Unexpected formation of 5-nitro-1H-benzimidazoles by nucleophilic recyclization of 1-methyl-5-nitropyridinium salts

Article abstract of DOI:10.1002/jhet.1876

The synthesis of substituted 5-nitro-2-phenyl-1H-benzimidazoles has been described via domino anionic process rearrangement of 3-benzoylamino-1,2-dimethyl-5-nitropyridinium salts in the presence of NaOH water-alcohol solution. Substituted N-benzoyl-o-phen

Full text of DOI:10.1002/jhet.1876

Month 2014
Unexpected Formation of 5-Nitro-1H-benzimidazoles by Nucleophilic
Recyclization of 1-Methyl-5-nitropyridinium Salts
*
Galina P. Sagitullina, Anna K. Garkushenko, Alexey N. Novikov, and Reva S. Sagitullin
Department of Organic Chemistry, F. M. Dostoevsky Omsk State University, 644077 Omsk, Russian Federation
*
E-mail: sagitullina@orgchem.univer.omsk.su
Received August 21, 2012
DOI 10.1002/jhet.1876
Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).
The synthesis of substituted 5-nitro-2-phenyl-1H-benzimidazoles has been described via domino anionic
process rearrangement of 3-benzoylamino-1,2-dimethyl-5-nitropyridinium salts in the presence of NaOH
water–alcohol solution. Substituted N-benzoyl-o-phenylenediamines was obtained via recyclization of
3-benzoylamino-1,2-dimethyl-5-nitropyridinium salts in the presence of aqueous methylamine solution.
J. Heterocyclic Chem., 00, 00 (2014).
INTRODUCTION
3-Aminopyridines (1a–c) were obtained earlier by different
sextet rearrangements (Curtius, Hofmann, and Schmidt
rearrangements) and described in our previous work [9].
Pyridinium salts (3a–c) were synthesized via alkylation of
3-benzoylamino-5-nitropyridines (2a–c) by dimethyl sulfate
and fluorosulfuric acid methyl ester (Scheme 1).
Recyclization of nitropyridinium salts (3a–c) in the
presence of aqueous methylamine solution at RT leads to
N-benzoyl-o-phenylenediamines (4a–c).
Benzimidazole is one of biologically significant hetero-
cycles. Benzimidazole nucleus is included in the structure
of vitamin В12. Several benzimidazoles belong to a new class
of universal non-natural nucleobases that are capable to
complementary binding with any natural nucleobase [1].
The first benzimidazole alkaloids (Kealiiquinone, Kealiinine
A, B, and C) were isolated from sponge Leucetta chagosensis
in the last two decades [2].
Apparently, transformation of pyridinium salts (3a–c) into
ortho-phenylenediamine (4a–c) proceeds through the nucleo-
philic attack by the hydroxide ion at the most electron-
deficient carbon atom in the pyridine ring at 6-position to form
pseudo-base A (a neutral analog of a s-complex). The follow-
ing base catalyzed ionic ring opening with C—N bond cleav-
age leads to open form B, which undergoes intramolecular
aldol–crotonic condensation involving methyl and carbonyl
groups. Recyclization of pyridinium salt (3b) leads to isomeric
ortho-phenylenediamine (4b) and para-phenylenediamine (5)
through intermediate pseudo-bases A and C (Scheme 2).
Benzimidazoles (6a–c) are the final compounds of
domino anionic reaction of 3-benzoylamino-1,2-dimethyl-
5-nitropyridinium salts (3a–c) with NaOH water–alcohol
solution. Intramolecular heterocyclization of rearrangement
products [N-benzoyl-o-phenylenediamines (4a–c)] leads to
benzimidazoles (6a–c) in the presence of strong base.
Imidazole ring of nitrobenzimidazoles (6a–c) are formed
via interaction of anion of arylmethylamino group of dianion
with carbonyl of amide group (Scheme 3).
Benzimidazole derivatives have a broad spectrum of
biological activity [3]. Many examples of widely used
classes of drugs containing the benzimidazole ring system
are known [4].
The classical method of synthesis of substituted benzimi-
dazoles includes a condensation of o-phenylenediamines
with acids and their derivatives, cyan bromide, and also with
aldehydes and ketones in the presence of oxidant (Phillips
reaction) [5]. Modern methods of synthesis of benzimida-
zoles are presented by Pd-catalyzed carbonylation of
aryl halides with o-phenylenediamines and intramolecular
Pd-catalyzed N-arylation of o-bromophenylamidines [6].
Also, the synthesis of benzimidazoles by cyclization of
Passerini reaction products in the presence of trifluoroacetic
anhydride is known [7]. Recently, a new method for the
synthesis of 2-hetaryl benzimidazoles by acid-catalyzed
quinoxaline–benzimidazole rearrangement was proposed [8].
RESULTS AND DISCUSSION
In the present work, we report a one-pot synthesis of substi-
tuted benzimidazoles (6a–c) from 3-benzoylaminopyridinium
salt (3a–c) in the presence of NaOH water–alcohol solution.
Pyridines (2a–c) were synthesized via benzoylation of
3-aminopyridines (1a–c) (Schotten–Baumann reaction).
CONCLUSION
In conclusion, we have demonstrated possibility of
the formation of imidazole ring of benzimidazoles from
N-benzoyl-o-phenylenediamines in the presence of base.
© 2014 HeteroCorporation

G. P. Sagitullina, A. K. Garkuskenko, A. N. Novikov, and R. S. Sagitullin
Vol 000
1520, 1340 cmÀ1; 1H-NMR (250 MHz, DMSO-d6): dH 2.56 (s, 3H,
2-CH3), 2.75 (s, 3H, 6-CH3), 7.52–7.65 (m, 3Н, Ph), 7.98–8.04
(m, 2Н, Ph), 8.53 (s, 1H, 4-H), 10.30 (s, 1H, NH); Anal. Calcd for
С14H13N3O3: С, 61.99; Н, 4.83; N, 15.49. Found: С, 61.89; Н,
4.81; N, 15.18.
Scheme 1
N-(2-Methyl-5-nitro-6-phenylpyridin-3-yl)benzamide (2c). Yield
80%, white crystals, mp 195–196ꢀC; IR: NH 3440, CO 1700, NO2
1520, 1320; 1H-NMR (250 MHz, DMSO-d6): dH 2.64 (s, 3H,
2-CH3), 7.46–7.62 (m, 8Н, Ph), 7.99–8.08 (m, 2Н, Ph), 8.59
(s, 1H, 4-H), 10.35 (s, 1H, NH); Anal. Calcd for С19H15N3O3.
С, 68.46; Н, 4.54; N, 12.61. Found: С, 68.92; Н, 4.28; N, 12.28.
General procedure for the synthesis of 3-benzoylamino-5-
nitropyridinium salts (3a, c). The mixture of pyridine (2a, c)
(5mmol) and Me2SO4 (15 mmol) was heated. Then, mixture was
chilled and washed with dry ether (3 Â 10 mL). The ether was
removed by decantation. The residue was dissolved in H2O
(5mL), and saturated aqueous solution of NaClO4 (5.3mol) was
added. Pyridinium perchlorates (3a, c) were filtered, dried, and
recrystallized from ethanol.
EXPERIMENTAL
The IR spectra were obtained on a Simex FT 801 instrument in
the solid phase with an attachment for a single broken internal re-
flection. The H-NMR spectra were recorded on a Bruker Avance
1
DRX-250 in CDCl3 and DMSO-d6, internal standard was the
residual protons of the solvent (CDCl3 d 7.25 and DMSO-d6
d 2.50ppm). 13C-NMR spectra were recorded on a Bruker
DRX-250 spectrometer with DMSO-d6 as internal standard
(d C 40.1 ppm). Elemental analysis was carried out on a Perkin-
Elmer 2400 series II CHN Analyzer. Column chromatography
was performed using Merck 60A silica gel, 0.060–0.200 mm. Mon-
itoring of the course of reactions and purity of the compounds
obtained was by TLC on Silufol UV-254 plates. 3-Aminopyridines
(1a-c) was synthesized according to the procedures described in [9].
General procedure for the synthesis of 3-benzoylamino-5-
nitropyridines (2a–c). Benzoyl chloride 1.08g (7.7 mmol) was
added dropwise to a solution of 3-aminopyridine (1a–c) [9]
(7 mmol) in absolute pyridine (5mL) at 0ꢀC. The mixture was
stirred 10 min at 0ꢀC and then 2 h at RT. After that, absolute
ethanol (1.5mL) was added, and the mixture was stirred 10min.
The reaction mixture was diluted with chilled water, and the
precipitate was filtered. Pyridines (2a–c) were recrystallized from
95% ethanol.
3-(Benzoylamino)-1,2-dimethyl-5-nitropyridinium perchlorate
(3a). Conditions 4 h and 70ꢀС, yield 71%, colorless crystals,
1
mp 223–224ꢀС. H-NMR (250 MHz, DMSO-d6): dH 2.82 (s, 3H,
2-CH3), 4.97 (s, 3H, N—CH3), 7.55–7.74 (m, 3Н, Ph), 8.01–8.08
4
4
(m, 2Н, Ph), 9.39 (d, J = 2.2Hz, 1Н, 6-H), 10.05 (d, J = 2.2Hz,
1H, 4-H), 11.04 (s, 1H, NH); Anal. Calcd for С14Н14ClN3O7:
С, 45.23; Н, 3.80; N, 17.30. Found: С, 45.39; Н, 3.65; N, 11.15.
3-(Benzoylamino)-1,2-dimethyl-5-nitro-6-phenylpyridinium
perchlorate (3c). Conditions 12h and 90ꢀС, yield 77%, colorless
crystals, mp 128–129ꢀС. 1H-NMR (250 MHz, DMSO-d6):
dH 2.84 (s, 3H, 2-CH3), 3.92 (s, 3H, N—CH3), 7.56–7.77
(m, 8Н, Ph), 8.01–8.11 (m, 2Н, Ph), 9.33 (s, 1H, 4-H), 11.10
(s, 1H, NH); Anal. Calcd for С20Н18ClN3O7: С, 53.64; Н, 4.05;
N, 9.38. Found: С, 53.89; Н, 3.89; N, 9.64.
N-(2-Methyl-5-nitropyridin-3-yl)benzamide (2a). Yield 85%;
3-(Benzoylamino)-1,2,6-trimethyl-5-nitropyridinium fluoridosulfate
(3b). The solution of MeSO3F (15 mol) in chlorobenzene (3 mL)
was added dropwise to a solution of pyridine (2b) (5 mmol)
in chlorobenzene (15 mL) at 0ꢀC with stirring. The mixture
was stirred 30 min at 0ꢀC and 5 days at RT. Then, the mixture
was diluted with diethyl ether. The precipitate was filtered and
recrystallized from ethanol. The colorless crystals were obtained
in 94% yield, mp 212–213ꢀС. 1H-NMR (250 MHz, DMSO-d6):
dH 2.82 (s, 3H, 2-CH3), 2.92 (s, 3H, 6-CH3), 4.29 (s, 3H,
white crystals, mp 183–184ꢀC; IR: NH 3450, CO 1690, NO2
1520, 1350 cmÀ1 1H-NMR (250 MHz, DMSO-d6): dH 2.75
;
(s, 3H, 2-CH3), 7.51–7.68 (m, 3Н, Ph), 8.01–8.10 (m, 2Н, Ph),
9.00 (d, 4J =2.5 Hz, 1Н, 6-H), 9.11 (d, 4J = 2.5Hz, 1H, 4-H), 9.45
(s, 1H, NH); Anal. Calcd for С13H11N3O3: С, 60.70; Н, 4.31; N,
16.33. Found: С, 60.64; Н, 4.28; N, 15.95.
N-(2,6-Dimethyl-5-nitropyridin-3-yl)benzamide (2b). Yield
77%, white crystals, mp 176–177ꢀC; IR: NH 3470, CO 1700, NO2
Scheme 2
Scheme 3
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
Unexpected Formation of 5-Nitro-1H-benzimidazoles by Nucleophilic
Recyclization of 1-Methyl-5-nitropyridinium Salts
N—CH3), 7.52–7.66 (m, 3Н, Ph), 8.06–8.11 (m, 2Н, Ph),
9.09 (s, 1H, 4-H), 11.04 (s, 1H, NH). Anal. Calcd for
С15Н16FN3O6S: С, 46.75; Н, 4.18; N, 10.90. Found:
С, 46.40; Н, 4.39; N, 10.62.
General procedure for the reaction of pyridinium salts (3a–c)
with aqueous solution MeNH2. The 41% aqueous solution
of MeNH2 (40 mL) was added to solution of salt (3a–c)
(2 mmol) in DMF (4 mL). The mixture was stirred 2 h at RT.
The reaction mixture was diluted with water twice, and the
precipitate was filtered. The precipitate was purified by column
chromatography (eluent chloroform–ethyl acetate, 9:1), recrystallized
from ethanol.
8.23 (dd, 3J=8.7Hz, 4J=0.7Hz, 1Н, 6-H), 8.69 (d, 4J=0.7Hz, 1H,
4-H). Anal. Calcd for С14Н11N3O2: С, 66.40; Н, 4.38; N, 16.59.
Found: С, 66.31; Н, 4.43; N, 16.64.
1,6-Dimethyl-5-nitro-2-phenyl-1H-benzimidazole (6b). YiÀel1d
67%, white crystals, mp 184–185ꢀС. IR: NO2 1513, 1310 cm
.
1Н-NMR (250 MHz, CDCl3): dH 2.64 (s, 3Н, 6-CH3), 2.81
(s, 3H, N—CH3), 7.47–7.63 (m, 3Н, Ph, 7-H), 7.82–7.91
(m, 3Н, Ph), 9.02 (s, 1Н, 4-H). Anal. Calcd for С15Н13N3O2: С,
67.40; Н, 4.90; N, 15.72. Found: С, 67.52; Н, 5.00; N, 15.61.
1-Methyl-5-nitro-2,6-diphenyl-1H-benzimidazole (6c). YiÀel1d
60%, white crystals, mp 201–202ꢀС. IR: NO2 1540, 1355 cm
.
1Н-NMR (250MHz, DMSO-d6): dH 3.93 (s, 3H, N—CH3),
7.34–7.63 (m, 10Н, Ph ), 7.78 (s, 1Н, 7-H), 8.33 (s, 1Н, 4-H).
Anal. Calcd for С20Н15N3O2: С, 72.94; Н, 4.59; N, 12.76. Found:
С, 73.07; Н, 4.33; N, 12.79.
N-[2-(Methylamino)-5-nitrophenyl]benzamide (4a).
71%, light yellow crystals, mp 204–205ꢀС (lit. mp 195ꢀС [10]);
IR: NH 3380, CO 1650, NO2 1550, 1310cmÀ1 1Н-NMR
Yield
.
(250 MHz, DMSO-d6): dH 2.84 (d, J = 4.6 Hz, 3H, NH—CH3),
6.71 (d, 3J = 8.8 Hz, 1Н, 3-H), 6.86 (br. s, 1H, NH—CH3),
7.50–7.59 (m, 3Н, Ph, 4-H), 7.98–8.14 (m, 4Н, Ph, 6-H), 9.82
(s, 1H, NH). Anal. Calcd for С14Н13N3O3: С, 61.99; Н, 4.83;
N, 15.49. Found: С, 62.05; Н, 4.71; N, 15.35.
REFERENCES AND NOTES
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N-[5-(Methylamino)-2-nitrobiphenyl-4-yl]benzamide (4c). Yield
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1655, NO2 1520, 1340 cmÀ1 1Н-NMR (250 MHz, CDCl3):
.
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dH 2.90 (br. s, 3H, NH—CH3), 4.95 (br. s, 1H, NH—CH3), 6.52
(s, 1H, 6-H), 7.25–7.31 (m, 2Н, Ph), 7.35–7.43 (m, 3Н, Ph),
7.45–7.61 (m, 3Н, Ph), 7.81 (s, 1H, NH), 7.87–7.95 (m, 2Н, Ph),
8.00 (s, 1H, 3-H). Anal. Calcd for С20Н17N3O3: С, 69.15; Н, 4.93;
N, 12.10. Found: С, 69.19; Н, 5.06; N, 11.94.
N-[4-Methyl-2-(methylamino)-5-nitrophenyl]benzamide (4b) and
N-[2-methyl-4-(methylamino)-5-nitrophenyl]benzamide (5). Were
separated by column chromatography (eluent chloroform–ethyl
acetate, 9:1), recrystallized from ethanol. For 4b: yield 40%, light
yellow crystals, mp 211–212ꢀС. IR: NH 3390, CO 1630, NO2
ꢀ
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1540, 1320 cmÀ1 1Н-NMR (250MHz, DMSO-d6): dH 2.61
.
(s, 3H, 4-CH3), 2.84 (d, J = 4.9 Hz, 3H, NH—CH3), 6.56 (s, 1Н,
3-H), 6.61 (q, J = 4.9Hz, 1H, NH—CH3), 7.50–7.62 (m, 3H, Ph),
8.00 (s, 1H, 6-H), 8.01–8.04 (m, 2H, Ph), 9.71 (s, 1H, NH).
13C-NMR (100MHz, DMSO-d6): dC 22.01, 29.51, 111.80,
120.52, 125.24, 127.98, 128.18, 131.59, 134.15, 134.97, 135.85,
149.64, 166.17. Anal. Calcd for С15Н15N3O3: С, 63.15; Н, 5.30;
N, 14.73. Found: С, 63.08; Н, 5.29; N, 14.72. For 5: yield 24%,
orange crystals, mp 220–221ꢀС. IR: NH 3277, CO 1651, NO2
1543, 1321 cmÀ1 1Н-NMR (250MHz, DMSO-d6): dH 2.29
.
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(s, 3H, 2-CH3), 2.99 (d, J = 5.0 Hz, 3H, NH—CH3), 6.92 (s, 1Н,
3-H), 7.50–7.63 (m, 3H, Ph), 7.94–8.00 (m, 2H, Ph), 8.05 (s, 1H,
6-H), 8.18 (q, J = 5.0 Hz, 1H, NH—CH3), 9.87 (s, 1H, NH).
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123.31, 124.80, 127.61, 128.40, 128.42, 131.62, 134.22, 144.40,
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General procedure for the reaction of pyridinium salts (3a–c)
with aqueous solution of NaOH.
The 10% aqueous solution
of NaOH (2mL) was added to suspension of salt (3a–c) (1mmol)
in ethanol (4mL). The reaction mixture was stirred 24h at
RT, diluted with water twice, and neutralized with 50%
acetic acid. The precipitate was filtered and purified by column
chromatography (eluent chloroform–ethyl acetate, 9:1),
recrystallized from ethanol.
1-Methyl-5-nitro-2-phenyl-1H-benzimidazole (6a). Yield 65%,
white crystals, mp 181–182ꢀС (lit. mp 189ꢀС [10]); IR: NO2
1520, 1350 cmÀ1
N—CH3), 7.45 (d, J= 8.7 Hz, 1H, 7-H), 7.53–7.77 (m, 5H, Ph),
.
1Н-NMR (250 MHz, CDCl3): dH 3.91 (s, 3H,
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3
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Vol 000
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