Oxidative cyclization of 2-arylhydrazonothioacetamides

Article abstract of DOI:10.1023/B:RUJO.0000044544.80187.49

Intramolecular oxidative cyclization of 2-arylhydrazonothioacetamides was studied, and applicability limits of this reaction for the synthesis of 2-aryl-1,2,3-thiadiazol-5(2H)-imines were determined.

Full text of DOI:10.1023/B:RUJO.0000044544.80187.49

Russian Journal of Organic Chemistry, Vol. 40, No. 6, 2004, pp. 818–828. Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 6, 2004,
pp. 859–868.
Original Russian Text Copyright © 2004 by Vasil’eva, Mukhacheva, Bel’skaya, Bakulev, Anderson, Groundwater.
Dedicated to Full Member of the Russian Academy of Sciences
O.N. Chupakhin on his 70th Anniversary
Oxidative Cyclization of 2-Arylhydrazonothioacetamides
M. L. Vasil’eva1, M. V. Mukhacheva1, N. P. Bel’skaya1, V. A. Bakulev1,
R. J. Anderson2, and P. V. Groundwater2
1 Ural State Technical University, ul. Mira 19, Yekaterinburg, 620002 Russia
e-mail: belska@htf.ustu.ru
2 University of Sunderland, Warncliffe Street, Sunderland SR1 3SD, UK
e-mail: roz.Anderson@sunderland.ac.uk
Received January 12, 2004
Abstract—Intramolecular oxidative cyclization of 2-arylhydrazonothioacetamides was studied, and applic-
ability limits of this reaction for the synthesis of 2-aryl-1,2,3-thiadiazol-5(2H)-imines were determined.
zonothioacetamides (which was proved on a few
examples) and determine its applicability limits for the
synthesis of a large series of 1,2,3-thiadiazole deriva-
tives. For this purpose, we examined intramolecular
dehydrogenation of arylhydrazonothioacetamides
having various substituents in the aromatic ring (both
electron-donor and electron-acceptor) and R' groups
(Scheme 1).
Thioamides are known to readily undergo oxida-
tion. Depending on the substrate structure, oxidant
nature, and reaction conditions, the products may be
both linear compounds [1] and complex heterocyclic
systems [1–30]. For example, primary thioamides are
converted into nitriles by the action of mild oxidants
[1, 3–5], or they undergo cyclization to 1,2,4-thiadi-
azoles through intermediate formation of dimers [1–9].
Oxidation of thiobenzamides provides a convenient
synthetic route to benzothiazoles [10–11]. Func-
tionalization of thioamides via introduction of addi-
tional oxidation-sensitive groups gives rise to mono-
cyclic and fused heterocyclic compounds [12–29].
Oxidative intramolecular cyclization of propanedithio-
amides leads to formation of 3,4-diamino-1,2-di-
thiolium salts [12–16]. When a thioamide molecule
contains a carbamoyl or amino group, various iso-
thiazoles can be obtained [17–21]. Oxidation of thio-
carbamoyl enamine derivatives could give benzo-
thiazoles, isothiazoles, and pyrroles [22–25], while
secondary thioamides derived from γ,δ-alkenes are
oxidized with iodine to afford γ-butyrothiolactones
with high stereoselectivity [27]. According to the data
of [28–30], oxidative cyclization of arylhydrazonothio-
acetamides yields 5-amino-2-phenyl-1,2,3-thiadiazo-
lium salts.
In all cases, the oxidation of arylhydrazonothio-
acetamides I with bromine in acetic acid afforded
2-aryl-5-imino-2,5-dihydro-1,2,3-thiadiazole hydro-
bromides II as the major products (yield 14–99%;
Table 1). Their structure was confirmed by the spectral
data (Tables 2–4) and elemental analyses (Table 1).
1
The H NMR spectra of compounds II (Table 2)
contained signals from protons in the aromatic ring and
substituent in position 4 of the thiadiazole ring; also,
two broadened one-proton singlets and one two-proton
singlet were present in the region of δ 10 ppm, which
correspond to protonated imino group. 1,2,3-Thia-
diazoles II showed in the mass spectra (Table 4)
the molecular ion peak with a relative intensity of 1.2
to 91% and peaks of fragment ions arising from
elimination of the side-chain substituents. Character-
istically, the electron impact mass spectra contained
peaks from stable fragment ions formed by decom-
position of the thiadiazole ring. For example, cleavage
of the N–S bond in the molecular ion, followed by
extrusion of sulfur, gives ion F6, and simultaneous
cleavage of the N–S and N–C2 bonds gives rise to the
Taking into account that some 1,2,3-thiadiazole
derivatives were recently shown to exhibit high bio-
logical activity [31–34], we planned to further develop
the procedure for dehydrocyclization of 2-arylhydra-
1070-4280/04/4006-0818 © 2004 MAIK “Nauka/Interperiodica”

OXIDATIVE CYCLIZATION OF 2-ARYLHYDRAZONOTHIOACETAMIDES
819
Scheme 1.
a: Br2, AcOH
b: I2, AcOH
c: NCS, AcOEt
R'
R'
H
H
N
NH2
N
NH2
N
N
R
R
S
S
Hlg Hlg
Ia–Ias
R'
R'
R'
H
H
N
N
NH2
N
NH
Hlg
N
N
NH
·HHlg
N
R
R
S
–HHlg
S
S
R
Hlg
Hlg–
Hlg–
A
B
IIa–IIap, IIIa–IIIc, IVa–IVc
I, R = 4-OMe, R' = CONH2 (a), CONHMe (b), CONHCH2CH2OMe (c), CONHC6H11 (d), CONHC6H4OMe-4 (e), CONHPh (f),
CONHC6H4Cl-4 (g), COOEt (h), CON(CH2CH2)2NMe (i); R = H, R' = CONH2 (j), COOEt (k); R = 4-F, R' = CONH2 (l),
CONHMe (m), CONHC6H11 (n), CONHCH2Ph (o), CONHC6H4OMe-4 (p), CONHPh (q), CONHC6H4Cl-4 (r), CN (s); R = 4-Cl,
R' = CONH2 (t), CONHMe (u), CONHC6H11 (v), CONHCH2Ph (w), CONHC6H4OMe-4 (x), CONHPh (y), CONHC6H4Cl-4 (z),
COOEt (aa), CN (ab), CON(CH2CH2)2NMe (ac), CON(CH2CH2)2 (ad); R = 4-CONH2, R' = CONH2 (ae), CONHMe (af),
CONHC6H11 (ag), CONHCH2Ph (ah), CONHPh (ai), CONHC6H4Cl-4 (aj), CON(CH2CH2)2 (ak); R = 4-COOEt, R' = CONH2 (al);
R = 4-NO2, R' = CONH2 (am); R = 3-CF3, R' = CON(CH2CH2)2 (an); R = 2-OMe, R' = CONHMe (ao); R = 2-Cl, R' = CONH2 (ap),
CONHMe (aq); R = 2,6-Cl2, R' = CON(CH2CH2)2NMe (ar), CONH(CH2CH2)O (as); II, Hlg = Br; R = 4-OMe, R' = CONH2 (a),
CONHMe (b), CONHCH2CH2OMe (c), CONHC6H11 (d), CONHC6H3Br-3-OMe-4 (e), CONHPh (f), CONHC6H4Cl-4 (g),
CON(CH2CH2)2NMe (h), COOEt (i); R = H, R' = CONH2 (j), COOEt (k); R = 4-F, R' = CONH2 (l), CONHMe (m),
CONHC6H11 (n), CONHCH2Ph (o), CONHPh (p), CONHC6H4Cl-4 (q), CN (r); R = 4-Cl, R' = CONH2 (s), CONHMe (t),
CONHC6H11 (u), CONHCH-2Ph (v), CONHPh (w), CONHC6H4Cl-4 (x), COOEt (y), CN (z), CON(CH2CH2)2NMe (aa),
CON(CH2CH2)2 (ab); R = 4-CONH2, R' = CONH2 (ac), CONHMe (ad), CONHC6H11 (ae), CONHCH2Ph (af), CONHPh (ag),
CONHC6H4Cl-4 (ah), CON(CH2CH2)2 (ai); R = 4-COOEt, R' = CONH2 (aj); R = 4-NO2, R' = CONH2 (ak); R = 2-OMe, R' =
CONHMe (al); R = 2-Cl, R' = CONH2 (am), CONHMe (an); R = 2,6-Cl2, R' = CON(CH2CH2)2NMe (ao), CON(CH2CH2)O (ap);
III, Hlg = I; R = 4-OMe, R' = CONHC6H4OMe-4 (a); R = 4-F, R' = CONHC6H4OMe-4 (b); R = 4-Cl, R' = CONHC6H4OMe-4 (c);
IV, Hlg = Cl; R = OMe, R' = CONH2 (a); R = C6H4CF3-3, R' = CON(CH2CH2)2 (b); R = 4-COOEt, R' = CONH2 (c).
Table 1. Yields, melting points, and elemental analyses of 1,2,3-thiadiazoles IIa–IIap, IIIa–IIIc, and IVa–IVc and
1,2,4-thiadiazoles Va–Vc
Found, %
Calculated, %
Comp.
no.
Methoda
Yield, %
mp, °C
Formula
N
S
N
S
a
a
a
a
a
a
a
a
a
a
a
a
a
51
99
90
99
86
72
99
65
83
51
60
81
97
266
250
195
241
223
215
238
226
242
225
205
221
250
19.63
16.57
16.02
13.42
10.56
11.46
13.50
17.25
11.79
18.38
12.90
17.34
16.08
10.05
09.52
09.22
07.73
06.43
08.56
07.48
08.02
09.04
10.73
10.00
10.61
09.46
C10H11BrN4O2S
C11H13BrN4O2S
C13H17BrN4O3S
C16H21BrN4O2S
C17H17Br2N4O3S
C12H14BrN3O3S
C16H14BrClN4O2S
C14H20BrN5O2S
C12H14BrN3O3S
C9H9BrN4OS
19.58
16.23
15.69
13.56
10.83
11.67
13.18
16.91
11.67
18.60
12.73
17.55
16.82
09.67
09.28
08.96
07.45
06.18
08.89
07.26
07.73
08.89
10.63
09.71
10.00
09.61
IIa
IIb
IIc
IId
IIe
IIf
IIg
IIh
IIi
IIj
C11H12BrN3O2S
C9H10BrFN4OS
C10H10BrFN4OS
IIk
IIl
IIm
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 6 2004

VASIL’EVA et al.
820
Table 1. Contd.
Comp.
Found, %
Calculated, %
Methoda
Yield, %
mp, °C
Formula
no.
N
S
N
S
a
a
81
52
95
98
69
84
90
52
86
87
96
23
55
94
99
99
76
81
97
78
92
56
39
13
69
81
79
83
52
65
67
33
69
55
78
99
95
25
263
260
13.33
13.18
11.53
13.28
14.87
16.89
16.45
13.70
13.38
13.78
12.98
11.79
14.40
16.91
14.92
20.20
19.76
16.80
16.16
16.84
15.32
14.15
15.44
20.49
16.60
16.81
16.19
15.63
12.63
11.21
12.01
11.10
19.63
14.52
15.65
22.43
13.50
28.25
08.25
07.51
06.48
07.82
10.89
09.17
09.35
07.85
07.74
07.95
07.25
08.13
10.15
07.83
08.48
09.50
09.15
07.69
07.52
07.81
07.22
08.35
08.43
09.32
08.98
07.72
09.17
07.32
07.42
06.73
06.98
06.79
11.32
08.58
09.03
06.48
05.18
06.52
C15H18BrFN4OS
C15H16BrFN4OS
C15H12BrFN4OS
C15H11BrClFN4OS
C9H6BrFN4S
13.97
13.69
11.79
13.05
14.66
16.71
16.06
13.43
13.18
13.63
12.58
11.52
14.10
16.75
14.39
20.35
19.55
16.43
16.20
16.67
15.42
14.61
15.01
20.23
16.23
16.72
16.05
15.49
12.73
11.55
11.84
11.49
19.58
14.81
15.38
22.22
13.43
28.11
07.98
07.82
06.74
07.46
10.63
09.55
09.17
07.67
07.53
07.79
07.19
07.89
10.06
07.66
08.23
09.30
08.94
07.51
07.37
07.62
07.05
08.04
08.58
09.25
09.29
08.01
09.23
07.08
07.29
06.59
06.77
06.54
11.19
08.45
08.79
06.35
05.00
06.43
IIn
IIo
a
266
IIp
a
286
IIq
a
>300>
253
IIr
a
C9H8BrClN4OS
C10H10BrClN4OS
C15H18BrClN4OS
C16H14BrClN4OS
C15H12BrClN4OS
C15H11BrCl2N4OS
C11H11BrClN3O2S
C9H6BrClN4S
IIs
a
>300>
>300>
263
IIt
a
IIu
a
IIv
a
267
IIw
IIx
a
275
a
193
IIy
a
>300>
>300>
270
IIz
a
C13H17BrClN5OS
C13H14BrClN4OS
C10H10BrN5O2S
C11H12BrN5O2S
C16H19BrN5O2S
C17H22BrN5O2S
C16H14BrN5O2S
C16H13BrN5O2S
C14H16BrN5O2S
C12H13BrN4O3S
C9H8BrN5O3S
IIaa
IIab
IIac
IIad
IIae
IIaf
IIag
IIah
IIai
IIaj
IIak
IIal
IIam
IIan
IIao
IIap
IIIa
IIIb
IIIc
IVa
IVb
IVc
Va
a
a
>300>
305
a
a
246
a
>300>
251
a
a
288
a
>300>
>300>
300
a
a
a
247
C10H11BrN4O2S
C9H8BrClN4OS
C10H10BrClN4OS
C14H16BrCl2N5OS
C13H13BrCl2N4O2S
C17H17IN4O3S
a
228
a
225
a
249
a
135
b
165
b
218
C16H14FIN4O2S
C16H14ClIN4O2S
C10H11ClN4O2S
C14H14ClF3N4OS
C12H13ClN4O3S
C20H18Cl2N8O2S
C30H32Cl2N8O2S
C18H14N10O6S
b
126
c
270
c
220
c
300
bab
bab
bab
249
250
Vb
300
Vc
a
Method a: oxidation with bromine in acetic acid at room temperature; method b: oxidation with iodine in acetic acid at room temperature;
method c: oxidation with N-chlorosuccinimide in ethyl acetate at room temperature.
b
Reflux, 10 min.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 6 2004

OXIDATIVE CYCLIZATION OF 2-ARYLHYDRAZONOTHIOACETAMIDES
821
Table 2. IR and 1H NMR spectra of 1,2,3-thiadiazoles IIa–IIap, IIIa–IIIc, and IVa–IVc and 1,2,4-thiadiazoles Va–Vc
Comp.
no.
IR spectrum, ν, cm–1
1H NMR spectrum (DMSO-d6), δ, ppm
1680 (C=O); 3220, 3360, 3.85 s (3H, OCH3), 7.12 d and 7.81 d (4H, Harom, J = 9.1 Hz), 7.98 s (1H, CONH),
IIa
3450 (NH)
8.35 s (1H, CONH), 9.75 s (2H, NH2+)
1660 (C=O); 2280, 3340, 2.88 d (3H, CH3, J = 4.9 Hz), 3.86 s (3H, OCH3), 7.13 d and 7.79 d (4H, Harom, J =
3420 (NH)
9.2 Hz), 8.85 q (1H, CONH, J = 4.9 Hz), 9.66 s (1H, NH2+), 9.74 s (1H, NH2+)
IIb
IIc
1660 (C=O); 2820, 2920 3.28 s (3H, OCH3), 3.47–3.52 m (4H, CH2CH2), 3.85 s (3H, OCH3), 7.18 d and
(CH); 3100, 3240 (NH)
7.84 d (4H, Harom, J = 9.1 Hz), 9.05 t (1H, CONH, J = 5.0 Hz), 9.64 s (1H, NH2+),
9.73 s (1H, NH2+)
1660 (C=O); 2850, 2930 1.30–1.89 m (10H, C6H11), 3.85 s (3H, OCH3), 4.68–4.84 m (1H, CH), 7.13 d and
IId
IIe
(CH); 3310, 3400 (NH)
7.85 d (4H, Harom, J = 9.1 Hz), 8.63 d (1H, CONH, J = 8.4 Hz), 9.56 s (1H, NH2+),
9.68 s (1H, NH2+)
1660 (C=O); 3250, 3320, 3.86 s (6H, OCH3), 7.07 d (1H, Harom, J = 9.2 Hz), 7.69 d.d (1H, Harom, J = 2.4,
3360 (NH)
6.4 Hz), 7.14 d and 7.91 d (4H, Harom, J = 9.2 Hz), 8.04 d (1H, Harom, J = 2.4 Hz),
9.72 s (1H, NH2+), 9.77 s (1H, NH2+), 10.52 s (1H, CONH)
1660 (C=O); 3100, 3180, 3.87 s (3H, OCH3), 7.11–7.18 m (2H, Harom), 7.37 t (2H, Harom, J = 8.2 Hz), 7.52 d
IIf
3310, 3450 (NH)
(1H, Harom, J = 8.8 Hz), 7.75 d and 7.89 d (4H, Harom, J = 8.8 Hz), 9.85 s (1H,
NH2+), 9.92 s (1H, NH2+), 10.48 s (1H, CONH)
1660 (C=O); 3200, 3310, 3.88 s (3H, OCH3), 7.14 d and 7.79 d (4H, Harom, J = 8.8 Hz), 7.36 d and 7.89 d (4H,
3450 (NH)
arom, J = 8.8 Hz), 9.76 s (2H, NH2+), 10.62 s (1H, CONH)
IIg
IIh
H
1620 (C=O); 2920, 2980, 2.83 s (3H, CH3), 3.33 s (3H, CH2), 3.86 s (3H, OCH3), 4.25 br.s (5H, CH2), 7.09 d
3060 (CH); 3340, 3420
(NH)
and 7.67 d (4H, Harom, J = 9.1 Hz), 11.70 s (2H, NH2+)
1680 (C=O); 2840, 2940, 1.39 t (3H, CH3, J = 7.3 Hz), 3.85 s (3H, OCH3), 4.47 q (2H, CH2, J = 7.3 Hz), 7.21 d
3000 (CH); 3310, 3450
(NH)
IIi
IIj
and 7.75 d (4H, Harom, J = 9.2 Hz), 9.75 s (2H, NH2+)
1660 (C=O); 3040, 3050 7.49–7.54 m (1H, Harom), 7.59–7.65 m (2H, Harom), 7.88–7.92 m (2H, Harom), 8.06 s
(CH); 3100, 3150, 3300
(NH)
(1H, CONH), 8.46 s (1H, CONH), 9.88 s (2H, NH2+)
1680 (C=O); 3010 (CH); 1.38 t (3H, CH3, J = 6.9 Hz), 4.48 q (2H, CH2, J = 6.9 Hz), 7.54–7.78 m (3H, Harom),
3100, 3160, 3300 (NH)
7.79–7.80 m (2H, Harom), 9.90 s (2H, NH2+)
1680 (C=O); 3180, 3280, 7.37 t (2H, Harom, J = 8.2 Hz), 7.92–7.98 m (3H, Harom, CONH), 8.30 s (1H, CONH),
3400, 3480 (NH)
10.00 s (2H, NH2+)
1660(C=O); 3060 (CH); 2.89 d (3H, CH3, J = 4.9 Hz), 7.36–7.43 m (2H, Harom), 7.89–7.97 m (2H, Harom),
IIk
IIl
IIm
3140, 3160, 3200, 3300,
3450 (NH)
8.88 q (1H, CONH, J = 4.9 Hz), 9.77 s (1H, NH2+), 9.87 s (1H, NH2+)
1660 (C=O); 2850, 2920 1.22–1.89 m (10H, C6H11), 3.78–3.89 m (1H, CH), 7.33–7.43 m (2H, Harom), 7.94–
IIn
(CH); 3200, 3240, 3340,
3360 (NH)
8.01 m (2H, Harom), 8.57 d (1H, CONH, J = 8.2 Hz), 9.76 s (1H, NH2+), 9.86 s (1H,
NH2+)
1650 (C=O); 2920, 3060 4.54 d (2H, CH2, J = 6.4 Hz), 7.19–7.44 m (7H, Harom), 7.90–7.97 m (2H, Harom),
(CH); 3280, 3450 (NH)
9.46 t (1H, CONH, J = 6.1 Hz), 10.01 s (2H, NH2+)
1680 (C=O); 2930, 3050 7.62–7.76 m (4H, Harom), 8.04–8.08 m (5H, Harom), 9.85 s (1H, NH2 ), 9.92 s (1H,
(CH); 3140, 3200, 3300,
3450 (NH)
IIo
IIp
+
NH2+), 10.81 s (1H, CONH)
1680 (C=O); 3250, 3350, 7.36–7.47 m (2H, Harom), 7.37 d and 7.79 d (4H, Harom, J = 8.8 Hz), 8.00–8.07 m (2H,
3450 (NH)
arom), 9.93 br.s (2H, NH2+), 10.64 s (1H, CONH)
1600 (C=O); 2250 (CH); 7.42–7.49 m (2H, Harom), 7.90–7.96 m (2H, Harom), 9.89 s (2H, NH2+)
3060, 3200, 3250 (NH)
IIq
IIr
H
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 6 2004

VASIL’EVA et al.
822
Table 2. Contd.
Comp.
no.
IR spectrum, ν, cm–1
1H NMR spectrum (DMSO-d6), δ, ppm
1680 (C=O); 3080 (CH); 7.59 d and 7.96 d (4H, Harom, J = 9 Hz), 8.02 s (1H, CONH), 8.41 s (1H, CONH),
3180, 3250, 3380, 3480
(NH)
IIs
10.04 s (2H, NH2+)
1670 (C=O); 2930, 3050 2.88 d (3H, CH3, J = 4.9 Hz), 7.59 d and 7.96 d (4H, Harom, J = 9 Hz), 8.85 q (1H,
(CH); 3240, 3310 (NH)
IIt
CONH, J = 4.9 Hz), 10.01 s (2H, NH2+)
–
1.21–1.91 m (10H, C6H11), 3.85 m (1H, CH), 7.59 d and 7.95 d (4H, Harom, J =
8.9 Hz), 8.59 d (1H, CONH, J = 7.9 Hz), 10.07 s (2H, NH2+)
IIu
IIv
IIw
1650 (C=O); 2910, 3050 4.54 d (2H, CH2, J = 6 Hz), 7.22–7.39 m (5H, Harom), 7.58 d and 7.91 d (4H, Harom
(CH); 3150, 3260 (NH)
,
J = 9 Hz), 9.50 t (1H, CONH, J = 6 Hz), 10.07 s (2H, NH2+)
1660 (C=O); 3090 (CH); 7.16 t (1H, Harom, J = 7.4 Hz), 7.38 t (2H, Harom, J = 8.0 Hz), 7.75 d (2H, Harom, J =
3280, 3350 (NH)
7.3 Hz), 7.63 d and 8.02 d (4H, Harom, J = 9.2 Hz), 10.12 br.s (2H, NH2+), 10.55 s
(1H, CONH)
1670 (C=O); 3040, 3090 7.49 d and 7.80 d (4H, Harom, J = 8.8 Hz), 7.75 d and 8.04 d (4H, Harom, J = 9.0 Hz),
(CH); 3210, 3340, 3420
(NH)
IIx
IIy
9.88 s (1H, NH2+), 9.96 s (1H, NH2+), 10.84 s (1H, CONH)
1750 (C=O); 2980, 3010 1.43 t (3H, CH3, J = 7.0 Hz), 4.49 q (2H, CH2, J = 7.0 Hz), 7.61 d and 7.82 d (4H,
(CH); 3120, 3270, 3450
(NH)
H
arom, J = 8.9 Hz), 9.99 s (2H, NH2+)
–
7.65 d and 7.90 d (4H, Harom, J = 8.9 Hz), 10.01 s (2H, NH2+)
IIz
1600 (C=O); 2905, 2970, 2.87 s (3H, CH3), 3.17–3.39 m (6H, CH2), 4.58 br.s (2H, CH2), 7.69 d and 7.79 d
3040 (CH); 3150, 3280,
3430 (NH)
IIaa
(4H, Harom, J = 9.0 Hz), 10.04 s (2H, NH2+)
1600 (C=O); 2870, 2980, 1.87–2.07 m (4H, CH2), 3.62 t (2H, CH2, J = 6.5 Hz), 3.93 t (2H, CH2, J = 6.5 Hz),
3080 (CH); 3230, 3450
(NH)
IIab
7.59 d and 7.76 d (4H, Harom, J = 8.9 Hz), 10.14 s (1H, NH2+), 10.19 s (1H, NH2+)
1680 (C=O); 3160, 3220, 8.04 s (1H, CONH), 7.97 d and 8.09 d (4H, Harom, J = 8.5 Hz), 8.48 s (1H, CONH),
3260, 3370 (NH)
9.88 s (2H, CONH2), 10.08 s (1H, NH2+), 10.13 s (1H, NH2+)
IIac
IIad
IIae
1660 (C=O); 3110, 3180, 2.88 d (3H, CH3, J = 4,6 Hz), 7.39 s (1H, CONH), 7.98–8.08 m (5H, Harom, CONH),
3240, 3340, 3405 (NH)
8.97 t (1H, CONH, J = 4.6 Hz), 10.05 s (2H, NH2+)
1680 (C=O); 2850, 2915, 1.20–1.90 m (10H, C6H11), 3.84 m (1H, CH), 7.38 s (1H, CONH), 7.98–8.09 m (5H,
3060 (CH); 3250, 3300,
3400 (NH)
H
arom, CONH), 8.67 d (1H, CONH, J = 7.0 Hz), 10.09 s (2H, NH2+)
1670 (C=O); 3050 (CH); 4.55 d (2H, CH2, J = 6.0 Hz), 7.21–7.39 m (6H, Harom, CONH), 7.97–8.09 m (5H,
3210, 3400 (NH)
arom, CONH), 9.56 t (1H, CONH, J = 6.0 Hz), 10.09 s (2H, NH2+)
IIaf
H
1650 (C=O); 3050, 3090 7.16 t (1H, Harom, J = 7.3 Hz), 7.38 m (3H, Harom, CONH), 7.79 d (2H, Harom, J =
(CH); 3180, 3210, 3400
(NH)
IIag
7.3 Hz), 8.13 m (5H, Harom, CONH2), 10.13 s (1H, NH2+), 10.22 s (1H, NH2+),
10.57 s (1H, CONH)
–
7.29–8.25 m (10H, Harom, CONH2), 10.13 s (1H, NH2+), 10.25 s (1H, NH2+), 10.73 s
(1H, CONH)
IIah
IIai
–
1.86–2.03 m (4H, CH2), 3.65 t (2H, CH2, J = 6.8 Hz), 3.92 t (2H, CH2, J = 6.5 Hz),
7.43 s (1H, CONH), 7.8 d and 8.01 d (4H, Harom, J = 8.8 Hz), 8.01 s (1H, CONH),
10.24 s (2H, NH2+)
1700 (C=O); 2980, 3030 1.35 t (3H, CH3, J = 7.1 Hz), 4.35 q (2H, CH2, J = 7.1 Hz), 8.04 d and 8.13 d (5H,
IIaj
(CH); 3160, 3260, 3400
(NH)
H
arom, CONH, J = 8.9 Hz), 8.56 s (1H, CONH), 10.07 s (1H, NH2+), 10.47 s (1H,
NH2+)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 6 2004

OXIDATIVE CYCLIZATION OF 2-ARYLHYDRAZONOTHIOACETAMIDES
823
Table 2. Contd.
Comp.
no.
IR spectrum, ν, cm–1
1H NMR spectrum (DMSO-d6), δ, ppm
1680 (C=O); 3000, 3050 8.09 s (1H, CONH), 8.21 d and 8.39 d (4H, Harom, J = 9.1 Hz), 8.54 s (1H, CONH),
(CH); 3100, 3160 3280,
3340, 3450 (NH)
IIak
10.27 s (1H, NH2+), 10.32 s (1H, NH2+)
–
2.89 d (3H, CH3, J = 4.6 Hz), 4.08 s (3H, OCH3), 7.15 t (1H, Harom, J = 7.3 Hz),
7.44 d (1H, Harom, J = 7.3 Hz), 7.47 t (1H, Harom, J = 7.3 Hz), 8.00 d (1H, Harom, J =
7.3 Hz), 8.86 q (1H, CONH, J = 4.6 Hz), 9.77 s (1H, NH2+), 9.87 s (1H, NH2+)
IIal
–
–
–
7.54–7.73 m (2H, Harom), 7.84–7.88 m (2H, Harom), 7.98 s (1H, CONH), 8.13 s (1H,
CONH), 10.00 s (1H, NH2+), 10.06 s (1H, NH2+)
IIam
IIan
IIao
2.86 d (3H, CH3, J = 4.8 Hz), 7.55–7.77 m (3H, Harom), 7.85 m (1H, Harom), 8.76 q
(1H, CONH, J = 4.8 Hz), 10.04 s (1H, NH2+), 10.08 s (1H, NH2+)
1.85–1.99 m (4H, CH2), 2.57 s (3H, CH3), 3.43–3.78 m (4H, CH2), 7.59–7.74 m (3H,
H
arom), 10.27 s (1H, NH2+), 10.49 s (1H, NH2+)
–
–
3.72 m (8H, CH2), 7.79 s (3H, Harom), 10.19 s (2H, NH2+)
IIap
IIIa
3.75 s (6H, OCH3), 6.89 d and 6.94 d (4H, Harom, J = 9.0 Hz), 7.52 d and 7.54 d (4H,
H
arom, J = 9.0 Hz), 9.19 s (1H, CONH), 9.45 s (2H, NH2+)
–
3.77 s (3H, OCH3), 7.54–7.58 m (2H, Harom), 7.01 d and 7.66 d (4H, Harom, J =
IIIb
IIIc
IVa
9.1 Hz), 8.07–8.11 m (2H, Harom), 9.69 br.s (2H, NH2+), 10.68 s (1H, CONH)
1660 (C=O); 2910, 3080 3.78 s (3H, OCH3), 7.00 d and 7.65 d (4H, Harom, J = 4.8 Hz), 7.75 d and 8.07 d (4H,
(CH); 3260, 3440 (NH)
H
arom, J = 4.8 Hz), 9.79 br.s (2H, NH2+), 10.69 s (1H, CONH)
–
4.09 s (3H, OCH3), 7.13–7.52 m (2H, Harom), 8.00–8.09 m (3H, Harom, CONH), 8.38 s
(1H, CONH), 9.54 s (1H, NH2+), 9.62 s (1H, NH2+)
–
2.51 m (4H, CH2), 3.64 t (2H, CH2, J = 6.7 Hz), 3.95 t (2H, CH2, J = 6.7 Hz), 7.76–
IVb
IVc
+
7.84 m (2H, Harom), 7.95–8.05 m (2H, Harom), 10.3 s (1H, NH2 ), 10.66 s (1H, NH2+)
1700 (C=O); 2900 2980, 1.35 t (3H, CH3, J = 7.1 Hz), 4.36 q (2H, CH2, J = 7.1 Hz), 8.03 d (2H, Harom, J =
3050 (CH); 3160, 3210
3350 (NH)
8.9 Hz), 8.11–8.15 m (3H, Harom, CONH), 8.56 s (1H, CONH), 10.07 s (1H, NH2+),
10.47 s (1H, NH2+)
1660 (C=O); 2930 3040, 2.99 d (6H, 2CH3, J = 4.6 Hz), 7.62 d and 7.91 d (8H, Harom, J = 8.9 Hz), 8.91 q (2H,
Va
Vb
Vc
3080 (CH); 3140, 3180
3300, 3380, 3420 (NH)
2CONH, J = 4.6 Hz), 9.82 s (1H, NH), 9.93 s (1H, NH)
1660 (C=O); 2920, 3020, 1.16–1.89 m (20H, 2C6H11), 3.82–3.85 m (2H, 2CH), 7.63 d and 7.96 d (8H, Harom
,
3080 (CH); 3120, 3260,
3340, 3440 (NH)
J = 9.2 Hz), 8.63 d (2H, 2CONH, J = 8.2 Hz), 9.85 s (1H, NH), 9.93 s (1H, NH)
1680 (C=O); 2860, 2890, 8.19–8.27 m (2H, CONH), 8.15 d and 8.42 d (8H, Harom, J = 9.1 Hz), 8.59 s (2H,
2920, 3020 (CH); 3120,
3220, 3270, 3360, 3420
(NH)
CONH), 10.20 s (1H, NH), 10.59 s (1H, NH)
ion [R1C6H4N2]+ The peak of fragment ion F5 is espe-
The oxidation of arylhydrazonothioacetamides Iu
and Iv in boiling acetic acid (118°C) gave 1,2,4-thia-
diazoles Va and Vb in 95 and 99% yield, respectively.
An analogous transformation was observed previously
[28, 29] when 2-phenyl-1,2,3-thiadiazol-5(2H)-imines
were heated in boiling pyridine over a period of 30–
40 min. Scheme 3 illustrates a probable mechanism of
the above transformation, which includes formation of
.
cially strong, and this ion is often the most abundant
(Scheme 2). In keeping with the data in Table 4,
introduction of electron-acceptor substituents into the
aromatic ring of 2-aryl-5-imino-2,5-dihydro-1,2,3-thia-
diazoles II leads to reduction in the relative intensity
of the molecular ion peak, indicating that its stability
decreases.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 6 2004

VASIL’EVA et al.
824
Scheme 2.
+·
R
+·
N
R
R
R
F2
F3
F4
F5
+·
N2
+·
R'
R'
N
N
NH
NH
N
N
S
S
+·
· HHlg
R
R
N
S
F1
+·
R'
N
+·
N
·
R'
R
NH
–S
N
F6
NH
F7
intermediate C via elimination of sulfur from com-
pound II. 1,5-H shift in C yields (arylhydrazono)aceto-
nitrile D which then reacts with the second molecule of
initial thiadiazole as a latent 1,3-dipole, leading to final
1,2,4-thiadiazole V. This scheme seems to be feasible
taking into account the mass spectra of 1,2,3-thiadi-
azoles II (Table 4): the formation of fairly abundant
fragment ion F6, whose molecular weight coincides
with that of azoketene imine C, was observed for
all the compounds II prepared. On the other hand,
1,2,4-thiadiazole system could also be formed via
oxidative condensation according to the mechanism
Scheme 3.
R'
R'
R'
N
N
·
N
NH
N
NH
N
N
NH
S
–S
R
R
R
II
C
D
R
R'
II
N
S
N
N
N
H
NH
N
R'
R
Va–Vc
V, R = Cl, R' = CONHMe (a); CONHC6H11 (b); R = NO2, R' = CONH2 (c).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 6 2004

OXIDATIVE CYCLIZATION OF 2-ARYLHYDRAZONOTHIOACETAMIDES
825
Table 3. 13C NMR spectra of 1,2,3-thiadiazoles IIa and IIy in DMSO-d6
a
11
10
CH3
O
O
NH2
O
10
9
2
2
N
N
N
N
1
1
4
7
4
7
NH·HBr
NH·HBr
5
6
5
6
S
S
3
8
3
8
9
H3C
O
Cl
IIa
IIz
Compound no.
Chemical shifts δC, ppm
55.8 q (C9, 1J = 144.3 Hz), 115.2 d.d (C5, C7, 1J = 163.3, 2J = 4.8 Hz,), 121.9 d.d (C4, C8, 1J = 164.1, 2J =
IIa
2
2
3
5.4 Hz), 131.6 d (C2, J = 7.8 Hz), 132.6 t.t (C3, J = 9.5, J = 2.8 Hz), 159.9 m (C6), 162.2 s (C10),
169.3 s (C1)
14.1 s (C11, 1J = 126.5, 2J = 2.7 Hz), 62.2 t.q (C10, 1J = 148.7, 2J = 4.4 Hz), 122.2 d.d (C5, C7, 1J = 172.7,
2J = 5.8 Hz), 130.3 d.d.d (C4, C8, 1J = 170.1, 2J = 5.5, 3J = 0.8 Hz), 131.3 s (C2), 134.1 t.t (C3, 2J = 10.4,
3J = 3.2 Hz), 138.0 t.t (C6, 2J = 9.5, 3J = 2.3 Hz), 160.2 t (C9, 2J = 3.6 Hz), 170.3 s (C1)
IIy
a
The signals were assigned, and the coupling constants were determined, using the Gate and BB techniques.
proposed in [2, 6] for alkylthioamides, i.e., by reaction
of adduct B (Scheme 1) with the second molecule of
initial arylhydrazonothioacetamide I, which is accom-
panied by elimination of hydrogen sulfide (Scheme 4).
Each of the above mechanisms may be operative
under the given conditions, and their probability is
determined by the stability of 1,2,3-thiadiazole II
(Scheme 3) and relative reactivities of the hydrazone
and thioamide nitrogen atoms in initial compound I
(Scheme 4). As a result, either intramolecular cycliza-
tion or intermolecular reaction occurs. An essential
difference between these mechanisms is elimination
of either sulfur (Scheme 3) or hydrogen sulfide
(Scheme 4). It should be noted that the oxidation
products were often contaminated with sulfur to
greater or lesser extent. However, in no cases evolution
of hydrogen sulfide was observed. This fact may
be regarded as an indirect evidence for the greater
probability for formation of 1,2,4-thiadiazoles via
initial intramolecular cyclization of thioacetamides I
into 1,2,3-thiadiazoles II according to Scheme 1.
The oxidative condensation of hydrazones Ia–Iak
by the action of bromine in acetic acid is characterized
by good yields. The yield of the final product tends to
decrease with rise in the electron-acceptor power of the
substituent in the aromatic ring. In the oxidation of
arylhydrazonothioacetamides Ial and Iam, the yields
were 39 and 13%, respectively, and a large amount
of the initial hydazone was present in the reaction
mixture. Presumably, electron-acceptor substituent in
the aromatic ring, despite its remoteness from the
reaction center, strongly reduces the nucleophilicity of
the sulfur atom, thus hampering formation of adduct B
(Scheme 1). The use of a harder reagent, N-chloro-
succinimide (NCS) allowed us to raise the yields of
the oxidation products from compounds Ial and Ian.
Scheme 4.
R
R'
N
S
R'
N
H
I
S
B
V
N
N
–H2S
H
NH HN
R
E
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 6 2004

VASIL’EVA et al.
Table 4. Mass spectra of 1,2,3-thiadiazole derivatives IIa–IIj, IIl–IIak and IIIa–IIIc, m/z (Irel, %)
826
Comp. no.
F1
F2
F3
F4
F5
F6
F7
250 (79.1)
264 (49.6)
308 (14.9)
332 (36.4)
435 (8.2)
107 (13.9)
107 (16.3)
107 (44.0)
107 (19.3)
107 (24.6)
107 (24.6)
107 (25.2)
107 (17.5)
107 (19.5)
77 (77.6)
121 (31.5)
121 (39.5)
121 (61.7)
121 (37.1)
121 (57.1)
121 (57.1)
121 (54.9)
121 (7.2)
135 (2.7)
135 (3.5)
135 (14.7)
135 (4.3)
135 (5.3)
135 (5.3)
135 (6.2)
135 (6.4)
135 (4.2)
105 (8.5)
123 (3.5)
123 (4.3)
153 (100)
153 (100)
153 (49.3)
153 (13.5)
153 (45.8)
153 (45.8)
153 (31.8)
153 (4.8)
153 (100)
123 (100)
141 (100)
141 (100)
218 (14.3)
232 (30.8)
276 (78.4)
401 (12.4)
294 (42.0)
294 (42.0)
328 (33.4)
301 (21.1)
247 (15.8)
188 (36.8)
206 (14.6)
220 (9.3)
97 (0)
IIa
IIb
IIc
IId
IIe
IIf
111 (0)
155 (9.1)
267 (0)
173 (6.7)
173 (6.7)
207.5 (0)
155 (9.1)
126 (2.1)
97 (2.6)
97 (1.2)
111 (0)
326 (45.8)
360 (20.5)
333 (3.6)
IIg
IIh
IIi
279 (93.7)
220 (41.7)
252 (27.6)
238 (39.9)
121 (49.6)
91 (24.0)
IIj
95 (31.5)
109 (32.8)
109 (30.8)
IIl
95 (24.5)
IIm
320 (37.6)
328 (10.6)
314 (28.8)
348 (51.6)
220 (9.8)
95 (32.7)
95 (15.7)
95 (74.1)
95 (49.5)
95 (30.1)
109 (38.2)
109 (18.1)
109 (100)
109 (66.7)
109 (11.5)
123 (14.0)
123 (4.4)
123 (15.2)
123 (9.5)
123 (3.4)
141 (100)
141 (39.2)
141 (83.0)
141 (53.2)
141 (3.4)
288 (25.9)
296 (8.3)
179 (8.8)
187 (1.2)
173 (70.7)
207.5 (0)
79 (0)
IIn
IIo
IIp
IIq
IIr
IIs
282 (10.2)
316 (34.7)
188 (6.1)
254.5 (40.7) 111.5 (31.2)
268.5 (27.8) 111.5 (26.1)
125.5 (29.7) 139.5 (3.2)
125.5 (27.1) 139.5 (5.8)
125.5 (28.8) 139.5 (12.4)
157.5 (100)
157.5 (100)
157.5 (100)
222.5 (21.1)
97 (0)
236.5 (18.8) 111 (0)
IIt
336.5 (7.6)
344.5 (4.2)
111.5 (35.0)
111.5 (8.7)
304.5 (46.1) 179 (18.5)
IIu
IIv
IIw
125.5 (7.0)
139.5 (1.6)
157.5 (14.9) 312.5 (9.8)
187 (1.2)
330.5 (20.4) 111.5 (21.1)
125.5 (16.9) 139.5 (3.6)
157.5 (19.7) 298.5 (27.4) 173 (1.5)
157.5 (33.1) 332.5 (23.0) 207.5 (2.8)
364.5 (35.2) 111.5 (36.5)
283.5 (52.7) 111.5 (29.7)
125.5 (38.9) 139.5 (5.4)
125.5 (41.0) 139.5 (4.9)
IIx
IIy
157.5 (100)
251.5 (14.1) 126 (1.8)
204.5 (1.0) 79 (8.6)
305.5 (28.0) 178 (2.5)
236.5 (9.5)
111.5 (48.7)
125.5 (5.7)
125.5 (4.3)
125.5 (6.5)
134 (18.7)
134 (8.7)
134 (13.3)
134 (2.5)
134 (5.1)
134 (2.6)
134 (2.8)
139.5 (2.4)
139.5 (6.4)
139.5 (4.7)
148 (3.0)
148 (2.2)
148 (5.1)
148 (0)
157.5 (2.3)
157.5 (2.5)
IIz
337.5 (20.4) 111.5 (17.7)
IIaa
IIab
IIac
IIad
IIae
IIaf
IIag
IIah
IIai
308.5 (2.3)
263 (3.7)
277 (13.8)
345 (5.3)
353 (1.7)
339 (4.1)
373 (2.1)
317 (0)
111.5 (15.9)
120 (25.5)
120 (19.0)
120 (29.3)
120 (8.8)
157.5 (16.9) 276.5 (8.2)
151 (2.7)
97 (0)
166 (2.2)
166 (51.2)
166 (20.0)
166 (5.7)
166 (7.7)
166 (3.7)
166 (6.4)
231 (81.8)
245 (30.6)
313 (52.4)
321 (81.8)
307 (21.9)
341 (7.4)
111 (0)
179 (2.8)
97 (0)
120 (19.8)
120 (15.5)
120 (21.9)
148 (1.6)
148 (0)
173 (0)
173 (0)
151 (2.4)
148 (2.0)
285 (13.0)
292 (48.8)
265 (10.4)
342 (41.7)
346 (23.9)
362.5 (1.2)
149 (39.8)
122 (22.1)
107 (24.3)
95 (22.1)
163 (35.6)
136 (10.0)
121 (44.5)
109 (7.5)
177 (2.4)
150 (5.6)
135 (5.3)
123 (100)
139.5 (3.0)
195 (85.9)
168 (18.5)
153 (4.8)
260 (100.0)
233 (48.5)
301 (21.1)
314 (2.6)
143 (0)
221 (0)
180 (0)
203 (0)
203 (0)
IIaj
IIak
IIIa
IIIb
IIIc
141 (8.6)
111.5 (18.8)
125.5 (3.9)
157.5 (100)
328 (19.9)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 6 2004

OXIDATIVE CYCLIZATION OF 2-ARYLHYDRAZONOTHIOACETAMIDES
827
However, the oxidation of 4-nitrophenylhydrazono-
thioacetamide Iam with NCS afforded 1,2,4-thiadi-
azole Vc as the only cyclic product.
succinimide, 6 mmol, was added under stirring to
a solution of 2 mmol of 2-phenylhydrazonothioacet-
amide I in 100 ml of ethyl acetate. The mixture was
stirred for 5 h at room temperature, and the precipitate
was filtered off and recrystallized from ethanol.
As follows from the results of oxidation of aryl-
hydrazonothioacetamides Iao–Ias having one or two
substituents in the ortho positions, steric factor does
not affect the intramolecular cyclization to an appre-
ciable extent. The oxidative cyclization of hydrazones
containing a 4-methoxyphenylcarbamoyl group by the
action of bromine was accompanied by bromination of
the aromatic ring. In order to avoid this side process,
we performed oxidation of hydrazones Ie, Ip, and Iy
with iodine under analogous conditions. In this case,
no halogenation of the aromatic ring occurred, and the
corresponding 2-aryl-5-imino-N-(4-methoxyphenyl)-
2,5-dihydro-1,2,3-thiadiazole-4-carboxamides IIIa–
IIIc were isolated in high yields.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 01-03-33173). M.L. Vasil’eva thanks CRDF for
support (grant no. 005).
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EXPERIMENTAL
The H and 13C NMR spectra were recorded on
1
a Bruker WM-400 spectrometer (400 and 100.00 MHz,
respectively) using DMSO-d6 as solvent and TMS as
internal reference. The mass spectra were obtained on
a Varian MATT-311A instrument; accelerating voltage
3 kV; energy of ionizing electrons 70 eV. The melting
points were not corrected. The progress of reactions
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Oxidation of arylhydrazones I with bromine
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of bromine in 5 ml of acetic acid was added with
stirring to a solution of 2 mmol of 2-phenylhydrazono-
thioacetamide I in 100 ml of acetic acid, heated to
40°C. The mixture was stirred for 5 h at room
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