1,3-Dipolar cycloaddition of 3-phenylamino-5-phenylimino-1,2,4-dithiazole to 1-acyl-2-phenylacetylenes - A new route to functionalized 1,3-thiazole derivatives

Article abstract of DOI:10.1134/S1070428008100230

3-Phenylamino-5-phenylimino-1,2,4-dithiazole reacted with 1-acyl-2-phenylacetylenes in ethanol or toluene on heating (78-80°C, 1 h) in chemo- and regioselective fashion to give previously unknown N-[5-acyl-3,4-diphenyl-1,3-thiazol-2(3H)-ylidene]-N′-phenyl

Full text of DOI:10.1134/S1070428008100230

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 10, pp. 1532–1537. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © T.E. Glotova, M.Yu. Dvorko, A.I. Albanov, O.N. Kazheva, G.V. Shilov, O.A. D’yachenko, 2008, published in Zhurnal Organicheskoi
Khimii, 2008, Vol. 44, No. 10, pp. 1554–1558.
Dedicated to Full Member of the Russian Academy of Sciences
B.A. Trofimov on his 70th anniversary
1,3-Dipolar Cycloaddition of 3-Phenylamino-5-phenylimino-
1,2,4-dithiazole to 1-Acyl-2-phenylacetylenes—A New Route
to Functionalized 1,3-Thiazole Derivatives
T. E. Glotovaa, M. Yu. Dvorkoa, A. I. Albanova, O. N. Kazhevab,
G. V. Shilovb, and O. A. D’yachenkob
a Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: glotova@irioch.irk.ru
b Institute of Chemical Physics Problems, Russian Academy of Sciences,
Chernogolovka, Moscow oblast, Russia
Received June 3, 2008
Abstract—3-Phenylamino-5-phenylimino-1,2,4-dithiazole reacted with 1-acyl-2-phenylacetylenes in ethanol
or toluene on heating (78–80°C, 1 h) in chemo- and regioselective fashion to give previously unknown
N-[5-acyl-3,4-diphenyl-1,3-thiazol-2(3H)-ylidene]-N′-phenylthioureas (yield 57–60%). The structure of
N-[5-benzoyl-3,4-diphenyl-1,3-thiazol-2(3H)-ylidene]-N′-phenylthiourea was proved by X-ray analysis.
DOI: 10.1134/S1070428008100230
Thiazoles constitute one of the most important
classes of heterocyclic compounds due to their role in
many biological processes. Thiazole ring is a structural
fragment of natural compounds (where it is formed
from cysteine fragments of peptides) such as thiamine
(vitamin B1), carboxylase, and penicillin and some
medical agents [1]. Many synthetic thiazole derivatives
exhibit diverse biological activity, in particular anti-
bacterial, fungicidal, spasmolytic, and antiinflamma-
tory [2–10]. 2-Amino-substituted thiazoles (e.g., thia-
zolylthioureas) were found to be active against tumor
cells [11] and human immunodeficiency virus [12–14].
Therefore, search for new functionalized thiazole de-
rivatives and development of convenient methods for
their preparation remain important problems.
The most commonly used procedure for building up
1,3-thiazole ring is based on the Hantzsch reaction of
α-halo ketones with thioamides and related compounds
[2, 4, 15–19]; thiazole derivatives were also obtained
by reactions of thioureas with acylbromoacetylenes
[20] and of thioamides with acetylenedicarboxylic acid
esters [21, 22].
The goal of the present study was to develop a new
synthetic approach to functionally substituted 1,3-thia-
zoles having an acyl group in the 5-position and a thio-
urea fragment in the 2-position via reaction of 1-acyl-
Scheme 1.
Ph
Ph
N
S
N
EtOH or MePh
78–80°C, 1 h
O
R
S
S
NH
S
N
S
+
+
Ph
R
S
NHPh
PhNH
PhNH
NPh
N
O
I
IIa–IIc
IIIa–IIIc
IV
R = Me (a), Ph (b), 2-thienyl (c).
1532

1,3-DIPOLAR CYCLOADDITION OF 3-PHENYLAMINO-5-PHENYLIMINO-...
1533
Scheme 2.
Ph
Ph
N
N
PhNH
I
+
IIa–IIc
IIIa–IIIc
S
S
O
R
A
2-phenylacetylenes with 3-phenylamino-5-phenyl-
imino-1,2,4-dithiazole. The latter is a representative of
amino-substituted 1,2,4-dithiazoles that are obtained
by oxidation of 2,4-dithiobiuret derivatives which are
readily synthesized from accessible thiourea of sub-
stituted thioureas and isothiocyanates [23–26]. It is
known that diamino-1,2,4-dithiazoles readily react
with dipolarophiles (such as dimethyl acetylenedicar-
boxylate, nitriles, isothiocyanates, carbon disulfide) to
give the corresponding N-(1,3-thiazol-2-ylidene-,
1,3,5-thiadiazol-2-ylidene, or 1,2,4-thiadiazol-5-
ylidene)thioureas [27–29]. Analogous reactions with
dipolarophilic 1-acyl-2-phenylacetylenes were not
reported.
N-(1,3-Benzothiazol-2-yl)-N′-phenylthiourea (IV)
is likely to be formed via intramolecular rearrangement
of initial 1,2,4-dithiazole I through intermediate B
(Scheme 3); this rearrangement is favored by thermal
instability of compound I. Analogous thermal or acid-
catalyzed rearrangements were described in [30, 31].
The molecular and crystalline structures of com-
pound IIIb were determined by X-ray analysis of
a single crystal which was obtained by isothermal
evaporation of a solution of 0.1 g of IIIb in 40 ml of
1
DMSO at 20°C; the IR and H and 13C NMR spectra
confirmed the structure of thiazoles IIIa–IIIc.
The (i) fragment in the molecule of N-[5-benzoyl-
3,4-diphenyl-1,3-thiazol-2(3H)-ylidene]-N′-phenyl-
We found that 3-phenylamino-5-phenylimino-1,2,4-
dithiazole (I) reacts with 1-acetyl-, 1-benzoyl-, and
1-(2-thenoyl)-2-phenylacetylenes IIa–IIc in toluene or
ethanol at 78–80°C (reaction time 1 h) to give 57–60%
of the corresponding N-[5-acyl-3,4-diphenyl-1,3-thia-
zol-2(3H)-ylidene]-N′-phenylthioureas IIIa–IIIc and
18–21% of N-(1,3-benzothiazol-2-yl)-N′-phenylthio-
urea (IV) (Scheme 1). Presumably, compounds IIIa–
IIIc are formed as a result of concerted process
through transition state A with circular delocalization
of electrons; electron density transfer along the closed
path is accompanied by closure of 1,3-thiazole ring,
while cleavage of the S–S bond gives rise to thiourea
fragment in position 2 of the newly formed thiazole
ring (Scheme 2). The concerted mechanism of the
process is supported by the fact that the yield of the
target product remains almost the same upon variation
of the solvent polarity (ε = 24.3 and 2.4 for ethanol and
toluene, respectively), other conditions (reaction time,
temperature, reactant concentration) being equal.
iii
iv
ii
N
S
N
S
v
HN
O
i
C23
C24
C19
C15
C22
C21
C20
C16
C17
C14
C13
C10
C18
N1
C6
C29
C28
C9
C30
C8
C31
N3
C2
S2
C4
C3
C7
C11
C25
C27
N2
C26
O1
C12
H2
S1
O2
S3
Scheme 3.
C33
C32
N
N
I
IV
Fig. 1. Structure of the molecule of N-[5-benzoyl-3,4-di-
phenyl-1,3-thiazol-2(3H)-ylidene]-N′-phenylthiourea (IIIb)
and solvate DMSO molecule according to the X-ray diffrac-
tion data.
S
NHPh
H
S
B
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 10 2008

GLOTOVA et al.
1534
form with molecules IIIb shortened intermolecular
a
contacts O2 ···N2 2.832(6) and O2 ···H2 2.03(6) Å
(the corresponding sums of the van der Waals radii are
3.1 and 2.7 Å [32]), the angle O2H2N2 being 161(6)°
(Figs. 2, 3).
Thus 1,3-dipolar cycloaddition of 3-phenylamino-
5-phenylimino-1,2,4-dithiazole to 1-acyl-2-phenylacet-
ylenes ensures one-step formation of a thiazole ring
and side-chain thiourea fragment. This reaction can be
regarded as a general synthetic route to new function-
alized 1,3-thiazolylthioureas that are promising as pre-
cursors of novel medicines.
b
0
c
EXPERIMENTAL
Fig. 2. Crystalline structure of N-[5-benzoyl-3,4-diphenyl-
1,3-thiazol-2(3H)-ylidene]-N′-phenylthiourea (IIIb) accord-
ing to the X-ray diffraction data.
The IR spectra were recorded in KBr on a Bruker
1
IFS25 spectrometer. The H and 13C NMR spectra
were measured on a Bruker-400 spectrometer (400.13
1
and 100.61 MHz for H and 13C, respectively) using
DMSO-d6 as solvent and hexamethyldisiloxane as
internal reference. X-Ray analysis was performed at
room temperature on a KM-4 Kuma Diffraction instru-
ment (MoKα irradiation, graphite monochromator,
ω/2θ scanning).
N-Phenyl-3-phenylimino-3H-1,2,4-dithiazol-5-
amine (I). A solution of 5 mmol of molecular iodine in
10 ml of ethanol was slowly added to a solution of
1.43 g (5 mmol) of 1,5-diphenyl-2,4-dithiobiuret (pre-
pared from N-phenylthiourea and phenyl isothiocya-
nate according to the procedure reported in [26]) in
100 ml of diethyl ether under vigorous stirring at 20°C.
The precipitate was filtered off, washed with diethyl
ether, and dried under reduced pressure. We thus ob-
tained 1.69 g (82%) of N-phenyl-3-phenylimino-3H-
1,2,4-dithiazol-5-amine hydroiodide as yellow crystals
with mp 177°C (from ethanol). IR spectrum: ν 2870–
O2
H2
N2
Fig. 3. Shortened contacts O2···N2 and O2···H2–N2 between
N-[5-benzoyl-3,4-diphenyl-1,3-thiazol-2(3H)-ylidene]-N′-
phenylthiourea (IIIb) and DMSO molecules in crystal.
2980 cm–1, br (NH2+). H NMR spectrum, δ, ppm:
1
7.31–7.60 m (10H, Harom), 12.13 br.s (NH). 13C NMR
spectrum, δC, ppm: 121.69, 127.14, 129.63, 137.83
(Carom); 177.10 (C3, C5). Found, %: C 40.92; H 2.73;
I 31.08; N 10.06; S 15.80. C14H11N3S2·HI. Calculated,
%: C 40.68; H 2.93; I 30.71; N 10.17; S 15.52.
thiourea (IIIb) (Fig. 1) is approximately planar: the
maximal deviation of non-hydrogen atoms from the
mean-square plane is 0.23 Å (O1). The dihedral angles
formed by the (i) plane, on the one hand, and benzene
ring planes (ii), (iii), (iv), and (v), on the other, are
159.4, 91.7, 113.5, and 124.3°, respectively; the di-
hedral angles between the (ii)–(iii), (ii)–(iv), (ii)–(v),
(iii)–(iv), (iii)–(v), and (iv)–(v) planes are, respectively,
103.3, 104.5, 108.2, 108.1, 94.0, and 155.5°.
N-Phenyl-3-phenylimino-3H-1,2,4-dithiazol-5-
amine hydroiodide, 0.83 g (2 mmol), was dispersed in
30 ml of acetonitrile, 15 ml of 12% aqueous ammonia
was added, the mixture was stirred for 15 min, 60 ml
of water was added, and the mixture was stirred for
an additional 1 h. The precipitate was filtered off,
washed with water, and dried under reduced pressure
over calcium chloride. Yield 0.53 g (93%), yellow
The crystalline structure of compound IIIb includes
channels accommodating DMSO molecules which
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 10 2008

1,3-DIPOLAR CYCLOADDITION OF 3-PHENYLAMINO-5-PHENYLIMINO-...
1535
amorphous substance, mp 170–172°C. IR spectrum:
N-[5-Acetyl-3,4-diphenyl-1,3-thiazol-2(3H)-
ylidene]-N′-phenylthiourea (IIIa). Yield 0.50 g
(58%) (a), 0.49 g (57%) (b); yellow finely crystalline
powder, mp 219–220°C. IR spectrum, ν, cm–1: 3220
(NH); 1650 (C=O); 1470, 1490, 1510, 1600 (C=C,
1
ν 3250 cm–1 (NH). H NMR spectrum, δ, ppm: 7.15–
7.66 m (10H, Harom), 11.19 br.s (1H, NH). 13C NMR
spectrum, δC, ppm: 120.64, 124.86, 129.69, 139.63
(Carom); 150.63, 168.99 (C3, C5). Found, %: C 58.90;
H 3.84; N 14.86; S 22.73. C14H11N3S2. Calculated, %:
C 58.92; H 3.88; N 14.72; S 22.47.
1
C=N, δNH). H NMR spectrum, δ, ppm: 1.91 (3H,
Me), 6.81–7.47 m (15H, Harom), 10.29 br.s (1H, NH).
13C NMR spectrum, δC, ppm: 28.52 (Me); 120.05,
122.56, 127.50, 128.16, 128.82, 129.10, 129.23,
129.37, 130.27, 130.99, 137.45, 137.78, 139.78 (C5,
Carom); 144.76 (C4); 169.37 (C2); 183.58 (C=S); 190.72
(C=O). Found, %: C 67.36; H 4.42; N 10.02; S 14.85.
C24H19N3OS2. Calculated, %: C 67.11; H 4.46; N 9.78;
S 14.93.
1-Acyl-2-phenylacetylenes IIa–IIc (general proce-
dure). The corresponding acetylenic alcohols were
prepared by the Iotsitch reaction. A solution of 30.6 g
(0.3 mol) of phenylacetylene in 20 ml of anhydrous
diethyl ether was added at 0–5°C to the Grignard com-
pound prepared from 7.2 g (0.3 mol) of magnesium
and 32.7 g (0.3 mol) of ethyl bromide in 250 ml of
anhydrous diethyl ether. The mixture was heated for
4 h on a water bath and cooled to 0–5°C, a solution of
0.3 mol of the corresponding aldehyde in 20 ml of
anhydrous diethyl ether was added, and the mixture
was stirred for 1 h and was left overnight. The mixture
was treated with a saturated solution of ammonium
chloride and extracted with diethyl ether (500 ml). The
extract was dried over MgSO4 and filtered, and the
filtrate was treated with 130.5 g (1.5 mol) of active
manganese dioxide at 20°C over a period of 5–6 h. The
precipitate of MnO2 was filtered off and washed with
diethyl ether (500 ml), and the solvent was distilled off
under reduced pressure to isolate compounds IIa–IIc.
N-[5-Benzoyl-3,4-diphenyl-1,3-thiazol-2(3H)-
ylidene]-N′-phenylthiourea (IIIb). Yield 0.59 g
(60%) (a), 0.58 g (59%) (b); yellow finely crystalline
powder, mp 219–220°C. IR spectrum, ν, cm–1: 3200
(NH); 1610 (C=O); 1460, 1480, 1510, 1590 (C=C,
1
C=N, δNH). H NMR spectrum, δ, ppm: 6.82–7.54 m
(20H, Harom), 10.44 br.s (1H, NH). 13C NMR spectrum,
δC, ppm: 120.22, 122.56, 127.50, 127.97, 128.16,
128.82, 129.10, 129.23, 129.37, 130.99, 132.22,
137.45, 137.78, 139.78 (C5, Carom); 144.76 (C4); 169.82
(C2); 183.24 (C=S); 189.34 (C=O). Found, %: C 70.69;
H 4.23; N 8.83; S 13.32. C29H21N3OS2. Calculated, %:
C 70.85; H 4.31; N 8.55; S 13.04.
X-Ray diffraction data for compound (IIIb).
C31H27N3O2S3, M 569.74, monoclinic crystals, space
group P21/n; unit cell parameters: a = 16.458(3), b =
9.932(2), c = 18.468(4) Å; β = 101.53(3)°; V =
2957.9(1) Å3; Z = 4; dcalc = 1.28 g/cm3; μ = 0.283 mm–1.
Total of 5467 reflections were measured, 4376 of
which were independent; 367 refined parameters; R =
0.061 for 2090 reflections with F0 > 4σ(F0). The struc-
ture was solved by the direct method with subsequent
Fourier syntheses using SHELXS-97 software [35].
The structure was refined by the least-squares proce-
dure in full-matrix anisotropic approximation for all
non-hydrogen atoms using SHELXL-97 program [36].
The positions of hydrogen atoms were calculated on
the basis of geometry considerations; the H2 atom was
localized experimentally. The sulfur atom in the
DMSO molecule was disordered by two positions with
populations of 0.86 and 0.14. The complete set of
crystallographic data (coordinates of atoms and tables
of bond lengths and bond angles) was deposited to
the Cambridge Crystallographic Data Center (entry
no. CCDC 684937).
4-Phenylbut-3-yn-2-one (IIa). Yield 36.3 g (84%),
bp 122–124°C (12 mm); published data [33]: bp 122–
128°C (12 mm).
1,3-Diphenylprop-2-yn-1-one (IIb). Yield 50.7 g
(82%), yellow crystals, mp 49–50°C; published data
[33]: mp 49–50°C.
3-Phenyl-1-(2-thienyl)prop-2-yn-1-one (IIc).
Yield 47.7 g (75%), yellow crystals, mp 63–64°C
(from EtOH); published data [34]: mp 54°C.
Reaction of N-phenyl-3-phenylimino-3H-1,2,4-
dithiazol-5-amine (I) with 1-acyl-2-phenylacetylenes
IIa–IIc (general procedure). Acylacetylene IIa–IIc,
2 mmol, was dissolved in 20 ml of (a) toluene or (b)
ethanol, 0.57 g (2 mmol) of compound I was added,
and the mixture was stirred for 1 h at 78–80°C. The
mixture was cooled, and the precipitate was filtered
off, washed with diethyl ether, and dried under reduced
pressure. We thus isolated compounds IIIa–IIIc; the
products were highly pure, and no recrystallization was
necessary to obtain analytically pure samples. The
filtrate was concentrated to a volume of 5–6 ml and
kept for 24 h at 0–5°C, and the precipitate was filtered
off. Yield of compound IV 0.1–0.12 g (18–21%).
N-[3,4-Diphenyl-5-(2-thienyl)-1,3-thiazol-2(3H)-
ylidene]-N′-phenylthiourea (IIIc). Yield 0.57 g
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 10 2008

GLOTOVA et al.
1536
11. Wilson, K.J., Illig, C.R., Subasinghe, N., Hoffman, J.B.,
Rudolph, M.J., Soll, R., Molloy, C.J., Bone, R.,
Green, D., Randall, T., Zhang, M., Lewandowski, F.A.,
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Johansson, N.G., Jordan, C.L., Kinnick, M.D., Lind, P.,
Morin, J.M., Jr., Noreen, R., Bo Öberg, Palkowitz, J.A.,
Parrish, C.A., Pranc, P., Sahlberg, C., Ternansky, R.J.,
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(57%) (a), 0.59 g (59%) (b); yellow finely crystalline
powder, mp 209–210°C. IR spectrum, ν, cm–1: 3200
(NH); 1605 (C=O); 1480, 1500, 1510, 1575 (C=C,
1
C=N, δNH). H NMR spectrum, δ, ppm: 6.79–7.88 m
(18H, Harom), 10.35 br.s (1H, NH). 13C NMR spectrum,
δC, ppm: 119.13, 120.64, 122.94, 128.22, 128.57,
129.53, 129.78, 131.19, 136.01, 136.08, 138.25,
140.23, 143.09 (C5, Carom); 143.65 (C4); 169.82 (C2);
180.33 (C=O); 183.44 (C=S). Found, %: C 65.24;
H 4.01; N 8.75; S 19.07. C27H19N3OS3. Calculated, %:
C 65.16; H 3.85; N 8.44; S 19.33.
13. Venkatachalam, T.K., Sudbeck, E.A., Mao, C., and
Uckun, F.M., Bioorg. Med. Chem. Lett., 2000, vol. 10,
p. 2071.
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Sgarabotto, P., J. Chem. Soc., Perkin Trans. 1, 1999,
p. 1363.
N-(1,3-Benzothiazol-2-yl)-N′-phenylthiourea
(IV). Light red crystals, mp 198–200°C; published
data [37]: mp 201°C. IR spectrum, ν, cm–1: 3220, 3150
(NH); 1490, 1505, 1560, 1580 (C=C, C=N, δNH).
1H NMR spectrum, δ, ppm: 7.09–7.82 m (9H, Harom),
10.82 s (1H, NH), 12.78 s (1H, PhNH). 13C NMR
spectrum, δC, ppm: 115.31, 118.92, 122.44, 123.01,
123.58, 124.43, 126.76, 128.57, 129.06, 139.59
(Carom); 166.34 (C2); 182.61 (C=S). Found, %: C 58.67;
H 3.90; N 14.53; S 22.67. C14H11N3S2. Calculated, %:
C 58.92; H 3.88; N 14.72; S 22.47.
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