Synthesis and Spectral, Electrochemical, and Antioxidant Properties of 2-(5-Aryl-6-R-3-phenyl-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl)-1,3-benzothiazoles

Article abstract of DOI:10.1134/S1070428020010078

New 2-(5-aryl-6-R-3-phenyl-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl)-1,3-benzothiazoles were synthesized from the corresponding formazans by alkylation and subsequent cyclization of N-alkyl derivatives. The products were characterized by ¹H and

Full text of DOI:10.1134/S1070428020010078

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2020, Vol. 56, No. 1, pp. 38–48. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Organicheskoi Khimii, 2020, Vol. 56, No. 1, pp. 52–64.
Synthesis and Spectral, Electrochemical, and Antioxidant
Properties of 2-(5-Aryl-6-R-3-phenyl-5,6-dihydro-
4H-1,2,4,5-tetrazin-1-yl)-1,3-benzothiazoles
T. G. Fedorchenkoa,*, G. N. Lipunovaa, b, A. V. Shchepochkina, b, M. S. Valovaa,
A. N. Tsmokalyukb, P. A. Slepukhina, b, and O. N. Chupakhina, b
a Postovsky Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620219 Russia
b Institute of Chemical Technology, Yeltsin Ural Federal University, Yekaterinburg, 620002 Russia
*e-mail: deryabina@ios.uran.ru
Received June 10, 2019; revised November 14, 2019; accepted November 22, 2019
Abstract—New 2-(5-aryl-6-R-3-phenyl-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl)-1,3-benzothiazoles were synthe-
sized from the corresponding formazans by alkylation and subsequent cyclization of N-alkyl derivatives. The
1
products were characterized by H and 13C NMR, IR, and mass spectra and X-ray diffraction data. Electro-
chemical properties and antioxidant activity of the synthesized benzothiazole derivatives were studied.
Keywords: 2-(5-aryl-6-R-3-phenyl-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl)-1,3-benzothiazoles, dihydrotetra-
zines, cyclic voltammetry, electrochemical properties, antioxidant activity.
DOI: 10.1134/S1070428020010078
Free radical-induced oxidative degradation of bio-
logical components in an organism often causes oxida-
tive stress which is responsible for many degenerative
diseases [1, 2]. Antioxidants, i.e., compounds capable
of quenching free radicals, are used to avoid or reduce
the effect of oxidative stress on living cells [3]. Well
known antioxidants are derivatives of phenols and
amines, both biogenic and synthetic, as well as of
nitrogen heterocycles (indole, carbazole, dihydropyri-
dine, dihydroacridine, etc.) [4–8]. Kozlova et al. [9]
previously reported antioxidant activity of tetrazolyl
derivatives of 5,6-dihydro-4H-1,2,4,5-tetrazine that are
precursors to verdazyls. The majority of antioxidants
are electrochemically active compounds capable of
forming stable radicals.
1H and 13C NMR, IR, and mass spectra, and X-ray
analysis of compound 4b (Fig. 1). Compounds 2a, 3a,
and 4a were reported by us previously [11] and were
used for comparison.
1
The H NMR spectra of 2–5 showed a singlet at
δ 9.52–9.62 ppm from the NH proton. Methylene
protons of 2a–2f resonated at δ 5.38–5.49 ppm. The
6-H signal of 3a–3e is shifted downfield relative to the
corresponding signal of 2a–2e and is observed in the
region δ 6.32–6.40 ppm (δ 6.08–6.18 ppm for 4a–4e).
In going from compounds 3 to 4 and then to 5, the 6-H
signal shifts upfield, and the 6-H proton of 5a–5e reso-
nates as a multiplet at δ 6.02–6.05 ppm. In the series of
compounds 3a–3e and 4a–4e, the strongest effect of
the halogen atom in the aromatic ring on the position
of the 6-H signal is observed for fluorine derivatives
3b and 4b, whereas there is no such effect for 5a–5e.
The position of the C6 signal in the 13C NMR spectra
of 2–5 depends on the 6-substituent (R). For com-
pounds 2a–2f, introduction of a fluorine atom into the
benzene ring on C5 shifts the C6 signal from δC 61.99
to 62.89 ppm, and an upfield shift of that signal to
δC 61.73 ppm is observed for 5-(4-iodophenyl) deriv-
ative 2e. A similar relation is characteristic of com-
pounds 3a–3e [δC 66.71 (3a), 67.19 (3b), 66.64–
66.39 ppm (3c–3e)] and 4a–4e [71.73 (4a), 72.24 (4b),
The goal of the present work was to study electro-
chemical and antioxidant properties of newly synthe-
sized 2-(5-aryl-6-R-3-phenyl-5,6-dihydro-4H-1,2,4,5-
tetrazin-1-yl)-1,3-benzothiazoles 2–5 and the relevant
structure–property relationships.
Compounds 2–5 were synthesized by alkylation of
1-aryl-5-(1,3-benzothiazol-2-yl)-3-phenylformazans 1
with haloalkanes in alcoholic alkali, followed by
cyclization of N-alkyl derivatives, according to the
procedure described previously [10] (Scheme 1). All
compounds were characterized by elemental analyses,
38

SYNTHESIS AND SPECTRAL, ELECTROCHEMICAL, AND ANTIOXIDANT PROPERTIES
39
Scheme 1.
X
X
N
N
R
(1) RCH2Hlg, NaOH
EtOH, Δ
(2) Heptane, Δ
S
S
NH
N
N
N
N
N
N
NH
Ph
1a–1e
Ph
2a–2f, 3a–3e, 5a–5e
1, X = H (a), F (b), Cl (c), Br (d), I (e); 2, R = H, X= H (a), F (b), Cl (c), Br (d), I (e), MeO (f); 3, R = Me, X= H (a), F (b), Cl (c),
Br (d), I (e); 4, R = Et, X = H (a), F (b), Cl (c), Br (d), I (e); 5, R = CH2=CH, X = H (a), F (b), Cl (c), Br (d), I (e).
71.64–71.39 ppm (4c–4e)]. It should be noted that the
chemical shifts of C6 in 6-vinyl derivatives 5a–5e (R =
CH2=CH) are similar to those of 4a–4e: 71.19 (5a),
71.70 (5b), 71.06 (5d), and 70.93 ppm (5e).
deviates from the N2C2C6 plane by 0.196 Å. The single
and double bonds are readily distinguishable (the dif-
ference in their lengths reaches 0.1 Å). Interestingly,
even larger difference in the C–N bond lengths of the
benzothiazole fragment [C2–N3 1.301(3) Å, N3–C13
1.397(3) Å] does not induce C–S bond asymmetry
[S1–C2 1.741(2) Å, S1–C18 1.743(3) Å]. The ethyl
group and 4-fluorophenyl substituent occupy (pseudo)-
axial positions and are oriented trans with respect to
each other. The N4 and N5 atoms have a trigonal–
pyramidal configuration. Molecules 4b in crystal are
linked together through intermolecular hydrogen bonds
N4–H···N3 [–x + 1/2, y – 1/2, –z + 1/2; N···N 2.996 Å,
N4H4N3 160°] (Fig. 1b) to form polymeric bands
extending along the 0b axis.
The IR spectra of 2–5 displayed an absorption band
in the region 3150–3260 cm–1 due to NH stretching
vibrations, and [M + H]+ ion peaks were present in
their mass spectra.
The structure of 4b was proved by X-ray analysis
(Fig. 1a). It crystallized in the centrosymmetric space
group belonging to the monoclinic crystal system. The
tetrahydrotetrazine ring is not planar, and the C6 atom
deviates by 0.619 Å from the mean-square plane
formed by the other five ring atoms whose deviations
from that plane do not exceed 0.04 Å. The phenyl
substituent on C3 is oriented approximately in the
heterocycle plane (torsion angle C7C3N2N1 175.9°),
and the benzothiazole fragment is slightly turned with
respect to the tetrazine ring plane (torsion angle
N2N1C2N3 169.9°). The N1 atom connecting the two
π-electron systems has a flattened configuration, but it
As shown previously [10, 12], the presence of
an electron-withdrawing substituent X in the aromatic
ring on N1 in initial formazans 1 favors further alkyla-
tion of 2 that can be regarded as dihydrotetrazine
derivatives. In the reaction with 1e (X = I), by column
chromatography we isolated compound 5e and one
(a)
(b)
C14
C15
C16
C17
C4
C13
N3
N1
H4
N4
C5
C6
C2
N3′
C18
C24
N5
N4′
H4′
C23
C22
N2
S1
C19
N3
N4
C3
C7
C12
C20
C11
C8
C9
C21
F1
C10
Fig. 1. (a) Structure of the molecule of 2-[6-ethyl-5-(4-fluorophenyl)-3-phenyl-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzo-
thiazole (4b) and (b) intermolecular hydrogen bonds in the crystal structure of 4b according to the X-ray diffraction data.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

FEDORCHENKO et al.
40
Scheme 2.
I
H2C
N
N
Ph
S
N
N
N
N
N
N
N
N
O
S
Me
CH2
Ph
Ph
6
7
more product which was assigned the structure of
2-[6-ethenyl-5-(4-iodophenyl)-3-phenyl-4-(prop-2-en-
1-yl)-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzo-
thiazole (6) on the basis of its mass spectrum and
1H NMR data (no NH signal was observed, but signals
typical of an allyl group were present). It should be
noted that alkylation at the N4 atom can also occur
under different conditions. For example, in an attempt
to obtain a copper complex of 2a in acetone, we isolat-
ed by column chromatography N-acetonyl derivative 7
(Scheme 2) whose structure was determined by X-ray
analysis (Fig. 2).
According to the X-ray diffraction data, the N4
atom in molecule 7 is linked to 2-oxopropyl group.
Compound 7 crystallized in the centrosymmetric space
group of the triclinic crystal system. The tetrahydro-
tetrazine ring is not planar, and its conformation signif-
icantly differs from that in molecule 4b. The N1, N2,
C3, and C6 atoms lie virtually in one plane (within
0.025 Å), and the N4 and N5 atoms deviate from that
plane by 0.330 and 0.847 Å, respectively. These nitro-
gen atoms have a trigonal pyramidal configuration, and
the substituents attached thereto appear in (pseudo)-
axial positions with trans orientation with respect to
each other. The phenyl ring on C3 is turned relative
to the tetrazine plane, so that the torsion angle
N2C3C16C17 is 32.9°. The bond length distribution over
the conjugation system including the hydrazone frag-
ment of the tetrahydrotetrazine ring is similar to that
found for compound 4b. The crystal packing of 7 is
characterized by the presence of short S···S contacts
[1 – x, 1 – y, –z] with an interatomic distance of
3.40 Å, which is shorter by 0.20 Å than the sum of van
C13
C14
C15
C12
S1
C11
C10
C2
N1
C17
N2
N3
C18
C6
C3
N4
C16
C27
N5
C19
C20
C21
C22
C23
C7
C8
O1
C26
C25
C24
C9
1
der Waals radii. In the H NMR spectrum of 7, the
C6H2 signal is shifted upfield to δ 4.33 ppm, and
methylene protons of the acetonyl group resonated as
two broadened singlets at δ 4.93 and 6.36 ppm.
Fig. 2. Structure of the molecule of 1-[4-(1,3-benzothiazol-2-
yl)-2,6-diphenyl-3,4-dihydro-1,2,4,5-tetrazin-1(2H)-yl]-
propan-2-one (7) according to the X-ray diffraction data.
60
40
20
0
The redox properties of dihydrotetrazine derivatives
2–5 were studied in acetonitrile by cyclic voltammetry
(CV); the results are collected in Table 1. All com-
pounds 2–5 showed two oxidation peaks, the first peak
at 0.10–0.18 V (except for 2f), and the second at 0.60–
0.81 V and only one reduction peak. Figure 3 shows
the cyclic voltammogram of compound 4a as an ex-
ample. The first oxidation step of 4a was studied by
recording the CV curve with the anodic potential not
exceeding the second oxidation step potential. The
oxidation peak area was 1.6 times larger than the
reduction peak area, and the reduction and oxidation
–20
–0.5
0.0
0.5
1.0
E, V
Fig. 3. Cyclic voltammogram of compound 4a.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

SYNTHESIS AND SPECTRAL, ELECTROCHEMICAL, AND ANTIOXIDANT PROPERTIES
41
1
2
0.12
0.08
0.04
0.00
Magnetic field, G
3540 3560
y = 1×10–7x + 2×10–5
R2 = 0.997
3460
3480
3500
3520
0
200
400
Time, s
600
800
Fig. 4. Plot of the concentration of paramagnetic species
generated by electrochemical oxidation of 4a versus time.
Fig. 5. ESR spectra of (1) electrochemically oxidized form of
4a and (2) verdazyl 9.
(a)
(b)
1
1
2
3
Magnetic field, G
3540 3560
Magnetic field, G
3540 3560
3460
3480
3500
3520
3460
3480
3500
3520
Fig. 6. (1) Experimental ESR spectrum of electrochemically oxidized form of 4a and calculated ESR spectra of (2) verdazyl 9 and
(3) radical cation 8.
peak potentials differed by 160 mV. Therefore, we
cannot define the process even as quasi-reversible.
Presumably, the oxidation of 4a at a potential close to
the first step involves transfer of a larger number of
electrons than in the reduction step.
ments were carried out under argon, we presumed that
the first oxidation step produces radical cation 8 as one
of the products (Scheme 3). The spin densities on the
nitrogens of 8 and 9 are likely to be similar, and
possible effect of the hydrogen atom on N4 in the
electrochemically oxidized form of 4a is not reflected
in the ESR spectrum because of its poor resolution at
room temperature.
In order to identify oxidation products, they were
electrochemically generated over periods of 400, 600,
and 900 s and examined by ESR, and the concentration
of paramagnetic species was measured. Figure 4 shows
the dependence of their concentration on the duration
of electrolysis. Comparison of the ESR spectrum of
the electrochemically generated paramagnetic species
with the spectrum of verdazyl 9 obtained by chemical
oxidation of 4a [11] showed their almost complete
identity (Fig. 5). Taking into account that CV experi-
In order to refine the structure of the paramagnetic
electrochemical oxidation product, we performed DFT
quantum chemical calculations of radical cation 8 and
verdazyl 9 with geometry optimization using the
UB3LYP functional and 6-31+G(d) basis state. The
hyperfine coupling constants (HCC) were calculated at
the UB3LYP/IGLO-III level [13]. The calculations
Scheme 3.
N
Et
N
Et
N
Et
–e
+e
Ph
Ph
Ph
S
S
S
N
N
N
N
N
N
N
N
N
N
·
NH
NH
Ph
Ph
Ph
4a
8
9
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

FEDORCHENKO et al.
Table 1. Electrochemical parameters of compounds 2–5
42
Compound no.
E
ox1, V
Eox2, V
Compound no.
Eox1, V
Eox2, V
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
0.10
0.13
0.14
0.14
0.15
0.03
0.12
0.12
0.13
0.13
0.15
0.66
0.73
0.70
0.70
0.70
0.60
0.73
0.75
0.75
0.74
0.74
4a
4b
4c
4d
4e
5a
5b
5c
5d
5e
0.11
0.11
0.11
0.12
0.14
0.16
0.16
0.17
0.17
0.18
0.70
0.74
0.62
0.75
0.72
0.73
0.76
0.81
0.72
were carried out using ORCA [14], and the ESR spec-
tra were simulated by EasySpin [15]. The experimental
ESR spectrum of the oxidized form of 4a almost
coincided with the calculated spectrum of verdazyl 9
(Fig. 6). These findings led us to conclude that elec-
trochemical oxidation of 4a at a potential correspond-
ing to the first oxidation peak gives verdazyl 9 rather
than radical cation 8. Presumably, the latter is stabi-
lized as verdazyl 9 via deprotonation in polar medium
(acetonitrile).
Vinyl derivatives 5a–5e (R = CH2=CH) showed
a small shift of the first oxidation potential to more
positive values in comparison to compounds 2a–2e
(R = H). In the series 2a–2f, compound 2f containing
the strongest electron-donating group (X = OMe)
was characterized by the least positive first oxidation
potential.
The antioxidant activity of dihydrotetrazines was
studied in the series 2a–2f (to trace the effect of the X
substituent) and 2a–5a (to trace the effect of R). The
antioxidant activity was evaluated by spectrophoto-
metric monitoring of the hydrogen transfer reaction
with a stable chromogen radical, 2,2-diphenyl-1-picryl-
hydrazyl (DPPH) [19] using vitamin C (Vc) as refer-
ence. A solution of DPPH in methanol with a concen-
tration of 200 μM was added to a solution of 2–5 in the
same solvent (concentration 5 to 50 μM). The reaction
vessel (test tube) was wrapped in foil and kept for
30 min at 30°C, and the optical density was measured
at λ 517 nm (DPPH absorption maximum). The anti-
oxidant activity (AO) was calculated by the formula
The second step of electrochemical oxidation of 4a
is irreversible. Most probably, this process involves
transformation of the tetrahydrotetrazine ring to tri-
azole. Examples of formation of triazole derivatives
from formazans [16] and verdazyls (as autotransforma-
tion products) [17] or as by-products in the synthesis of
verdazyls [18] have been reported; in the latter case,
the structure of substituted triazole was confirmed by
X-ray analysis.
The natures of the substituent R and halogen atom
only slightly affect the oxidation potentials (Table 1).
30
28.2
AO = (1 – Atest/Acontr)×100%,
25
where Atest is the optical density of a solution contain-
ing a compound to be tested and DPPH, and Acontr is
the optical density of a solution containing DPPH
alone. The half inhibitory concentration (IC50) corre-
sponding to the reduction of the initial DPPH concen-
tration by 50% was determined from the DPPH inhibi-
tion percentage plotted against concentration of 2–5
using OriginPro 8.5 program (Model DoseResp). The
results are presented in Figs. 7 and 8.
21.4
19.6
20
15
13.2
11.8
10.5
10
5
9.2
7.2
6.1
4.1
0
2f 2b 2a 2d Vc 2e 2c 4a 5a 3a
It was found that unsubstituted dihydrotetrazine 2a
(IC50 = 7.2 μM) reacted with DPPH most effectively;
compounds 4a (R = Et) and 5a (R = CH2=CH) showed
Fig. 7. Diagram of IC50 values of dihydrotetrazines 2a–2f
and 3a–5a.
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SYNTHESIS AND SPECTRAL, ELECTROCHEMICAL, AND ANTIOXIDANT PROPERTIES
43
(a)
(b)
100
75
50
25
0
6
7
1
100
80
60
40
20
0
12
2
8
9
4
5
3
10
11
0
10
20
30
40
50
0
20
Concentration, μM
40
Concentration, μM
Fig. 8. Concentration dependences of DPPH inhibition by dihydrotetrazines and vitamin C (Vc): (1, 6) Vc, (2, 7) 2a, (3) 3a, (4) 4a,
(5) 5a, (8) 2b, (9) 2c, (10) 2d, (11) 2e, and (12) 2f.
fairly similar IC50 values (19.6 and 21.4 μM, respec-
tively), but were significantly inferior to vitamin C
(IC50 = 10.5 μM; Fig. 8a). Unexpectedly, methyl-sub-
stituted dihydrotetrazine 3a proved to be least active in
this series (IC50 = 28.2 μM). The effect of the X sub-
stituent in the aromatic fragment is determined by its
donor–acceptor properties. The stronger the electron-
donor power, the higher the antioxidant activity. With
respect to their antioxidant activity compounds 2a–2f
ranked as follows MeO > F > H > Br > Vc > I > Cl
(Fig. 8b). Despite a strong negative inductive effect of
fluorine, its positive mesomeric effect appeared to be
so significant that the antioxidant activity of fluoro-
phenyl-substituted dihydrotetrazine 2b (IC50 = 6.1 μM)
was only slightly lower than the activity of methoxy
analog 2f (IC50 = 4.1) and much higher than the
activity of vitamin C. As might be expected, more
electrochemically active dihydrotetrazines 2f, 2a, 2b,
and 2d exhibited higher antioxidant activity.
purity of the isolated compounds were monitored by
TLC on Sorbfil PTSKh-AF-A-UF plates. Column
chromatography was performed using Kieselgel 60
silica gel (grain size 0.040–0.063 mm or 230–
400 mesh). The NMR spectra were recorded on
a Bruker Avance III-500 spectrometer operating at
1
500 MHz for H. The IR spectra were recorded on
a Perkin Elmer Spectrum One spectrometer equipped
with a diffuse reflectance accessory. The UV spectra
were measured from solutions in methanol on
a Shimadzu UV2600 spectrophotometer (Japan). The
mass spectra (electrospray ionization) were obtained
with a Bruker Daltonics maXis impact HD instrument.
Elemental analysis was performed on a Perkin Elmer
2400 Series II automated CHNS analyzer. The ESR
spectra were recorded on a Bruker Elexsys E 500
X-band spectrometer equipped with an ER4131VT
system; solutions of samples in acetonitrile were
diluted to a concentration of about 10–4 M.
Thus, the newly synthesized 2-(5-aryl-6-R-3-phe-
nyl-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl)-1,3-benzo-
thiazoles are readily oxidizable compounds which
show antiradical activity.
The X-ray diffraction data for compounds 4b and 7
were obtained at the Spectroscopy and Analysis of
Organic Compounds joint center (Institute of Organic
Synthesis, Ural Branch, Russian Academy of Sciences)
on an Xcalibur 3 automated four-circle diffractometer
with a CCD detector according to standard procedure
[Mo Kα radiation, graphite monochromator, ω-scanning
with a step of 1°, temperature 295(2) K]. A correction
for absorption was applied empirically. The structures
of 4b and 7 were solved by the direct statistical method
and were refined against F2 by the full-matrix least-
squares method in anisotropic approximation for all
EXPERIMENTAL
All solvents were dried and distilled prior to use
according to standard procedures. Commercially avail-
able reagents were purchased from Sigma–Aldrich and
were used without further purification. The melting
points were measured with a Stuart SMP3 melting
point apparatus. The progress of reactions and the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

FEDORCHENKO et al.
44
non-hydrogen atoms. Hydrogen atoms linked to car-
bons were placed in geometrically calculated positions,
and the positions of NH hydrogens were refined
independently in isotropic approximation. All calcula-
tions were performed using SHELXTL package [20].
201 mg (62%), mp 191–193°C (from MeOH). IR spec-
trum, ν, cm–1: 3136, 1595, 1533, 1503, 1446, 1279,
1166, 1058, 744, 687. 1H NMR spectrum, δ, ppm: 5.49
br.s (2H, CH2), 7.07 t (1H, Harom, J = 7.7 Hz), 7.24–
7.39 m (5H, Harom), 7.47–7.59 m (4H, Harom), 7.77 d
(1H, Harom, J = 7.6 Hz), 7.85–7.95 m (2H, Harom),
9.58 br.s (1H, NH). 13C NMR spectrum, δC, ppm:
62.89, 119.03, 119.20, 121.34, 121.46, 125.80, 126.06,
126.35, 128.61, 129.06, 130.66, 130.85, 131.26,
145.04, 148.47, 152.08, 166.69. Mass spectrum:
m/z 406.0880 [M + H]+. Found, %: C 62.12; H 3.96;
N 17.23. C21H16ClN5S. Calculated, %: C 62.14;
H 3.97; N 17.25.
Cyclic voltammetry experiments were carried out
using a Metrohm Autolab PGSTAT128N potentiostat
with a standard three-electrode cell comprising a glassy
carbon disc (d = 2 mm) as a working electrode,
a 0.01 M Ag/AgNO3 reference electrode, and a glassy
carbon rod as a counter electrode. The measurements
were performed under argon in anhydrous acetonitrile
containing 0.1 mol/L of tetrabutylammonium tetra-
fluoroborate as a supporting electrolyte; potential scan
rate 100 mV/s. The Ag/AgNO3 electrode was calibrated
against ferrocene/ferrocenium (Fc/Fc+) redox couple.
2-[5-(4-Bromophenyl)-3-phenyl-5,6-dihydro-4H-
1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole (2d). Yield
187 mg (52%), mp 182–184°C (from MeOH). IR spec-
trum, ν, cm–1: 3143, 1597, 1532, 1502, 1445, 1279,
Initial formazans 1a–1e were synthesized according
to the procedures described in [10, 21, 22].
1
1165, 1058, 745, 689. H NMR spectrum, δ, ppm:
5.49 br.s (2H, CH2), 7.09 t (1H, Harom, J = 7.3 Hz),
7.24–7.31 m (3H, Harom), 7.47–7.58 m (6H, Harom),
7.77 d (1H, Harom, J = 7.7 Hz), 7.87–7.91 m (2H,
2-(5-Aryl-3-phenyl-5,6-dihydro-4H-1,2,4,5-tetra-
zin-1-yl)-1,3-benzothiazoles 2–5 (general procedure).
Formazan 1a–1e (0.8 mmol) was dispersed in 20 mL of
ethanol, a 30% aqueous solution of sodium hydroxide
(0.9 mmol) was added, the corresponding alkyl halide
(8.0 mmol) was added to the dark violet solution, and
the mixture was refluxed for 15 min. The solvent was
distilled off under reduced pressure, 30 mL of heptane
was added to the residue, and the mixture was refluxed
for 1 h. The solvent was distilled off under reduced
pressure, and the product was isolated from the residue
by column chromatography on silica gel using hexane–
chloroform (2:1) as eluent.
H
arom), 9.57 br.s (1H, NH). 13C NMR spectrum, δC,
ppm: 61.86, 114.29, 119.04, 119.62, 121.34, 121.46,
125.81, 126.06, 128.62, 130.67, 130.86, 131.26,
145.02, 148.91, 152.08, 166.69. Mass spectrum:
m/z 450.0256 [M + H]+. Found, %: C 55.98; H 3.55;
N 15.53. C21H16BrN5S. Calculated, %: C 56.01;
H 3.58; N 15.55.
2-[5-(4-Iodophenyl)-3-phenyl-5,6-dihydro-4H-
1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole (2e). Yield
215 mg (54%), mp 175–177°C (from MeOH). IR spec-
trum, ν, cm–1: 3161, 1594, 1525, 1500, 1446, 1278,
2-(3,5-Diphenyl-5,6-dihydro-4H-1,2,4,5-tetrazin-1-
yl)-1,3-benzothiazoles 2a, 3a, and 4a were reported
previously [11].
1
1170, 1058, 751, 691. H NMR spectrum, δ, ppm:
5.48 br.s (2H, CH2), 7.08–7.14 m (3H, Harom), 7.29 t
(1H, Harom, J = 7.5), 7.50–7.64 m (4H, Harom), 7.62 d
(2H, Harom, J = 8.8 Hz), 7.77 d (1H, Harom, J = 7.7 Hz),
7.87–7.91 m (2H, Harom), 9.56 br.s (1H, NH). 13C NMR
spectrum, δC, ppm: 61.73, 85.97, 119.04, 119.92,
121.37, 121.47, 125.82, 126.06, 128.63, 130.67,
130.86, 131.27, 137.77, 144.99, 149.46, 152.09,
166.67. Mass spectrum: m/z 498.0240 [M + H]+.
Found, %: C 50.70; H 3.22; N 14.07. C21H16IN5S.
Calculated, %: C 50.71; H 3.24; N 14.08.
2-[5-(4-Fluorophenyl)-3-phenyl-5,6-dihydro-4H-
1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole (2b). Yield
137 mg (44%), mp 171–173°C (from MeOH). IR spec-
trum, ν, cm–1: 3144, 1598, 1530, 1503, 1447, 1280,
1
1171, 1059, 762, 685. H NMR spectrum, δ, ppm:
5.45 br.s (2H, CH2), 7.08–7.17 m (3H, Harom), 7.56–
7.50 m (4H, Harom), 7.76 d (1H, Harom, J = 7.1 Hz),
7.89–7.91 m (2H, Harom), 9.56 br.s (1H, NH). 13C NMR
spectrum, δC, ppm: 55.15, 62.89, 115.67, 115.86,
118.99, 119.37, 119.43, 121.34, 125.79, 126.04,
128.61, 130.63, 130.85, 131.32, 145.17, 145.96,
152.11, 156.98, 158.88, 166.75. Mass spectrum:
m/z 390.1183 [M + H]+. Found, %: C 64.74; H 4.11;
N 17.95. C21H16FN5S. Calculated, %: C 64.76;
H 4.14; N 17.98.
2-[5-(4-Methoxyphenyl)-3-phenyl-5,6-dihydro-
4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole (2f).
Yield 135 mg (42%), mp 191–193°C (from MeOH). IR
spectrum, ν, cm–1: 3331, 1595, 1530, 1508, 1444,
1
1278, 1177, 1064, 755, 686. H NMR spectrum, δ,
ppm: 3.66 s (3H, OCH3), 5.38 br.s (2H, CH2), 6.87 d
(2H, Harom, J = 9.1 Hz), 7.07 t (1H, Harom, J = 7.3 Hz),
7.17 d (2H, Harom, J = 9.1 Hz), 7.27 t (1H, Harom, J =
2-[5-(4-Chlorophenyl)-3-phenyl-5,6-dihydro-4H-
1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole (2c). Yield
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SYNTHESIS AND SPECTRAL, ELECTROCHEMICAL, AND ANTIOXIDANT PROPERTIES
45
7.3 Hz), 7.49 d (1H, Harom, J = 7.8 Hz), 7.52–7.55 m
(3H, Harom), 7.75 (1H, Harom, J = 7.3 Hz) 7.86–7.90 m
(2H, Harom), 9.52 br.s (1H, NH). 13C NMR spectrum,
δC, ppm: 55.15, 62.89, 114.39, 118.91, 119.21, 121.29,
125.75, 126.01, 128.56, 130.54, 130.83, 131.43,
142.98, 145, 145.27, 152.17, 155.09, 166.59. Mass
spectrum: m/z 400.1230 [M – H]+. Found, %: C 65.78;
H 4.73; N 17.42. C22H19N5OS. Calculated, %: C 65.81;
H 4.77; N 17.44.
Harom, J = 7.6 Hz), 7.84–7.98 m (2H, Harom), 9.62 br.s
(1H, NH). 13C NMR spectrum, δC, ppm: 15.90, 66.59,
114.46, 118.99, 119.20, 121.33, 121.40, 125.77,
125.94, 128.67, 130.65, 130.71, 131.00, 131.97,
143.97, 149.50, 152.22, 166.00. Mass spectrum:
m/z 464.0364 [M + H]+. Found, %: C 56.88; H 3.90;
N 15.06. C22H18BrN5S. Calculated, %: C 56.90;
H 3.91; N 15.08.
2-[5-(4-Iodophenyl)-6-methyl-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(3e). Yield 143 mg (35%), mp 196–198°C (from
MeOH). IR spectrum, ν, cm–1: 3165, 1595, 1525, 1505,
2-[5-(4-Fluorophenyl)-6-methyl-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(3b). Yield 164 mg (51%), mp 197–199°C (from
MeOH). IR spectrum, ν, cm–1: 3154, 1594, 1526, 1503,
1
1447, 1274, 1191, 1011, 751, 694. H NMR spectrum,
1
1446, 1276, 1179, 1011, 754, 693. H NMR spectrum,
δ, ppm: 1.50 d (3H, CH3, J = 6.2 Hz), 6.40 q (1H, 6-H,
J = 6.2 Hz), 7.29 t (1H, Harom, J = 7.9 Hz), 7.07 and
7.77 AB (2H, Harom, J = 7.3 Hz), 7.11 and 7.62 AA′BB′
(4H, Harom, J = 8.5 Hz), 7.48–7.58 m (4H, Harom),
7.91 d (1H, Harom, J = 8.5 Hz), 7.88–7.96 m (2H,
Harom), 9.61 br.s (1H, NH). 13C NMR spectrum, δC,
ppm: 15.84, 66.39, 118.95, 120.15, 121.25, 121.33,
125.69, 125.87, 128.59, 130.55, 130.67, 130.98,
137.73, 143.92, 150.00, 152.18, 165.94. Mass spec-
trum: m/z 512.0395 [M + H]+. Found, %: C 51.65;
H 3.54; N 13.66. C22H18IN5S. Calculated, %: C 51.67;
H 3.55; N 13.69.
δ, ppm: 1.50 d (3H, CH3, J = 6.2 Hz), 6.32 q (1H, 6-H,
J = 6.2 Hz), 7.07 t (1H, Harom, J = 7.6 Hz), 7.14 t
(2H, Harom, J = 9.0 Hz), 7.23–7.36 m (3H, Harom), 7.47–
7.61 m (4H, Harom), 7.75 d (1H, Harom, J = 7.6 Hz),
7.88–7.97 m (2H, Harom), 9.60 br.s (1H, NH). 13C NMR
spectrum, δC, ppm: 16.00, 67.19, 115.62, 115.80,
118.91, 119.64, 119.71, 121.24, 121.29, 125.68,
125.87, 128.59, 130.53, 130.67, 131.05, 144.12,
146.60, 152.21, 156.99, 158.89, 166.03. Mass spec-
trum: m/z 404.1336 [M + H]+. Found, %: C 65.47;
H 4.48; N 17.34. C22H18FN5S. Calculated, %: C 65.49;
H 4.50; N 17.36.
2-[6-Ethyl-5-(4-fluorophenyl)-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(4b). Yield 127 mg (38%), mp 211–213°C (from
MeOH). IR spectrum, ν, cm–1: 3160, 1603, 1535, 1501,
1447, 1278, 1182, 988, 749, 693. 1H NMR spectrum, δ,
ppm: 1.11 t (3H, CH3, J = 7.3 Hz), 1.73–1.88 m (2H,
CH2), 6.05–6.11 m (1H, 6-H), 7.06 t (1H, Harom, J =
7.4 Hz), 7.13 t (2H, Harom, J = 8.6 Hz), 7.19–7.31 m
(3H, Harom), 7.45–7.62 m (4H, Harom), 7.73 d (1H,
2-[5-(4-Chlorophenyl)-6-methyl-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(3c). Yield 141 mg (42%), mp 203–205°C (from
MeOH). IR spectrum, ν, cm–1: 3178, 1595, 1529, 1507,
1
1447, 1277, 1186, 1011, 750, 696. H NMR spectrum,
δ, ppm: 1.51 d (3H, CH3, J = 6.2 Hz), 6.40 q (1H, 6-H,
J = 6.2 Hz), 7.09 t (1H, Harom, J = 7.6 Hz), 7.22–7.41 m
(5H, Harom), 7.45–7.64 m (4H, Harom), 7.76 d (1H,
H
arom, J = 7.6 Hz), 7.88–7.99 m (2H, Harom), 9.62 br.s
Harom, J = 7.8 Hz), 7.85–7.94 m (2H, Harom), 9.55 br.s
(1H, NH). 13C NMR spectrum, δC, ppm: 15.88, 66.64,
118.95, 119.46, 121.26, 121.34, 125.70, 125.89,
126.46, 128.61, 129.03, 130.58, 130.68, 130.99,
143.97, 149.03, 152.18, 165.98. Mass spectrum:
m/z 420.1008 [M + H]+. Found, %: C 62.92; H 4.32;
N 16.68. C22H18ClN5S. Calculated, %: C 62.92;
H 4.32; N 16.68.
(1H, NH). 13C NMR spectrum, δC, ppm: 9.61, 22.81,
72.24, 115.71, 115.88, 118.87, 119.70, 119.70, 121.23,
121.26, 125.72, 125.95, 128.66, 130.64, 130.69,
131.06, 144.55, 146.72, 152.28, 156.99, 158.89,
166.21. Mass spectrum: m/z 418.1496 [M + H]+.
Found, %: C 66.15; H 4.81; N 16.78. C23H20FN5S.
Calculated, %: C 66.17; H 4.83; N 16.77.
2-[5-(4-Bromophenyl)-6-methyl-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(3d). Yield 144 mg (39%), mp 205–207°C (from
MeOH). IR spectrum, ν, cm–1: 3173, 1596, 1527, 1506,
1447, 1275, 1189, 1011, 750, 695. H NMR spectrum,
δ, ppm: 1.50 d (3H, CH3, J = 6.2 Hz), 6.40 q (1H, 6-H,
J = 6.2 Hz), 7.08 t (1H, Harom, J = 7.5 Hz), 7.24 and
Crystallographic data: C23H20FN5S; monoclinic
crystal system, space group P21/n; unit cell parameters:
a = 10.4546(9), b = 11.2072(9), c = 17.7583(16) Å; β =
91.670(8)°; V = 2079.8(3) Å3; Z = 4; μ = 0.184 mm–1.
Total of 13448 reflection intensities were measured in
the range 3.48 < θ < 30.82°, including 5534 indepen-
dent reflections (Rint = 0.0439). Final divergence
factors: R1 = 0.1391, wR2 = 0.1634 (all independent
reflections); R1 = 0.0566, wR2 = 0.1170 [reflections
1
7.47 AA′BB′ (4H, Harom, J = 8.9 Hz), 7.28 t (1H, Harom
,
J = 7.5 Hz), 7.50–7.62 m (4H, Harom), 7.76 d (1H,
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FEDORCHENKO et al.
46
with I > 2σ(I)]; goodness of fit S = 1.004; residual
electron density peaks 0.175/–0.344 ēÅ-3. The com-
plete set of X-ray diffraction data for compound 4b
was deposited to the Cambridge Crystallographic Data
Centre (CCDC entry no. 1965415).
ppm: 9.54, 22.65, 71.39, 118.91, 120.20, 121.28,
125.74, 125.96, 128.66, 130.66, 130.68, 130.98,
137.78, 144.33, 150.19, 152.24, 166.12. Mass spec-
trum: m/z 526.0548 [M + H]+. Found, %: C 52.57;
H 3.81; N 13.32. C23H20IN5S. Calculated, %: C 52.58;
H 3.84; N 13.33.
2-[5-(4-Chlorophenyl)-6-ethyl-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(4c). Yield 111 mg (32%), mp 243–245°C (from
MeOH). IR spectrum, ν, cm–1: 3155, 1595, 1534, 1503,
1447, 1277, 1190, 987, 750, 693. 1H NMR spectrum, δ,
ppm: 1.11 t (3H, CH3, J = 7.4 Hz), 1.69–1.98 m (2H,
CH2), 6.13–6.22 m (1H, 6-H), 6.96 t (1H, Harom, J =
7.8 Hz), 7.13 t (2H, Harom, J = 8.6 Hz), 7.24–7.32 m
(3H, Harom), 7.32–7.41 m (2H, Harom), 7.50 d (1H,
2-[6-Ethenyl-3,5-diphenyl-5,6-dihydro-4H-
1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole (5a). Yield
165 mg (52%), mp 177–178°C (from MeOH). IR spec-
trum, ν, cm–1: 3203, 1594, 1526, 1506, 1447, 1277,
1
1180, 1011, 750, 693. H NMR spectrum, δ, ppm:
5.33–5.37 m (2H, =CH2), 6.01–6.07 m (1H, CH), 6.84–
6.89 m (1H, CH), 6.95–7.00 m (1H, Harom), 7.07 t (1H,
H
arom, J = 7.3 Hz), 7.24–2.26 m (5H, Harom), 7.47–
H
arom, J = 8.3 Hz), 7.45–7.60 m (3H, Harom), 7.74 d
7.58 m (4H, Harom), 7.75 d (1H, Harom, J = 7.6 Hz),
7.85–7.92 m (2H, Harom), 9.59 br.s (1H, NH). 13C NMR
spectrum, δC, ppm: 71.19, 79.17, 117.74, 118.54,
118.96, 121.34, 122.74, 125.77, 125.99, 128.63,
129.29, 130.62, 130.76, 131.09, 131.52, 144.81,
149.65, 152.21, 166.36. Mass spectrum: m/z 398.1434
[M + H]+. Found, %: C 69.48; H 4.83; N 17.60.
C23H19N5S. Calculated, %: C 69.50; H 4.82; N 17.62.
(1H, Harom, J = 7.8 Hz), 7.85–7.99 m (2H, Harom),
9.57 br.s (1H, NH). 13C NMR spectrum, δC, ppm: 9.54,
22.69, 71.64, 118.91, 119.51, 121.28, 125.74, 125.97,
126.39, 128.67, 129.09, 130.69, 130.99, 144.38,
149.21, 152.24, 166.15. Mass spectrum: m/z 434.1201
[M + H]+. Found, %: C 63.64; H 4.64; N 16.13.
C23H20ClN5S. Calculated, %: C 63.66; H 4.65;
N 16.14.
2-[6-Ethenyl-5-(4-fluorophenyl)-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(5b). Yield 142 mg (43%), mp 198–200°C (from
MeOH). IR spectrum, ν, cm–1: 3203, 1599, 1526, 1502,
2-[5-(4-Bromophenyl)-6-ethyl-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(4d). Yield 141 mg (37%). mp 234–236°C (from
MeOH). IR spectrum, ν, cm–1: 3150, 1596, 1531, 1502,
1446, 1276, 1192, 987, 750, 692. H NMR spectrum,
δ, ppm: 1.10 t (3H, CH3, J = 7.3 Hz), 1.72–1.96 m
1
1447, 1278, 1183, 1012, 749, 695. H NMR spectrum,
1
δ, ppm: 5.26–5.48 m (2H, =CH2), 5.96–6.10 m (1H,
CH), 6.75–6.84 m (1H, CH), 6.95–7.00 m (1H, Harom),
7.08 t (1H, Harom, J = 7.5 Hz), 7.15 t (2H, Harom, J =
8.8 Hz), 7.24–2.36 m (3H, Harom), 7.45–7.58 m (4H,
(2H, CH2), 6.13–6.23 m (1H, CH), 7.08 t (1H, Harom
,
J = 7.9 Hz), 7.23 and 7.47 AA′BB′ (4H, Harom, J =
9.3 Hz), 7.27 t (1H, Harom, J = 7.9 Hz), 7.47–7.59 m
(4H, Harom), 7.74 d (1H, Harom, J = 7.9 Hz), 7.88–
7.95 m (2H, Harom), 9.57 br.s (1H, NH). 13C NMR
spectrum, δC, ppm: 9.54, 22.67, 71.52, 114.34, 118.92,
119.92, 121.28, 125.74, 125.97, 128.67, 130.68,
130.69, 130.98, 144.35, 149.64, 152.24, 166.14. Mass
spectrum: m/z 478.0696 [M + H]+. Found, %: C 57.73;
H 4.18; N 14.62. C23H20BrN5S. Calculated, %:
C 57.74; H 4.21; N 14.64.
Harom), 7.76 d (1H, Harom, J = 7.5 Hz), 7.84–7.90 m
(2H, Harom), 9.61 br.s (1H, NH). 13C NMR spectrum,
δC, ppm: 71.70, 115.74, 115.93, 118.59, 118.98, 119.74,
119.79,121.34, 121.39, 125.78, 125.99, 128.62, 130.66,
130.77, 131.03, 131.43, 144.85, 146.09, 152.18,
157.08, 158.99, 166.45. Mass spectrum: m/z 416.1340
[M + H]+. Found, %: C 66.48; H 4.35; N 16.84.
C23H18FN5S. Calculated, %: C 66.49; H 4.37; N 16.86.
2-[5-(4-Chlorophenyl)-6-ethenyl-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(5c). Yield 152 mg (44%), mp 200–203°C (from
MeOH). IR spectrum, ν, cm–1: 3195, 1593, 1525, 1504,
2-[6-Ethyl-5-(4-iodophenyl)-3-phenyl-5,6-dihy-
dro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole (4e).
Yield 130 mg (31%). mp 233–235°C (from MeOH).
IR spectrum, ν, cm–1: 3126, 1595, 1529, 1500, 1447,
1276, 1194, 988, 750, 693. 1H NMR spectrum, δ, ppm:
1.09 t (3H, CH3, J = 7.3 Hz), 1.69–1.94 m (2H, CH2),
6.12–6.21 m (1H, 6-H), 7.07 t (1H, Harom, J = 7.8 Hz),
7.09 and 7.61 AA′BB′ (4H, Harom, J = 9.0 Hz), 7.27 t
(1H, Harom, J = 7.9 Hz), 7.47–7.59 m (4H, Harom),
7.74 d (1H, Harom, J = 7.4 Hz), 7.87–7.93 m (2H,
1
1446, 1275, 1189, 1012, 749, 694. H NMR spectrum,
δ, ppm: 5.29–5.40 m (2H, =CH2), 5.97–6.09 m (1H,
CH), 6.85–6.93 m (1H, CH), 7.08 t (1H, Harom, J =
7.5 Hz), 7.28 t (1H, Harom, J = 7.5 Hz), 7.36 and
7.33 AA′BB′ (4H, Harom, J = 9.4 Hz), 7.50 d (1Harom
,
J = 7.8 Hz) 7.51–7.57 m (2H, Harom), 7.83–7.91 m (2H,
Harom), 9.62 br.s (1H, NH). 13C NMR spectrum, δC,
ppm: 71.09, 115.15, 115.72, 118.63, 119.08, 119.84,
H
arom), 9.56 br.s (1H, NH). 13C NMR spectrum, δC,
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SYNTHESIS AND SPECTRAL, ELECTROCHEMICAL, AND ANTIOXIDANT PROPERTIES
47
121.36, 121.40, 125.83, 126.02 128.74, 130.75, 130.82,
131.13, 131.99, 144.78, 148.10, 152.19, 166.43. Mass
spectrum: m/z 432.1024 [M + H]+. Found, %: C 63.93;
H 4.17; N 16.20. C23H18ClN5S. Calculated, %:
C 63.95; H 4.20; N 16.21.
Harom), 7.54–7.99 m (2H, Harom), 7.63 d (2Harom, J =
8.8 Hz), 7.72–7.78 m (2H, Harom). Mass spectrum:
m/z 564.0715 [M + H]+. Found, %: C 55.41; H 3.92;
N 12.41. C26H22IN5S. Calculated, %: C 55.42; H 3.94;
N 12.43.
1-[4-(1,3-Benzothiazol-2-yl)-2,6-diphenyl-3,4-di-
hydro-1,2,4,5-tetrazin-1(2H)-yl]propan-2-one (7).
A hot solution of 67 mg (0.28 mmol) of copper(II)
chloride in 4 mL of acetone was added with stirring to
a hot solution of 100 mg (0.26 mmol) of tetrazine 2a in
5 mL of acetone, and the mixture was stirred at room
temperature for 24 h. The solvent was distilled off
under reduced pressure, the residue was passed through
50 mL of silica gel using chloroform–acetone (10:1) as
eluent, the eluate was evaporated under reduced pres-
sure, and the residue was purified by column chro-
matography with chloroform as eluent. Yield 55 mg
2-[5-(4-Bromophenyl)-6-ethenyl-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(5d). Yield 156 mg (41%), mp 200–202°C (from
MeOH). IR spectrum, ν, cm–1: 3195, 1593, 1525, 1504,
1
1446, 1275, 1189, 1012, 749, 694. H NMR spectrum,
δ, ppm: 5.28–5.44 m (2H, =CH2), 5.97–6.08 m (1H,
CH), 6.84–6.93 m (1H, CH), 7.09 t (1H, Harom, J =
7.3 Hz), 7.25–7.33 m (3H, Harom), 7.46–7.52 m (6H,
Harom), 7.77 d (1H, Harom, J = 7.8 Hz), 7.84–7.91 m
(2H, Harom), 9.62 br.s (1H, NH). 13C NMR spectrum,
δC, ppm: 71.06, 114.61, 118.72, 119.02, 119.95,
121.39, 121.46, 125.81, 126.02, 128.64, 130.71,
130.78, 130.96, 131.21, 132.04, 144.68, 149.02,
152.16, 166.38. Mass spectrum: m/z 476.0539
[M + H]+. Found, %: C 57.98; H 3.78; N 14.69.
C23H18BrN5S. Calculated, %: C 57.99; H 3.81;
N 14.70.
1
(32%), mp 204–206°C (from MeOH). H NMR spec-
trum, δ, ppm: 2.05 s (3H, CH3), 4.17–4.46 m (2H,
CH2), 4.79–5.08 m (1H, CH), 6.23–6.52 m (2H, CH2),
6.94 t and 7.11 t (2H, Harom, J = 7.3 Hz), 7.23–7.35 m
(3H, Harom), 7.37–7.44 m (2H, Harom), 7.50–7.62 m
(4H, Harom), 7.72–7.82 m (3H, Harom). Mass spectrum:
m/z 428.1543 [M + H]+. Found, %: C 67.41; H 4.94;
N 16.39. C24H21N5OS. Calculated, %: C 67.43;
H 4.95; N 16.38.
2-[6-Ethenyl-5-(4-iodophenyl)-3-phenyl-5,6-di-
hydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-benzothiazole
(5e). Yield 163 mg (39%), mp 194–196°C (from
MeOH). IR spectrum, ν, cm–1: 3164, 1595, 1530, 1502,
Crystallographic data: C24H21N5OS; triclinic crystal
system, space group P-1; unit cell parameters: a =
8.8591(9), b = 9.6878(10), c = 13.9252(19) Å; α =
107.923(13), β = 107.267(10), γ = 94.244(8)°; V =
1067.8(2) Å3; Z = 2; μ = 0.178 mm–1. Total of 16033
reflection intensities were measured in the range
3.20 < θ < 33.70°, including 7294 independent reflec-
tions (Rint = 0.0343). Final divergence factors: R1 =
0.1316, wR2 = 0.0867 (all independent reflections);
R1 = 0.0443, wR2 = 0.0814 [reflections with I > 2σ(I)];
goodness of fit S = 1.002; residual electron density
peaks 0.324/–0.261 ēÅ–3. The complete set of X-ray
diffraction data for compound 7 was deposited to the
Cambridge Crystallographic Data Centre (CCDC entry
no. 1965416).
1
1447, 1275, 1194, 1010, 751, 692. H NMR spectrum,
δ, ppm: 5.26–5.49 m (2H, =CH2), 5.94–6.12 m (1H,
CH), 6.83–6.93 m (1H, CH), 7.09 t (1H, Harom, J =
7.2 Hz), 7.15 and 7.63 AA′BB′ (4H, Harom, J = 8.7 Hz),
7.29 t (1H, Harom, J = 7.2 Hz), 7.48–7.59 m (4H, Harom),
7.77 d (1Harom, J = 8.1 Hz), 7.82–7.92 m (2H, Harom),
9.61 br.s (1H, NH). 13C NMR spectrum, δC, ppm:
70.93, 118.72, 119.02, 120.23, 121.38, 121.45, 125.81,
126.01, 128.64, 130.69, 130.78, 130.97, 131.19,
137.85, 144.66, 149.57, 152.16, 166.36. Mass spec-
trum: m/z 524.0392 [M + H]+. Found, %: C 52.77;
H 3.45; N 13.39. C23H18IN5S. Calculated, %: C 52.78;
H 3.47; N 13.38.
2-[6-Ethenyl-5-(4-iodophenyl)-3-phenyl-4-(prop-
2-en-1-yl)-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl]-1,3-
benzotihazole (6) was isolated as a by-product in the
synthesis of 5e. Yield 16 mg (3.4%), mp 88–90°C
(from MeOH). IR spectrum, ν, cm–1: 3161, 1592, 1528,
ACKNOWLEDGMENTS
The spectral and analytical data were obtained using the
facilities of the Spectroscopy and Analysis of Organic
Compounds joint center at the Postovskii Institute of Organic
Synthesis (Ural Branch, Russian Academy of Sciences).
1
1506, 1446, 1275, 1194, 1009, 748, 693. H NMR
spectrum, δ, ppm: 3.89–4.01 m (2H, CH2), 5.12 d and
5.43 d (2H, =CH2, J = 10.2 Hz), 5.15 d and 5.29 d
(2H, =CH2, J = 17.1 Hz), 5.85–6.00 m (1H, CH), 6.20–
6.33 m (1H, CH), 6.97–7.00 m (1H, Harom), 7.09 t and
7.28 t (2H, Harom, J = 7.6 Hz), 7.27 d (1H, Harom, J =
8.8 Hz), 7.46–7.54 m (2H, Harom), 7.54–7.60 m (2H,
FUNDING
This study was performed in the framework of state
assignment (project nos. AAAA-A19-119012290117-6,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

FEDORCHENKO et al.
48
AAAA-A19-119012490006-1, AAA-A19-119011790130-3)
and under financial support by the Ural Branch, Russian
Academy of Sciences (project no. 18-3-3-16).
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CONFLICT OF INTEREST
The authors declare the absence of conflict of interest.
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