-a]quinoxalin-4-one system has been applied to the synthesis of various bis(imidazo[1,5-a]quinoxalin-4-ones).

Full text of DOI:10.1023/B:RUJO.0000045201.90930.ff

Russian Journal of Organic Chemistry, Vol. 40, No. 7, 2004, pp. 1041–1046. Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 7, 2004,
pp. 1082–1087.
Original Russian Text Copyright © 2004 by Mamedov, Kalinin, Gorbunova, Bauer, Habicher.
Fused Polycyclic Nitrogen-Containing Heterocycles:
IX.* Oxidative Fusion of Imidazole Ring
to 3-Benzoylquinoxalin-2-ones
V. A. Mamedov,1 A. A. Kalinin,1 E. A. Gorbunova,1 I. Bauer2, and W. D. Habicher2
1 Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center, Russian Academy of Sciences,
ul. Arbuzova 8, Kazan, 420088 Tatarstan, Russia
e-mail: mamedov@iopc.kcn.ru
2 Drezden University of Technology, Institute of Organic Chemistry, Drezden, D-01062 Germany
Received July 24, 2003
Abstract—3-α-Chlorobenzyl- and 3-benzoylquinoxalin-2-ones react with benzylamine in DMSO to give
intermediate 3-(α-benzyliminobenzylidene)quinoxalin-2-one which is capable of existing in several tautomeric
forms. The subsequent oxidative cyclocondensation leads to imidazo[1,5-a]quinoxalin-4-one. This new
procedure for building up imidazo[1,5-a]quinoxalin-4-one system has been applied to the synthesis of various
bis(imidazo[1,5-a]quinoxalin-4-ones).
imidazo[1,5-a]quinoxalin-4-ones I having no substit-
uent in position 1 (X = H): The reaction with the cor-
responding imidazoles III (X = H) yields exclusively
isomeric imidazo[1,2-a]-quinoxalin-6-ones VI [3–5, 9].
Quinoxaline and imidazo[1,5-a]quinoxalin-4-one
ring systems constitute structural fragments of various
biologically active substances and medicines; there-
fore, new functionalized derivatives of quinoxalines
and azoloquinoxalines are often used as key com-
pounds in the synthesis of biologically active sub-
stances. For example, they have been used as template
reagents in the synthesis of GABA/diazepine receptor
agonists and antagonists [2], cAMP and cGMP phos-
phodiesterase inhibitors [3], A1- and A2a-adenosine
receptor agonists [4], and key materials in the prepara-
tion of numerous pharmacologically active compounds
[5–8]. Prior to our studies, several procedures for the
synthesis of imidazo[1,5-a]quinoxalin-4-ones I have
been reported. One of these includes a three-step
process. In the first step, nucleophilic substitution
of the fluorine atom in 2-fluoronitrobenzenes II by
imidazoles III, (X ≠ H, Z = H) gives 1-(2-nitro-
phenyl)imidazoles IV (X ≠ H, Z = H) [3–5, 9]. Com-
pounds IV are then reduced to imidazolylanilines V
(X ≠ H, Z = H) which react with carbonyldiimidazole
to afford imidazo[1,5-a]quinoxalin-4-ones. Although
this proce-dure has been developed in sufficient detail
and is very convenient for the synthesis of 1-sub-
stituted imidazo-[1,5-a]quinoxalin-4-ones I (X ≠ H)
[3–5], it cannot be applied to the preparation of
The second procedure is based on reactions of
diethyl imidazole-4,5-dicarboxylates III (Y = Z =
CO2Et) with 2-fluoronitrobenzene, which result in
formation of 1-(2-nitrophenyl)imidazole-4,5-dicar-
boxylates IV (Y = Z = CO2Et) [8]. Reduction of the
latter gives the corresponding anilines V (Y = Z =
CO2Et) which undergo cyclization to ethyl 4-oxoimi-
dazo[1,5-a]quinoxaline-3-carboxylates I (Y = CO2Et)
[8]. According to the third method, 2,3-dioxoquino-
xalines VII are converted into phosphates VIII which
react with aryl isocyanides to afford 3-arylimidazo-
[1,5-a]quinoxalin-4-ones I [2, 6, 7]. Finally, the fourth
procedure includes reaction of p-tolylsulfonylmethyl
isocyanide with various quinoxalin-2-ones IX having
no substituent at C3. This method provides the pos-
sibility for preparing imidazo[1,5-a]quinoxalin-4-ones
I with free positions 1 and 3 (X = Y = H) [10].
We previously developed new procedures for the
synthesis of imidazo[1,5-a]quinoxalin-4-ones on the
basis of retrosynthetic analysis of the target structures.
The key steps in these procedures include reactions
of 3-α-amino- and 3-α-chlorobenzylquinoxalin-2-ones
X and XI with synthetic equivalents of one- and
two-atom building blocks, respectively. The proposed
* For communication VIII, see [1].
1070-4280/04/4007-1041 © 2004 MAIK “Nauka/Interperiodica”

MAMEDOV et al.
1042
X
X
X
N
Z
N
Z
N
X
Y
Y
N
F
N
N
Y
N
R
R
R
R
HN
Y
N
H
O
NO2
NO2
NH2
Z
I
II
III
IV
V
Y
X
H
N
N
N
O
O
N
OP(O)(OEt)2
O
N
R
R
R
R
N
H
O
N
H
N
N
R'
O
R'
VI
VII
VIII
IX
NH2
Cl
N
N
R
Ar
R
R
N
H
O
N
O
H
X
XI
procedures ensured formation of both substituted and
1-unsubstituted imidazo[1,5-a]quinoxalin-4-ones I
(X = H, SH, OH, SAlk, Me, Ar; Y = Ar) in high yields
[11–14]. It should be noted that in the first case we
were able to use almost all kinds of synthetic equiv-
alents of the RC2+ unit, while in the second case only
potassium thiocyanate (KSCN) and sodium cyanate
(NaOCN) were used as equivalents of the C+=N–
synthon. In continuation of these studies, in the present
work we examined reactions of 3-α-chlorobenzyl-
quinoxalin-2-one (XI) and 3-benzoylquinoxalin-2-one
(XII) with benzylamine (XIII) and m-bis(amino-
methyl)benzene (XIV) with a view to obtain imidazo-
[1,5-a]quinoxalin-4-ones I.
Ph, R=H) on heating in DMSO for 2 h or under
conditions of thermolysis at 225±3°C (10 min)
(Scheme 1). Obviously, imidazole ring fusion in com-
pound XV involves oxidation to Schiff base XVIa
which can give rise to tautomers XVIb and XVIc.
Nucleophilic attack by the N4 atom on the C=N carbon
atom in XVIc leads to closure of imidazole ring and
formation of imidazoquinoxaline ring system XVId;
the subsequent oxidation of XVId with atmospheric
oxygen or DMSO [15] leads to tricyclic structure I
(X = Y = Ph, R = H; Scheme 2).
In order to elucidate the way of formation of com-
pound I (X = Y = Ph, R = H), we examined the
reaction of 3-benzoylquinoxalin-2-one (XII) [11, 16]
with benzylamine (XIII). It was presumed that the
reaction could also give initially Schiff base XVIa and
that oxidative intramolecular cyclization of the latter
will lead to product I. In fact, heterocyclic ketone XII
reacted with benzylamine (XIII) in DMSO at about
We have found that 3-(α-chlorobenzyl)quinoxalin-
2-one (XI) reacts with benzylamine (XIII) in DMSO
at room temperature to give 3-(α-benzylaminobenzyl)-
quinoxalin-2-one (XV) which undergoes intramole-
cular ring closure to imidazoquinoxaline I (X = Y =
Scheme 1.
Ph
N
Ph
O
Ph
PhCH2NH2 (XIII)
DMSO, 20°C, 48 h
N
N
N
Ph
Cl
N
Ph
DMSO, 150°C, 2 h
H
N
H
N
O
N
H
O
H
XI
XV
I
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 7 2004

FUSED POLYCYCLIC NITROGEN-CONTAINING HETEROCYCLES: IX.
1043
Scheme 2.
Ph
O
Ph
Ph
O
N
N
N
O
PhCH2NH2 (XIII)
N
Ph
N
Ph
–H2O
N
H
N
O
N
H
H
XI
XVIa
XVIb
Ph
NH
Ph
H
N
N
Ph
[O]
–H2O
N
Ph
I
N
H
O
N
H
O
XVIc
XVId
150°C (2 h), and the corresponding imidazoquino-
xaline I was formed in quantitative yield. An ana-
logous reaction was successful with compounds con-
taining two 3-benzoylquinoxalin-2-one fragments, e.g.,
with 1,3-bis(3-benzoyl-2-oxoquinoxalin-1-ylmethyl)-
benzene (XVII) which is readily available via alkyla-
tion of XII with 1,3-bis(dibromomethyl)benzene
(XVIII) in boiling dioxane in the presence of KOH
(Scheme 3).
proved by independent synthesis, by reaction of com-
pound I (X = Y = Ph, R = H) with 1,3-bis(bromo-
methyl)benzene (XVIII). Samples of XIX obtained by
the two methods had identical IR and 1H NMR spectra
and melting points (no depression of the melting point
was observed on mixing).
Ph
Ph
N
N
N
N
N
N
Ph
Ph
Scheme 3.
O
O
Br
XII
+
Br
XIX
XVIII
By reaction of 3-benzoylquinoxalin-2-one (XII)
with 1,3-bis(aminomethyl)benzene (XIV) instead of
dibromo derivative XVIII, we obtained chelate-like
compound XX of a different type. This product is
promising not only as ligand but also as building block
for macroheterocyclic compounds due to the presence
of lactam moieties in the two fixed imidazoquinoxaline
fragments. The yield of XX attained 97% when
the reaction was carried out in DMSO for 72 h at
150±2°C under argon.
Ph
Ph
O
N
N
N
N
O
O
KOH, dioxane
O
XVII
The reaction of XVII with benzylamine occurred
under the conditions given above for the reaction of
XII and was complete in 4 h; the product was 1,3-bis-
(1,3-diphenyl-4-oxoimidazo[1,5-a]quinoxalin-5-yl-
methyl)benzene (XIX). The IR spectrum of XIX
contained no ketone carbonyl absorption bands, and
signals from 32 aromatic protons (four phenyl groups
and three o-phenylene fragments) were present in the
1H NMR spectrum. The structure of XIX was also
5
6
1
4
3
1'
2
N
N2'
3'
9'
N
10'N
9a'
Ph
Ph
8'
3a'
4'
7'
5'
N
H
5a'
O
N
H
O
6'
XX
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 7 2004

MAMEDOV et al.
1044
COSY, 46 min
proton-containing fragments: 1,3-phenylene, two ortho-
fused benzene rings, two phenyl groups, and two NH
groups. The COSY spectrum shown in (Fig. 1) clearly
indicates correlations between three protons of the
m-phenylene fragment (δ 7.87, 8.02, and 8.08 ppm),
three protons of the phenyl groups (δ 7.37, 7.44, and
8.21 ppm), and four protons of the fused benzene rings
(δ 6.97, 7.29, 7.31, and 7.34 ppm), separately from
each other. These signals were unambiguously as-
signed on the basis of their multiplicity, position, and
intensity in the 1H NMR spectrum. Taking into account
these data and cross peaks in the HSQC spectrum
(Fig. 2), we identified signals in the 13C NMR spec-
trum, which belong to carbon atoms attached to
protons. Signals from carbon atoms with no protons
attached thereto were assigned using the HMBC tech-
nique (Fig. 3) which is based on correlation of long-
range proton–carbon constants (2JCH). The HMBC
spectrum also allowed us to distinguish signals from
protons in positions 6/9 and 7/8, which have similar
multiplicities. Protons in positions 6 and 8 give cross
peaks with C9a, while those at C7 and C9, with C5a.
Fig. 1. Two-dimensional homonuclear 1H NMR spectrum
(COSY) of compound XX in the region δ 6.9-8.3 ppm.
EXPERIMENTAL
HSQC, 1 h 43 min
The melting points were determined on a Boetius
device. The IR spectra were recorded on a UR-20
spectrometer from samples dispersed in mineral oil.
1
The H NMR spectra were measured on a Bruker
MCL-250 spectrometer at 250.13 MHz. The two-
dimensional NMR spectra of compound XX were ob-
tained on a Bruker DRX-500 instrument (500.13 MHz
for 1H and 125.75 MHz for 13C).
1,3-Diphenylimidazo[1,5-a]quinoxalin-4(5H)-one
(I, X = Y = Ph, R = H). a. Quinoxaline XV, 0.20 g
(0.6 mmol), was placed in a test tube and was heated
for 10 min at 225±3°C on an oil bath. After cooling,
10 ml of acetone was added, and the mixture was
heated for 5 min under reflux and cooled, and the pre-
cipitate was filtered off. Yield 0.11 g (56%) (cf. [13]).
b. A solution of 0.30 g (0.9 mmol) of quinoxaline
XV in 7 ml of DMSO was heated for 2 h at 150°C. It
was then cooled and poured into water, and the
precipitate was filtered off and washed with water.
Yield 0.27 g (91%).
Fig. 2. Two-dimensional heteronuclear 13C–1H NMR spec-
trum (HSQC) of compound XX in DMSO.
The structure of compound XX was established
on the basis of its elemental composition and IR and
1H and 13C NMR spectra (including two-dimensional
NMR techniques). The 1H and 13C NMR spectra of XX
were interpreted using a combination of double homo-
nuclear (COSY) and heteronuclear resonance (HSQC
and HMBC) [17, 18]. Molecule XX consists of four
c. Benzylamine, 0.80 g (7.5 mmol), was added to
a solution of 1.20 g (4.8 mmol) of quinoxaline XII in
10 ml of DMSO. The mixture was heated for 2 h at
150°C, cooled, and poured into water, and the pre-
cipitate was filtered off and washed with water. Yield
1.10 g (98%).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 7 2004

FUSED POLYCYCLIC NITROGEN-CONTAINING HETEROCYCLES: IX.
HMBC, 4 h 46 min
1045
3-(α-Benzylaminobenzyl)quinoxalin-2(1H)-one
(XV). Benzylamine, 0.80 g (7.5 mmol), was added to
a solution of 1.00 g (3.7 mmol) of quinoxaline XI in
15 ml of DMSO, and the mixture was stirred for 3 h
and was left to stand for 2 days. The solution was
poured into water, and the precipitate was filtered
off and washed with water. Yield 97%, mp >180°C
(decomp.; from i-PrOH). IR spectrum, ν, cm–1: 700,
755 , 777, 960, 1095, 1220, 1415, 1480, 1670, 2500–
1
3300. H NMR spectrum (DMSO-d6), δ, ppm: 3.72 d
(1H, CHAHBPh, J = 13.72 Hz), 3.75 d (1H, CHAHBPh,
J = 13.72 Hz), 5.29 s (1H, CHPh), 7.20–7.55 m (13H,
2C6H5, 6-H, 7-H, 8-H), 7.84 d.d (1H, 5-H, J = 8.36,
1.52 Hz). Found, %: C 77.60; H 5.47; N 12.46.
C22H19N3O. Calculated, %: C 77.40; H 5.61; N 12.31.
1,3-Bis(3-benzoyl-2-oxo-1,2-dihydroquinoxalin-
1-ylmethyl)benzene (XVII). A mixture of 0.80 g
(3.2 mmol) of quinoxaline XII, 0.30 g (5.4 mmol) of
KOH, and 30 ml of dioxane was heated for 1 min
under reflux, 0.45 g (1.7 mmol) of 1,3-bis(bromo-
methyl)benzene was added, and the mixture was
heated for 3 h under reflux. The solvent was distilled
off, water was added to the residue, and the precipitate
was filtered off and washed with a solution of KOH
and water. Yield 78%, mp 118–120°C (from acetone–
methanol, 1:1). IR spectrum, ν, cm–1: 615, 693, 725,
1119, 1169, 1254, 1324, 1344, 1400, 1560, 1602, 1651,
Fig. 3. Two-dimensional heteronuclear 13C–1H NMR spec-
trum (HMBC) of compound XX in DMSO.
N 11.04. C50H36N6O2. Calculated, %: C 79.77;
H 4.82; N 11.16.
b. m-Bis(bromomethyl)benzene, 0.12 g (0.45 mmol),
was added to a mixture of 0.30 g (0.89 mmol) of
compound I (X = Y = Ph, R = H), 0.10 g (1.8 mmol) of
KOH, and 10 ml of DMSO. The mixture was stirred
for 3 h and was left overnight. It was then poured into
water, and the precipitate was filtered off and washed
with water. Yield 75%.
1
1683. H NMR spectrum (DMSO-d6), δ, ppm: 5.50 s
(2H, CH2), 7.19 d (2H, 4-H, 6-H, J = 7.58 Hz), 7.22–
7.31 m (4H, 8'-H, 2-H, 5-H), 7.35 d.d.d (2H, 6'-H or
7'-H, J = 7.45, 7.45, 0.6 Hz), 7.40–7.55 m (6H, p-H,
m-H), 7.63 d.d (2H, 7'-H or 6'-H, J = 7.58, 7.15 Hz),
7.92 d.d (2H, 5'-H, J = 8.00, 1.68 Hz), 8.01 d.d (4H,
o-H, J = 7.70, 1.25 Hz). Found, %: C 75.80; H 4.47;
N 9.01. C38H26N4O4. Calculated, %: C 75.73; H 4.35;
N 9.30.
1,3-Bis(3-phenyl-4(5H)-oxoimidazo[1,5-a]quino-
xalin-1-ylmethyl]benzene (XX). 1,3-Bis(amino-
methyl)benzene, 0.35 g (2.6 mmol), was added to
a solution of 1.00 g (4.8 mmol) of quinoxaline XII in
10 ml of DMSO, and the mixture was heated for 72 h
at 150°C. It was then cooled, and the precipitate was
filtered off and washed with isopropyl alcohol.
IR spectrum, ν, cm–1: 704, 759, 910, 1104, 1342, 1486,
1,3-Bis(1,3-diphenyl-2-oxoimidazo[1,5-a]quino-
xalin-5-ylmethyl)benzene (XIX). a. Benzylamine,
0.10 g (0.93 mmol), was added to a solution of 0.20 g
(0.33 mmol) of quinoxaline XVII in 7 ml of DMSO.
The mixture was heated for 4 h at 150°C, cooled, and
poured into water, and the precipitate was filtered off
and washed with water. Yield 57%, mp 296–298°C
(from DMSO). IR spectrum, ν, cm–1: 696, 714, 745,
873, 1176, 1223, 1259, 1301, 1378, 1604, 1651.
1H NMR spectrum (DMSO-d6), δ, ppm: 5.40 s (4H,
CH2), 6.77 d.d (2H, 7'-H or 8'-H, J = 8.00, 7.58 Hz),
6.90–7.70 m (26H, 8'-H or 7'-H, 9'-H, 6'-H, 2-H, 4-H,
5-H, 6-H, 1-C6H5, m-H and p-H in 3-Ph), 7.92–8.02 m
(4H, o-H in 3-Ph). Found, %: C 79.87; H 4.52;
1
1562, 1608, 1660, 2500–3220. H NMR spectrum
(DMSO-d6), δ, ppm: 6.97 d.d.d (2H, 8'-H, J = 7.67,
7.67, 1.54 Hz), 7.29 d.d (2H, 7'-H, J = 8.21, 7.49 Hz),
7.31 d (2H, 9'-H, J = 7.49 Hz), 7.34 d.d (2H, 6'-H, J =
8.04, 1.54 Hz), 7.37 d.d (2H, p-H, J = 7.24, 7.24 Hz),
7.44 d.d (4H, m-H, J = 7.70, 7.25 Hz), 7.87 d.d (1H,
5-H, J = 7.81, 7.81 Hz), 8.02 d.d (2H, 4-H, 6-H, J =
7.81, 1.52 Hz), 8.08 s (1H, 2-H), 8.21 d.d (4H, o-H,
J = 7.82, 1.22 Hz), 11.47 s (2H, NH). 13C NMR
spectrum, δC, ppm: 116.76 (C6'), 116.97 (C7'), 118.68
(C3a'), 121.37 (C9a'), 121.91 (C8'), 127.10 (C9'), 127.70
(Cm), 128.15 (Cp), 129.52 (Co), 129.82 (C5a'), 129.92
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 7 2004

MAMEDOV et al.
1046
(C5), 130.82 (C2), 131.30 (C4 C6), 132.79 (C1 C3),
Caccia, S., and Mennini, T., J. Med. Chem., 1999,
vol. 42, p. 4362.
,
,
132.87 (Ci), 143.35 (C3'), 143.47 (C1'), 155.22 (C4').
10. Chen, P., Barrish, J.C., Iwanovich, E., Lin, J., Bed-
narz, M.S., and Chen, B-Ch., Tetrahedron Lett., 2001,
vol. 42, p. 4293.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 03-03-32865), by the joint program of CRDF and
Ministry of Education of the Russian Federation
“Basic Research and Higher Education” (project no.
REC-007), and (in part) by the Charitable Foundation
for Promotion of Domestic Science.
11. Kalinin, A.A., Mamedov, V.A., and Levin, Ya.A.,
Abstracts of Papers, Peterburgskie vstrechi-98. Khimiya
i primenenie fosfor-, sera- i kremniiorganicheskikh
soedinenii (St. Petersburg Meetings-98. Chemistry and
Application of Organophosphorus, Organosulfur, and
Organosilicon Compounds), St. Petersburg, 1998,
p. 102.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 7 2004