The reaction of 5-aryl-(hetaryl)-2-aroylmethylthio-1,3,4-oxadiazoles with aryldiazonium tetrafluoroborates

Article abstract of DOI:10.1023/A:1017612223514

5-Aryl(hetaryl)-2-aroylmethylthio-1,3,4-oxadiazoles behave as CH acids and readily react with aryldiazonium tetrafluoroborates at the active methylene group to give azo coupling products. The spectroscopic properties of the compounds synthesized have been

Full text of DOI:10.1023/A:1017612223514

Chemistry of Heterocyclic Compounds, Vol. 37, No. 4, 2001
THE REACTION OF 5-ARYL-
(HETARYL)-2-AROYLMETHYLTHIO-
1,3,4-OXADIAZOLES WITH ARYLDIAZONIUM
TETRAFLUOROBORATES
A. N. Krasovsky, A. P. Andrushko, and A. M. Demchenko
5-Aryl(hetaryl)-2-aroylmethylthio-1,3,4-oxadiazoles behave as CH acids and readily react with
aryldiazonium tetrafluoroborates at the active methylene group to give azo coupling products. The
spectroscopic properties of the compounds synthesized have been studied.
Keywords: 5-aryl(hetaryl)-2-aroylmethylthio-1,3,4-oxadiazoles, 5-aryl(hetaryl)-2-(1-aroyl-1-hydrazino-
methylthio)-1,3,4-oxadiazole, azo coupling reaction with diazonium tetrafluoroborates.
In a continuation of a study on the synthesis and properties of compounds containing active methylene
groups [1-6], 5-aryl(hetaryl)-2-aroylmethylthio-1,3,4-oxadiazoles (2a-i), which can exist as two tautomeric
forms A and B [8], have been obtained by the reaction of 5-aryl(hetaryl)-1,3,4-oxadiazole-2(3H)-thiones (1a-f)
1
with substituted phenacyl bromides [7]. Analysis of the H NMR and IR spectroscopic data (Tables 1 and 2)
shows unambiguously that compounds 2a-i exist in the form of the open chain tautomer A, analogously to
N-substituted 2-acylmethylthiobenzimidazoles [9]. In fact the protons of the methylene groups of the phenacyl
substituents in compounds 2a-i appear as a singlet in the 1H NMR spectra in the 5.03-5.26 ppm region, whereas
for the form B the signals characteristic of an AB system would be expected as a result of the presence of an
asymmetric center. In addition the IR spectra contain bands characteristic of the C=O stretching vibrations in the
region of 1670-1690 cm-1, which confirms structure A.
O
R1
R1
H
N
1
O
+
BrCH2COR
N
N
N
N
N
R
O
S
R
O
S
R
O
A
S
B
1a–f
2a–i
1a R = C6H5; b R = 3-BrC6H4; c R = 4-FC6H4; d R = C6H5CH2; e R = 3-C5H4N; f R = 4-C5H4N. 2a* R = R1 = C6H5;
b R = 3-BrC6H4, R1 = C6H5; c R = 3-BrC6H4, R1 = 4-ClC6H4; d R = 3-BrC6H4, R1 = 4-O2NC6H4;
e R = 4-FC6H4, R1 = 4-CH3OC6H4; f R = C6H5CH2, R1 = 4-ClC6H4;
g* R = 3-C5H4N, R1 = C6H5; h* R = 4-C5H4N, R1 = C6H5; i R = 4-C5H4N, R = 4-ClC6H4
(* compounds whose synthesis and properties have been described in [7]).
__________________________________________________________________________________________
Chernigov Technological Institute, Chernigov 250027, Ukraine; e-mail: demch@cn.relc.com. Translated
from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, 544-547, April 2001. Original article submitted
September 1, 1999.
496
0009-3122/01/3704-0496$25.00©2001 Plenum Publishing Corporation

Compounds 2a-i are CH acids which react readily with aryldiazonium tetrafluoroborates at the active
methylene group to give azo coupling products (3a-m). The mobility of the methylene group hydrogen atom is
1
indicated in the H NMR spectra of compounds 2 by the disappearance of the CH2 proton singlet and the
appearance of CH singlet at 5.0-5.1 ppm as a result of substitution of the proton on deuterium when D2O is
added.
It is theoretically possible for compounds 3a-m to exist in three tautomeric forms: the keto hydrazone
(A), azo ketone (B) or azo enol forms (C). Formation of intramolecular hydrogen bonds between atoms O(1) and
N(3) of the molecules is not excluded.
1
The H NMR spectra of compounds 3a-m contain signals of the NH group protons as singlets in the
10.78-11.89 ppm region, while the IR spectra include absorption bands characteristic of the CO and NH groups
at 1650-1670 and 3128-3210 cm-1 regions respectively (Table 2), so that they are assigned the structure of the
corresponding keto hydrazones (A).
TABLE 1. Characteristics of Compounds 2a-i* and 3a-m
Found, %
——————
Compound
Empirical formula
mp, °C
Yield, %
Calculated, %
N
S
С16H11BrN2O2S
C16H10BrClN2O2S
C16H10BrN3O4S
C17H13FN2O3S
C17H13ClN2O2S
C15H10ClN3O2S
C24H20N4O2S
7.39
7.47
8.45
8.54
118.5-119
162-163
81
85
92
83
75
91
54
72
75
64
67
72
65
68
75
74
70
67
76
2b
2c
2d
2e
2f
6.58
7.80
6.84
7.83
9.89
10.0
7.58
7.63
147-148.5
154-155
8.05
9.20
8.11
9.24
7.98
8.12
9.21
9.30
106-107
12.2
9.60
150-151
2i
12.7
9.65
13.5
13.1
8.02
7.48
168-171
3a
3b
3c
3d
3e
3f
C22H14BrN5O4S
C22H13BrClN5O4S
C22H13BrCl2N4O2S
C23H16BrN5O5S
C23H16FN5O5S
C24H19ClN4O3S
C23H16ClN5O4S
C22H17N5O2S
12.8
6.21
267-268
13.4
6.11
12.9
12.5
5.70
5.73
252-253
11.0
6.01
184.5-185
210-210.5
253-254.5
204-205
10.2
5.84
12.1
12.6
5.82
5.76
13.8
6.52
14.2
6.49
11.3
11.7
6.73
6.69
3g
3h
3i
14.0
6.51
241-242
14.2
6.48
16.4
16.9
7.93
7.70
194-194.5
247-248.5
196-197
C21H14N6O4S
19.0
7.23
3j
18.8
7.17
C21H14N6O4S
18.5
18.8
7.20
7.17
3k
3l
C22H16ClN5O3S
C21H13ClN6O4S
14.5
6.91
227-227.5
262-262.5
15.0
6.87
17.1
17.5
6.71
6.67
3m
_______
* Compounds 2a,g,h are described in [7].
497

O
R1
R1
H
N
O
[R2N2]BF4
N
N
N
N
R2
N
R
S
R
S
O
O
A
2a–i
3a–m
R1
OH
R1
N
O
N
N
N
N
N
R2
R2
N
N
R
S
R
S
O
O
B
C
3a R = R1 = C6H5, R2 = 4-C2H5C6H4; b R = 3-BrC6H4, R1 = C6H5, R2 = 4-O2NC6H4;
c R = 3-BrC6H4, R1 = 4-ClC6H4, R2 = 4-O2NC6H4; d R = 3-BrC6H4, R1 = C6H5,
R2 = 2,4-Cl2C6H3; e R = 3-BrC6H4, R1 = 4-O2NC6H4, R2 = 4-CH3OC6H4; f R = 4-FC6H4,
R1 = 4-CH3OC6H4, R2 = 4-O2NC6H4; g R = C6H5CH2, R1 = 4-ClC6H4, R2 = 4-CH3OC6H4;
h R = C6H5CH2, R1 = 4-ClC6H4, R2 = 4-O2NC6H4; i R = 3-C5H4N, R1 = C6H5, R2 = 4-CH3C6H4;
j R = 3-C5H4N, R1 = C6H5, R2 = 4-O2NC6H4; k R = 4-C5H4N, R1 = C6H5, R2 = 4-O2NC6H4;
l R = 4-C5H4N, R1 = 4-ClC6H4, R2 = 4-CH3OC6H4; m R = 4-C5H4N, R1 = 4-ClC6H4,
R2 = 4-O2NC6H4
1
TABLE 2. H NMR and IR Spectroscopic Data for Compounds 2a-i* and
3a-m
1H NMR spectra, δ, ppm
IR spectra,
Com-
pound
ν, cm-1
S–CH2–CO
(2H, s)
N–NH–
H–Ar
other signals
(1H, s)
(м)
1672
1670
1672
1690
1670
1680
1650, 3120
5.22
5.18
5.26
5.12
5.03
5.20
7.56-8.12 (9H)
7.52-8.12 (8H)
7.52-8.43 (8H)
7.08-8.05 (8H)
7.29-8.01 (9H)
7.62-8.81 (8H)
7.40-8.21 (14H)
2b
2c
2d
2e
2f
3.88 (3H, s, OCH3)
4.24 (2H, s, CH2)
2i
11.30
1.23 (3H, t, CH3);
2.70 (2H, q, CH2)
3a
1650, 3126
1650, 3120
1650, 3100
1650, 3130
1660, 3160
1660, 3184
11.55
11.58
11.34
11.44
11.44
10.78
7.50-8.41 (13H)
7.50-8.41 (12H)
7.48-8.15 (12H)
7.10-8.39 (12H)
7.17-8.50 (12H)
7.09-8.18 (13H)
3b
3c
3d
3e
3f
3.83 (3H, s, OCH3)
3.90 (3H, s, OCH3)
3.81 (3H, s, OCH3);
3g
3.53 (2H, s, CH2)
1660, 3170
1650, 3160
1650, 3130
1670, 3128
1660, 3168
1660, 3126
10.85
11.49
11.69
11.89
11.56
11.76
7.21-8.24 (13H)
7.36-9.03 (13H)
7.61-9.06 (13H)
7.62-8.88 (13H)
7.11-8.75 (12H)
7.71-8.79 (12H)
3.57 (2H, s, CH2)
3h
3i
2.38 (3H, s, OCH3)
3j
3k
3l
3m
3.83 (3H, s, OCH3)
_______
* Compounds 2a,g,h are described in [7].
498

EXPERIMENTAL
1
IR spectra of KBr disks were recorded with a UR-20 spectrometer. H NMR spectra of DMSO-d6
solutions with TMS as internal standard were obtained with a Bruker-300 (300 MHz) instrument.
5-R-2-Aroylmethylthio-1,3,4-oxadiazoles (2a-i). 1,3,4-Oxadiazole-2(3H)-thione (1a-f) (0.01 mol) was
dissolved in aqueous ethanol (40 ml) containing KOH (0.56 g, 0.01 mol) and α-halo ketone (0.01 mol) dissolved
in ethanol (20 ml) was added. The reaction mixture was kept for 10-15 h at 18-20°C, after which water (50 ml)
was added, the precipitate was filtered off and washed with water.
5-R-2-[1-(R2-Hydrazono)-2-R1-2-oxoethylthio]-1,3,4-oxadiazoles
(3a-m).
Suspension
of
aryldiazonium tetrafluoroborate (0.01 mol) in mixture of AcOH (20 ml) and Ac2O (5 ml) was added to solution
of 5-R-2-aroylmethylthio-1,3,4-oxadiazole (2a-i) (0.01 mol) and anhydrous AcONa (1 g) in mixture of AcOH
(30 ml) and Ac2O (5 ml). The reaction mixture was kept in the dark at 18-20°C for 20-24 h and the precipitate
was filtered off.
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