Facile synthesis of 1-amino[1,3,5]-triazino[1,2a]benzimidazolo-2-one and pyrimidino[1,2a]benzimidazolo-4-one derivatives

Article abstract of DOI:10.1080/00397911.2010.515366

N-(1-Carboethoxy-benzimidazol-2-yl) 1 reacted with different hydrazines to give [1,3,5]triazino[1,2a]benzimidazole derivatives 2. Treatment of compound 1 with tBuOK and EtONa yielded pyrimidino[1,2a]benzimidazole derivatives 3 in good yields. Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2010.515366

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Facile Synthesis of 1-
Amino[1,3,5]triazino[1,2a]-
benzimidazolo-2-one and
Pyrimidino[1,2a]benzimidazolo-4-one
Derivatives
Azhar Hajri a & Raoudha Abderrahim a
a Laboratory of Lamellaires Materials and Hybrids Nanomaterials,
University of Carthage, Faculty of Science of Bizerte, Bizerte,
Tunisia
Version of record first published: 29 Jun 2011
To cite this article: Azhar Hajri & Raoudha Abderrahim (2011): Facile Synthesis of 1-
Amino[1,3,5]triazino[1,2a]-benzimidazolo-2-one and Pyrimidino[1,2a]benzimidazolo-4-one
Derivatives, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 41:19, 2920-2926
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Synthetic Communications1, 41: 2920–2926, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.515366
FACILE SYNTHESIS OF 1-AMINO[1,3,5]-
TRIAZINO[1,2a]BENZIMIDAZOLO-2-ONE AND
PYRIMIDINO[1,2a]BENZIMIDAZOLO-4-ONE
DERIVATIVES
Azhar Hajri and Raoudha Abderrahim
Laboratory of Lamellaires Materials and Hybrids Nanomaterials, University
of Carthage, Faculty of Science of Bizerte, Bizerte, Tunisia
GRAPHICAL ABSTRACT
Abstract N-(1-Carboethoxy-benzimidazol-2-yl) 1 reacted with different hydrazines to give
[1,3,5]triazino[1,2a]benzimidazole derivatives 2. Treatment of compound 1 with tBuOK
and EtONa yielded pyrimidino[1,2a]benzimidazole derivatives 3 in good yields.
Keywords Hydrazine; N-2(1-carboethoxy-benzimidazol-2-yl); pyrimidino[1,2a]benzimi-
dazole; [1,3,5]triazino[1,2a]benzimidazole
INTRODUCTION
We are currently interested in developing routes for the synthesis of a new
family of substituted benzimidazoles because of their pharmacological activity. Fur-
thermore, many condensed heterocyclic systems, especially when linked to a pyrim-
idine ring, play important roles in analgesic and anti-inflammatory drugs and have
antimicrobial activities.[1,2] Many of them are widely used as antidepressive[3] and
antiviral drugs.[4] Some heterocycles containing pyrimidine moieties were reportedly
used as antagonists at the A1 adenosine receptor (A1AR)[5] and in antitumor drugs.[6]
Pyrimidino[1,2-a]benzimidazoles have been found to have significant analgesic
and anti-inflammatory,[7] antiproliferative,[8] anticancer,[9] and macrofilaricidal
Received May 27, 2010.
Address correspondence to Raoudha Abderrahim, Laboratory of Lamellaires Materials and
Hybrids Nanomaterials, University of Carthage, Faculty of Science of Bizerte, 7021 Jarzouna, Bizerte,
Tunisia. E-mail: Abderrahim_raoudha@yahoo.fr
2920

REACTIVITY OF FUNCTIONALIZED IMINOETHERS
2921
effects,[10] and they act as diuretics.[11] [1,3,5]Triazinobenzimidazole derivatives have
a very interesting heterocyclic ring system because of their wide range of pharmaco-
logical applications.
A variety of biological[12] effects have been attributed to the heterocyclic
nucleus s-triazino[1,2-a]benzimidazole; in particular, amino-[1,3,5]triazino[1,2-a]-
benzimidazoles have been found to possess both antibacterial[13] and dihydrofolate
reductase (DHFR) inhibitory effects of malarial plasmodium,[14] They are used to
treat parasitic[15] infections and as anticancer,[16] and antitubercular agents.[17] In
continuation of our recent work on the synthesis of fused heterocycles containing
the triazine or pyrimidine ring,[18–20] we herein describe an efficient route to the syn-
thesis of triazino benzimidazole and pyrimido benzimidazole in good yields.
The methodology was based on the reaction of N-ethoxycarbonyl iminoesters
1 with different hydrazines to give triazino benzimidazole, and treatment of 1 with
tBuOK or EtONa afforded pyrimidino benzimidazole.
RESULTS AND DISCUSSION
N-Ethoxycarbonyl iminoesters 1 were obtained by the reaction of iminoethers
derived from 2-aminobenzimidazole with ethyl chloroformate.[21,22]
Treatment of N-ethoxycarbonyl iminoester 1 with hydrazine derivatives under
reflux of ethanol afforded benzimidazolo-triazine 2 (Scheme 1). The results obtained
1
from elemental analysis, infrared (IR), H NMR, and 13C NMR data as well as the
mass spectra are in agreement with the assigned structures 2. ꢀT1he IR spectrum of 2
showed absorption bands at 1701 cmꢀ1 (C O) and 1630 cm (C N) and a new
absorption band at around 3220–3331 cmꢀ1 attributed to NH2 (if hydrazine
hydrate).
=
=
The 1H NMR spectrum of compound 2 revealed the disappearance of a signal
specific to the ethoxy group and the presence of methyl or phenyl groups introduced
by hydrazine. The 13C NMR revealed the signal of the different carbons and con-
firmed the formation of 2.
From a mechanistic viewpoint, there is no indication whatsoever of initial
attack of the hydrazine group on the carbon of iminoether or on the carbon of
carbamate. We may consider that the cyclization process occurs throughout the
Scheme 1. Synthesis of 2.

2922
A. HAJRI AND R. ABDERRAHIM
formation of intermediate A, because the carbon of carbamate was more electrophi-
lic than the carbon of the iminoether group.[23] The attack on the carbon of carba-
mate by the nitrogen atom of hydrazine forms intermediate A, which cannot be
isolated. The latter undergoes intramolecular nucleophilic cyclization to give benzi-
midazolo triazine 2 (Scheme 2).
On the other hand, the reaction of N-ethoxycarbonyl iminoesters 1 with
tBuOK in anhydrous tetrahydrofuran (THF) at 0 ꢁC under reflux of nitrogen leads
to pyrimido[1,2a]benzimidazole derivatives 3. Compound 3 was also independently
synthesized through another pathway via the condensation of EtONa with the
N-ethoxycarbonyl iminoesters 1. The structures of compounds 3a–c were established
on the basis of their elemental analysis and spectral data (IR, 1H NMR, 13C NMR).
The reaction of compound 1 with tBuOK or EtONa yielded pyrimido benzimi-
dazoles 3 in good yields (Scheme 3). When the base was EtONa, the compounds 3a–c
were obtained in better yield than when we employed the tBuOK. The results
1
obtained from elemental analysis of some products and the IR, H NMR, and 13C
1
NMR data are in agreement with the assigned structures 3. The H NMR and 13C
NMR spectra of compound 3 are consistent with the presence of one isomer.
Scheme 2. Proposed mechanism of synthesis of 2.

REACTIVITY OF FUNCTIONALIZED IMINOETHERS
2923
Scheme 3. Synthesis reaction of compound 3.
The methyl and hydrogen regions of the 1H NMR spectrum of 3c exhibit one doub-
let for CH3 and one quadruplet for H. This is confirmed by 13C NMR spectrum of
compound 3c, which shows a singlet at 11.21 ppm and singlet at 44.31 ppm assigned
respectively to the carbon of CH3 and to the carbon of CH of the new stereocenter.
The IR absorption spectrum of compound 3 was characterized by the presence
of a band at 1710 cmꢀ1 for C O group, as well as intense stretching bands for C N
=
=
at 1615 cmꢀ1 and C C at 1600 cmꢀ1. 1H NMR of 3 exhibited a multiplet for the aro-
=
matic protons around 7.5 ppm, the disappearance of the sharp line of one ethoxy
peak, and the presence of the peak of ethoxy or methoxy protons.13C NMR spec-
trum was consistent with the proposed structures and showed the absence of the
carbon peaks of ethoxy and methoxy groups.
EXPERIMENTAL
IR spectra were recorded on a Perkin-Elmer Paragon 1000 PC spectrometer in
CHCl3 solution.1H and 13C NMR spectra were recorded with (CD3)2SO or CDCl3 sol-
vent containing tetramethylsilane (TMS) on a Bruker 300 spectrometer (1H: 300 MHz,
13C: 75.47 MHz). The chemical shifts (d) are reported in ppm relative to TMS (internal
reference). For the 1H NMR, the multiplicities of signals are indicated by the following
abbreviations: s, singlet; d, doublet; t, triplet; q, quartet; and m, multiplet.
Melting points were obtained using a Buchi melting-point apparatus and are
¨
uncorrected. Elemental microanalysis was performed on a Perkin-Elmer CHN-
2400 analyzer apparatus.
Mass spectra was recorded on a HP-5890 A using the impact mode (70 eV).
N-Ethoxycarbonyl Iminoesters 1
Ethyl chloroformate (0.11 mol) was added dropwise to a mixture of iminoester
(0.11 mmol) (iminoester was obtained by condensation of 2-aminobenzimidazole
with an excess of orthester) and 0.12 mol of pyridine in 50 mL of anhydrous ether
at 0 ꢁC. The mixture was stirred for 3 h. The pyridinium chlorhydrate obtained
was filtered. The solvent was removed under vacuum, and the resulting solid was
filtered off and dried.

2924
A. HAJRI AND R. ABDERRAHIM
Compound 1a. Yield: 65%, mp: 165 ꢁC. IR (CHCl3, n (cmꢀ1): n ¼ 1750
1
=
=
(C O), n ¼ 1670 (C N). H NMR (CDCl3): d 4.50 (q, 4H, CH2-), 1.40 (s, 3H,
CH3), 1.50 (t, 6H, 2CH3), 7.30 (m, 4H, Harom).
Compound 1b. Yield: 70%, mp: 65 ꢁC. IR (CHCl3, n (cmꢀ1): n ¼ 1750
1
=
=
(C O), n ¼ 1670 (C N). H NMR (CDCl3): d 4.50 (q, 4H, CH2-), 1.40 (t, 9H,
3CH3), 2.50 (q, 2H, CH2), 7.30 (m, 4H, Harom).
[1,3,5]Triazino[1, 2-a]benzimidazole 2
Hydrazine (2.1 mmol) was added to a solution of imidate 1 (2 mmol) in ethanol
(10 mL). The reaction mixture was stirred and heated under reflux for 48 h. The sol-
vent was removed under vacuum, and the resulting solid was filtered off, dried and
crystallized.
Compound 2a. Yield: 65%, mp: 218 ꢁC. IR (CHCl3, n (cmꢀ1): n ¼ 1701
1
=
=
(C O), n ¼ 1630 (C N). H NMR (CDCl3): d 2.30 (s, 3H, CH3), 7.10 (broad s,
1H, NH deuterium exchangeable), 6.76–7.43 (m, 9Harom).13C NMR (CDCl3): d
13.87, 113.70, 115.15, 123.99, 129.70, 141.86, 151.02, 153.26. Calcd. for C16H13N5O
(%): C, 65.97; H, 4.46; N, 24.05. Found (%): C, 65.90; H, 4.30; N, 23.95.
Compound 2b. Yield: 55%, mp: 210 ꢁC. IR (CHCl3, n (cmꢀ1): n ¼ 1701
(C O), n ¼ 1630 (C N). 1H NMR (CDCl3): d 1.36 (t, 3H, CH3), 2.49 (q, 2H,
CH2), 7.15 (s, 1H, NH deuterium exchangeable), 6.93–7.58 (m, 9Harom). 13C
NMR (CDCl3): d 10.77, 21.62, 112.90, 115.45, 122.19, 129.70, 142.86, 150.02, 152.96.
=
=
Compound 2c. Yield: 52%, mp: 220 ꢁC. IR (CHCl3, n (cmꢀ1): n ¼ 3310–3231
1
=
=
(NH2), n ¼ 1701 (C O), n ¼ 1630 (C N). H NMR (CDCl3): d 2.60 (s, 3H, CH3),
6.76–7.50 (m, 6H, NH2 deuterium exchangeable and 4Harom). 13C NMR (CDCl3):
d 13.21, 112.52, 121.24, 134.96, 149.75, 152.02, 153.71, 156.10. Calcd. for
C10H9N5O) (%): C, 55.81; H, 3.72; N, 32.55. Found (%): C, 55.83; H, 3.75; N, 32.57.
Compound 2d. Yield: 45%, mp: 222 ꢁC. IR (CHCl3, n (cmꢀ1), n ¼ 3320–3231
1
=
=
(NH2), n ¼ 1701 (C O), n ¼ 1645 (C N). H NMR (CDCl3): d 1.30 (t, 3H, CH3),
2.70 (q, 2H, CH2), 6.82–7.36 (m, 6H, NH2 deuterium exchangeable and 4Harom).
13C NMR (CDCl3): d 10.21, 23.42, 111.92, 120.28, 137.01, 150.05, 151.02, 154.71,
155.39. M=s (%): 229 (10), 200 (80), 170 (18), 158 (16), 133 (100), 105 (40), 90 (30),
78 (10).
Compound 2e. Yield: 65%, mp 240 ꢁC. IR (CHCl3, n (cmꢀ1), n ¼ 3320–3231
1
=
=
(NH2), n ¼ 1701(C O), n ¼ 1645 (C N). H NMR (CDCl3): d 2.40 (s, 3H, CH3),
3.70 (s, 3H, NCH3), 4.50 (s, 1H, NH deuterium exchangeable), 7.10 (m, 4H, Harom).
13C NMR (CDCl3): d 13.20, 37.22, 111.90, 116.21, 121.19, 131.70, 141.86, 150.22,
1523.01.
1
Compound 2f. Yield: 60%, mp 230 ꢁC. H NMR (CDCl3): d 1.41 (t, 3H,
CH3), 2.70 (q, 2H, CH2), 3.50 (s, 3H, NCH3), 4.80 (s, 1H, NH deuterium exchange-
able), 7.10–7.55 (m, 4H, Harom). 13C NMR (CDCl3): d 11.00, 26.22, 37.15, 112.90,
116.01, 122.19, 128.70, 142.86, 150.02, 152.96. Calcd. for C12H13N5O (%): C,
59.29; H, 5.34; N, 28.64. Found (%): C, 59.26; H, 5.32; N, 28.67.

REACTIVITY OF FUNCTIONALIZED IMINOETHERS
2925
Pyrimidino[1, 2-a]benzimidazole Derivatives 3
N-2-(1-Carbethoxybenzimidazol-2-yl) imidate 1 (5 mmol) in 30 mL of THF
was added dropwise with stirring to a cooled THF solution of potassium tert-butox-
ide (7 mmol, tBuOK) in 10 mL THF at 0 ꢁC under reflux of nitrogen. In a similar
reaction, 1 reacted with 7 mmol of EtONa (0.16 g of Na added to 0.41 mL of EtOH
dissolved in 20 mL of anhydrous diethyl ether). When all substrate 1 was added, the
reaction mixture was allowed to reach room temperature and stirred for 24 h. The
obtained solution was hydrolyzed with freshly prepared, NH4Cl and extracted three
times with 20 mL of diethyl ether. The organic extract was dried over anhydrous
MgSO4. The solvent was removed under vacuum, and the resulting solid was filtered
off, dried, and crystallized from CCl4.
Compound 3a. Yield: 73%, mp: 115 ꢁC. IR (CHCl3), n (cmꢀ1), n ¼ 3030
1
=
=
=
(CHarom), 1615 (C N), 1700 (C O), 1600 (C C). H NMR (CDCl3): d 2.30 (s,
2H, O C-CH2), 3.90 (s, 3H, O-CH3), 7.30 (mu, 4H, CHarom). 13C NMR (CDCl3):
=
d 45.30, 51.10, 113.00, 118.22, 121.01, 124.10, 132.30, 144.05, 148.20, 161.23, 169.15.
Compound 3b. Yield: 76%, mp: 148 ꢁC. IR (CHCl3), n (cmꢀ1), n ¼ 3030
1
=
=
=
(CHarom), 1615 (C N), 1700 (C O), 1600 (C C). H NMR (CDCl3): d 2.30 (s,
=
2H, O C-CH2), 1.31 (t, 3H, O-CH2-CH3), 4.22 (q, 2H, O-CH2), 7.23 (mu, 4H,
CHarom). 13C NMR (CDCl3) d 14.03, 44.30, 59.20, 113.04, 119.25, 122.20, 124.51,
131.02, 143.22, 147.12, 161.00, 168.00. Anal. calcd. for C11H12N3O2 (%): C, 62.88;
H, 4.8; N, 18.34. Found: C, 62.60; H, 4.71; N, 18.30.
Compound 3c. Yield: 70%, mp: 165 ꢁC. IR (CHCl3), n (cmꢀ1), n ¼ 3030
1
=
=
=
(CHarom), 1615 (C N), 1700 (C O), 1600 (C C). H NMR (CDCl3), d 2.30 (q,
1H, CH), 1.11 (d, 3H, CH3), 1.20 (t, 3H, O-CH2-CH3), 4.30 (q, H, CH3-CH2-O),
7.22 (mu, 4H, CHarom). 13C NMR (CDCl3) d 11.21, 14.00, 44.31, 64.02, 113.11,
119.20, 121.30, 124.00. 132.02, 144.10, 149.05, 163.01, 170.02. Anal. calcd. for
C12H14N3O2 (%): C, 62.06; H, 6.03; N, 18.10. Found: C, 62.10; H, 5.98; N, 18.15.
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