Ring contraction in reactions of 3-benzoylquinoxalin-2-ones with 1,2-phenylenediamines. Quinoxaline-benzoimidazole rearrangement

Article abstract of DOI:10.1023/B:RUCB.0000024846.27508.76

The reactions of 3-benzoylquinoxalin-2-one and its N(1)-alkyl derivatives with 1,2-phenylenediamines were accompanied by ring contraction as a result of the quinoxaline-benzoimidazole rearrangement giving rise to 2-benzoimidazolyl- substituted quinoxalhies. The possible pathways of these reaction are discussed.

Full text of DOI:10.1023/B:RUCB.0000024846.27508.76

164
Russian Chemical Bulletin, International Edition, Vol. 53, No. 1, pp. 164—175, January, 2004
Ring contraction in reactions of
3ꢀbenzoylquinoxalinꢀ2ꢀones with 1,2ꢀphenylenediamines.
Quinoxalineꢀbenzoimidazole rearrangement*
V. A. Mamedov,ꢀ A. A. Kalinin, A. T. Gubaidullin, A. V. Chernova,
I. A. Litvinov, Ya. A. Levin, and R. R. Shagidullin
A. E. Arbuzov Institute of Organic and Physical Chemistry,
Kazan Research Center of the Russian Academy of Sciences,
8 ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843 2) 73 2253. Eꢀmail: mamedov@iopc.kcn.ru
The reactions of 3ꢀbenzoylquinoxalinꢀ2ꢀone and its N(1)ꢀalkyl derivatives with
1,2ꢀphenylenediamines were accompanied by ring contraction as a result of the quinoxalineꢀ
benzoimidazole rearrangement giving rise to 2ꢀbenzoimidazolylꢀsubstituted quinoxalines. The
possible pathways of these reaction are discussed.
Key words: 3ꢀbenzoylquinoxalinꢀ2ꢀones, 1,2ꢀphenylenediamines, benzoimidazole,
pyrazineꢀimidazole ring contraction, rearrangements, IR spectra, 1H NMR spectra, Xꢀray
diffraction analysis.
The presence of several closelyꢀspaced electrophilic
six of which are broadened. This 13C NMR spectral
and nucleophilic centers in readily available2,3 polyꢀ
functional ketone of the quinoxaline series, viz., 3ꢀbenꢀ
zoylꢀ2ꢀoxoꢀ1,2ꢀdihydroquinoxaline (1), is responsible for
its unpredictable behavior with respect to multicenter reꢀ
agents due to which compound 1 can be involved in unꢀ
expected reactions.
pattern can be assigned, for example, to the isomer
of quinoxalinobenzodiazepine 3, viz., benzoimidazolylꢀ
quinoxaline 4, in which benzoimidazole prototropy
leads to broadening of the signals for six carbon atoms
of the benzo fragment of the benzoimidazole system1
(Scheme 1).
The present study was aimed at establishing the strucꢀ
tures of compounds produced in the reactions of ketone 1
and its N(1)ꢀalkyl derivatives with 1,4ꢀbinucleophiles,
viz., oꢀphenylenediamine (oꢀPDA, 2a), 4ꢀnitroꢀ1,2ꢀpheꢀ
nylenediamine (2b), and 3,4ꢀdiaminotoluene (2c), and
elucidating possible pathways of their formation. By
analogy with the reactions with 1,2ꢀbinucleophiles (hydrꢀ
azine, arylhydrazines, and thiosemicarbazide) in refluxꢀ
ing AcOH giving rise to annelation products, viz., pyrazoꢀ
lo[3,4ꢀb]quinoxalines (flavazoles),4 the reaction of keꢀ
tone 1 with oꢀPDA would be expected to form quinoxaꢀ
lino[2,3ꢀb]benzoꢀ1,5ꢀdiazepine system 3. Actually, the
reaction performed under these conditions involved conꢀ
densation accompanied by elimination of two water molꢀ
ecules to give a product with composition C21H14N4.
However, this reaction did not produce expected quinꢀ
oxalinobenzodiazepine 3. Although the IR and 1H NMR
spectra of the reaction product do not contradict strucꢀ
ture 3, this compound cannot give the observed 13C NMR
spectrum, in which 21 carbon atoms appear as 19 signals,
Scheme 1
* For the preliminary communication, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 159—169, January, 2004.
1066ꢀ5285/04/5301ꢀ0164 © 2004 Plenum Publishing Corporation

Quinoxalineꢀbenzoimidazole rearrangement
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
165
C(16)
C(17)
C(17A)
C(15)
C(8)
N(11)
C(12)
N(1)
C(8A)
C(7)
C(6)
C(14)
C(13A)
C(2)
N(13)
C(5)
C(4A)
N(4)
C(3)
C(18)
C(20)
C(22)
Fig. 1. Molecular structure of compound 4 in the crystal.
The above assumption was confirmed by the results of
Xꢀray diffraction analysis of this compound, according to
which it has the structure of 2ꢀ(benzoimidazolꢀ2´ꢀyl)ꢀ3ꢀ
phenylquinoxaline (4). Compound 4 crystallizes in the
monoclinic system with one molecule per asymmetric
unit (Fig. 1). The quinoxaline and benzoimidazole fragꢀ
ments of the molecule are planar within the experimental
error (0.05(1) and 0.01(1) Å, respectively). The dihedral
angle between these planes is 26.58(6)°. The dihedral angle
between the planes of the Ph substituent and the quinoxaꢀ
line fragment is 40.30(8)°. In the crystal, the molecules
are linked in infinite chains along the crystallographic
axis 0x via intermolecular N—H...N hydrogen bonds
(d(H(1)...N(21´)), 2.20(1) Å; N(10)—H(1)...N(21´),
tion of molecular rearrangements as chemical reactions
associated with a change in the sequence of bonds (moꢀ
lecular skeleton) and violation of the principle of miniꢀ
mum structural changes.5
The reaction can follow several pathways. In particuꢀ
lar, it can be assumed that benzoylquinoxalinone 1 (like,
for example, its oxygen analog, viz., 3ꢀformylꢀ2ꢀphenylꢀ
benzoꢀ1,4ꢀdioxine6) undergoes recyclization under the
action of AcOH as a result of the ringꢀchain transforꢀ
mation through an unstable openꢀchain form. In the latꢀ
ter, the intramolecular addition of the amino group ocꢀ
curs at the more reactive carbonyl group of the benzoyl
fragment through the intermediate formation of mixed
anhydride A. Hence, the formation of final product 4 can
be represented as the Phillips—Landenburg reaction7 of
oꢀPDA 2a with either anhydride A or a product of its
hydrolysis, viz., 3ꢀphenylquinoxalineꢀ2ꢀcarboxylic acid B
(Scheme 2).
However, this sequence of reactions cannot be reꢀ
sponsible for the quinoxalineꢀbenzoimidazole rearrangeꢀ
ment and the formation of compound 4, because the startꢀ
ing compound in the reactions of benzoylquinoxalinone 1
with acetic, hydrochloric, and sulfuric acids at differꢀ
ent concentrations and at different temperatures alꢀ
most always remained unconsumed and, consequently,
the quinoxalineꢀquinoxaline recyclization did not take
place.
158.6(2)°; the symmetry operation 1/2
1/2 – y, 1/2 + z).
+
x,
The carbon fragment Ph—C—C—C of the starting
benzoylquinoxalinone 1 is completely transferred to comꢀ
pound 4 with insertion into the structures of both the
phenylꢀsubstituted quinoxaline ring that formed and the
newly constructed benzoimidazole ring. Hence, the C(2)
atom in the latter should correspond to the C(2) atom in
the starting quinoxalinone (pyrazinone) ring. This imꢀ
plies that the quinoxalineꢀbenzoimidazole rearrangement
is accompanied by the quinoxalineꢀring contraction; the
benzoimidazole ring is built from oꢀPDA and one of the
pyrazine C atoms of the starting quinoxalinone system.
The new phenylpyrazine ring is constructed through the
insertion of the ketone C atom of the benzoyl group into
the ring. This reaction falls under the most general definiꢀ
To conclusively exclude the possibility of the reaction
occurring through the quinoxalineꢀquinoxaline recyclizaꢀ
tion according to Scheme 2, we studied the behavior of

166
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
Mamedov et al.
Scheme 2
N(1)ꢀalkylated derivatives of benzoylquinoxalinone 5—10
with respect to oꢀPDA in refluxing AcOH in the expectaꢀ
tion that (regardless of the N(1)ꢀalkylated derivative of
quinoxaline used) this rearrangement giving rise to the
final products through the intermediates C and D would
afford products E 2ꢀhydroxyꢀNꢀalkylated at the quinoxaꢀ
line N(1) atom (Scheme 3).
under standard conditions8 (in refluxing dioxane in the
presence of KOH). The structures of compounds 5—10
were proved by elemental analysis data, the fact that the
IR spectra of the products retain vibrational frequencies
of the lactam carbonyl group at 1670—1685 cm–1, and
1
the fact that the H NMR spectra do not show a broadꢀ
ened singlet at very low field (δ 12.92) corresponding to
the proton at the N atom in the starting compound 1
(Tables 1 and 2).
Scheme 3
Condensation of N(1)ꢀalkyl or benzyl derivatives 5—10
of 3ꢀbenzoylꢀ2ꢀoxoꢀ1,2ꢀdihydroquinoxaline (1) with
oꢀPDA in refluxing AcOH proceeded smoothly and afꢀ
forded crystalline products in high yields. The composiꢀ
tions of these products correspond to N(1)ꢀsubstituted
benzoimidazolylquinoxalines 11—16, whose IR spectra
have no absorption bands of carbonyl groups (Scheme 4,
1
Tables 1 and 2). In the H NMR spectra, the multipliciꢀ
ties of the signals for the protons of the benzo fragments
Scheme 4
Compounds 5—9 were prepared by alkylation of
3ꢀbenzoylquinoxalinone 1 with alkyl iodides. Compound
10 was synthesized by alkylation with benzyl chloride
R = Me (5, 11), Et (6, 12), Prn (7, 13), Bun (8, 14),
nꢀC5H11 (9, 15), PhCH2 (10, 16)

Quinoxalineꢀbenzoimidazole rearrangement
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
167
Table 1. Characteristics of compounds 5—19
and the Ph group of compounds 11—16 are analogous to
those observed in the spectrum of compound 4 (see
Table 2), i.e., Nꢀsubstitution does not hinder the quinoxaꢀ
lineꢀbenzoimidazole rearrangement.
Comꢀ M.p.
pound /°C
Yield
(%)
Found
Calculated
Molecular
formula
(%)
N
Xꢀray diffraction analysis of methyl homolog 11 conꢀ
firmed its structure. Compound 11 crystallizes in the triꢀ
clinic system with one independent molecule per asymꢀ
metric unit (Fig. 2). The quinoxaline and benzoimidazole
rings in molecule 11 are planar to within the experimental
error (0.03(2) and 0.01(1) Å, respectively). The dihedral
angle between these planes is 64.7(2)°. The dihedral angle
between the Ph substituent and the plane of the quinoxaꢀ
line fragment is 48.9(2)°. This mutual arrangement does
not hinder the formation of an intramolecular C—H...N
contact between the H(23) proton of the Ph substituent
and the N(4) atom (H(23)...N(4), 2.70(2) Å).
The molecular packing in the crystal of 11 is deterꢀ
mined by weak intermolecular C—H...N, C—H...π, and
π—π interactions. The interactions between the electron
systems of the quinoxaline fragments of the molecules
related to each other by a translation along the axis 0x give
rise to tilted stacks of the molecules extended along the
crystallographic axis (the shortest distance between the
planes of the rings is 4.23(2) Å; the dihedral angle is
2.5(2)°) (Fig. 3). The intermolecular interactions between
the H(243) protons of the methyl groups and the N(1´)
atoms of the molecules related by the symmetry operaꢀ
tion –1 + x, y, z (d(H(243)...N(1´)), 2.64(2) Å;
C(24)—H(243)...N(1´), 113.3°) are also responsible for
the formation of stacks. The molecules, which are related
by the center of symmetry, are involved in formation of
stacks with an antiparallel orientation of the molecules
through the aboveꢀmentioned interactions. These stacks
are linked in a threeꢀdimensional supramolecular strucꢀ
ture with a rather high packing coefficient (67.7%) via
C
H
5
151—153
(MeOH)
101—103
(PriOH)
83—85
(PriOH)
103—105
(MeOH)
95—98
(MeOH)
126—128
(MeOH)
186—188
(MeOH)
117—119
(PriOH)
166—168
(PriOH)
105—107
(MeOH)
65—67
54
66
68
57
58
54
81
79
87
87
86
56
39
44
81
82
72.80 4.67 10.56 С16H12N2O2
72.72 4.58 10.60
73.56 4.89 10.31 С17H14N2O2
73.37 5.07 10.07
73.79 5.87 9.56 С18H16N2O2
73.95 5.52 9.58
74.40 6.06 9.35 С19H18N2O2
74.49 5.92 9.14
74.87 6.52 8.78 С20H20N2O2
74.98 6.29 8.74
77.59 4.55 8.26 С22H16N2O2
77.63 4.74 8.23
78.36 4.67 16.56 С22H16N4
78.55 4.79 16.66
78.66 5.03 16.26 С23H18N4
78.83 5.18 15.99
79.38 5.37 15.39 С24H20N4
79.10 5.53 15.37
79.56 5.89 15.08 С25H22N4
79.34 5.86 14.80
79.33 6.08 14.47 С26H24N4
79.56 6.16 14.27
81.50 4.79 13.63 С28H20N4
81.53 4.89 13.58
68.99 3.15 19.03 С21H13N5O2
68.86 3.30 19.12
68.94 3.35 19.06 С21H13N5O2
68.86 3.30 19.12
67.61 3.78 16.95 С23H15N5O3
67.48 3.69 17.11
78.86 4.79 16.58 С22H16N4
78.79 4.51 16.71
6
7
8
9
10
11
12
13
14
15
16
(MeOH)
150—153
(MeOH)
17a 246—248
(DMSO)
17b 321—324
(DMSO)
18
216—218
19
262—278
(DMSO)
Table 2. IR and 1H NMR spectra of compounds 5—19
Comꢀ
pound
IR, ν/cm–1
1H NMR, δ (J/Hz)
(solvent)
5
6
7
550, 600, 690, 730, 760, 940,
1160, 1180, 1260, 1320, 1450,
1470, 1560, 1595, 1640, 1670
3.70 (s, 3 H, Me); 7.56 (ddd, 1 H, H(6) or H(7), J = 7.6, J = 6.7,
J = 1.4); 7.66 (dd, 2 H, mꢀHPh, J = 7.9, J = 7.4); 7.74—7.92 (m, 3 H,
H(6) or H(7), H(8), pꢀHPh); 7.91 (dd, 1 H, H(5), J = 7.9, J = 1.4);
8.05 (dd, 2 H, oꢀHPh, J = 8.1, J = 1.4) (DMSOꢀd6)
694, 728, 766, 827, 945, 1169,
1324, 1448, 1560, 1586, 1602,
1646, 1681
1.37 (t, 3 H, Me, J = 7.3); 4.39 (q, 2 H, СH2, J = 7.3); 7.45 (ddd, 1 H,
H(6) or H(7), J = 8.3, J = 6.1, J = 2.4); 7.56 (dd, 2 H, mꢀHPh, J = 7.3);
7.67—7.77 (m, 3 H, H(6) or H(7), H(8), pꢀHPh); 7.87 (dd, 1 H,
H(5), J = 7.7); 8.02 (dd, 2 H, oꢀHPh, J = 7.7, J = 1.6) (acetoneꢀd6)
0.88 (t, 3 H, Me, J = 7.7); 1.79—1.95 (m, 2 H, MeСH2); 4.34 (t, 2 H, NСH2,
J = 7.7); 7.44 (ddd, 1 H, H(6) or H(7), J = 8.3, J = 5.7, J = 2.8); 7.56
(dd, 2 H, mꢀHPh, J = 8.1, J = 7.3); 7.67—7.77 (m, 3 H, H(6) or H(7),
H(8), pꢀHPh); 7.87 (dd, 1 H, H(5), J = 7.7); 8.02
694, 729, 765, 826, 906, 959,
1170, 1255, 1321, 1342, 1561,
1601, 1648, 1681
(dd, 2 H, oꢀHPh, J = 8.1, J = 1.6) (acetoneꢀd6)
(to be continued)

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
Mamedov et al.
Table 2 (continued)
Comꢀ
pound
IR, ν/cm–1
1H NMR, δ (J/Hz)
(solvent)
8
695, 700, 715, 1170, 1325,
1380, 1450, 1470, 1580, 1600,
1640, 1680
1.02 (t, 3 H, Me, J = 7.6); 1.45—1.63 (m, 2 H, MeСH2(СH2)2); 1.76—1.90
(m, 2 H, MeСH2СH2СH2); 4.39 (t, 2 H, Me(СH2)3СH2, J = 7.6); 7.49
(ddd, 1 H, H(6) or H(7), J = 7.9, J = 6.4, J = 2.1); 7.61 (ddd, 2 H,
mꢀHPh, J = 7.6, J = 7.1, J = 1.5); 7.72—7.81 (m, 3 H, H(6) or H(7), H(8),
pꢀHPh); 7.92 (dd, 1 H, H(5), J = 7.9, J = 1.4); 8.07 (dd, 2 H, oꢀHPh
J = 7.9, J = 1.5) (acetoneꢀd6)
,
9
715, 735, 945, 1010, 1110,
1170, 1270, 1330, 1350, 1380,
1460, 1470, 1560, 1580, 1600,
1640, 1680
1.03 (t, 3 H, Me, J = 6.7); 1.42—1.65 (m, 4 H, Me(СH2)2(СH2)2); 1.80—1.92
(m, 2 H, Me(СH2)2СH2СH2); 4.38 (t, 2 H, Me(СH2)3СH2, J = 7.9); 7.51
(ddd, 1 H, H(6) or H(7), J = 7.4, J = 6.5, J = 1.1); 7.63 (dd, 2 H, mꢀHPh
,
J = 7.9, J = 7.0); 7.68—7.85 (m, 3 H, H(6) or H(7), H(8), pꢀHPh); 7.95 (dd,
1 H, H(5), J = 7.9, J = 1.4); 8.00 (dd, 2 H, oꢀHPh, J = 7.6, J = 1.40) (DMSOꢀd6)
5.67 (s, 2 H, СH2); 7.25—7.40 (m, 5 H, CH2Ph); 7.45 (dd, 1 H, H(6) or H(7),
J = 7.4, J = 7.4); 7.56—7.82 (m, 5 H, pꢀHPhCO, mꢀHPhСО, H(6) or H(7),
10
11
535, 595, 725, 900, 1170, 1320,
1380, 1450, 1460, 1550, 1600,
1650, 1685
H(8)); 7.93 (dd, 1 H, H(5), J = 8.0, J = 1.1); 8.02 (d, 2 H, oꢀHPhСО
J = 6.9) (DMSOꢀd6)
,
580, 700, 720, 750,765, 780, 990,
1005, 1075, 1085, 1135, 1215,
1340, 1380, 1450, 1470, 1550, 1615
702, 771, 992, 1067, 1126, 1183,
1247, 1270, 1335, 1416
3.86 (s, 3 H, Me); 7.22—7.43, 7.50—7.68, 7.92—8.08, 8.20—8.32
(all m, 5 H + 4 H + 2 H + 2H, H arom.) (DMSOꢀd6)
12
13
1.43 (t, 3 H, Me, J = 7.3); 4.44 (q, 2 H, СH2, J = 7.3); 7.22—7.40, 7.56—7.70,
7.90—8.10, 8.15—8.28 (all m, 5 H + 4 H + 2 H + 2H, H arom.) (acetoneꢀd6)
1.04 (t, 3 H, Me, J =7.7); 1.75—1.90 (m, 2 H, MeСH2); 4.30 (t, 2 H, NСH2,
J = 7.7); 7.20—7.40, 7.55—7.70, 7.90—8.10, 8.15—8.30 (all m,
5 H + 4 H + 2 H + 2H, H arom.) (acetoneꢀd6)
698, 751, 768, 991, 1070, 1126,
1184, 1249, 1280, 1335, 1415
14
15
435, 550, 565, 695, 710, 750,
760, 1000, 1080, 1130, 1170,
1220, 1250, 1280, 1330, 1380,
1410, 1460, 1480, 1610
560, 700, 750, 765, 1080, 1340,
1410, 1610
0.88 (t, 3 H, Me, J =7.6); 1.22—1.38 (m, 2 H, MeСH2(СH2)2); 1.73—1.90
(m, 2 H, MeСH2СH2СH2); 4.37 (t, 2 H, Me(СH2)2СH2, J = 7.6);
7.20—7.40, 7.55—7.68, 7.88—8.04, 8.15—8.28 (all m,
5 H + 4 H + 2 H + 2H, H arom.) (DMSOꢀd6)
0.78 (t, 3 H, Me, J = 6.8); 1.10—1.32 (m, 4 H, Me(СH2)2(СH2)2);
1.75—1.90 (m, 2 H, Me(СH2)2СH2СH2); 4.36 (t, 2 H, Me(СH2)2СH2,
J = 7.7); 7.20—7.40, 7.55—7.68, 7.88—8.04, 8.15—8.28 (all m,
5 H + 4 H + 2 H + 2H, H arom.) (acetoneꢀd6)
16
695, 730, 760, 770, 970, 1090,
1170, 1335, 1380, 1410, 1460,
1605
5.69 (s, 2 H, СH2); 7.02—7.46, 7.58—7.68, 7.90—8.08, 8.12—8.28
(all m, 10 H + 4 H + 2 H + 2H, H arom.) (acetoneꢀd6)
17a
435, 650, 700, 740, 760, 840, 910,
1075, 1130, 1200, 1310, 1330,
1350, 1410, 1440, 1460, 1515,
1610, 3240—3470
7.34—7.60 (m, 9 H, H arom.); 8.51 (d, 1 H, H(5), J = 9.0);
8.72 (dd, 1 H, H(6), J = 9.0, J = 2.2); 9.06 (d, 1 H, H(8), J = 2.2);
13.18 (br.s, NH) (DMSOꢀd6)
17b
18
620, 700, 735, 750, 830, 1080,
1200, 1310, 1330, 1345, 1460,
1530, 1615, 3385
694, 751, 823, 984, 1047, 1100,
1146, 1199, 1262, 1307, 1431,
1532, 1541, 1623, 1719
7.22—7.75 (m, 9 H, H arom.); 8.47 (d, 1 H, H(8), J = 8.9);
8.67 (dd, 1 H, H(7), J = 8.9, J = 2.5); 9.01 (d, 1 H, H(5), J = 8.9);
13.16 (br.s, NH) (DMSOꢀd6)
1.93 (s, 3 H, Me); 7.22—7.80 (m, 7 H, Ph, H(5) and H(6) of benzoimidazole);
7.60 (d, 1 H, H(4) or H(7) of benzoimidazole, J = 7.6);
7.87 (d, 1 H, H(4) or H(7) of benzoimidazole, J = 7.6); 8.43 (d, 1 H, H(8), J = 9.2);
8.64 (dd, 1 H, H(7), J = 9.2, J = 2.3); 9.04 (d, 1 H, H(5), J = 3.0) (DMSOꢀd6)
7.20—7.74 (m, 9 H, H arom.); 7.88 (dd, 1 H, H(7), J = 8.3, J = 1.9);
8.08 (br.s, 1 H, H(5)); 8.18 (d, 1 H, H(6), J = 8.3); 8.20 (d, 1 H, H(8), J = 8.3);
12.99 (br.s, NH) (DMSOꢀd6)
19
545, 695, 755, 770, 810, 830,
1100, 1220, 1315, 1350, 1380,
1430, 1450, 1460, 1485, 1620,
2800—3400
numerous C—H...N and C—H...π contacts with the H...X
distances varying from 4.06 to 4.48 Å.
The results of Xꢀray diffraction analysis unambiguꢀ
ously showed that the reactions of Nꢀalkylated benzoylꢀ
quinoxalinones with oꢀPDA are actually accompanied by
the contraction of the Nꢀalkylated quinoxaline ring rather
than proceed through the quinoxalineꢀquinoxaline rearꢀ
rangement.

Quinoxalineꢀbenzoimidazole rearrangement
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
169
C(22)
C(23)
C(18)
C(21)
C(20)
C(5)
N(4)
C(4a)
C(6)
C(7)
C(3)
C(19)
C(24)
C(8a)
C(8)
C(2)
N(11)
N(1)
C(12)
N(13)
C(17a)
C(17)
C(13a)
C(16)
C(14)
C(15)
Fig. 2. Molecular structure of compound 11 in the crystal.
Fig. 3. Molecular packing of compound 11 in the crystal (H atoms are omitted) projected along the crystallographic axis 0x.
It can also be supposed that, like the reaction of 2,3ꢀdiꢀ
phenylquinoxaline with potassium amide giving rise to
2ꢀphenylbenzoimidazole,9,10 the reaction of 3ꢀbenzoylꢀ
quinoxalinone 1 with substantially less nucleophilic
oꢀPDA involves the addition of the amino group at the
C(3) atom of quinoxalinone 1 as the first step, and the ring
contraction proceeds with the cleavage of the C(3)—N(4)
bond in the intermediate tricyclic system F. The next step
involves the nucleophilic attack of the second amino group
at the benzoyl fragment to form (after elimination of two
water molecules) the quinoxaline derivative containing
the benzoimidazole fragment at position 2 (Scheme 5).
Finally, it can be suggested that the first step of the
reaction involves the nucleophilic attack of the amino

170
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
Mamedov et al.
Scheme 5
oꢀPDA 2a can involve the initial attack not only at the
C(3) atom of the quinoxaline fragment (see Scheme 5),
which has been proposed for the reactions of quinoxaline
derivatives with potassium amide,9 but also at the C atom
of the carbonyl group of the benzoyl fragment. To eluciꢀ
date the pathways of the reactions of benzoylquinoxaꢀ
lines 1 and 5—10 with oꢀPDA (with the attack of the
amino group of oꢀPDA either at the C(3) atom or at the
carbonyl C atom of the benzoyl group), we carried out the
reaction of compound 1 with 4ꢀnitroꢀ1,2ꢀphenylenediꢀ
amine (2b) assuming that the more active second amino
group (in the meta position with respect to the nitro group)
rather than the first amino group (which is deactivated
under the influence of the nitro group) is responsible for
the first step of both reactions. As can be seen from
Scheme 5, the reactions, which proceed with the pyrazineꢀ
ring contraction and involve the initial attack at the C(3)
atom of the quinoxaline fragment, would afford comꢀ
pound 17a rather than its isomer 17b as the only or major
product.
group at the benzoyl group of compound 1 followed by
the attack of the second amino group at the C(3) atom of
the quinoxaline system with the intermediate formation
of the compound G. The latter can be transformed into
final structure 4 following at least two pathways, viz.,
through the intermediate compound H (path A) and the
intermediate compounds I and J (path B) (Scheme 6).
We studied the behavior of oꢀphenylenediamines conꢀ
taining the NO2 and Me substituents in the benzene ring,
which exhibit substantially different electronic effects, in
the reaction with 3ꢀbenzoylꢀ2ꢀoxoꢀ1,2ꢀdihydroquinꢀ
oxaline (1).
Due to the presence of the reactive benzoyl fragment
in quinoxaline derivatives 5—10, their reactions with
Scheme 6

Quinoxalineꢀbenzoimidazole rearrangement
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
171
In the case of the initial attack of the amino group at
the benzoyl fragment (see Scheme 6), the reaction would
afford compound 17b rather than 17a as the major prodꢀ
uct. However, the reaction of compound 1 with diamine
2b always gave rise to two products in virtually equal
yields. These products can readily be isolated from
the reaction mixture. One of these products with m.p.
321—324 °C (17a) precipitated in refluxing AcOH in the
course of the reaction (as shown below). Another product
with m.p. 246—248 °C (17b) was precipitated from AcOH
with water. In spite of the fact that these two compounds
differ substantially not only in the melting points but also
in solubility, they give similar IR spectra and the signals
in their 1H and 13C NMR spectra are virtually identical in
positions and multiplicities. The NMR spectra call for
more detailed investigation with the use of calculation
methods and 2D NMR experiments. The results of this
investigation will be published elsewhere.
(∼1•10–2 mol L–1) and CCl4 (∼1•10–3 mol L–1). It was
found that the above characteristic feature observed for
the crystalline state is retained in solutions. In the spectra
of solutions in CHCl3, νas(NO2) for compound 17b
(1546 cm–1) is higher than that for compound 17a
(1533 cm–1), in spite of the fact that the position of the
ν(NH) band in solutions (at 3445 in CHCl3 and 3452 cm–1
in CCl4) is indicative of the monomeric form of the molꢀ
ecules.
Therefore, the results of the present study demonꢀ
strate that hydrogen bonds are not responsible for the
frequency effect (νas(NO2)) under consideration, and this
effect can be related to different positions of the nitro
group in the benzo fragment. It is known that the asymꢀ
metric vibrations of NO2, which are sensitive to the elecꢀ
tronic properties of the para substituent, are shifted to
higher frequencies in the presence of electronꢀwithdrawꢀ
ing substituents (1560—1540 cm–1) or to lower frequenꢀ
cies (1550—1490 cm–1) in the presence of electronꢀreꢀ
leasing substituents.11,12 Taking into account that the
benzoimidazole substituent at position 2 of the quinoxaline
system has a specific πꢀdeficient center, viz., the µꢀcarbon
atom, bearing a substantially higher positive charge13 than
that on the ipsoꢀcarbon atom of the Ph substituent at
position 3, the frequency νas(NO2) would be expected to
be higher for isomer 17b containing the nitro group at
position 6 than that for isomer 17a.
Since we failed to grow crystals of either highꢀmelting
or lowꢀmelting isomers suitable for Xꢀray diffraction study,
we analyzed the IR spectra of these compounds, which
were recorded both for the condensed phase and their
solutions.
As mentioned above, the spectra of both compounds
(in KBr) are, on the whole, similar and have absorption
bands ν(NH) (3384 cm–1), ν(C=C), ν(C=N) (1618, 1575,
and 1474 cm–1), νas(NO2) (1518 (17a) and 1532 cm–1
(17b)), νs(NO2) (1349 (17a) and 1346 cm–1 (17b)), and
ν(CH) (742 (17a) and 752 cm–1 (17b)) characteristic of
these structures. At the same time, a comparison of the
spectra shows that the antisymmetric vibrations of the
NO2 group are most sensitive to structural changes
(Table 3). Unlike the frequencies νs(NO2), which are virꢀ
tually identical in the spectra of both compounds, the
frequency νas(NO2) for compound 17b is higher than that
for 17a by ∼24 cm–1. To exclude the influence of specific
interactions, whose presence in the crystalline samples is
evident from the lowꢀfrequency shifts of the NH absorpꢀ
tion bands with ν(NH) = 3384 cm–1 (in KBr) relative to
free ν(NH) (3454 cm–1), we recorded the IR spectra
of solutions of compounds 17a and 17b in CHCl3
To confirm the structures of compounds 17a,b, which
were proposed based on the IR spectroscopic data, we
synthesized acetyl derivative 18 of lowꢀmelting compound
17b and prepared highꢀquality single crystals of this deꢀ
rivative.
Table 3. IR spectra of compounds 17a,b
Isomer
IR, ν/cm–1
Conditions
of measurement
ν(NH, free)
ν(NH, bound)
ν (NO2)
ν (NO2)
as
s
17a
17a
17a
17a
17b
17b
17b
17b
—
—
3452
3445
—
—
3452
3445
3384
3382
—
1518
1518
—
1533
1532
1536
—
1350
1350
—
1348
1346
1345
—
In KBr
In Nujol mulls
In CCl4
In CHCl3
In KBr
In Nujol mulls
In CCl4
—
3384
3386
—
—
1546
1348
In CHCl3

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
Mamedov et al.
C(22)
C(21)
C(20)
O(61)
N(6)
C(23)
N(4)
C(5)
C(18)
C(3)
C(4A)
C(8A)
C(19)
O(62)
C(6)
C(7)
O(24)
C(24)
C(25)
C(2)
C(12)
C(8)
N(11)
C(17A)
N(1)
N(13)
C(13A)
C(14)
C(17)
C(16)
C(15)
Fig. 4. Molecular structure of compound 18 in the crystal.
Compound 18 crystallized in the monoclinic space
group P21/c with one independent molecule per asymꢀ
metric unit (Fig. 4).
symmetry operation –x, –1/2 + y, 1/2 – z; H...O, 2.56 Å;
C—H...O, 146°) give rise to zigzag chains of hydrogenꢀ
bonded molecules along the crystallographic axis 0y. In
the crystal of the starting compound 11, the H(253) proꢀ
ton of the Me group is involved in the intermolecular
contact with the O(62″) atom of the nitro group of anꢀ
other molecule (1 + x, 1/2 – y, 1/2 + z; H...O, 2.51 Å;
C—H...O, 130°), and the molecules are linked by these
contacts in zigzag chains along the diagonal x0z. Finally,
chains of hydrogenꢀbonded molecules along the crystalꢀ
lographic axis 0x are formed via the interactions between
another proton of the Me group (H(252)) and the N(13´)
atom of the adjacent molecule (1 + x, y, z; H...O, 2.74 Å;
C—H...O, 116°).
In addition to the aboveꢀdescribed intermolecular conꢀ
tacts, there are also numerous π—π interactions. In the
crystal structure, the benzoquinoxaline fragments of all
molecules are perpendicular to the crystallographic axis
0х, the planes of the Ph rings slightly deviate from this
axis, whereas the planes of the benzoimidazole fragments
are coplanar to this axis. This arrangement of the molꢀ
ecules in the crystal is characterized by a rather high packꢀ
ing coefficient (69.5%). The involvement of the electron
systems of the benzoquinoxaline fragments and the Ph
rings in π—π interactions (the distances between the cenꢀ
ters of the rings vary from 3.28 to 3.64 Å; the dihedral
angles are in the range of 0—5.4°) gives rise to a threeꢀ
dimensional supramolecular structure with pseudoꢀ
The conformation of molecule 18 is similar to that of
compound 11 described above. The only difference is the
angle of rotation of the Ph substituent and the benzoimidꢀ
azole fragment with respect to the quinoxaline moiety.
However, in spite of similar conformations of these
molecules, a redistribution of the bond lengths (signifiꢀ
cant within the experimental errors) is observed in the
quinoxaline fragments (Table 4), which may be indicative
of the different role of steric interactions in these molꢀ
ecules.
Interestingly, the nitro group in compound 18 lies
virtually in the plane of the quinoxaline fragment (the
O(62)—N(6)—C(6)—C(5) torsion angle is 176.8(4)°),
which is favorable for the formation of intramolecuꢀ
lar C—H...O contacts, viz., C(7)—H(7)...O(62) and
C(5)—H(5)...O(61) (O...H, 2.42(2) and 2.41(2) Å, reꢀ
spectively).
In the crystal of compound 18, the molecules are inꢀ
volved in various intermolecular contacts. Analysis of these
interactions revealed the phenomenon of supramolecular
isomerism in the crystal consisting in the formation of
various types of supramolecular structures depending on
the type of contacts. For example, the intermolecular
C—H...O contacts between the H(20) proton of the Ph
substituent and the O(62´) atom of the nitro group (the

Quinoxalineꢀbenzoimidazole rearrangement
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
173
Table 4. Selected geometric parameters of molecules 4, 11, and
18 (bond lengths (d), bond angles (ω), and torsion angles (τ))
channels parallel to the crystallographic axis 0x (Fig. 5).
These channels are occupied by the benzoimidazole fragꢀ
ments of the molecules, and these fragments are involved
in π—π interactions only in parallel with the correspondꢀ
ing centrosymmetrical pair (the distance between the cenꢀ
ters of the rings is 3.48 Å; the dihedral angle is 0°). Preꢀ
sumably, the crystals of this compound possessing such a
special direction should exhibit also substantial anisoꢀ
tropy of physical properties.
Parameter
4
11
18
Bond
d/Å
N(1)—C(2)
N(1)—C(8A)
N(4)—C(3)
N(4)—C(4A)
N(11)—C(12)
N(11)—C(17A)
N(13)—C(12)
N(13)—C(13A)
C(2)—C(3)
C(2)—C(12)
1.323(2) 1.313(4) 1.301(4)
1.359(3) 1.366(3) 1.353(4)
1.320(2) 1.317(3) 1.290(4)
1.366(2) 1.357(4) 1.382(4)
1.363(2) 1.359(3) 1.394(4)
1.361(3) 1.373(3) 1.413(4)
1.328(2) 1.316(4) 1.289(4)
1.388(2) 1.387(3) 1.401(4)
1.439(2) 1.440(4) 1.459(4)
1.463(3) 1.484(3) 1.492(5)
1.394(3) 1.396(4) 1.395(5)
1.398(2) 1.397(4) 1.398(5)
1.405(2) 1.413(4) 1.416(4)
ω/deg
The reaction of benzoylquinoxalinone 1 with 3,4ꢀdiꢀ
aminotoluene (2c), like that of nitro derivative 2b, afꢀ
forded a mixture of two isomers in virtually equal amounts,
1
as evident from the H NMR spectra of this mixture. It
should be noted that the reaction conditions have no
noticeable influence on the ratio between the products.
Unlike compounds 17a,b, we failed to isolate these isoꢀ
mers and, hence, Tables 1 and 2 give the physicochemical
and spectroscopic characteristics for a mixture of isomers.
The composition of this mixture corresponds to a mixture
of 2ꢀ(benzoimidazolꢀ2ꢀyl)ꢀ7ꢀmethylꢀ3ꢀphenylquinoxaꢀ
line (19a) and its 6ꢀmethyl isomer (19b).
Therefore, the quinoxalineꢀbenzoimidazole rearrangeꢀ
ment considered in the present study has a rather general
character. If the first steps presented in Schemes 5 or 6 are
rateꢀdetermining steps in the reactions giving rise to comꢀ
pounds 4 and 17a,b, the reaction according to Scheme 5
would be expected to give predominantly compound 17a,
because this process corresponds to the faster reaction of
the more nucleophilic amino group in the meta position
with respect to the nitro group. Correspondingly, the reꢀ
action according to Scheme 6 should afford predomiꢀ
nantly isomer 17b. However, as mentioned above, isoꢀ
mers 17a,b were produced in nearly equal amounts.
Hence, either Schemes 5 and 6 are equally probable in the
C(13а)—C(14)
C(13а)—C(17а)
C(4а)—C(8а)
Angle
C(2)—N(1)—C(8а)
C(3)—N(4)—C(4а)
C(12)—N(11)—C(17а)
C(12)—N(13)—C(13а)
C(3)—C(2)—C(12)
N(4)—C(3)—C(18)
N(11)—C(12)—C(2)
N(4)—C(4а)—C(8а)
C(2)—C(3)—C(18)
Angle
118.1(2) 117.5(2) 117.9(3)
118.5(2) 118.1(2) 118.4(3)
107.8(2) 106.6(2) 105.1(3)
104.6(2) 104.1(2) 105.3(3)
125.7(2) 121.9(2) 124.3(3)
115.0(3) 116.7(2) 115.8(3)
119.7(2) 123.0(2) 124.4(3)
120.6(2) 121.3(2) 119.6(3)
124.5(2) 122.9(2) 123.3(3)
τ/deg
C(2)—N(1)—C(8а)—C(4а)
2.1(4)
2.5(4)
1.7(5)
C(12)—N(13)—C(13а)—C(17а)–0.5(2) –0.6(3) –1.5(3)
C(2)—C(3)—C(18)—C(23) 150.2(2) 134.0(3) 149.4(3)
N(4)—C(4а)—C(8а)—N(1)
N(4)—C(3)—C(18)—C(23) –35.5(3) –45.8(4) –32.3(4)
N(1)—C(2)—C(3)—N(4) –9.9(3) –1.0(4) –5.4(5)
C(3)—C(2)—C(12)—N(11) 163.2(5) –66.8(3) –70.8(4)
C(12)—C(2)—C(3)—C(18) –19.2(3) –1.1(4) –3.7(5)
–7.4(3)
–1.0(5) –4.2(5)
Fig. 5. Formation of pseudochannels in the crystal structure of compound 18 projected along the crystallographic axis 0x. Only
H atoms involved in intermolecular contacts are shown.

174
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
Mamedov et al.
Z = 4, dcalc = 1.34 g cm–3, space group P21/n. Crystals of 11,
C22N4H16, are triclinic, at 20 °C, a = 6.389(1) Å, b =
11.697(4) Å, c = 12.621(6) Å, α = 71.19(4)°, β = 89.86(3)°, γ =
course of the quinoxalinoneꢀbenzoimidazole rearrangeꢀ
ment, or the first steps of these schemes are not rateꢀ
determining, or, alternatively, none of these schemes takes
places.
77.18(2)°, V = 868.1(6) Å3, Z = 2, dcalc = 1.29 g cm–3, space
–
group P1. Crystals of 18, C23N5O3H16, are monoclinic, at 20 °C,
a = 7.487(8) Å, b = 21.28(2) Å, c = 12.245(6) Å, β 102.07(5)°,
V = 1908(3) Å3, Z = 4, dcalc = 1.43 g cm–3, space group P21/c.
The unit cell parameters and intensities of 3534 (for comꢀ
pound 4), 2057 (for compound 11), and 4194 (for compound
18) reflections, of which 1874 (4), 1539 (11), and 2257 (18)
reflections were with I ≥ 3σ, were measured at 20 °C (λMoꢀKα
(4 and 11) and λCuꢀKα radiation (18), graphite monochromator,
ω/2θ scanning technique, θ ≤ 26.3° (4 and 11) and θ ≤ 74.2° (18)).
The intensities of three check reflections showed no decrease in
the course of Xꢀray data collection. Absorption was ignored
(µ(Mo) = 0.76 (4), 0.73 cm–1 (11), and µ(Cu) = 7.66 cm–1 (18)).
The structures were solved by direct methods using the SIR
program14 and refined first isotropically and then anisotropiꢀ
cally. The H atoms were revealed from difference electron denꢀ
sity syntheses. For 4, the contributions of the H atoms to the
structure amplitudes were refined in the final steps of the leastꢀ
squares in the isotropic approximation. For 11 and 18, the
H atoms were included in the refinement with fixed positional
and isotropic thermal parameters. The final reliability factors
were as follows: R = 0.040, Rw = 0.044 based on 1874 indepenꢀ
dent reflections with F 2 ≥ 3σ (for 4), R = 0.042, Rw = 0.122
based on 1472 independent reflections with F 2 ≥ 2σ (for 11),
and R = 0.059, Rw = 0.074 based on 1780 reflections with F 2 ≥ 3σ
(for 18). Calculations for the structure of 11 were carried out
using the SHELXLꢀ97 program package and the WinGX proꢀ
gram on a personal computer. Calculations for the structures of
4 and 18 were performed using the MolEN program package15
on an AlphaStation 200 computer. Selected geometric paramꢀ
eters of the all structures are given in Table 4. The molecular
structures and molecular packings in the crystals were drawn
and the intramolecular and intermolecular interactions were
calculated with the use of the PLATON program.16
Experimental
The melting points were measured on a Boetius hotꢀstage
apparatus. The IR spectra were recorded on a URꢀ20 spectromꢀ
eter in Nujol mulls. The IR spectra of compounds 17a,b were
additionally measured on a Vectorꢀ22 (Bruker) Fourierꢀtransꢀ
form spectrometer in the following conditions: resolution was
1 cm–1, 64 scans were accumulated, the scan time was 16 s. The
1H NMR spectra were recorded on a BrukerꢀMCLꢀ250 specꢀ
trometer (250.13 MHz) using signals of the corresponding solꢀ
vent as the internal standard.
1ꢀAlkylꢀ3ꢀbenzoylquinoxalinꢀ2ꢀones 5—10 (general proꢀ
cedure). A mixture of compound 1 (4.0 mmol) and KOH
(5.4 mmol) in dioxane (50 mL) was refluxed for 1 min. Then a
solution of the corresponding alkyl halide (4.7 mmol) in dioxane
(5 mL) was added. The reaction mixture was refluxed for 4 h and
poured into water. The crystals that precipitated were filtered
off, washed with a solution of KOH and water (∼30 mL), dried
in air, and recrystallized from the corresponding solvent. The
physicochemical characteristics of compounds 5—10 are given
in Tables 1 and 2.
2ꢀ(1ꢀAlkylbenzoimidazolꢀ2ꢀyl)ꢀ3ꢀphenylquinoxalines 11—16
(general procedure). A solution of the corresponding 1ꢀalkylꢀ3ꢀ
benzoylquinoxalinꢀ2ꢀone (0.95 mmol) and oꢀPDA (1.04 mmol)
in AcOH (10 mL) was refluxed for 1 h, cooled, and poured into
water. Then a solution of sodium carbonate was added. The
crystals that precipitated were filtered off, washed with water
(∼30 mL), dried in air, and recrystallized from the correspondꢀ
ing solvent. The physicochemical characteristics of compounds
11—16 are given in Tables 1 and 2.
2ꢀ(Benzoimidazolꢀ2ꢀyl)ꢀ7ꢀnitroꢀ3ꢀphenylꢀ and ꢀ6ꢀnitroꢀ3ꢀ
phenylquinoxalines (17a,b). A solution of compound 1 (0.40 g,
1.60 mmol) and 4ꢀnitroꢀ1,2ꢀphenylenediamine (0.28 g,
1.85 mmol) in AcOH (15 mL) was refluxed for 1 h. The crystals
that precipitated were filtered off from the hot solution and
washed with PriOH to isolate isomer 17a. The solution in AcOH
was poured into water. The crystals that precipitated were filꢀ
tered off and isomer 17b was isolated.
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos. 03ꢀ03ꢀ32865
and 02ꢀ03ꢀ32280) and, in part, by the Charity Foundaꢀ
tion for Support of Russian Science.
2ꢀ(1ꢀAcetylbenzoimidazolꢀ2ꢀyl)ꢀ6ꢀnitroꢀ3ꢀphenylquinoxaline
(18). A solution of compound 17b (50 mg, 0.14 mmol) in Ac2O
(1 mL) was refluxed for 10 min, cooled, and poured into water.
The crystals that precipitated were filtered off and washed
with PriOH.
2ꢀ(Benzoimidazolꢀ2ꢀyl)ꢀ7ꢀmethylꢀ3ꢀphenylꢀ and 6ꢀmethylꢀ3ꢀ
phenylquinoxalines 19a,b. A solution of compound 1 (0.40 g,
1.60 mmol) and 3,4ꢀdiaminotoluene (0.22 g, 1.8 mmol) in
AcOH (5 mL) was refluxed for 1 h, cooled, and poured
into water. Then a solution of sodium carbonate was added.
The crystals that precipitated were filtered off and washed with
water.
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Quinoxalineꢀbenzoimidazole rearrangement
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
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Received July 24, 2003;
in revised form November 4, 2003