Synthesis, DFT calculations, cyclic voltammetry and antibacterial activities of a new blue-violet dye and a new blue-green fluorescent heterocyclic system

Article abstract of DOI:10.1016/j.tetlet.2014.10.118

The new blue-violet dye 2-(3-hydroxyimino-2,3-dihydroimidazo[1,2-a]pyridin-2-yliden)-2-(2-thienyl)acetonitrile was prepared in high yield from the reaction of 3-nitroimidazo[1,2-a]pyridine with 2-(2-thienyl)acetonitrile by nucleophilic substitution of hydrogen. Acylation of the hydroxyl group led to a new heterocyclic system, (pyrido[2′,1′:2,3] imidazo[4,5-b]thieno[2,3-e]pyridine-11-carbonitrile) with very strong blue-green fluorescent properties. Physical, spectral and analytical data have confirmed the structures of the synthesized dyes. The optical and solvatochromic properties of these compounds were investigated and showed interesting photophysical properties. Density functional theory calculations of blue-violet and fluorescent dyes were performed to provide the optimized geometries, Mulliken atomic charges, relevant frontier orbitals and the prediction of ¹H NMR chemical shifts. The electrochemical properties of these dyes were investigated by cyclic voltammetry and an oxidation wave was observed at a half-wave potential of -0.143 V versus SCE for the blue-violet dye. Also, these new compounds exhibited potent antibacterial activity against Gram positive and negative bacterial species.

Full text of DOI:10.1016/j.tetlet.2014.10.118

Tetrahedron Letters 55 (2014) 6925–6930
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis, DFT calculations, cyclic voltammetry and antibacterial
activities of a new blue-violet dye and a new blue-green fluorescent
heterocyclic system
⇑
Mozhgan Mazloum Farsi Baf, Mehdi Pordel , Leila Rezaei Daghigh
Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The new blue-violet dye 2-(3-hydroxyimino-2,3-dihydroimidazo[1,2-a]pyridin-2-yliden)-2-(2-thie-
nyl)acetonitrile was prepared in high yield from the reaction of 3-nitroimidazo[1,2-a]pyridine with 2-
Received 14 April 2014
Revised 3 October 2014
Accepted 22 October 2014
Available online 28 October 2014
(
2-thienyl)acetonitrile by nucleophilic substitution of hydrogen. Acylation of the hydroxyl group led to
0
0
a new heterocyclic system, (pyrido[2 ,1 :2,3] imidazo[4,5-b]thieno[2,3-e]pyridine-11-carbonitrile) with
very strong blue-green fluorescent properties. Physical, spectral and analytical data have confirmed the
structures of the synthesized dyes. The optical and solvatochromic properties of these compounds were
investigated and showed interesting photophysical properties. Density functional theory calculations of
blue-violet and fluorescent dyes were performed to provide the optimized geometries, Mulliken atomic
Keywords:
3
-Nitroimidazo[1,2-a]pyridine
Density functional theory
Cyclic voltammetry
1
charges, relevant frontier orbitals and the prediction of H NMR chemical shifts. The electrochemical
properties of these dyes were investigated by cyclic voltammetry and an oxidation wave was observed
at a half-wave potential of ꢀ0.143 V versus SCE for the blue-violet dye. Also, these new compounds
exhibited potent antibacterial activity against Gram positive and negative bacterial species.
Ó 2014 Elsevier Ltd. All rights reserved.
Fluorescence
Emission and absorption spectra
1
Solvent dyes can be found among azo, disperse, anthraquinone,
cationic, phthalocyanine dyes, etc. The only common characteristic
is a chemical structure devoid of sulfonic and carboxylic groups,
except for cationic dyes as salts with an organic base as the anion.
Solvent dyes function as colourants for certain polymers, such as
polyacrylonitrile, polystyrene, polymath acrylates and polyester,
in which they are soluble. Many relatively simple amino and
hydroxyanthraquinone derivatives show a high degree of order
in liquid-crystalline systems and are therefore suitable as dichroic
dyes for host–guest displays. Several new dyes for this application
Taking this body of research into consideration and in continu-
ation of our studies on the synthesis of new solvent dyes and nitro-
gen and sulfur–nitrogen fluorescent heterocyclic compounds,9
we have synthesized a new blue-violet dye, 2-(3-hydroxyimino-
2,3-dihydroimidazo[1,2-a]pyridin-2-yliden)-2-(2-thienyl)acetonitrile,
–14
1
5
via nucleophilic substitution of hydrogen, and a new blue-green
0
0
sulfur–nitrogen fluorescent heterocyclic system, pyrido[2 ,1 :2,
3]imidazo[4,5-b]thieno[2,3-e]pyridine-11-carbonitrile, in excellent
yields. DFT calculations and cyclic voltammetry analysis were
performed and the antibacterial activities of these dyes were also
studied.
2
have been described.
On the other hand, fluorescent heterocyclic compounds are of
particular interest, because they exhibit unique electrical and opti-
Synthesis and structures of new compounds 3 and 4
3
cal properties such as emitters for electroluminescence devices,
4
molecular probes for biochemical research, in traditional textile
The precursor of 3-nitroimidazo[1,2-a]pyridine 1 was obtained
in two steps from the reaction of 2-aminopyridine with 2-bromo-
5
6
and polymer fields, fluorescent whitening agents and photocon-
7
ducting materials. Also, interest has been rapidly growing in gain-
1
2 4 3
,1-dimethoxyethane. Nitration in H SO and HNO was achieved
1
6
ing insight into the properties and transformations of the family of
sulfur–nitrogen heterocycles. The physicochemical properties of
these compounds have relevance in the design of new materials,
especially organic conductors.8
by adopting a literature method. When 3-nitroimidazo[1,2-a]
pyridine (1) and 2-(2-thienyl)acetonitrile (2) were reacted in basic
MeOH solution, 2-(3-hydroxyimino-2,3-dihydroimidazo[1,2-a]
pyridin-2-yliden)-2-(2-thienyl)acetonitrile (3) was obtained in
excellent yield via nucleophilic substitution of hydrogen15
(Scheme 1). In this reaction, no heterocyclization occurred at room
temperature or under long reflux conditions, in contrast to most of
⇑
Corresponding author. Tel.: +98 511 841 4182; fax: +98 511 842 4020.
E-mail address: mehdipordel58@mshdiau.ac.ir (M. Pordel).
http://dx.doi.org/10.1016/j.tetlet.2014.10.118
040-4039/Ó 2014 Elsevier Ltd. All rights reserved.
0

6
926
M. M. F. Baf et al. / Tetrahedron Letters 55 (2014) 6925–6930
Br
S
1
. HCl, reflux
CH CN
2
3 2 4
HNO , H SO
+
O
2. NaHCO , 22 h reflux
3
N
N
N
N
N
NH
2
O
1,4-dioxane, H O
2
2
2
O N
KOH, MeOH
2 h, reflux
pyridin-2-amine
2-bromo-1,1-
dimethoxyethane
imidazo[1,2-a]pyridine
1
CN
S
N
CN
N
CN
N
CN
6
π
AcCl, pyridine
N
N
N
N
N
S
-
HOAc
8 h, reflux
S
S
N
N
N
N
HO
AcO
AcO
H
3
4
Scheme 1. Synthesis of new blue-violet dye 3 and fluorescent dye 4.
In the next step, conversion of the hydroxyl group of 3 into a
better leaving group by acylation with acetyl chloride in pyridine
led to heterocyclization and the formation of the new sulfur–
N
N
N
0
0
N
nitrogen heterocyclic system, pyrido[2 ,1 :2,3]imidazo [4,5-b]thie-
N
Tautomerization
H
3
O
CN
no[2,3-e]pyridine-11-carbonitrile, (4) via an electrocyclic pathway
-
2
H O
O
N
CN
9
(
Scheme 1). The probable mechanism for this transformation is
O
S
also shown in Scheme 1. Structural assignments of compound 4
were based on its spectral and microanalytical (C, H and N) data
S
(
Supporting information). The FT-IR spectrum of 4 in KBr showed
ꢀ1
Scheme 2. The reaction mechanism for the formation of 3.
an absorption band at 2225 cm
corresponding to the cyano
group. This evidence in conjunction with the molecular ion peak
+
at m/z 250 (M ) strongly supports the fused tetracyclic structure
our own previous research (in which the heterocyclization occurred
in a one-pot reaction and pyrazolo or imidazo acridines were
of compound 4.
10–13
obtained at room temperature),
and that of Davis in which
the heterocyclization led to the formation of isoxazoles.17 This phe-
nomenon had also been observed in the reaction of 5-nitroindazole
and 3-nitroimidazo[1,2-a]pyridine with different substituted aryl
acetonitriles under reflux conditions, in which the main products
were uncyclized green or violet dyes.9,14 Also, the structure of the
intermediate 3 could be deduced from the similar structure estab-
lished by DFT calculations previously.14 Thus, it can be concluded
that all nitroarenes on treatment with aryl acetonitriles, do not
react exactly in the same way, and that these reactions are depen-
dent on the nitroarenes, aryl acetonitriles and the conditions (tem-
perature, concentration of base and reaction time). A plausible
mechanism to explain the formation of 3 is shown in Scheme 2.
The initial steps follow those proposed for the condensation of 1
and 2 in basic MeOH solution.9
Photophysical properties of 3 and 4
Visible absorption spectra of 3 and 4 in different solvents were
obtained in the range of 200–1000 nm. Figure 1 shows the visible
absorption spectrum of blue-violet dye 3 and blue-green fluores-
ꢀ6
ꢀ1
cent 4 at concentrations of 5 ꢁ 10 mol L in different solvents.
Characteristics of the absorption spectra of 3 and 4 are presented
in Table 1. The extinction coefficients (e) calculated as the slope
of the plot of absorbance vs concentration are very high.
As depicted in Scheme 3, there are efficient intramolecular
charge transfer (ICT) states from the donor sites (OH group and
endocyclic N) to the acceptor moiety (CN group) in dye 3, which
are manifested in the absorption spectra in the visible (blue-violet)
area.
,14
In the spectral data of 3, the presence of one exchangeable peak
The visible absorption spectra of dye 3 at different pH values
showed that the absorbance of compound 3 increases as hydrogen
is removed from the hydroxyl group, which is a stronger donor site
in basic medium (pH >7). On the other hand, protonation of the
1
ꢀ1
at d 9.75 (OH) in the H NMR spectrum, weak 2202 cm (CN) and
ꢀ1
broad 3455 cm (OH) absorption bands in the FT-IR spectrum and
+
a molecular ion peak at m/z 268 (M ) confirmed the structure of 3.
ꢀ
6
ꢀ1
Figure 1. (a) Visible absorption spectra of compounds 3 and 4 in different solvents (5 ꢁ 10 mol L ). (b) Visible absorption spectra of 3 in H
2
O–MeOH (95:5) at different pH
values (2 ꢁ 10ꢀ mol L ).
6
ꢀ1

M. M. F. Baf et al. / Tetrahedron Letters 55 (2014) 6925–6930
6927
Table 1
Spectroscopic data for dyes 3 and 4 at 298 K in different solvents
Dye
Solvent
3
3
e
4
4
e
a
ꢁ 10ꢀ4 (L mol cm )b
ꢀ1
ꢀ1
a
ꢁ 10ꢀ4 (L mol cm )b
ꢀ1
ꢀ1
kabs (nm)
k
abs (nm)
MeOH
DMF
THF
541, 585
538, 581
535, 580
533, 580
531, 580
523, 570
19.4
14.6
15.0
14.0
12.0
11.9
420, 445
420, 440
415, 435
412, 432
412, 430
410, 430
18.4
18.2
15.6
15.0
14.5
14.2
EtOAc
1
,4-Dioxane
Toluene
a
Wavelengths of maximum absorbance.
Extinction coefficient.
b
N
N
N
N
N
C
N
C
N
C
N
C
N
N
N
N
S
S
S
S
N
N
N
N
HO
HO
HO
HO
3
A
3
B
Scheme 3. Neutral and charge-separated mesomeric structures of compound 3.
fluorescein as a standard sample in 0.1 M NaOH and MeOH solu-
1
8
tion. The emission quantum yield (
This value for 4 is one of the highest among the fluorescent
heterocyclic compounds that we have previously synthesized.
F
U ) of the dye 4 is 0.94.
U
F
9–13
A comparison between some of these and compound 4 in terms
of the wavelength of fluorescence emission (in chloroform) and
the quantum yield can be found in the Supporting information.
The intramolecular charge transfer (ICT) states from the donor
endocyclic nitrogen and sulfur to the acceptor CN group can be
considered as the main reason for the fluorescence intensity of
9
–13
blue-green fluorescent 4.
In Scheme 4, neutral and charge-sep-
arated mesomeric structures of compound 4 are presented.
The solvatochromic properties of compounds 3 and 4 were
deduced from Figures 1 and 2. The visible absorption spectra of 3
and fluorescence absorption and emission spectra of 4 in polar sol-
vents undergo a relatively modest red shift. Increasing the solvent
polarity stabilizes the ICT excited-state molecule relative to the
ground-state molecule with the observed red shift of the absorp-
tion maximum as the experimentally observed result (Tables 1
and 2). For example, in the absorption spectra of compound 4, kabs
shifts from 410 to 420 nm as the solvent changes from toluene to
methanol (Table 1).
Figure 2. Emission spectra of compound 4 in different solvents.
five-membered ring nitrogen in acidic medium leads to a decrease
in the absorbance of compound 3 (Fig. 1). The absorbance of com-
pound 3 at higher or lower pH (pH >11 and pH <1.8) remains sub-
stantially unchanged.
The fluorescence spectra of 4 were measured at concentrations
ꢀ7
ꢀ1
Theoretical calculations
of 5 ꢁ 10 mol L in different solvents. Figure 2 shows the emis-
sion spectra of compound 4 and the data are presented in Table 2.
The fluorescence excitation (kex) wavelength at 400 nm (kex /nm)
was used for compound 4. The fluorescence quantum yield (U )
F
of compound 4 was determined via comparison methods, using
We performed DFT calculations at the B3LYP/6-311+G(d,p) level
in order to obtain the optimized geometries, Mulliken atomic
charges, calculated chemical shifts (d) and HOMO and LUMO fron-
tier orbitals of 3 and 4. The optimized geometries of compounds 3
and 4 are shown in Figure 3. The C@C bond lengths (1.36–1.46 Å) of
the aromatic rings are in the expected range, and all of these
rings and the cyano group are essentially planar in dyes 3 and 4.
Tables with calculated bonds and Mulliken charges can be found
in the Supporting information. The DFT calculated chemical shifts
1
9
Table 2
Spectroscopic data for compound 4 at 298 K in different solvents
a
b
Solvent
k
ex (nm)
kem (nm)
MeOH
DMF
MeCN
400
400
400
400
400
400
480
(d) of compound 4 (Table 3) are in good agreement with the exper-
462, 485
456, 480
450, 480
450, 478
446, 475
imental values, confirming the validity of the optimized geometry
of the structure of 4.
The energy difference between the HOMO and LUMO frontier
orbitals is one of the important characteristics of molecules, which
has a determining role in such cases as electric properties, elec-
tronic spectra and photochemical reactions. The HOMO and LUMO
CHCl
,4-Dioxane
Toluene
3
1
a
Wavelength of fluorescence excitation.
Wavelength of fluorescence emission.
b

6
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M. M. F. Baf et al. / Tetrahedron Letters 55 (2014) 6925–6930
N
C
N
C
N
C
N
C
N
N
S
N
N
S
N
N
S
N
N
S
N
N
N
N
4
4
Scheme 4. Resonance structures of 4.
Figure 3. Optimized geometries of the synthesized dyes.
lower than in dye 5. This implies that the energy levels of the
HOMO in compound 3 are higher than those of compound 5
because of the higher electron density in the thiophene ring com-
pared to the benzene ring (Fig. 4). However, the Ph ring in 5 is tilted
by ortho-repulsion with respect to the rest of the molecule so that
Table 3
DFT calculated and experimental 1H NMR chemical shifts of compound 4
Atom
number
Chemical shift
calcd
Exp. Atom
number
chemical shift
calcd
Exp.
H20
H21
H24
9.26
7.93
7.90
8.95 H23
7.91 H22
7.92 H19
7.88
7.72
7.06
7.76
7.72
7.13
the overlap of its
p-system is less efficient than that of the thio-
phene fragment, which makes their comparison less grounded.
The TD-DFT electronic spectra calculations on 3 show that there
are two electronic transition bands: a relatively sharp peak at
⁄
3
75 nm (oscillator strength: 0.2833), which can be linked to p–p
maps of 3 and 4 are shown in Figure 4. Separation energies
between the HOMO and LUMO ( HOMO) in the dyes
and 4 are 2.43 and 3.40 eV, respectively. The role of the thio-
phene ring on the of dye 3 can be analysed by comparing the
estimated energies of the HOMO and LUMO levels in compound
(2.43 eV) with the structurally related dye 5 (2.68 eV), which
transitions (donor endocyclic nitrogen to the acceptor CN group),
and a broad band in the range of 450 to 700 nm with an oscillator
strength of 0.3625 at 568 nm, compared with the experimental
D
e
=
e
LUMO
ꢀ
e
3
D
e
values of 470–650 nm. The latter peak located in the visible light
⁄
range can be attributed to n–
p
transitions from the donor OH
3
group to the acceptor CN group in 3. Also, the TD-DFT electronic
spectra calculations on 4 show two bands in the range of
9
we had previously synthesized (Fig. 4). The results show that
the separation energy between the HOMO and LUMO in dye 3 is
3
10–500 nm which correspond to the experimental data
Figure 4. The HOMO and LUMO frontier orbitals of compounds 3, 4 and 5.

M. M. F. Baf et al. / Tetrahedron Letters 55 (2014) 6925–6930
6929
ꢀ
4
ꢀ1
Figure 5. (A) Cyclic voltammogram of dye 3 (1 ꢁ 10 mol L ) in MeCN at a scan rate of 100 mV/s; (B) cyclic voltammogram of: (a) TBAP (supporting electrolyte) in MeCN
ꢀ
1
ꢀ4
ꢀ1
(
0.1 mol L ) at a scan rate of 100 mV/s and dye 3 (10 mol L ) in TBAP at scan rates: (b) 100, (c) 300, (d) 500, (e) 700 mV/s.
Investigation of the electrochemical properties of the fluoro-
N
N
phore 4 upon scanning the potential from ꢀ1 to +1 V showed an
irreversible oxidation wave at a half-wave potential of 0.254 V ver-
sus SCE.
N
C
N
C
N
- e
N
S
S
N
N
Antibacterial studies
HO
HO
3
A
The antibacterial activity of new products 3 and 4 was tested
against a panel of strains of Gram positive Staphylococcus aureus
methicillin resistant S. aureus (MRSA) clinical isolated and Bacillus
subtilis (ATCC 6633), and Gram negative Pseudomonas aeruginosa
(ATCC 27853) and Escherichia coli, (ATCC 25922) species (Table 5),
Scheme 5. Radical cation formation of the dye 3 at the anode.
(
3
370–470 nm) with oscillator strengths of 0.0913 and 0.1542 at
38 and 416 nm, respectively. These bands can be linked to
⁄
20
p–p
using the broth microdilution method as previously described.
transitions from the donor endocyclic nitrogen and sulfur to the
acceptor CN group. The calculated electronic absorption spectra
of compounds 3 and 4 are shown in the Supporting information.
Ampicillin, penicillin G and sulfamethoxazole were used as refer-
ences. The lowest concentration of the antibacterial agent that pre-
vented growth of the test organism, as detected by a lack of visual
turbidity (matching the negative growth control), is designated the
minimum inhibitory concentration (MIC). Experimental details of
Electrochemical properties
2
1
the tests can be found in our earlier study.
The antimicrobial tests performed on compounds 3 and 4 con-
firmed that only compound 4 was effective against both Gram-
positive and Gram-negative bacteria, and 3 showed inhibitory
activity against Gram-negative bacteria only. Also, the results
revealed that new compound 4 displayed greater antibacterial
activity against the tested organisms compared to the well-known
antibacterial agents ampicillin and sulfamethoxazole in most cases
Cyclic voltammetry with acetonitrile as the solvent in the pres-
ence of tetrabutylammonium perchlorate (TBAP) as the supporting
electrolyte, using Pt working and counter electrodes and Ag/AgCl
as reference electrode, was applied to investigate the electrochem-
ical properties of compounds 3 and 4.
Upon scanning the potential from ꢀ1 to +1 V, an oxidation wave
was observed with an anodic peak potential of ꢀ0.143 V and a
cathodic peak potential of ꢀ0.260 V versus SCE (ipa/ipc ꢂ1) in dye
(Table 5).
In conclusion, we have synthesized a new donor–acceptor blue-
3
(Fig. 5). This wave can be attributed to the formation of the rad-
violet solvent dye 3 and a new blue-green fluorescent heterocyclic
system 4 in excellent yields, which both demonstrate interesting
optical properties including high extinction coefficients and a very
high quantum yield (in fluorophore 4). Density functional theory
calculations were performed to gain a deeper insight into the
charge transfer properties and optimized geometries by using the
B3LYP hybrid functional and the 6-311+G(d,p) basis set. The results
showed that the geometry of the new fluorophore 4 was rigid and
ical cation A (Scheme 5). The observed peak separation for the
reversible waves was larger than the value of 59/n mV expected
for a reversible system, suggesting that the redox couple has a
quasi-reversible behaviour. Scan rate studies (Fig. 5) showed that
the anodic and cathodic peak currents (ipa, ipc) of the oxidation
1
/2
wave were proportional to the square root of the scan rate (
t
)
indicating diffusion control (Supporting information). The results
are shown in Table 4.
Table 4
Cyclic voltammetric data of dye 3 at scan rates of 100–700 mV/s
Table 5
Antibacterial activity (MIC,
ꢀ
l
g mL 1) of dyes 3 and 4 and the reference compounds
0
Compound Scan rate (mV/
s)
Epa
(mV)
Epc
(mV)
D
(mV)
EP
E0
(mV)
Compound
MRSA
ATCC 6633
ATCC 27853
ATCC 25922
Ferrocene
100
100
300
500
700
559
ꢀ143
ꢀ144
ꢀ143
ꢀ144
473
ꢀ260
ꢀ262
ꢀ261
ꢀ261
86
117
118
118
117
516
ꢀ202
ꢀ203
ꢀ202
ꢀ203
3
4
250
10
62
0.06
16
150
4
0.50
8
15
8
125
—
10
5
8
—
16
3
3
3
3
Ampicillin
Penicillin G
Sulfamethoxazole
16
62

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930
M. M. F. Baf et al. / Tetrahedron Letters 55 (2014) 6925–6930
ꢀ
1
(CN). 1H NMR
planar and the separation energies between the HOMO and LUMO
in dyes 3 and 4 were 2.43 and 3.40 eV, respectively. Cyclic voltam-
metry analysis was accomplished for more efficient characteriza-
tion and electrochemical studies of these dyes. The high
antibacterial activity together with unique optical properties of
compound 4 offers an excellent opportunity for the study of phys-
iological functions of bacteria at single-cell level.22 Further investi-
gation into the scope and application of these new dyes such as in
solar cells is in progress and will be reported soon.
(78%), mp 329–331 °C; IR (KBr):
(400 MHz, CDCl ) d 7.13 (1H, td, J
d, J = 5.6 Hz), 7.76 (1H, td, J
m
2225 cm
3
1
= 6.8 Hz, J
= 6.4 Hz, J
2
= 0.8 Hz), 7.72 (1H,
= 1.2 Hz), 7.91–7.93 (2H,
m), 8.95 (1H, d, J = 6.8 Hz); C NMR (100 MHz, CDCl ): d 111.9,
117.6, 117.7, 118.1, 118.5, 123.5, 124.0, 124.3, 124.4, 124.8,
125.2, 130.7, 133.9; El MS (m/z) 250 (M ). Anal. Calcd for
13 6 4
C H N S (250.3): C, 62.39; H, 2.42; N, 22.39; S, 12.81, Found: C,
1
1
2
3
3
+
62.11; H, 2.38; N, 22.18; S, 13.08.
Supplementary data
Synthesis of 3 from 1 and 2
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.tetlet.2014.
10.118.
To a solution of KOH (20 g, 357 mmol) in MeOH (50 mL), 1
(
1.63 g, 10 mmol) and 2 (1.48 g, 12 mmol) were added with stir-
ring. The mixture was refluxed with stirring for 2 h, and then
poured into H O. After neutralization with dilute HCl, the precipi-
tate was collected by filtration, washed with H O and then air-
2
References and notes
2
1.
Colour Index International. Pigments and Solvent Dyes; The Society of Dyers
and Colourists; Bradford, UK. 4th ed. online, 2002.
dried to give crude 3. Purification was achieved by crystallization
from n-hexane-EtOAc (50:50).
2.
Seki, H.; Uchida, T.; Shibata, Y. Mol. Cryst. Liq. Cryst. 1986, 138, 349.
2
-(3-Hydroxyimino-2,3-dihydroimidazo[1,2-a]pyridin-2-yliden)-
3. Hunger, K. Industrial Dyes; WILEY-VCH: Weinheim, Germany, 2003; pp 569–
72.
4. Dmitry, A.; Pavel, A. Chem. Commun. 2003, 1394.
5
2
-(2-thienyl)acetonitrile (3) was obtained as dark red powder,
yield (90%), mp 185–187 °C; IR (KBr): 3455 cm
202 cm
= 7.2 Hz, J
= 1.6 Hz), 7.42 (1H, dd, J
ꢀ1
(OH),
5
6
7
.
.
.
Gold, H. In The Chemistry of Synthetic Dyes; Venkataraman, H., Ed.; Academic
Press: Pergamon New York, 1971; pp 535–542.
Belgodere, E.; Bossio, R.; Chimichi, S.; Passini, V.; Pepino, R. Dyes Pigm. 1985, 4,
ꢀ1
1
2
(CN); H NMR (400 MHz, CDCl
= 1.2 Hz), 7.04–7.09 (2H, m), 7.35 (1H, td, J
= 4.8 Hz, J = 0.8 Hz), 7.55 (1H, d,
3
) d 6.37 (1H, td,
J
J
1
2
1
= 5.2 Hz,
59.
2
1
2
Kalle, A. G. British Patent, 895(001), Chem. Abstr. 1962, 57, 14578.
13
J = 5.2 Hz), 8.91 (1H, d, J = 7.2 Hz), 9.75 (1H, br s); C NMR
100 MHz, CDCl ): d 112.4, 116.7, 117.4, 124.2, 126.0, 127.0,
27.8, 128.2, 131.7, 135.1, 143.0, 144.3, 148.9; El MS (m/z) 268
8. Cava, M. P.; Lakshmikantham, M. V.; Hoffmann, R.; Williams, R. M. Tetrahedron
2011, 67, 6771.
(
1
(
3
9. Rahimizadeh, M.; Pordel, M.; Bakavoli, M.; Eshghi, H. Dyes Pigm. 2010, 86, 266.
1
1
0. Sahraei, R.; Pordel, M.; Behmadi, H.; Razavi, B. J. Lumin. 2013, 136, 334.
1. Pakjoo, V.; Roshani, M.; Pordel, M.; Hoseini, T. Arkivoc 2012, ix, 195.
+
M ). Anal. Calcd for C13
8 4
H N OS (268.3): C, 58.20; H, 3.01; N,
2
0.88; S, 11.95, Found: C, 57.91; H, 2.96; N, 20.61; S, 12.23.
12. Pordel, M. J. Chem. Res. 2012, 595.
3. Rahimizadeh, M.; Pordel, M.; Ranaei, M.; Bakavoli, M. J. Heterocycl. Chem. 2012,
9, 208.
14. Pordel, M.; Beyramabadi, S. A.; Mohammadinejad, A. Dyes Pigm. 2014, 102, 46.
1
4
Synthesis of 4 from 3
1
1
1
5. M a˛ kosza, M.; Wojciechowski, K. Chem. Rev. 2004, 104, 2631.
6. Paolini, J. P.; Robins, R. K. J. Org. Chem. 1965, 30, 4085.
7. Davis, R. B.; Pizzini, L. C. J. Org. Chem. 1884, 1960, 25.
AcCl (0.47 g, 6 mmol) was added with stirring to a solution of
the 3 (1.1 g, 4 mmol) in dry pyridine (30 mL) and the mixture
was refluxed for 8 h. The pyridine was evaporated under reduced
pressure and the resulting solid residue was refluxed in EtOH
18. Umberger, J. Q.; LaMer, V. K. J. Am. Chem. Soc. 1945, 67, 1099.
1
2
9. Dal, H.; Süzen, Y.; Sß ahin, E. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2007,
6
7, 808.
0. Sztaricskai, F.; Pintér, G.; Röth, E.; Herczegh, P.; Kardos, S.; Rozgonyi, F.; Boda, Z.
and H
2
O (50:50) for 5 min. The precipitated solid was collected
O to give pure compound 4.
J. Antibiot. 2007, 60, 529.
21. Rahimizadeh, M.; Pordel, M.; Bakavoli, M.; Rezaeian, Sh.; Sadeghian, A. World J.
Microbiol. Biotechnol. 2010, 26, 317.
by filtration and washed with H
Pyrido[2 ,1 :2,3]imidazo[4,5-b]thieno[2,3-e]pyridine-11-carbo-
nitrile (4) was obtained as shiny yellow needles (toluene), yield
2
0
0
22. Joux, F.; Lebaron, P. Microbes Infect. 2000, 2, 1523.