Synthesis of N-substituted dibenzoazepine–pyridazine derivatives as potential neurologically active drugs

Article abstract of DOI:10.1080/00397911.2020.1828925

Syntheses of pyridazine derivatives of dibenzoazepine, starting from N-substituted-dibenzoazepines, are reported here for the first time. In the reaction sequence, N-substitute dibenzoazepine derivatives were synthesized and then, examined inverse electro

Full text of DOI:10.1080/00397911.2020.1828925

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Synthesis of N-substituted
dibenzoazepine–pyridazine derivatives as
potential neurologically active drugs
Musa Erdoğan & Arif Daştan
To cite this article: Musa Erdoğan & Arif Daştan (2020): Synthesis of N-substituted
dibenzoazepine–pyridazine derivatives as potential neurologically active drugs, Synthetic
Communications, DOI: 10.1080/00397911.2020.1828925
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https://doi.org/10.1080/00397911.2020.1828925
Synthesis of N-substituted dibenzoazepine–pyridazine
derivatives as potential neurologically active drugs
Musa Erdo gꢀ ana,b
b
and Arif Da s¸ tan
a
Department of Food Engineering, Faculty of Engineering and Architecture, Kafkas University, Kars,
b
Turkey; Department of Chemistry, Faculty of Sciences, Atat €u rk University, Erzurum, Turkey
ABSTRACT
ARTICLE HISTORY
Syntheses of pyridazine derivatives of dibenzoazepine, starting from
N-substituted-dibenzoazepines, are reported here for the first time.
In the reaction sequence, N-substitute dibenzoazepine derivatives
were synthesized and then, examined inverse electron demand
Diels–Alder (IEDDA) reactions between N-substituted dibenzoazepine
derivatives and tetrazines. While in some reactions, targeted prod-
ucts were obtained using phenyliodo-bis(trifluoroacetate) (PIFA), in
other reactions, they were obtained directly with tetrazines which
also behaved as the oxidizing agent. Structures of these compounds
were fully characterized by NMR, IR, and HRMS spectroscopic techni-
ques.
Received 28 August 2020
KEYWORDS
Azepine; 5H-
dibenzo[b,f]azepine; iminos-
tilbene; inverse electron
demand Diels–Alder; PIFA;
pyridazine; tetrazine
GRAPHICAL ABSTRACT
Introduction
Nitrogeneous heterocyclic aromatic compounds are an important class of organic com-
pounds, due to their physical, chemical, and biological properties arising both from
[
1,2]
their reactivity and stability.
These species are used in several applications such as
the pharmaceutical industries and in agrochemical researches. Tricyclic heteroaromatic
compounds containing nitrogen atoms have become attractive targets for synthetic
chemists due to their biological and pharmacological activities, and their structural
CONTACT Arif Da s¸ tan
adastan@atauni.edu.tr
Department of Chemistry, Faculty of Sciences, Atat u€ rk University,
Erzurum, Turkey
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
M. ERDOĞAN AND A. DAŞTAN
Figure 1. Some pharmaceutically important derivatives of dibenzoazepine 1.
[
3–5]
diversity.
The 5H-dibenzo[b,f]azepine (1), commonly known as iminostilbene, and
which contains a seven-membered ring, is a very common tricyclic amine used as an
[
6]
intermediate or starting compound in the synthesis of anticonvulsant drugs (Fig. 1).
Additionally, the 5H-dibenzo[b,f]azepine (1) nucleus forms the main skeleton of medi-
cinal and pharmacologically important antidepressant drug structures that are particu-
[
7]
larly effective in the central nervous system. These anticonvulsant or antiepileptic
drugs are used in the treatment of epilepsy, chizophrenia, panic attack, etc. one of the
common chronic neurological disorders, in bipolar disorders and in the prevention of
[
8]
neuropathic pain. Dibenzoazepine and its derivatives possess a remarkably broad
spectrum of pharmacological activities including antidepressant, antiallergic, antihista-
mine, spasmolytic, seratonin antagonistic, anticonvulsive, antiemetic, antiepileptic, anti-
[
9]
inflammatory, sedative, and fungicidal activity. Carbamazepine 2 and oxcarbazepine 3
(
Trileptal) started to be used under the trade name Tegretol and belongs to a group of
[
10]
drugs called ‘antiepileptics’ (Fig. 1).
Many of the drugs that activate the central ner-
vous system, such as carbazepine 2, imipramine 7, clomipramine HCl 9, and opipranol
[
9]
1
0, have tricyclic dibenzoazepine 1 core and its 10-11 dihydro version (Fig. 1).
Eslicarbazepine acetate 4 (Zebinix), (S)-Licarbazepine 5, Clozapine 6 (clozaryl),
Imipramine 7 (Tofranil), Olanzapine 8, Clomipramine HCl 9 and Opipramol 10 belong
[
11]
to a type of antipsychotic drug group known as tricyclic antidepressants (Fig. 1).
In
addition, the dibenzoazepine 1 is widely used in materials chemistry, as an organic
field-effect transistors (OFET), a light emitting diodes (OLED), and hole transport
[
12,13]
material due to their electron donor properties.
On the other hand, diazine scaf-
2
fold containing two sp -hybridized adjacent nitrogen atoms is very important classes of
six-membered heterocyclic compounds. Pyridazines are a family of diazine compounds
and they have a wide application in medicine, pharmacy, cosmetics, and agriculture.
The pyridazine core is a part of the structure of some therapeutic agents such as cadra-
[
14]
[
15,16]
lazine 11, minaprine 12, pipofezine 13, etc. commercially on the market (Fig. 2).

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Figure 2. Structure of some pyridazine-based drugs.
To generate new pyridazine-based bioactive cores, the conversion of the tetrazine
[
17]
unit into pyridazine-derivatives is an extremely advantageous method.
With the
above considerations in mind, as part of biologically and pharmaceutically active
dibenzoazepine and diazine, we decided to synthesize novel dibenzoazepine–pyrida-
zine derivatives and developed a strategy that engaged the N-substitute-dibenzoaze-
pines with tetrazines in an inverse electron demand Diels–Alder reaction (IEDDA)
to give the corresponding the dibenzoazepine–pyridazine hybrid derivatives.
Results and discussions
The IEDDA reaction is a cycloaddition between highest occupied molecule orbital
(
HOMO) energy of an electron-rich dienophile and lowest un-occupied molecular
[
18]
orbital (LUMO) energy of an electron-poor diene.
zines and olefins are very common procedures to generate pyridazine skeletons.
IEDDA reactions between s-tetra-
[
19]
These reactions conclusion in the formation of bicyclic intermediates via nitrogen elim-
ination readily and then rearranging, giving dihydropyridazines that can be oxidized to
[
20]
pyridazines.
Here, we examined the IEDDA reactions between N-substituted dibenzoazepine
derivatives 1–2 and 14–17 and tetrazines, dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate
(
(
DET) (18) and 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine (DPT) (19). 5H-dibenzo[b,f]azepine
1), which was commercially available, became the key structure that allowed us to
afford N-substituted dibenzoazepine derivatives 1–2 and 14–17 (Fig. 3).
Dibenzoazepine derivatives 5H-dibenzo[b,f]azepine-5-carboxamide (2),
[
21]
5-methyl-
[
22]
[23]
5H-dibenzo[b,f]azepine (14),
5-(prop-2-yn-1-yl)-5H-dibenzo[b,f]azepine (15),
and
[
10]
1-(5H-dibenzo[b,f]azepin-5-yl)ethan-1-one (16)
were synthesized according to a pre-
viously reported methods. Treatment of N,N-dimethylsulfamoyl chloride with pyridine
ꢀ
in toluene at 80 C for 1 h followed by the addition of 5H-dibenzo[b,f]azepine (1) gave
N,N-dimethyl-5H-dibenzo[b,f]azepine-5-sulfonamide (17) in 96% yield.
Following the same sequence of Diels–Alder (DA), of retro-Diels–Alder (rDA), and
of 1,3-prototropic H-shifting reactions (Scheme 1), the adducts 20–27 were obtained
when the electron-rich dienophile N-substituted dibenzoazepine derivatives 1–2 and
4
–15 were reacted with tetrazines 18 and 19 (1.1 equiv.) in a sealed tube in dry toluene
ꢀ
at 110–180 C for 12–72 h (Scheme 2). Then, the cycloadducts 20–27 was used directly
in the next reaction without requiring separation and oxidized with PIFA to access to
target products 28–35 in dry methylene chloride in excellent yields (74–98%).
As known, the IEDDA reaction is a cycloaddition between HOMO energy of an elec-
tron-rich dienophile and LUMO energy of an electron-poor diene. Electron-

4
M. ERDOĞAN AND A. DAŞTAN
Figure 3. N-substituted dibenzoazepine derivatives.
Scheme 1. Route of synthesis of N-substituted dibenzoazepine-pyridazine derivatives 28–35.
Scheme 2. Synthesis mechanism of 28–35 via the IEDDA reaction.
withdrawing groups (EWGs) decrease both HOMO and LUMO energy of the cycload-
dends while electron-donating groups (EDGs) increase both HOMO and LUMO energy.
Therefore, the adducts 20–27 were obtained via IEDDA reactions of the electron-rich

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Table 1. Synthesis of 28–39 from N-substituted dibenzoazepine derivates (1–2, 14–17) and tetra-
zines (18 and 19).
ꢀ
Entry
Products
Me
Temperature ( C)
Time (h)
Yields (%)
a
1
2
3
4
5
6
7
8
9
28; G ¼ H, R ¼ CO
2
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
130
180
140
180
12
12
12
12
12
12
12
12
12
24
15
96
95
a
29; G ¼ Me, R ¼ CO
2
Me
95
a
30; G ¼ Propargyl, R: CO
2
Me
90
a
31; G ¼ Carboxamide [–C(¼O)NH
2
], R ¼ CO
2
Me
90
50
65
95
a
32; G ¼ H, R ¼ 2-Py
a
33; G ¼ Me, R: 2-Py
a
34; G ¼ Propargyl, R ¼ 2-Py
a
35; G ¼ Carboxamide [-C(¼O)NH
2
], R ¼ 2-Py
85
b
36; G ¼ Ac, R ¼ CO
2
Me
50
15
50
35
b
1
1
1
a
0
1
2
37; G¼ N,N-dimethylsulfamoyl, R ¼ CO
38; G ¼ Ac, R ¼ 2-Py
2
Me
b
b
39; G¼ N,N-dimethylsulfamoyl, R ¼ 2-Py
All reactions were carried out in dry CH
2 2 2
at r.t. under N atm.
Cl
b
All reactions were carried out in a sealed tube in toluene (see the experimental section for details).
Scheme 3. Synthetic route of N-substituted dibenzoazepine-pyridazine derivatives 36–39.
dienophile N-substituted dibenzoazepine derivatives 1–2 and 4–15 with tetrazines 18–19
Scheme 2). These reactions took place under milder conditions and no oxidation prod-
(
uct was formed as a result of the reaction. Therefore, the PIFA was used as an oxidizing
agent to access targeted products 28–35 (Scheme 2, Table 1).
The reaction of N-substituted dibenzoazepine derivatives 16–17 containing EWGs
under similar conditions with tetrazines 18–19 progressed more slowly and a higher
reaction temperature was required to carry out the aimed transformation (Scheme 3).
Interestingly, the direct oxidation products 36–39 were obtained by changing the reac-
tion conditions, i.e. increasing the temperature and extending the reaction time. When
the reaction was performed under a higher reaction temperature in a sealed tube in dry
ꢀ
toluene at 110–150 C for 12–24 h, the formation of dihydrotetrazines 40–41 along with
3
6–39 was observed (Scheme 3). Since tetrazines 18–19 behaves as an oxidizing
agent at the same time, using 1.1 equiv. of 18–19 with 16–17 for 3 days led to the
[
24,25]
formation of 36–39 and 40–41.
The chemical structures of all N-substituted
dibenzoazepine–pyridazine derivatives synthesized in this study were determined by
NMR, IR, and HRMS analyses.
Conclusion
In conclusion, we designed and synthesized novel 12 heterocyclic compounds 28–35
and 36–39 which contain the two important scaffolds for drug discovery, namely

6
M. ERDOĞAN AND A. DAŞTAN
dibenzoazepine and pyridazine heterocycles. This new heterocyclic hybride skeleton
may be applicants for the development of neurologically active drug agents. Further
studies along this line are underway in our group on the evaluation of pharmaco-
logical activity of the aforementioned heterocyclic compounds. The newly synthesized
compounds may be interesting with their potential pharmacological and bio-
logical activities.
Experimental section
General
All reactions were carried out under nitrogen and monitored by thin-layer chromatog-
raphy (TLC). All solvents were dried and distilled before use. Column chromatography
was performed on silica gel (60 mesh, Merck, Kenilworth, NJ, USA). TLC was carried
out on silica gel 60 HF254 aluminum plates (Fluka, Buchs, Switzerland). Melting points
1
13
are uncorrected. The one- and two-dimensional H and C NMR spectra were
recorded on a Varian-400 or a Bruker-400 spectrometer using tetramethylsilane as the
ꢀ
internal reference. All spectra were recorded at 25 C and coupling constants (J values)
are given in Hz. Chemical shifts are given in parts per million (ppm). Mass spectra
were recorded on an Agilent Technologies 6530 Accurate-Mass Q-TOF-LC/MS (Agilent
Technologies, Santa Clara, CA, USA). IR spectra were recorded on Perkin Elmer FT-IR
spectrometer (PerkinElmer, Waltham, MA, USA).
Synthesis
General procedure A: Reaction of N-substituted dibenzoazepine derivatives 1–2,
4–15 with tetrazines 18–19 (Step I): oxidation of obtained the products with PIFA
(
Step II)
Step I: N-substituted dibenzoazepine derivatives 1–2 or 14–15 (1.000 mmol) and tetra-
zines 18–19 (1.100 mmol) were dissolved in toluene in a sealed tube and the resulting
reaction mixture was heated at the required temperature. The reaction was monitored
by TLC. The resulting reaction mixture was then cooled to r.t and the solid precipitated
to the bottom of the thermolysis tube was washed with a 10 mL ether/n-hexane (4:1)
mixture and dried under reduced pressure. The crude product was directly used in the
oxidation step with PIFA without purification.
Step II: In this step, the cycloadducts 20–27 (1.000 mmol) and PIFA (1.200 mmol)
were dissolved in dry CH Cl at r.t. under N atm. The resulting reaction mixture was
2
2
2
stirred at r.t. for 12 h. The reaction was monitored by TLC and the solvent was removed
under reduced pressure. The crudes were purified an appropriate method described in
Supporting Information.
General procedure B: Reaction of N-substituted dibenzoazepine derivatives 16–17
with tetrazines 18–19 and to yield diazin-dibenzoazepine derivates 36–39
N-Substituted dibenzoazepine derivatives 16–17 (1.000 mmol) and tetrazines 18–19
(1.100 mmol) were dissolved in solvent toluene in a sealed tube and the resulting

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reaction mixture was heated at the required temperature. The reaction was monitored
by TLC. The resulting reaction mixture was then cooled to r.t. and the solvent was
removed under reduced pressure. The crude was purified an appropriate method
described in Supporting Information.
1
13
Full experimental details, H NMR, C NMR, and HRMS spectra can be found via
the “Supplementary Content” section of this article’s webpage.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
The authors are grateful to Atat u€ rk University for financial support.
ORCID
Musa Erdo ꢀg an
Arif Da ¸s tan
http://orcid.org/0000-0001-6097-2862
http://orcid.org/0000-0002-9577-2251
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