Synthesis of novel aza-heterocyclic derivatives from diester and diacid chlorides having the dibenzobarrelene skeleton

Article abstract of DOI:10.1080/00397911.2018.1437449

When attempting to synthesize the symmetric aza-heterocyclic-substituted dibenzobarrelene derivatives from the 2-aminobenzimidazole (or 2-aminoimidazoline) with diacid chlorides and diester in the presence of various organic bases, different products were isolated in high yield. NMR spectroscopic analysis proved these products to be dibenzobarrelene-substituted fused benzimidazodiazepine, imidazolinediazepine, and dicarboxamides derivatives. Cyclic or noncyclic dicarboxamides with the dibenzobarrelene skeleton have been synthesized for the first time using these methods.

Full text of DOI:10.1080/00397911.2018.1437449

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
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Synthesis of novel aza-heterocyclic derivatives
from diester and diacid chlorides having the
dibenzobarrelene skeleton
İrfan Çapan & Süleyman Servi
To cite this article: İrfan Çapan & Süleyman Servi (2018): Synthesis of novel aza-heterocyclic
derivatives from diester and diacid chlorides having the dibenzobarrelene skeleton, Synthetic
Communications, DOI: 10.1080/00397911.2018.1437449
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SYNTHETIC COMMUNICATIONS®
https://doi.org/10.1080/00397911.2018.1437449
Synthesis of novel aza-heterocyclic derivatives from diester
and diacid chlorides having the dibenzobarrelene skeleton
İrfan Çapana
and Süleyman Servib
aDepartment of Polymer Technology, Technical Sciences Vocational College, Gazi University, Ankara, Turkey;
bDepartment of Chemistry, Faculty of Science, Fırat University, Elazığ, Turkey
ABSTRACT
ARTICLE HISTORY
Received 10 December 2017
When attempting to synthesize the symmetric aza-heterocyclic-
substituted dibenzobarrelene derivatives from the 2-aminobenzimi-
dazole (or 2-aminoimidazoline) with diacid chlorides and diester in the
presence of various organic bases, different products were isolated in
high yield. NMR spectroscopic analysis proved these products to be
dibenzobarrelene-substituted fused benzimidazodiazepine, imidazoli-
nediazepine, and dicarboxamides derivatives. Cyclic or noncyclic
dicarboxamides with the dibenzobarrelene skeleton have been
synthesized for the first time using these methods.
KEYWORDS
Benzimidazolediazepine;
dibenzobarrelene;
dicarboxamides; guanidine;
imidazolinediazepine
GRAPHICAL ABSTRACT
Introduction
Benzimidazole and imidazolines of natural or synthetic origin are found in the molecular
structure of many drugs. Since these compounds have a wide range of chemotherapeutic
applications, they are widely used in the medicine design strategy.[1–6] There are different
methods for the synthesis of 2-substituted benzimidazole and imidazoline compounds in
CONTACT Süleyman Servi
23169 Turkey.
sservi@firat.edu.tr
Department of Chemistry, Faculty of Science, Fırat University, Elazığ,
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data (experimental procedures and supplementary data associated with the synthesized compounds; data
include experimental and the spectra (1H-, 13C-, and HETCOR-NMR) of the aza-heterocyclic derivatives (compounds 7, 8, 10,
12, and 14) having the dibenzobarrelene skeleton) can be accessed on the publisher’s website.
© 2018 Taylor & Francis

2
İ. ÇAPAN AND S. SERVI
Scheme 1. The phthaloylation reaction of 2-aminobenzimidazole with phthaloyl chloride.
the literature.[7–11] In the synthesis of these compounds, in addition to classical synthesis
methods, solid support, solvent-free, ionic liquids and microwave-assisted synthesis
methods are also used.[7]
Diazepine core is considered as a privileged structure to access active compounds
displaying a wide range of pharmacological activities. In particular, polyfused diazepine
derivatives led to the discovery of compounds with anticancer potency.[12] Moreover,
heterocycles containing the imidazo[4,5-e][1,3]diazepine ring system have shown potent
in vitro activity at low micromolar concentrations against lung, breast, ovarian, and
prostate cancer cell lines.[13,14] As chemical structures of these drugs are investigated more
closely, it is understood that the carboxamide functional group is the major component of
five-, six-, or seven-membered heterocyclic ring structures.[14]
In the literature, the reaction of phthaloyl chloride with different 2-aminobenzimida-
zoles has been mechanistically investigated to conclude a discussion that began in previous
years.[15] The reaction of these compounds resulted in either benzimidazoylisoindolin-1,3-
dione (a) or the benzimidazo-[1,3]-diazepinedione (b) (Scheme 1). The structures of the
obtained products with the phthaloylation reaction were clarified using 1H-NMR
spectroscopy. The benzimidazo-[1,3]-diazepinedione (b) is stable at room temperature
but can easily be converted into the thermodynamic more stable benzimidazoylisoindo-
lin-1,3-dione (a).[15] This conversion is dependent on the substituents on the 2-aminoben-
zimidazole, the solvent used, the base, and type of the guanidine nucleophiles.[15,16]
Unlike heteroaromatic-substituted benzene dicarboxamides, benzimidazole or
imidazoline derivatives which contain diazepine, imide, and dicarboxamides fused to the
dibenzobarrelene skeleton are not known in the literature. In this work, we aimed at the
synthesis of imidazoline and benzimidazole-substituted novel dibenzobarrelene derivatives.
Results and discussion
The aza-heterocyclic derivatives incorporated into the dibenzobarrelene skeleton were
synthesized from diacid chlorides (or diester) with the 2-aminobenzimidazole (9) or
2-aminoimidazoline p-toluenesulfonate (11) in the presence of various bases. The com-
pounds 7, 8, 10, and 14 were synthesized using new methods (Methods A and B), while
compound 13 was synthesized by modifying the known Method C.[17] The synthetic routes
for the preparation of different aza-heterocyclic derivatives are outlined in Schemes 2–6.
Diels–Alder cycloaddition reaction was used to synthesize the starting reactants from
the different dienophiles and anthracene. Diacid chlorides 4 and 6, and the diester-2,
which have the dibenzobarrelene skeleton, were used as the starting reagents. The diacid
chloride-4 was synthesized from the reaction of SOCl2 with the diacid, which obtained
from the hydrolysis of the diester-2 in the basic medium. Similarly, the diacid chloride-6
was synthesized from the reaction SOCl2 with the diacid, which was obtained from the

SYNTHETIC COMMUNICATIONS®
3
Scheme 2. Synthesis of diacid chlorides (4, 6) and diester (2) compounds used as the starting reagents.
Reagents and conditions: (i) DMAD, argon atmosphere, 170–180 °C; (ii) NaOH; (iii) SOCl2, benzene, 3-h
reflux; (iv) fumaric acid, 1,4-dioxane, 72-h reflux.
reaction of anthracene and fumaric acid (Scheme 2). Starting compounds 2, 4, and 6 were
described in the literature.[18]
To synthesize the Expected product-1 by the nucleophilic addition–elimination reaction
on acyl carbon, the reaction was performed under the argon atmosphere at 0 °C in THF. In
this reaction, when the diacid chloride-4/9/Et3N reagents were used in the molar ratio of
1/2/2, the benzimidazolediazepine 7 was obtained in 82.8% yield instead of Expected
product-1 (Method A). NaH was used as the base instead of the Et3N in THF in
Method B. When the acid chloride-4/9/NaH molar ratio of 1/1/2 was used, compound
8 was isolated in 74.3% yield.
The methods for the synthesis of compounds 7 and 8 are given in Scheme 3. In the
FT-IR spectrum of the isolated product, the observation of amide carbonyl at 1634 cm−1
suggested that Expected product-1 was formed. However, a detailed NMR evaluation
1
(1H-, 13C-, and COSY) revealed that the isolated product was compound 7. In the H-
NMR spectrum, while in the Expected product-1 structure required 16 protons in the
aromatic region, there were 12 protons in this region. The bridgehead proton signals
(H-1 and H-4) were observed at 6.13 and 5.99 ppm as two different signals. In the
13C-APT-NMR spectrum of compound 7, the presence of two different amide carbonyl
(C-9 and C-10) signals at 167.95 and 164.64 ppm proved that the molecular structure of
Scheme 3. Synthesis of compounds 7 and 8 from the reaction of compound 4 with 9. Reagents and
conditions: (i) Et3N, anhyd. THF, 0 °C, argon atmosphere; (ii) NaH, anhyd. THF, 0 °C, argon atmosphere.
The molar ratio of Method A: comp. 4 (1 equiv.), comp. 9 (2 equiv.), Et3N (2 equiv.); Method B: comp. 4
(1 equiv.), comp. 9 (1 equiv.), NaH (2 equiv.).

4
İ. ÇAPAN AND S. SERVI
the benzimidazolediazepine was not symmetric. In the FT-IR spectrum of compound 8,
only one stretching vibration was observed belonging to the amide carbonyl at
1
1633 cm−1. In the H-NMR spectrum, the H-1 and H-4 bridgehead protons resonated as
2H singlet at the same chemical shift. The 13C-APT-NMR spectrum proved that the
molecular structure is the symmetrical imide, since the C-1 and C-4 bridgehead carbons
observed at 53.53 ppm were equivalent. (Details of the NMR analysis of compounds 7,
8, 10, 12, and 14 can be found in the Supporting Information section.)
The trans-diacid chloride-6 was used in the next stage of this work; instead of
benzimidazolediazepine 10, it was thought that the Expected product-2 compound could
be easily obtained. However, compound 10 was isolated in 71.9% yield instead of Expected
product-2 at the same reagent molar ratios used in the Method A (Scheme 4) for the
synthesis of compound 7. In the NMR spectra of compound 10, findings similar to
1
compound 7 were obtained. In addition to this similar data in the H-NMR spectrum,
the signals for the H-7 and H-8 protons were observed between 3.45 and 3.35 ppm. The
mass spectrum data supported this structure.
In the literature, there is the method for the synthesis of 2-imidazoline derivatives from
the reaction of the ester compounds with the 2-aminoimidazoline p-toluenesulfonate.[17] In
this method, N-substituted (imidazolidin-2-ylidene) amides have been synthesized in yields
between 40 and 75% in methanol in the presence of sodium methoxide as the base. In our
study, this method was used by modifying to synthesize compound 12 (Scheme 5,
Method C). This compound was obtained in 39.1% yield from the reaction of the
diester-2 with compound 11, which was synthesized according to the cited reference.[17]
1
In the H-NMR spectrum taken in DMSO-d6, the imidazoline methylene protons were
not observed clearly because they coincided with the signals of the proton residues of the
DMSO-d6. For this reason, the spectrum was taken up in CDCl3 by adding two drops of
acetic acid. In symmetrical imidazoline compounds, the CH2 proton signals are observed
as the singlet, while in other unsymmetrical 2-imidazoline compounds, these protons are
observed as the triplet. The imine–enamine dynamic tautomerization makes the CH2 pro-
tons equivalent. At the same time, this effect causes lowering of the order of the spectra
(Δυ/J ¼ 0).[19] When the spectrum data were analyzed, the signal of the methylene protons
on the imidazoline ring appeared equivalent with a 8H singlet observed at 3.65 ppm. The
bridgehead proton signals observed 2H singlet at 6.01 ppm. In the 13C-APT-NMR spec-
trum, the imidazoline methylene carbon signals were observed at 42.95 ppm, while the
bridgehead carbon signal was observed at 53.57 ppm. In the HETCOR spectrum, the
Scheme 4. Synthesis of compound 10 from the reaction of compound 6 with 9. Reagents and
conditions: Et3N, anhyd. THF, 0 °C, argon atmosphere. The molar ratio of Method A: comp. 6 (1 equiv.),
comp. 9 (2 equiv.), Et3N (2 equiv.).

SYNTHETIC COMMUNICATIONS®
5
Scheme 5. Synthesis of compound 12 from the reaction of compound 2 with 11. Reagents and
conditions: metallic Na, CH3OH, and room temperature. The molar ratio of Method C: comp. 2 (1 equiv.),
comp. 11 (2.6 equiv.), and metallic Na (2.8 equiv.).
Scheme 6. Synthesis of compound 14 from the reaction of compound 4 with 11. Reagents and
conditions: NaH, anhyd. THF, argon atmosphere. The molar ratio for Method B: comp. 4 (1 equiv.), comp.
11 (1 equiv.), and NaH (2 equiv.).
CH2 proton signals at 3.65 ppm coincided with the CH2 carbon signals at 42.95 ppm and
the bridgehead proton signal at 6.01 ppm coincided with the carbon signal at 53.57 ppm.
We aimed to synthesize the 2-imidazoline derivative of diacid chloride-4 after compound
8 has been isolated and characterized. Under the same molar ratios and the experimental
condition for the synthesis of compound 8, compound 14 was obtained in 68.9% yield
instead of the targeted Expected product-3 (Method B, Scheme 6). In the 13C-APT-NMR
spectrum, the observation of two different amide carbonyl signals, bridgehead methine car-
bons, and imidazoline methylene carbon signals confirmed that the molecule was unsym-
1
metrical. When the H-NMR spectrum of compound 14 was analyzed, it was understood
that the chemical structure contained 1-mol ethyl acetate. Therefore, the signals belonging
to ethyl acetate were observed in the NMR spectra of this compound.
Experimental section
The synthetic routes for the preparation of compounds are outlined in Schemes 2–6. The
preparation of these compounds is briefly described as follows.
General synthesis of 8,13-dihydro-6H-8,13-[1,2]benzenobenzo [4,5]imidazo
[1,2-a] naphtho [2,3-e][1,3]diazepin-7,14-dione (7) and 7a, 8,13,13a-tetrahydro-
6H-8,13[1,2]benzenobenzo[4,5] imidazo[1,2-a]naphtho[2,3-e][1,3]diazepin-7,14-
dione (10) (Method A)
A total of 0.810 g of compound 9 (6.08 mmol) was dissolved in anhydrous THF (50 mL)
and cooled at 0 °C in an ice bath under an argon atmosphere. Then, 0.615 g (0.86 mL,

6
İ. ÇAPAN AND S. SERVI
6.08 mmol) of triethylamine and 3.04 mmol of compound 4 (or compound 6) were added
consecutively to the cold solution. The reaction mixture turned light yellow. The solution
was stirred at 0 °C for 1 h. The mixture was allowed to warm to room temperature and
stirred under an argon atmosphere for 24 h. The resulting white solid was filtered and
the solvent was evaporated under reduced pressure. The crude product was dissolved in
10 mL of methanol and precipitated by dropwise addition of methanol solution to
200 mL of water. The obtained solid was filtered, dried, and then crystallized from benzene
(methanol for compound 10).
8,13-Dihydro-6H-8,13-[1,2]benzenobenzo[4,5]imidazo[1,2-a]naphtho[2,3-e][1,3]
diazepin-7,14-dione (7)
Yield 82.8%, yellow powder, mp: 238–240 °C; IR (ATR, cm−1): 3376, 3061, 3026, 2923,
1
2851, 1634, 1546, 1457, 1370, 1274, 744; H NMR: (400 MHz, DMSO-d6) δ 12.16 (1H,
br), 7.51–7.31 (6H, m), 7.07 (2H, dd, J ¼ 5.4 and 2.9 Hz), 7.02 (4H, dd, J ¼ 5.1 and 3.2 Hz),
6.13 (1H, s), 5.99 (1H, s); 13C NMR: (100 MHz, DMSO-d6) δ (ppm): 167.95–164.64
=
(C O), 154.57 (Cipso-benzimidazole), 148.04–143.86 (Cipso-benzimidazole), 145.68–145.51
(Cipso-DBB), 125.21, 124.11, 123.78, 122.37, 121.53, 111.99 (CH-aromatic), 55.41–
51.67 (CH-bridgehead), 46.24–9.11 (triethylamine salt); Anal. calc. for C25H15N3O2
(389,41): C, 77.11; H, 3.88, N, 10.79; found C, 77.29; H, 3.96; N, 11.03.
General synthesis of 13-(1H-benzimidazol-2-yl)-9,10-dihydro-9,10-[3,4]
epipyrroloanthracene-12,14-dione (8) (Method B)
A total of 0.405 g of compound 9 3.04 mmol of compound 9 (0.405 g) was dissolved in
anhydrous THF (50 mL) and cooled at 0 °C in an ice bath under an argon atmosphere.
Then, 0.243 g of NaH (60%, 6.08 mmol) and 3.04 mmol of compound 4 were added to
the cold solution, respectively. The color of the reaction mixture turned red. The solution
was stirred for 1 h at 0 °C. The mixture was allowed to warm to room temperature and stir-
red under the argon atmosphere for 24 h. The mixture was filtered and the solvent was eva-
porated under reduced pressure. The crude product was dissolved in 10 mL of methanol.
The crude product was precipitated by dropwise addition of methanol solution to 200 mL
of water. The crude product was dried, filtered, and then crystallized from methanol.
13-(1H-benzimidazol-2-yl)-9,10-dihydro-9,10-[3,4]epipyrroloanthracene-12,14-dione (8)
Yield 74.3%, colorless powder, mp: 281–282 °C; IR (ATR, cm−1): 3316, 3066, 2951, 2922,
1
2851, 1683, 1633, 1537, 1456, 1362, 1272, 742; H NMR: (400 MHz, DMSO-d6) δ 12.36
(1H, br), 7.38 (4H, dd, J ¼ 5.3 and 3.2 Hz), 7.34 (2H, dd, J ¼ 5.9 and 3.2 Hz), 7.20 (2H,
dd, J ¼ 5.9 and 3.2 Hz), 6.98 (4H, dd, J ¼ 5.3 and 3.1 Hz), 5.97 (2H, s); 13C NMR: (100
=
=
MHz, DMSO-d6) δ 166.08 (C O), 151.31 (Cipso-benzimidazole), 150.00 (C C), 145.55
=
(Cipso-DBB), 130.94 (C C, Ar-benzimidazole), 125.11–123.96 (CH-DBB), 123.18–111.82
(CH-benzimidazole), 53.53 (CH-bridgehead). Anal. calc. for C25H15N3O2 (389,41): C,
77.11; H, 3.88, N, 10.79; found C, 77.44; H, 3.89; N, 10.84.
Synthesis of N11,N12-di(imidazolidin-2-ylidene)-9,10-dihydro-9,
10-ethenoanthracene-11,12-dicarboxamide (12) (Method C)
A total of 0.100 g Na (4.35 mmol) was dissolved in anhydrous methanol (10 mL) and the
mixture was stirred at room temperature for 10 min. To the resulting sodium methoxide

SYNTHETIC COMMUNICATIONS®
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solution, 2-aminoimidazoline p-toluenesulfonate (1.029 g, 4.00 mmol) was added as solid
in one portion. The reaction mixture was stirred for 10 min followed by the addition of
compound 2 (0.50 g, 1.56 mmol). The mixture was stirred at room temperature for 4 days,
and then the solvent was evaporated under reduced pressure. The yellow crude product
was crystallized from water. After 2 days, the solid was decanted off and recrystallized from
methanol.
N
11,N12-Di(imidazolidin-2-ylidene)-9,10-dihydro-9,10-ethenoanthracene-11,
12-dicarboxamide (12)
Yield 39.1%, colorless powder, mp: 293–294.93 °C. From the DSC and TGA analysis, it was
understood that this compound held 1-mol water in its chemical structure. IR (ATR,
1
cm−1): 3509, 3338, 3127, 3024, 2975, 2898, 1689, 1676, 1595, 1544, 1456, 1374; H NMR:
(400 MHz, CDCl3 þ 2 drop CH3COOH) δ 11.60 (acetic acid), 7.82–7.50 (4H, br.), 7.42–
7.41 (4H, d, J ¼ 3.4 Hz), 7.0–6.99 (4H, d, J ¼ 3.4 Hz), 6.01 (2H, s), 3.65 (8H, s), 2.09 (acetic
acid); 13C NMR: (100 MHz, CDCl3-d þ 2 drop CH3COOH) δ (ppm) 177.85 (acetic acid),
=
=
168.75 (C O), 160.76 (C N), 150.83, 144.28 (ArC-ipso), 125.12, 123.82 (CH-aromatic),
53.57 (CH), 42.95 (CH2). Anal. Calc. for C24H22N6O2, (426.48): C, 64.85; H, 5.44; N,
18.91; found C, 65.59; H, 5.72; N, 19.43.
Conclusion
In this study, attempts to obtain the symmetrical dibenzobarrelene-substituted imidazoline
and benzimidazole derivatives (Expected product-1–3) were unsuccessful and instead
obtained some novel products resulted from intramolecular cyclization. As a result, we have
synthesized different and completely new imidazoline and benzimidazole derivatives, which
have the dibenzobarrelene skeleton using simple synthetic methods. In these synthesis meth-
ods, we obtained unexpected products by changing the nature of the base and the reagent
ratios. The synthesized compounds are dicarboxamide derivatives which contain together
1.3-diazepine and guanidine main structures. The coexistence of two functional groups in
one molecule may potentially contribute positively to the biological activity of these com-
pounds. Based on chemical structures, new compounds 8, 12 and dibenzobarrelene-substi-
tuted benzimidazole and imidazoline fused with 1.3-diazepinedione ring derivatives (7, 10,
and 14) appear to be ideal candidates for medicinal investigations.
Funding
We are indebted to the Firat University Research Project Coordination Unit (Project Number
FF.16.10 and FF.13.04) for financial support of this work.
ORCID
İrfan Çapan
Süleyman Servi
http://orcid.org/0000-0002-9555-1555
http://orcid.org/0000-0003-0827-8624
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