Synthesis of the 4,7-Dibromo Derivative of Highly Electron-Deficient [1,2,5]Thiadiazolo[3,4-d]pyridazine and Its Cross-Coupling Reactions

Article abstract of DOI:10.1002/ejoc.201800961

An efficient synthesis of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine is reported. For the first time, palladium-catalysed cross-coupling reactions of a dihalo derivative was found to be a powerful tool for the selective formation of various mono- and

Full text of DOI:10.1002/ejoc.201800961

A Journal of
Accepted Article
Title: Synthesis of 4,7-dibromo derivative of ultrahigh electron-deficient
[1,2,5]thiadiazolo[3,4-d]pyridazine heterocycle and its cross-
coupling reactions
Authors: Timofey Chmovzh, Ekaterina Knyazeva, Ludmila
Mikhalchenko, Ivan Golovanov, Stanislav Amelichev, and
Oleg A Rakitin
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201800961
Link to VoR: http://dx.doi.org/10.1002/ejoc.201800961
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10.1002/ejoc.201800961
European Journal of Organic Chemistry
FULL PAPER
Synthesis of 4,7-dibromo derivative of ultrahigh electron-deficient
[1,2,5]thiadiazolo[3,4-d]pyridazine heterocycle and its cross-
coupling reactions
Timofey N. Chmovzh,[a] Ekaterina A. Knyazeva,[a],[b] Ludmila V. Mikhalchenko,[a] Ivan S. Golovanov,[a]
Stanislav A. Amelichev,[a] and Oleg A. Rakitin*[a],[b]
Abstract: An efficient synthesis of 4,7-dibromo[1,2,5]thiadiazolo[3,4-
d]pyridazine is reported. For the first time, palladium-catalysed cross-
couplings chemistry for a dihalo derivative was found to be a powerful
tool for the selective formation of various mono- and bis-derivatives of
strong electron accepting heterocycles. Suzuki-Miyaura coupling can
be successfully employed for the preparation of mono-arylated
derivatives, whereas Stille coupling is useful for both mono- and di-
aryl(hetaryl)ated heterocycles. The cyclic voltammogram showed that
4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine can be easily oxidized
to form a stable anion radical. The calculated values of ЕLUMO
confirmed that [1,2,5]thiadiazolo[3,4-d]pyridazine is one of the
strongest electron acceptor system.
successfully used as electrochromic materials.9 Several different
structural motifs have been intensely studied in the past few
decades: more simple D-A, D-π-A, D-A-D or A-D-A, or more
complex ones where different acceptors or donors were used: D-
A1-π-A2, A- π-D-π-A, etc.1c Recently, heterocycles with high
electron affinity as electron-acceptor central blocks have been
given a great attention.10 Although 2,1,3-benzothiadiazole has
proven as an exceptional electron-accepting building block,11
there is a strong demand to design a building block with ultrahigh
electron deficiency in order to increase light absorption in the near
infrared region, and therefore to use the solar light more efficiently
in organic photovoltaics with the main purpose of replacing the
currently used and expensive fullerene derivatives. Another
purpose is to construct efficient air-stable electron-transport
materials.9b The first idea on how to increase the electron-
accepting ability of 2,1,3-benzothiadiazole was to attach strong
electron-withdrawing groups at the 5- and 6-positions. In fact, 5,6-
difluoro-2,1,3-benzothiadiazole has been employed in a variety of
materials including small molecules in DSSCs chromophore,
white and color light emitters, polymer molecules in OLEDs,
OFETs, and OPVs.9b Another way to increase the electron-
accepting strength of the 2,1,3-benzothiadiazole core was the
heteroannulation at the 5- and 6-positions to afford acceptors
such as [1,2,5]thiadiazolo[3,4-g]quinoxaline (TDQ)12 and
benzo[1,2-c:4,5-c΄]bis[1,2,5]thiadiazole (benzo-bis-thiadiazole,
BBT).13 The third way is to change carbon atoms in 5- or/and 6-
Introduction
Electron-acceptor building blocks have been widely used in the
synthesis of various photovoltaic materials including dye
sensitized solar cells,1 organic near-infrared molecules,2 organic
light emitting diodes (OLEDs),3 charge transfer materials,4
bioimaging5 and others. Their presence in a π-conjugated organic
molecule is important to tune such properties as light absorption,
light emission and charge carrier mobility in the materials. The
energies of the frontier orbitals: the highest occupied molecular
orbital (EHOMO) and the lowest unoccupied molecular orbital
(ELUMO), as well as the difference between these energies (Eg),
are fundamental properties of molecules and are crucial for high
performance of the materials based on these molecules. Electron-
acceptor building blocks (A) can be used in π-conjugated small
molecules where such a block is linked with an electron donor (D)
either directly, or more favorably, through a π-conjugated bridge
(π). The important feature of the acceptor part is the electron
affinity which is related to the energies of the lowest unoccupied
molecular orbital (ELUMO). The electron-acceptor building blocks
with high electron deficiency may be used in the construction of
compounds for such devices as light absorption materials in bulk
heterojunction solar cells (BHJ),6 donor-acceptor dyes with near
infrared absorption and emissions,7 and n-type organic field-effect
transistors.8 Moreover, polymeric molecules with an electron-
deficient moiety in the structure, (-D-A-)n or (-D-π-A-)n, have been
positions
to
electronegative
nitrogen
atoms.
4,7-
Dibromo[1,2,5]thiadiazolo[3,4-c]pyridine was effectively used for
the preparation of DSSCs and other materials.14 To complete this
way, it is necessary to incorporate [1,2,5]thiadiazolo[3,4-
d]pyridazine core in the design and preparation of photovoltaic
materials.
In order to reveal the electronic nature of the
[1,2,5]thiadiazolo[3,4-d]pyridazine block, the energy levels of the
frontier orbitals along with other properties have been calculated
and compared with the same properties of some relevant
acceptors. Thiadiazolopyridazine has the lowest LUMO energy
level among the compounds shown in Figure 1, excluding
benzobis(thiadiazole). Hence, thiadiazolopyridazine possesses
an ultrahigh electron deficiency. It may lead to unusual and even
extreme physicochemical properties, and development of its
chemistry requires special attention. As previously noted, the
value of Egap is also an important characteristic of the constituent
parts of molecules for photoelectronic materials. We calculated
the optical energy gap of the same molecules in the first excited
electronic state in chloroform solution. It was found that the
[1,2,5]thiadiazolo[3,4-d]pyridazine block had the maximum
difference between EHOMO and ELUMO, which should ensure high
[a]
[b]
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of
Sciences, 47 Leninsky Prospekt, 119991 Moscow, Russia. e-mail:
orakitin@ioc.ac.ru; fax (+)7-499-1355327: tel. (+)7-499-1355328
Nanotechnology Education and Research Center, South Ural State
University, 454080 Chelyabinsk, Russia
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201800961
European Journal of Organic Chemistry
FULL PAPER
stability of the molecules in excited state and, as a result, high
electron conductivity.
d]pyridazine-4,7-dione 3 with brominating agents (POBr3, PBr5,
PBr3) was investigated. The results are summarized in Table 1.
Table 1. Bromination of 5,6-dihydro[1,2,5]thiadiazolo[3,4-d]pyridazine-4,7-
dione 3.
Yields (%)
Temp.
(oC)
25
Entry
Reagent
Time (h)
3
1
1
4
1
2
PBr3
PBr3
4
4
4
4
4
4
8
4
8
4
8
9
9
6
6
4
4
8
4
8
4
8
9
90
80
75
70
88
70
50
55
40
45
30
25
10
20
15
78
60
45
35
25
25
5
5
Figure 1. Calculated LUMO and HOMO energy levels and optical energy gaps
of relevant acceptors.
60
2
6
3
PBr3
80
3
10
12
4
4
PBr3
110
25
4
para-Dihalogenated (most often dibromo) representatives of
the electron acceptor heterocycles shown in Figure 1 are used for
the synthesis of various photovoltaic materials.1c,11b Although
dibromo derivatives of all heterocyclic acceptors shown in Figure
1, are known, their substitution chemistry has been studied
fragmentally, and the possibility of synthesizing photovoltaic
materials from them is unclear. For example, the heterocycle with
5
POBr3
POBr3
POBr3
POBr3
POBr3
POBr3
POBr3
POBr3
POBr3
POBr3 + DMF
POBr3 + C6H6
PBr5
5
6
60
6
10
20
10
11
8
7
60
7
8
80
8
9
80
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
110
110
110
130
110
110
25
10
11
12
13
14
15
16
17
18
19
20
21
22
75
20
22
25
40
35
8
the strongest electron accepting properties
–
3,7-
dibromobenzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole – was studied in
Stille reactions only.15 The chemistry of 3,6-dibromo-1,2,5,6-
tetrazine is unknown,16 while the 3,6-dichloro derivative was
slightly studied in Stille coupling.17 In general, careful studies of
cross-coupling displacement of halogen atoms in extremely
electron-poor heteroarenes are very rare and still remain a
challenge.
PBr5
60
20
25
20
28
20
15
8
PBr5
60
PBr5
80
Herein,
we
describe
the
synthesis
of
4,7-
PBr5
80
dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine and their SNAr and
cross-coupling reactions as a basis for the preparation of
compounds which are of interest as photovoltaic materials.
PBr5
105
105
105
PBr5
PBr5
0
It has been found that the nature of the brominating reagent
and the reaction temperature affect the yield of the target dibromo
product 1 significantly. At room temperature, none of the reagents
used reacted with compound 3. PBr3 did not convert dione 3 into
bromo derivatives at higher temperatures either. Traces of
dibromo compound 1 were isolated after heating at 110 oC for four
hours (Entry 4, Table 1). Better results were obtained using POBr3.
Prolonged heating of the reaction mixture at 110 °C gave the
target dibromo derivative in moderate yield (Entry 12, Table 1);
significant amounts of mono- and diones (4 and 3) were isolated
from the reaction mixture. The use of organic solvents (benzene
or DMF) did not afford any significant success; the yields of the
target compound remained practically the same (Entries 14, 15,
Table 1). The best yield of 1 was achieved using PBr5 as the most
powerful brominating reagent. Careful investigation of the
reaction conditions allowed us to reach the yield of 75% by
heating the reaction mixture at 105 °C for 9 h (entry 23, Table 1).
Small amounts of mono- and diones (4 and 3) were isolated. This
fact can be explained by partial hydrolysis of the target compound
1 during work-up of the reaction mixture.
Results and Discussion
Synthesis of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine 1
[1,2,5]Thiadiazolo[3,4-d]pyridazines are a well known class of
heterocycles. To the best of our knowledge, about 50 compounds
were described in the literature according to SciFinder and
Reaxys search. As concerns 4,7-dihalo[1,2,5]thiadiazolo[3,4-
d]pyridazines, which are of interest for the preparation of various
photovoltaic materials, dichloro derivative 2 is the only known
compound.18 This derivative has been prepared by the reaction of
5,6-dihydro[1,2,5]thiadiazolo[3,4-d]pyridazine-4,7-dione19 (3) with
POCl3. Unfortunately neither spectral or analytical data, nor
reactions which could confirm this structure, have been given. We
repeated this reaction and confirmed that dichloro derivative 2
was very unstable and could not be purified or involved in
substitution reactions. On the other hand, it is known that bromo
derivatives can react in substitution reactions (especially cross-
couplings) much more successfully than the corresponding chloro
derivatives. In order to obtain 4,7-dibromo[1,2,5]thiadiazolo[3,4-
d]pyridazine 1, the reaction of 5,6-dihydro[1,2,5]thiadiazolo[3,4-
4,7-Dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine 1 is a high-
melting yellow solid with mp 199-200 °C. It is fairly stable to
hydrolysis at room temperature and can be kept in a freezer under
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10.1002/ejoc.201800961
European Journal of Organic Chemistry
FULL PAPER
argon for a few months without noticeable changes. Its structure
was fully proved by NMR, mass and IR spectroscopy.
The behavior of dibromothiadiazolopyridazine
Suzuki-Miyaura cross-coupling conditions was studied. The
1
under
In order to reveal the possibility to construct various
photovoltaic materials from dibromo derivative 1, its reactivity in
aromatic nucleophilic substitution and cross-coupling palladium
catalyzed reactions was studied. In these sections we aimed at
finding conditions for the substitution of one or two bromine atoms
to expand the number of structures.
nearest
analog
of
this
derivative
-
4,7-
dibromo[1,2,5]thiadiazolo[3,4-c]pyridine - reacted readily with
aryl-20 and heteroaryl-14b,21 boronic acids or their cyclic esters to
give the corresponding 4-aryl(hetaryl) derivatives in moderate
yields. Treatment of dibromothiadiazolopyridazine
1
with
phenylboronic acid, Pd(PPh3)4 and K2CO3 in water-dioxane
solutions led to hydrolysis to give 7-bromo[1,2,5]thiadiazolo[3,4-
d]pyridazin-4(5H)-one 4 in good yield. So, it is necessary to focus
on nonaqueous protocols in order to limit the base-catalyzed
hydrolysis of starting dibromide 1. Similar anhydrous protocols
were successfully used for Suzuki-Miyamura cross-couplings of
highly reactive 3,5-dichloroisothiazole-4-carbonitrile.22
Cross-coupling
reactions
of
4,7-
bromo[1,2,5]thiadiazolo[3,4-d]pyridazines
Dibromothiadiazolopyridazine 1 has been investigated in the
palladium-catalyzed Suzuki-Miyamura and Stille coupling
reactions
in
order
to
obtain
mono-
and
bis-
aryl(hetaryl)thiadiazolopyridazines.
Suzuki-Miyaura coupling
Table 2. Suzuki-Miyaura coupling of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine 1 with aryl- and heteroaryl-boronic acids.
Yields (%)
ArB(OH)2
Entry
Solvent
Catalyst
Base
Temp. (°C)
Time (h)
(equiv.)
5a (1)
5a (1)
5a (1)
5a (1)
5a (1)
5a (1)
5a (1)
5a (1)
5a (1)
5a (2)
5a (2)
5a (2)
5a (2)
5a (2)
5a (2)
5b (1)
5b (2)
5c (1)
5c (2)
5d (1)
5d (2)
5e (1)
5e (2)
5f (1)
5f (2)
5g (1)
5g (2)
5h (1)
5h (2)
5i (1)
6
0
7
0
0
0
0
0
0
0
0
0
8
0
0
0
0
0
1
60
40
30
34
17
15
8
0
0
0
8
0
0
0
0
30
0
25
0
28
0
0
0
32
0
30
0
0
0
0
0
0
1
2
3
4
5
6
7
8
THF
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd2(dba)3
K2CO3
K2CO3
K2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
66
101
110
66
101
110
110[a]
60
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
60
8
8
8
8
8
dioxane
toluene
THF
15
20
20
36
50
5
dioxane
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
6
0.17
18
12
8
8
8
8
8
8
6
8
6
9
6
8
12
8
12
18
12
12
48
14
24
8
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
30
0
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Pd(PPh3)4
Pd(OAc)2
60
15
35
45
0
Pd(OAc)2, BINAP
Pd(OAc)2, dppf
Pd(OAc)2, P(Cy)3
Pd(OAc)2, XPhos
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
5
34
58
29
53
23
45
40
60
0
0
0
0
41
0
n.d.[b]
4
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
18
35
0
20
4
50
3
110
60
110
60
110
60
110
49
0
54
0
5i (2)
5k (1)
5k (2)
65
9
35
4
8
0
[a] In microwave oven at MW=150 W
[b] Not detected
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10.1002/ejoc.201800961
European Journal of Organic Chemistry
FULL PAPER
dioxane under reflux conditions cannot be stopped at the
formation of the mono-aryl derivative, even if one equivalent of
stannane 8a is employed (Entry 1, Table 3); if two equivalents of
stannane 8a were used, dithienylthiadiazolopyridazine 7a was
formed in a moderate yield (Entry 2, Table 3). Better results were
obtained in toluene as the solvent (Entries 3-5, Table 3), and
diaryl derivative was isolated in a high yield according to
Procedure D. Careful temperature control in THF permitted us to
find the best conditions for the synthesis of mono-aryl derivative
6a, namely, heating the reaction mixture at 55 °C for 8 h according
to Procedure C (Entry 7, Table 3). The conditions found for the
synthesis of mono- and bis-thienyl derivatives were explored
further. In general, this protocol worked well for
aryltributylstannanes bearing electron donating groups, and less
successfully for stannanes with electron accepting substituents
such as furyl- or 4-chlorophenyl groups (Entries 12, 13 and 16, 17,
Table 3).
Scheme 1. Partial hydrolysis of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine
1 under Suzuki-Miyaura coupling conditions
The investigation of Suzuki reaction conditions for the
arylation of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine 1 with
thiopheneboronic acid 5a under anhydrous conditions included
varying the base, solvent, and reaction temperature. Potassium
carbonate was found to be less effective than cesium carbonate,
apparently due to its lower solubility (compare Entries 1-3 and
Entries 4-6, Table 2). Using palladium catalysts other than
Pd(PPh3)4 (Pd2(dba)3 and Pd(OAc)2) led to partial of full
decomposition of the starting dibromide 1 with low yields of
arylated products (Entries 9, 11-15, Table 2). Of the solvents
screened, toluene gave the better yields of arylated products,
followed by dioxane or THF (Entries 4-6, Table 2). Surprisingly,
employment of two equivalents of thienylboronic acid 5a gave
traces of bis-thienylated derivative 7a, while the yield of mono-
thienylated product 6a increased (Entry 10 in Table 2, Procedure
A). Yield of the bis-product 7a was not risen by the increasing of
the reaction time or boronic acid 5a quantity because of
decomposition of mono-substituted compound 6a by further
heating. Apparently, compound 6a is much less reactive than
starting dibromide 1 and decomposed more quickly than formed
bis-substituted product 7a. The scope of Suzuki coupling was
then studied. Hetarylboronic acids 5(a-e) yielded mono-adducts
6(a-e) in moderate to high yields by heating at reflux in toluene
with one equivalent of 4,7-dibromo[1,2,5]thiadiazolo[3,4-
d]pyridazine 1 in the presence of Pd(PPh3)4 and Cs2CO3
according to Procedure A (Entries 17, 19, 21, 23, Table 2). In
contrast to these results, arylboronic acids (f-i) and thiophen-3-
ylboronic acid (k) under Procedure A conditions afforded bis-
arylated products 7f-I,k in moderate to low yields, mono-arylated
compounds were detected in the reaction mixtures in trace
amounts only (Entries 25, 27, 29, 31, 33, Table 2). It was found
that in the cases of p-tolyl-(h), 4-methoxyphenyl(i)-boronic acids
and thiophen-3-ylboronic acid (k), the reaction path can be
directed to the selective formation of mono-arylated adducts 6(h,
i, k) by heating the reaction mixtures at 60 °C in toluene with one
equivalent of the corresponding arylboronic acids according to
Procedure B (Entries 28, 30, 32, Table 2).
Table 3. Stille coupling of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine 1
with aryl- and heteroaryl-tributylstannates
Yields (%)
ArSnBu3
(eqv.)
8a (1)
8a (2)
8a (1)
8a (1)
8a (2)
8a (1)
8a (1)
8a (1)
8a (1)
8b (1)
8b (2)
8c (1)
8c (2)
8f (1)
8f (2)
8g (1)
8g (2)
8h (1)
8h (2)
8i (1)
Temp.
(oC)
101
101
55
110
110
66
55
45
45
55
110
55
110
55
110
55
110
55
110
55
110
110
55
Time
(h)
9
9
8
9
9
8
8
8
12
8
10
8
8
Entry
Solvent
1
35
0
18
40
0
6
0
0
40
0
7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
dioxane
dioxane
toluene
toluene
toluene
THF
THF
THF
THF
THF
toluene
THF
toluene
THF
toluene
THF
toluene
THF
toluene
THF
toluene
toluene
THF
25
45
8
40
80
30
10
8
12
8
74
0
57
0
32
0
24
0
55
0
0
0
0
50
75
30
40
70
0
64
0
0
0
0
0
40
0
20
0
0
0
0
0
9
36
0
28
0
16
18
12
18
12
18
12
8
So,
Suzuki-Miayura
coupling
of
4,7-
0
0
0
0
0
0
0
dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine 1 led mainly to mono-
aryl(hetaryl) thiadiazolopyridines 6 in moderate yields.
52
0
0
68
0
8i (2)
8j (2)
8k (1)
8k (2)
67
65
12
76
Stille coupling
8
9
toluene
110
In
order
to
obtain
both
mono-aryl
and
diaryl[1,2,5]thiadiazolo[3,4-d]pyridazines, the palladium catalyzed
Stille coupling was investigated. Treatment of thienyltributyl
stannane 8a with dibromo derivative 1 in the presence of
PdCl2(PPh3)2 showed that mono- 6 and diaryl 7 derivatives were
formed depending on the conditions used. The quantities of the
stannane, the nature of the solvent and the reaction temperature
affected the results significantly (Table 3). The reaction with 8a in
Cyclic voltammetry of fused 1,2,5-thiadiazoles
In order to evaluate the energy of frontier orbitals in dibromo
derivative 1 and compare them with the corresponding values of
pyrido- and benzothiadiazolo counterparts 9, 10, their formal
reduction potentials were measured by the cyclic voltammetry
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10.1002/ejoc.201800961
European Journal of Organic Chemistry
FULL PAPER
method. The cyclic voltammograms of compounds 1, 9 and 10
are given in Figure 2.
obtained indicate that AR 9 is the least stable in the series of
compounds 1, 10 and 9.
The energy of the lowest unoccupied molecular orbital ELUMO
for 1 was estimated from the value of the formal potential of the
first reversible stage of 1 ER in DMF and acetonitrile using
platinum and glass-carbon electrodes. The formal reduction
potentials (Table 4) were determined as the average values of
peak potentials for direct and reverse scanning of the respective
redox system: Ered = (Еcathode + Еanode)/2. For conversion to the
absolute scale of potentials, the values of Ered were determined
relative to the reversible oxidation potential of ferrocene (EFc/Fc+),
which was used as the internal reference. Taking into account the
value of absolute oxidation potential of ferrocene, which is equal
to 5.1 V,24 the energy values of ELUMO was calculated according
to the equation:
ЕLUMO = - |e|(ЕFc/Fc+red+ 5.1) (eV)
Table 4. Determination of ELUMO from CV curves of 1 on platinum (Pt) and glassy
carbon (GC) electrodes in DMF and acetonitrile, v =0.1Vs-1.
Solvent
DMF
Electrode
ЕSCE red, V
-0.521
-0.522
ЕFc/Fc+red , V
-1.008
-1.011
ELUMO, eV
-4.092
-4.089
Pt
GC
Pt
Figure 2. Cyclic voltammograms: (1) compound 1 (2.0·10–3 М); (2) compound
10 (1.9·10–3 М) and (3) compound 9 (2.0·10–3 М) on a platinum electrode at a
potential scan rate of 0.1 V·s–1 in DMF containing 0.1 М Bu4NClO4 as the
CH3CN
-0.597
-0.987
-4.113
GC
-0.598
-0.994
-4.106
As follows from the data obtained (Table 4), the ELUMO value
remained almost invariable regardless of changes in the nature of
the electrode or solvent. The ELUMO values for 23 and 24 were
calculated from the CV in DMF on a platinum electrode (Table 5).
background electrolyte.
The first reduction stage of 1 (Fig. 2, curve 1) is reversible and
corresponds to the transfer of one electron to the molecule. The
ratio of the anodic peak of anion-radical (AR) oxidation to the
cathodic peak of its formation is close to one at low potential
sweep rates of 100 mV·s–1. Therefore, the resulting AR1 seems
to be quite stable. The stability of AR1 can be explained by
delocalization of the electron density of the unpaired electron due
to the electron-acceptor effect of the thiadiazole ring and nitrogen
atoms in the six-membered ring. For comparison, the reduction
potential of 1 is only slightly more negative than the potential of
benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole 11 (-0.35 V)13a, which has
two thiadiazole rings in the structure and forms a stable AR by
electroreduction.
Table 5. Cyclic voltammetry data for 4,7-dibromo[1,2,5]thiadiazolo[3,4-
d]pyridazine
1,
4,7-dibromo[1,2,5]thiadiazolo[3,4-c]pyridine
10,
4,7-
dibromobenzo[c][1,2,5]thiadiazole
9
and benzo[1,2-c;4,5-
c′]bis[1,2,5]thiadiazole 11 in DMF (0.1 М Bu4NClO4) on a platinum electrode at
a potential scan rate of 0.1 V·s–1.
The electroreduction of heterocycles 10 and 9 (Table 4 and
Fig. 2) occurs at more negative potentials than that of 1. The
presence of electronegative nitrogen atoms in the six-membered
ring leads to a positive shift in the reduction potentials in the
sequence 9 → 10 → 1. It is curious that the electrochemical
behavior of pyridine derivative 10 is similar to that of pyridazine 1.
CV curves of benzothiadiazole 9 at low potential sweep rates (v ≤
100 mV-1) showed that the ratio of the oxidation current of AR 9
to the cathodic current of its formation becomes less than one. In
addition, electroreduction peaks were observed at more negative
potentials than the potential of AR 9 formation; they disappear
with an increase in v to 1 Vs-1. The same pattern in v changes was
observed at recordings of CV curves in acetonitrile. As it was
shown before23 the first reduction stage for compound 9 is
irreversible at very low potential sweep rate (16 Vs-1). These facts
suggest that AR 9 participates in slow chemical reactions leading
to the formation of electrochemically active products. The data
Compound
ESCEred, V[a]
-0.52
-0.72
-1.00
-0.35
EFcred, V[a]
-1.01
-1.22
-1.52
-
ELUMO, eV[b]
-4.09
-3.87
1
10
9
-3.58
1112a
-4.26[c]
[a]
E
red and EFcred - formal potentials of reduction peaks for the compounds
SCE
relative to saturated calomel electrode (SCE) and to the reversible oxidation
[b]
potential of ferrocene (ЕFc/Fc+ = 0.48 V relative to SCE) respectively.
E
LUMO
red
was calculated from EFc
according to the equation ЕLUMO = -
|e|(ЕFc/Fc+red+ 5.1) (eV). The value ELUMO was calculated taking into
account the experimentally determined potential ЕFc/Fc+ = 0.49 V
relative to SCE in CH2Cl2
[c]
The ЕLUMO values obtained confirm that [1,2,5]thiadiazolo[3,4-
d]pyridazine is one of the strongest electron-acceptor system that
is slightly weaker than benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole 11.
The ЕLUMO values of electron-acceptor molecules in the ground
state are proportional to the values of electron affinity (EA), which
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10.1002/ejoc.201800961
European Journal of Organic Chemistry
FULL PAPER
(8k),32 tributyl(4-methoxyphenyl)stannane (8i),33 tributyl(p-tolyl)stannane
(8h)34 were prepared according to the published methods and
characterized by NMR spectra. All synthetic operations were performed
under a dry argon atmosphere. Solvents were purified by distillation from
the appropriate drying agents.
is
a fundamental molecular property and is crucial for
determination of the prospects of their application in materials
chemistry. The values of the electron affinity calculated by
electron propagator theory25 showed that replacement of carbon
atoms by nitrogen atoms in fused 2,1,3-benzothiadiazoles results
in a decrease in these values and, as a consequence, to an
increase in the stability of the resulting anion radicals (Figure 3).
Melting points were determined on a Kofler hot-stage apparatus and are
uncorrected. 1H and 13C NMR spectra were taken with a Bruker AM-300
machine (at frequencies of 300.1 and 75.5 MHz) in CDCl3 or DMSO-d6
solutions, with TMS as the standard. J values are given in Hz. MS spectra
(EI, 70 eV) were obtained with a Finnigan MAT INCOS 50 instrument.
High-resolution MS spectra were measured on a Bruker micrOTOF II
instrument using electrospray ionization (ESI). The measurement was
performed in a positive ion mode (interface capillary voltage –4500 V) or
in a negative ion mode (3200 V); mass range was from m/z 50 to m/z 3000
Da; external or internal calibration was done with Electrospray Calibrant
Solution (Fluka). Syringe injection was used for solutions in acetonitrile,
methanol, or water (flow rate 3 L/min–1). Nitrogen was applied as a dry
gas; interface temperature was set at 180°C. IR spectra were measured
with a Bruker “Alpha-T” instrument in KBr pellets.
Figure 3. Calculated electron affinities of the dibromo derivatives
1, 9, 10.
The calculated patterns and experimental results obtained
characterize an increased reactivity of [1,2,5]thiadiazolo[3,4-
d]pyridazine in orbital-controlled ionic and radical reactions of
nucleophilic nature and in donor-acceptor interactions as well.
Cyclic voltammetry measurements were carried out in a dry argon
atmosphere using an IPC Pro potentiostat/galvanostat and a three-
electrode electrochemical cell. A three-electrode system consisting of
platinum or glass carbon as the working electrode, platinum wire as the
counter electrode and saturated calomel electrode (SCE) as the reference
electrode was employed. The reduction and oxidation potentials were
determined in DMF and CH3CN, using 0.1 M tetrabutylammonium
perchlorate (n-Bu4NClO4) as the supporting electrolyte. The first reduction
potentials are referenced to the internal standard redox couple Fc/Fc+.
Ferrocene was added to each sample solution at the end of the experiment,
and employed for calibration.
Conclusions
4,7-Dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine was synthesized
in good yield by treatment of 5,6-dihydro[1,2,5]thiadiazolo[3,4-
d]pyridazine-4,7-dione with PBr5. Nucleophilic aromatic
substitution and palladium catalyzed cross-coupling reactions in
4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine were successfully
used for the selective synthesis of various mono- and bis-
substituted derivatives, including functional and aryl(hetaryl)
substituents. Oxygen and nitrogen nucleophiles could selectively
form both mono- and bis-substituted derivatives. In the case of
thiols, the reaction cannot be stopped at the stage of mono-thiols,
and bis-thiols were isolated in high yields regardless of the
reaction conditions. Cross-coupling reactions should be
performed under anhydrous conditions due to the high hydrolytic
ability of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine. Suzuki-
Miyaura coupling was found to be useful for the preparation of
mono-aryl(hetaryl)thiadiazolopyridazines, whereas the Stille
reaction allowed us to prepare both mono- and bis-derivatives.
4,7-Dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine
(1).
5,6-
Dihydro[1,2,5]thiadiazolo[3,4-d]pyridazine-4,7-dione
3 (650 mg, 3.82
mmol) was added to PBr5 formed by addition of bromine (1.18 ml, 22.92
mmol) to PBr3 (2.16 ml, 22.92 mmol) at 0 °C. The mixture was stirred for 9
h at 105 °C. The resulting mixture was cooled to the room temperature,
poured into ice, washed with CCl4, extracted with CHCl3 (3×40ml) and
dried over MgSO4. The CHCl3 was evaporated under reduced pressure.
The residue was purified by column chromatography (silica gel Merck 60,
CH2Cl2) to give the title compound 1. Yield 845 mg (75%), yellow solid. Mp
= 199 – 200 °С. (Rf = 0.5, CH2Cl2 IR νmax (KBr, cm–1): 1369, 1361, 1343,
1257, 959, 863, 504. 13C NMR (75 MHz, CDCl3): δ 142.5, 149.6. HRMS
(ESI-TOF), m/z: calcd for С481Br2HN4S [M+H]+, 296.8262, found, 296.8269.
MS, m/z (%): 298 ([M+2]+, 22), 296 (M+, 49), 294 ([M-2]+, 28), 217 (27),
215 (28), 136 (52), 84 (67), 32 (100)
The organic layer was extracted with EtOAc (2×25ml) and dried over
MgSO4. The solvent was evaporated under reduced pressure. The residue
was purified by column chromatography (silica gel Merck 60, EtOAc) to
give 7-bromo[1,2,5]thiadiazolo[3,4-d]pyridazin-4(5H)-one 4. Yield 71 mg
(8%), orange solid. Mp = 222 – 224 °С. IR νmax (KBr, cm–1): 3189, 3147,
3073, 3030, 1691, 1669, 1450, 1419, 1289, 1157, 975, 859, 844, 675, 614,
508. (Rf = 0.12, CH2Cl2). 1H NMR (300 MHz, DMSO-d6): δ 13.22 (s, 1H).
13C NMR (75 MHz, DMSO-d6): δ 123.6, 150.5, 153.8, 156.8. HRMS (ESI-
TOF), m/z: calcd for C4H79BrN4OSNa [M + Na]+, 254.8947, found,
254.8939. MS (EI, 70eV), m/z (I, %): 235 ([M+2]+, 4), 234 ([M+1]+, 100),
233 (M+, 3), 232 ([M-1]+, 96), 177 (15), 125 (8), 46 (40).
The
electron-acceptor
properties
of
4,7-
dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine were confirmed by
cyclic voltammetry, based on its high reduction potential and
ЕLUMO and calculated electron affinities.
Experimental Section
General Information. The reagents were purchased from commercial
sources and used as received. 5,6-Dihydro[1,2,5]thiadiazolo[3,4-
d]pyridazine-4,7-dione (3)19 (for details see Supporting Information), (5-
(1,3-dioxolan-2-yl)thiophen-2-yl)boronic acid (5b),26 (9-hexyl-9H-carbazol-
3-yl)boronic acid (5d),27 (4-(diphenylamino)phenyl)boronic acid (5l),28 (4-
(p-tolyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl)boronic
(5m),29 (5-(1,3-dioxolan-2-yl)thiophen-2-yl)tributylstannane (8b),30 [2,2'-
bithiophen]-5-yltributylstannane (8j),31 tributyl(thiophen-3-yl)stannane
7-Bromo[1,2,5]thiadiazolo[3,4-d]pyridazin-4(5H)-one
(4).
5,6-
Dihydro[1,2,5]thiadiazolo[3,4-d]pyridazine-4,7-dione 3 (50 mg, 0.29 mmol)
was added to POBr3 (332 mg, 1.16 mmol) in 4 ml of dry DMF and the
reaction mixture was stirred for 6 h at 80 oC. The resulting mixture was
cooled to the room temperature, poured into ice, extracted with CHCl3
(3×40ml) and dried over MgSO4. The CHCl3 was evaporated under
reduced pressure. The residue was purified by column chromatography
acid
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10.1002/ejoc.201800961
European Journal of Organic Chemistry
FULL PAPER
(silica gel Merck 60, CH2Cl2) to give the title compound 1. Yield 25 mg
(30%), yellow solid. Then the water layer was extracted with EtOAc
(2×25ml) and dried over MgSO4. The solvent was evaporated under
reduced pressure. The residue was purified by column chromatography
(silica gel Merck 60, EtOAc) to give the title compound 4. Yield 27 mg
(40%). The water layer was evaporated under reduced pressure to give
compound 3. Yield 10 mg (20%).
4-(5-(1,3-Dioxolan-2-yl)thiophen-2-yl)-7-bromo[1,2,5]thiadiazolo[3,4-
d]pyridazine (6b). Yellow solid, 43 mg (58%, procedure A) or 52 mg (70%,
procedure C), Rf
=
0.2 (CH2Cl2). Mp
=
174
–
176 °С.
Eluent - CH2Cl2:hexane, 1:1 (v/v). IR νmax (KBr, cm–1): 2984, 2960, 2898,
2875, 1737, 1727, 1395, 1382, 1355, 1335, 1302, 1211, 1166, 1082, 1024,
967, 939, 865, 831, 788, 522. 1H NMR (300 MHz, CDCl3): δ 4.03 – 4.23
(m, 4H), 6.19 (s, 1H), 7.30 (d, J = 3.8 Hz, 1H), 8.56 (d, J = 3.8 Hz, 1H).13
C
NMR (75 MHz, CDCl3): δ 65.5, 100.0, 127.5, 133.5, 133.8, 136.9, 139.5,
147.2, 149.5, 149.7. HRMS (ESI-TOF), m/z: calcd for C11H879BrN4O2S2 [M
+ H]+, 370.9267, found, 370.9260. MS (EI, 70eV), m/z (I, %): 372 ([M+1]+,
15), 371 (M+, 8), 370 ([M-1]+, 12), 369 ([M-2]+, 10), 291 (25), 262 (100),
183 (30).
General procedure for the preparation of mono-substituted products
6 and bis-substituted products 7 under Suzuki coupling conditions
(Procedure A).
A
mixture of 4,7-dibromo[1,2,5]thiadiazolo[3,4-
d]pyridazine 1 (60 mg, 0.2 mmol), boronic acid 5(a-i, k) (0.4 mmol),
Cs2CO3 (130 mg, 0.4 mmol), Pd(PPh3)4 (34 mg, 15% mmol) in dry toluene
o
(4 ml) was degassed by argon and heated at 110 C in a sealed vial. On
4-Bromo-7-(furan-2-yl)[1,2,5]thiadiazolo[3,4-d]pyridazine (6c). Yellow
solid, 30 mg (53%, procedure A) or 36 mg (64%, procedure C), Rf = 0.2
(CH2Cl2). Mp = 169 – 171 °С. Eluent - CH2Cl2:hexane, 1:1 (v/v). IR νmax
(KBr, cm–1): 3096, 1574, 1490, 1342, 1230, 1209, 1018, 972, 866, 790,
643, 591, 511. 1H NMR (300 MHz, CDCl3): δ 6.77 (dd, J = 3.6, 1.7 Hz, 1H),
7.88 (d, J = 1.7 Hz, 1H), 8.03 (d, J = 3.6 Hz, 1H). 13C NMR (75 MHz,
CDCl3): δ 113.2, 119.4, 145.5, 147.0, 147.2, 147.7, 147.9, 148.9. HRMS
(ESI-TOF), m/z: calcd for C8H479BrN4OS [M + H]+, 282.9284, found,
282.9286. MS (EI, 70eV), m/z (I, %): 285 ([M+2]+, 10), 284 ([M+1]+, 70),
283 (M+, 8), 282 ([M-1]+, 67), 238 (100), 203(55).
completion (monitored by TLC), the mixture was poured into water and
extracted with CH2Cl2 (3×35ml). The combined organic layers were
washed with brine, dried over MgSO4, filtered, and concentrated under
reduced pressure. The crude product was purified by column
chromatography.
General procedure for the preparation of mono-substituted products
6 under Suzuki coupling conditions (Procedure B). A mixture of 4,7-
dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine 1 (60 mg, 0.2 mmol), boronic
acid 5(a-c, h, i, k) (0.2 mmol), Cs2CO3 (78 mg, 0.24 mmol), Pd(PPh3)4 (34
mg,15% mmol) in dry toluene (4 ml) was degassed by argon and heated
at 60 oC in a sealed vial. On completion (monitored by TLC), the mixture
was poured into water and extracted with CH2Cl2 (3×35ml). The combined
organic layers were washed with brine, dried over MgSO4, filtered, and
concentrated under reduced pressure. The crude product was purified by
column chromatography.
4-Bromo-7-(9-hexyl-9H-carbazol-3-yl)[1,2,5]thiadiazolo[3,4-d]pyridazine
(6d): Orange solid, 42 mg (45 %, procedure A), Rf = 0.4 (CH2Cl2). Mp =
129 – 131 °С. Eluent – CH2Cl2:hexane, 1:1 (v/v). IR νmax (KBr, cm–1): 2954,
2923, 2853, 1594, 1466, 1440, 1399, 1356, 1355, 1314, 1272, 1152, 960,
875, 810, 788, 745, 729, 661, 507. 1H NMR (300 MHz, CDCl3): δ 0.89 (t, J
= 6.9 Hz, 3H), 1.31 – 1.45 (m, 6H), 1.89 – 1.99 (m, 2H), 4.37 (t, J = 7.3 Hz,
2H), 7.32 (t, J = 7.3 Hz, 1H), 7.46 (d, J = 7.7 Hz, 1H), 7.51 (t, J = 7.3 Hz,
1H ), 7.57 (d, J = 8.8 Hz, 1H), 8.23 (d, J = 7.7 Hz, 1H), 8.85 (dd, J = 8.8
Hz, 1.5 Hz, 1H), 9.50 (d, J = 1.5 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ
14.1, 22.6, 27.0, 29.0, 31.6, 43.4, 109.2, 109.3, 119.9, 120.8, 123.2, 123.4,
123.5, 123.6, 126.4, 127.7, 139.2, 141.0, 142.6, 148.9, 150.7, 154.6.
HRMS (ESI-TOF), m/z: calcd for C22H2179BrN5S [M + H]+, 466.0696, found,
466.0684. MS (EI, 70eV), m/z (I, %): 468 ([M+2]+, 5), 467 ([M+1]+, 53), 466
(M+, 6), 465 ([M-1]+, 51), 396 (74), 205 (80), 179 (100).
General procedure for the preparation of mono-substituted products
6 under Stille coupling conditions (Procedure C). To a solution of 4,7-
dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine
1 (60 mg, 0.2 mmol) in
anhydrous THF (4 ml) were added PdCl2(PPh3)2 (21 mg, 15% mmol) and
stannane 8(a-c, h, i, k) (0.2 mmol). The resulting cloudy yellow mixture
was stirred and degassed by argon in a sealed vial. The resulting yellow
mixture was then stirred at 55 oC for the desired time. On completion
(monitored by TLC), the mixture was washed with water and the organic
layer was extracted with CH2Cl2 (3×35ml), dried over MgSO4 and then
concentrated in vacuo. The crude product was purified by column
chromatography.
4-Bromo-7-(9-(p-tolyl)-2,3,4,4a,9,9a-hexahydro-1H-carbazol-6-yl)-
[1,2,5]thiadiazolo[3,4-d]pyridazine (6e). Violet solid, 57 mg (60%,
procedure A), Rf = 0.4 (CH2Cl2). Mp = 53 – 55 °С. Eluent - CH2Cl2:hexane,
1:1 (v/v). IR νmax (KBr, cm–1): 2926, 2863, 1603, 1513, 1460, 1395, 1329,
1297, 1270, 1137, 1117, 1035, 873, 811, 794, 732, 509. 1H NMR (300 MHz,
CDCl3): δ 1.42 – 1.61 (m, 4H), 1.73 – 1.77 (m, 2H), 1.82 – 1.87 (m, 1H),
1.93 – 1.95 (m, 1H), 2.40 (s, 3H), 3.36 – 3.43 (m, 1H), 4.21 – 4.27 (m, 1H),
6.85 (d, J = 8.5 Hz, 1H), 7.21(d, J = 8.7 Hz, 2H), 7.25 (d, J = 8.7 Hz, 2H),
8.51 (s, 1H), 8.54 (dd, J = 8.5, 1.9 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ
21.02, 21.05, 22.4, 25.8, 27.8, 40.1, 64.9, 108.4, 122.9, 123.5, 124.7,
130.0, 131.4, 134.4, 135.5, 137.9, 139.1, 148.8, 150.5, 152.7, 153.7.
HRMS (ESI-TOF), m/z: calcd for C23H2179BrN5S [M + H]+, 478.0696, found,
478.0679. MS (EI, 70eV), m/z (I, %): 480 ([M+2]+, 25), 479 ([M+1]+, 98),
478 (M+, 28), 477 ([M-1]+, 100), 434 (75), 267 (45).
General procedure for the preparation of bis-substituted products 17
under Stille coupling conditions (Procedure D). To a solution of 4,7-
dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine
1 (60 mg, 0.2 mmol) in
anhydrous toluene (4 ml) were added PdCl2(PPh3)2 (21 mg, 15% mmol)
and stannane 8(a-c, f-k) (0.4 mmol). The resulting cloudy yellow mixture
was stirred and degassed by argon in a sealed vial. The resulting yellow
mixture was then stirred at 110 oC for the desired time. On completion
(monitored by TLC), the mixture was washed with water and the organic
layer was extracted with CH2Cl2 (3×35ml), dried over MgSO4 and then
concentrated in vacuo. The crude product was purified by column
chromatography.
4-Bromo-7-(p-tolyl)[1,2,5]thiadiazolo[3,4-d]pyridazine (6h). Yellow solid,
25 mg (41%, procedure B) or 25 mg (40%, procedure C), Rf = 0.35
(CH2Cl2). Mp = 139 – 141 °С. Eluent - CH2Cl2/hexane, 1:1 (v/v). IR νmax
(KBr, cm–1): 2955, 2854, 1466, 1415, 1395, 1327, 1283, 1192, 966, 877,
830, 790, 663, 574, 519. 1H NMR (300 MHz, CDCl3): δ 2.50 (s, 3H), 7.43
(d, J = 8.1 Hz, 2H), 8.55 (d, J = 8.1 Hz, 2H). 13C NMR (75 MHz, CDCl3): δ
21.7, 129.8, 130.1, 130.2, 140.4, 142.6, 148.8, 150.7, 154.3. HRMS (ESI-
TOF), m/z: calcd for C11H879BrN4S [M + H]+, 306.9648, found, 306.9646.
MS (EI, 70eV), m/z (I, %): 309 ([M+2]+, 5), 308 ([M+1]+, 25), 307 (M+, 6),
306 ([M-1]+, 20), 227 (100), 143 (60), 69 (98).
4-Bromo-7-(thiophen-2-yl)[1,2,5]thiadiazolo[3,4-d]pyridazine (6a). Yellow
solid, 36 mg (60%, procedure A) or 45 mg (75%, procedure C), Rf = 0.2
(CH2Cl2). Mp = 170 – 172 °С. Eluent - CH2Cl2:hexane, 1:1 (v/v). IR νmax
(KBr, cm–1): 3036, 1691, 1670, 1561, 1528, 1411, 1386, 1338, 1289, 1257,
1158, 976, 861, 839, 508. 1H NMR (300 MHz, CDCl3): δ 7.28 (dd, J = 5.2,
3.9 Hz, 1H), 7.70 (dd, J = 5.2 Hz, 1.0 Hz, 1H), 8.67 (dd, J = 3.9 Hz, 1.0 Hz,
1H). 13C NMR (75 MHz, CDCl3): δ 129.0, 132.6, 134.0, 136.5, 139.2, 147.2,
149.5, 149.8. HRMS (ESI-TOF), m/z: calcd for C8H479BrN4S2 [M + H]+,
298.9055, found, 298.9060. MS (EI, 70eV), m/z (I, %): 301 ([M+2]+, 16),
300([M+1]+, 45), 299 (M+, 15), 298 ([M-1]+, 48), 219 (100), 39 (55).
4-Bromo-7-(4-methoxyphenyl)[1,2,5]thiadiazolo[3,4-d]pyridazine
(6i).
Yellow solid, 32 mg (49%, procedure B) or 34 mg (52%, procedure C), Rf
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10.1002/ejoc.201800961
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FULL PAPER
= 0.25 (CH2Cl2). Mp = 158 – 160 °С. Eluent - CH2Cl2. IR νmax (KBr, cm–1):
2963, 2925, 2840, 1603, 1515, 1461, 1397, 1332, 1266, 1191, 1098, 1022,
880, 844, 801, 589, 525. 1H NMR (300 MHz, CDCl3): δ 3.94 (s, 3H), 7.12
(d, J = 8.0 Hz, 2H), 8.67 (d, J = 8.0 Hz, 2H). 13C NMR (75 MHz, CDCl3): δ
55.6, 114.5, 125.4, 131.8, 131.9, 139.8, 148.7, 153.6, 162.8. HRMS (ESI-
TOF), m/z: calcd for C11H879BrN4OS [M + H]+, 322.9597, found, 322.9603.
MS (EI, 70eV), m/z (I, %): 325 ([M+2]+, 6), 324 ([M+1]+, 10), 323 (M+, 8),
322 ([M-1]+, 11), 243 (100), 159 (72), 92 (55), 77 (98).
4,7-Di-p-tolyl[1,2,5]thiadiazolo[3,4-d]pyridazine (7h). Yellow solid, 32 mg
(50%, procedure A) or 35 mg (55%, procedure D), Rf = 0.3 (CH2Cl2). Mp =
193 – 195 °С. Eluent - CH2Cl2:hexane, 1:1 (v/v). IR νmax (KBr, cm–1): 2956,
2853, 1415, 1400, 1188, 886, 825, 721, 662, 609, 523. 1H NMR (300 MHz,
CDCl3): δ 2.51 (s, 6H), 7.44 (d, J = 8.1 Hz, 4H), 8.65 (d, J = 8.1 Hz, 4H).
13C NMR (75 MHz, CDCl3): δ 21.5, 129.5, 129.7, 131.3, 141.5, 149.7,
152.8. HRMS (EI-MS): calcd. for C18H15N4S 319.1012 [M + H]+, found
319.1008. MS, m/z (%): 320 ([M+2]+, 6), 319 ([M+1]+, 25), 318 (M+, 100),
168 (26), 91 (16).
4-Bromo-7-(thiophen-3-yl)[1,2,5]thiadiazolo[3,4-d]pyridazine (6k). Yellow
solid, 21 mg (54%, procedure B) or 41 mg (68%, procedure C), Rf = 0.2
(CH2Cl2). Mp = 135 – 137 °С. Eluent - CH2Cl2:hexane, 1:1 (v/v). IR νmax
(KBr, cm–1): 1515, 1455, 1433, 1262, 1100, 1029, 801.683, 509. 1H NMR
(300 MHz, CDCl3): δ 7.53 (dd, J = 5.2, 2.9 Hz, 1H), 8.31 (dd, J = 5.2, 1.3
Hz, 1H), 8.99 (dd, J = 3.0, 1.3 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ 126.6,
127.6, 132.1, 134.9, 139.7, 143.1, 148.3, 150.0. HRMS (ESI-TOF), m/z:
calcd for C8H479BrN4S2 [M + H]+, 298.9055, found, 298.9062. MS (EI,
70eV), m/z (I, %): 301 ([M+2]+, 10), 300 ([M+1]+, 100), 299 (M+, 8), 298
([M-1]+, 98), 219 (65), 135 (6), 28 (5).
4,7-Bis(4-methoxyphenyl)[1,2,5]thiadiazolo[3,4-d]pyridazine (7i). Orange
solid, 46 mg (65%, procedure A) or 47 mg (67%, procedure D), Rf = 0.1
(CH2Cl2). Mp = 210 – 212 °С. Eluent - CH2Cl2. The spectral data
correspond to the literature.33 1H NMR (300 MHz, CDCl3): δ 3.95 (s, 6H),
7.15 (d, J = 8.9 Hz, 4H), 8.78 (d, J = 8.9 Hz, 4H). 13C NMR (75 MHz,
CDCl3): δ 55.5, 114.3, 126.9, 131.5, 149.8, 152.0, 162.2. HRMS (ESI-TOF),
m/z: calcd for C18H15N4O2S [M + H]+, 351.0910, found, 351.0910. MS (EI,
70eV), m/z (I, %): 351, ([M+1]+, 22), 350 (M+, 100), 184 (48), 90 (30).
4,7-Di([2,2'-bithiophen]-5-yl)[1,2,5]thiadiazolo[3,4-d]pyridazine (7j). Red
solid, 61 mg (65%, procedure D), Rf = 0.4 (CH2Cl2). Mp = 178 – 180 °С.
Eluent - CH2Cl2:hexane, 1:1 (v/v). IR νmax (KBr, cm–1): 2923, 1510, 1447,
1366, 1346, 1335, 1295, 1268, 1257, 1227, 1162, 1062, 991, 963, 884,
864, 846, 836, 814, 787, 728, 709, 637, 534, 506. 1H NMR (300 MHz,
CDCl3): δ 7.12 (dd, J = 3.9, 3.5 Hz, 2H), 7.36 (d, J = 3.5 Hz, 2H), 7.37 (d,
J = 3.9 Hz, 2H), 7.42 (d, J = 3.5 Hz, 2H), 8.63 (d, J = 3.9 Hz, 2H). 13C NMR
(75 MHz, CDCl3): δ 120.7, 122.2, 122.5, 123.9, 124.1, 132.4, 135.5, 136.8,
139.7, 151.1. HRMS (ESI-TOF), m/z: calcd for C20H11N4S5 [M + H]+,
466.9582, found, 466.9578.
4,7-Di(thiophen-2-yl)[1,2,5]thiadiazolo[3,4-d]pyridazine (7a). Red solid, 48
mg (80%, procedure D) or 5 mg (8%, procedure A), Rf = 0.3 (CH2Cl2). Mp
= 193 – 195 °С. Eluent - CH2Cl2:hexane, 1:1 (v/v). ). IR νmax (KBr, cm–1):
3065, 1528, 1435, 1419, 1400, 1228, 1044, 847, 733, 718, 676, 652, 520.
1H NMR (300 MHz, CDCl3): δ 7.28 (dd, J = 4.9, 3.6 Hz, 2H), 7.65 (d, J =
4.9 Hz, 2H), 8.67 (d, J = 3.6 Hz, 2H). 13C NMR (75 MHz, CDCl3): δ 128.5,
131.3, 132.5, 138.1, 147.8, 148.2. HRMS (ESI-TOF), m/z: calcd for
C12H7N4S3 [M + H]+, 302.9827, found, 302.9831. MS (EI, 70eV), m/z (I, %):
304 ([M+2]+, 12), 303 ([M+1]+, 15), 302 (M+, 100), 109 (26), 45 (48).
4,7-Bis(5-(1,3-dioxolan-2-yl)thiophen-2-yl)[1,2,5]thiadiazolo[3,4-
4,7-Di(thiophen-3-yl)[1,2,5]thiadiazolo[3,4-d]pyridazine (7k). Orange solid,
11 mg (35%, procedure A) or 46 mg (76%, procedure D), Rf = 0.35
(CH2Cl2). Mp = 186 – 188 °С. Eluent - CH2Cl2:hexane, 1:1 (v/v). ). IR νmax
(KBr, cm–1): 3081, 1853, 1508, 1441, 1234, 1109, 1078, 951, 864, 798,
690, 617, 512. 1H NMR (300 MHz, CDCl3): δ 7.54 (dd, J = 5.1, 3.0 Hz, 2H),
8.41 (d, J = 5.1 Hz, 2H), 9.01 (d, J = 3.0 Hz, 2H). 13C NMR (75 MHz,
CDCl3): δ 126.1, 127.4, 130.7, 136.0, 148.5, 149.0. HRMS (ESI-TOF), m/z:
calcd for C12H7N4S3 [M + H]+, 302.9827, found, 302.9822. MS (EI, 70eV),
m/z (I, %): 302 (M+, 100), 301 ([M+1]+, 15), 302 ([M+2]+, 8), 185 (20), 149
(12)..
d]pyridazine (7b). Orange solid, 66 mg (74%, procedure D) or 3 mg (4%,
procedure A), Rf = 0.1 (CH2Cl2). Mp = 168 – 170 °С. Eluent - CH2Cl2:EtOAc,
1:1 (v/v). IR νmax (KBr, cm–1): 2955, 2924, 2854, 1662, 1542, 1525, 1476,
1459, 1402, 1387, 1329, 1298, 1206, 1151, 1082, 1067, 1034, 970, 940,
882, 864, 855, 819, 800, 678, 656, 525. 1H NMR (300 MHz, CDCl3): δ 4.04
– 4.24 (m, 8H), 6.22 (s, 2H), 7.31 (d, J = 3.9 Hz, 2H), 8.57 (d, J = 3.9 Hz,
2H). 13C NMR (75 MHz, CDCl3): δ 65.4, 100.2, 127.3, 132.5, 138.5, 147.9,
148.3, 148.3. HRMS (ESI-TOF), m/z: calcd for C18H15N4O4S3 [M + H]+,
447.0250, found, 447.0252. MS (EI, 70eV), m/z (I, %): 447 ([M+1]+, 5), 446
(M+, 25), 445 ([M-1]+, 3), 120 (35), 73 (55), 45 (100).
4,7-Di(furan-2-yl)[1,2,5]thiadiazolo[3,4-d]pyridazine (7c). Orange solid, 31
mg (57%, procedure D), Rf = 0.1 (CH2Cl2). Mp = 112 – 114 °С.
Eluent - CH2Cl2:EtOAc, 1:1 (v/v). IR νmax (KBr, cm–1): 3102, 1578, 1486,
1460, 1389, 1267, 1058, 1017, 976, 870, 594, 515. 1H NMR (300 MHz,
CDCl3): δ 6.76 (dd, J = 3.6, 1.7 Hz, 2H), 7.87 (d, J = 1.7 Hz, 2H), 7.99 (d,
J = 3.6 Hz, 2H). 13C NMR (75 MHz, CDCl3): δ 112.9, 118.0, 144.3, 146.6,
147.3, 148.3. HRMS (ESI-TOF) , m/z: calcd for C12H7N4O2S [M + H]+,
271.0284, found, 271.0280. MS (EI, 70eV), m/z (I, %): 272 ([M+2]+, 10),
271 ([M+1]+, 25), 270 (M+, 100), 149 (12), 57 (8).
Acknowledgements
We gratefully acknowledge financial support from the Russian
Science Foundation (grant no. 15-13-10022). Authors are grateful
to Dr. E. A. Chulanova for conducting preliminary calculations,
and to Professor A. S. Mendkovich for valuable advices.
Keywords: [1,2,5]thiadiazolo[3,4-d]pyridazine; cross-coupling;
4,7-Diphenyl[1,2,5]thiadiazolo[3,4-d]pyridazine (7f). Yellow solid, 20 mg
(35%, procedure A) or 19 mg (32%, procedure D), Rf = 0.35 (CH2Cl2). Mp
= 207 – 208 °С. Eluent - CH2Cl2/hexane, 1:1 (v/v). The spectral data
correspond to the literature.35 HRMS (ESI-TOF), m/z: calcd. for C16H11N4S
291.0699 [M + H]+, found 291.0697.
palladium
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10.1002/ejoc.201800961
European Journal of Organic Chemistry
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10.1002/ejoc.201800961
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FULL PAPER
Introduction
[1,2,5]Thiadiazolo[3,4-d]pyridazine
Results and discussion
Conclusions
Timofey N. Chmovzh, Ekaterina A.
Knyazeva, Ludmila V. Mikhalchenko,
Ivan S. Golovanov, Stanislav A.
Amelichev, Oleg A. Rakitin*
Experimental section
Acknowledgments
References
Page No. – Page No.
Synthesis of 4,7-dibromo derivative
of
ultrahigh
electron-deficient
[1,2,5]thiadiazolo[3,4-d]pyridazine
heterocycle and its cross-coupling
reactions
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