Reactions of 2-aminothiophenol with pyridineand imidazolecarboxaldehydes

Article abstract of DOI:10.1007/s11172-015-1103-3

Reflux of imidazole-2-carboxaldehyde, 1-methylimidazole-2-carboxaldehyde, imidazole4-carboxaldehyde, or 5-bromopyridine-2-carboxaldehyde with 2-aminothiophenol in ethanol in the presence of air oxygen for 1.5 h affords the corresponding 2-hetaryl-substituted 1,3-benzothiazoles. The reaction of 2-(1-methyl-1H-imidazol-2-yl)-1,3-benzothiazole with Cu(ClO₄)₂?6H₂O gives bis[2-(1-methyl-1H-imidazol-2-yl)-1,3-benzothiazole]copper(ii) diperchlorate monohydrate.

Full text of DOI:10.1007/s11172-015-1103-3

Russian Chemical Bulletin, International Edition, Vol. 64, No. 8, pp. 1975—1977, August, 2015
1975
Reactions of 2ꢀaminothiophenol with pyridineꢀ and imidazolecarboxaldehydes*
E. S. Barskaya, E. K. Beloglazkina, A. G. Mazhuga, I. V. Yudin, and N. V. Zyk
Chemistry Department, M. V. Lomonosov Moscow State University,
1/3 Leninskie Gory, 119991 Moscow, Russian Federation.
Eꢀmail: bel@org.chem.msu.ru
Reflux of imidazoleꢀ2ꢀcarboxaldehyde, 1ꢀmethylimidazoleꢀ2ꢀcarboxaldehyde, imidazoleꢀ
4ꢀcarboxaldehyde, or 5ꢀbromopyridineꢀ2ꢀcarboxaldehyde with 2ꢀaminothiophenol in ethanol
in the presence of air oxygen for 1.5 h affords the corresponding 2ꢀhetarylꢀsubstituted
1,3ꢀbenzothiazoles. The reaction of 2ꢀ(1ꢀmethylꢀ1Нꢀimidazolꢀ2ꢀyl)ꢀ1,3ꢀbenzothiazole with
Сu(СlO4)2•6H2O gives bis[2ꢀ(1ꢀmethylꢀ1Нꢀimidazolꢀ2ꢀyl)ꢀ1,3ꢀbenzothiazole]copper(II)
diperchlorate monohydrate.
Key words: benzothiazoles, 2ꢀpyridinecarboxaldehyde, imidazolecarboxaldehyde, copper(II)
complex.
It is known that reactions of condensation of aldeꢀ
hydes 1 with 2ꢀaminothiophenol can afford organic prodꢀ
ucts of two types (Scheme 1): 1,3ꢀbenzothiazolines 2 (see
Refs 1—7) and products of their oxidative aromatization,
1,3ꢀbenzothiazoles 3.8—11 Benzothiazolines 2 are often
oxidized to benzothiazoles 3 with air oxygen in the course
of the reaction or during isolation from the reaction mixꢀ
ture.12 There are literature data that substituent R in posiꢀ
tion 2 of benzothiazoline (see Scheme 1) plays the key role
in the determination of the oxidation rate, since the oxiꢀ
dation occurs, as a rule, much more rapidly at R = aryl,
furyl, pyrrolyl, and thienyl that in the case of R = 2ꢀPy.
On the basis of the data of quantum chemical calculations
and Xꢀray diffraction analysis, the authors explained13 this
To check this hypothesis, we studied the reactions of
various imidazoleꢀ (1a—c) and pyridinecarboxaldehydes
(1d,e) with 2ꢀaminothiophenol in ethanol in the presence
of air oxygen. In all cases, formed 2ꢀhetarylbenzothiazoꢀ
lines contain the donor nitrogen atom in the ꢀposition of
the heterocycle and, hence, can form a hydrogen bond
with the benzothiazoline fragment. It was found that the
corresponding 2ꢀhetarylbenzothiazoles 3a—e were formed
as reaction products in the yields from 39 to 93% in all
cases (Scheme 2). Note that assumed benzothiazolines 2
were not isolated as reaction products even when the reacꢀ
tion was carried out under argon in a degassed solvent: it is
most likely that the oxidation to benzothiazole 3 occurs,
in this case, when the reaction mixture is filtered and the
product is dried in air.
...
fact by the presence of the N—H(thiazoline) N(pyridyl)
hydrogen bond that impedes oxidation with hydrogen atom
detachment from the nitrogen atom of the thiazoline cycle.
Scheme 2
Scheme 1
1, 3
a
b
c
d
R
Yield of 3 (%)
Imidazolꢀ2ꢀyl
1ꢀMethylimidazolꢀ2ꢀyl
Imidazolꢀ4ꢀyl
Pyridinꢀ2ꢀyl
5ꢀBromopyridinꢀ2ꢀyl
47
52
39
93
68
e
To additionally confirm the structures of the obtained
compounds, we synthesized copperꢀcontaining complex
3b by the reaction of this benzothiazole with copper(II)
perchlorate hexahydrate. It is known that in the reactions
with bivalent metal complexes 2ꢀhetarylbenzothiazoles
* Based on the materials of the XXVI International Chugaev
Conference on Coordination Chemistry (October 6—10, 2014,
Kazan, Russia).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1975—1977, August, 2015.
1066ꢀ5285/15/6408ꢀ1975 © 2015 Springer Science+Business Media, Inc.

1976
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 8, August, 2015
Barskaya et al.
N, 20.79, S, 15.68. C10H7N3S. Calculated (%): С, 59.68; Н, 3.51;
N, 20.88; S, 15.93.
form metal complexes containing one or two initial orꢀ
ganic ligands coordinated to the corresponding metal
ion,14—18 whereas 2ꢀhetarylbenzothiazolines undergo
benzothiazoline ring opening to form tautomeric iminoꢀ
thiophenol, the reaction of which with M2+ gives the corꢀ
responding bis(ligand) iminothiolate complex.18—25 The
reaction of imidazoleꢀsubstituted benzothiazole 3b with
Сu(СlO4)2•6H2O affords copper complex 4 having, acꢀ
cording to the elemental analysis data, empirical formula
L2Cu(ClO4)2•H2O similarly to the earlier synthesized17
coordination compound of СuII with 2ꢀ(2ꢀpyridyl)benzoꢀ
thiazole 1d (Scheme 3).
2ꢀ(1ꢀMethylꢀ1Нꢀimidazolꢀ2ꢀyl)ꢀ1,3ꢀbenzothiazole (3b). The
reaction of 2ꢀaminothiophenol (0.56 mL, 4.65 mmol) and
1ꢀmethylꢀ1Нꢀimidazoleꢀ2ꢀcarboxaldehyde (0.51 g, 4.65 mmol) in
EtOH (15 mL) gave compound 3b (0.52 g, 52%) as a brown
powder, m.p. 133—135 C (Ref. 26: m.p. 134—136 C). 1Н NMR
(DMSOꢀd6), : 8.10 (d, 1 Н, J = 8.0 Hz); 8.05 (d, 1 Н, J = 8.0 Hz);
7.55 (t, 1 Н, J = 7.2 Hz); 7.50 (s, 1 Н); 7.46 (т, 1 Н, J = 7.2 Hz);
7.15 (s, 1 Н); 4.20 (s, 3 Н). 13С NMR (DMSOꢀd6), : 156.28,
153.66, 152.30, 144.85, 141.09, 134.62, 131.10, 127.07, 125.97,
122.86, 35.87. IR, /cm–1: 1610. Found (%): С, 61.36; Н, 4.18;
N, 19.33; S, 15.13. C11H9N3S. Calculated (%): С, 61.37; Н, 4.21;
N, 19.52; S, 14.89.
2ꢀ(1НꢀImidazolꢀ4ꢀyl)ꢀ1,3ꢀbenzothiazole (3c). The reaction
of 2ꢀaminothiophenol (0.6 mL, 5 mmol) and 1Нꢀimidazoleꢀ2ꢀ
carboxaldehyde (0.48 g, 5 mmol) in EtOH (15 mL) gave comꢀ
pound 3c (0.375 g, 39%), m.p.. 166—168 C (Ref. 27: m.p. 136 C).
1Н NMR (DMSOꢀd6), : 8.05 (d, 1 Н, J = 7.1 Hz); 7.93 (s, 1 Н);
7.88 (d, 1 Н, J = 7.1 Hz); 7.83 (s, 1 Н); 7.45 (t, 1 Н, J = 7.1 Hz);
7.33 (t, 1 Н, J = 7.1 Hz). 13С NMR (DMSOꢀd6), : 172.43,
154.25, 150.15, 135.82, 131.54, 126.54, 124.86, 122.47, 116.49,
115.22. IR, /cm–1: 1577. Found (%): С, 59.38; Н, 4.04; N, 20.75,
S, 15.78. C10H7N3S. Calculated (%): С, 59.68; Н, 3.51; N, 20.88;
S, 15.93.
2ꢀ(5ꢀBromopyridinꢀ2ꢀyl)ꢀ1,3ꢀbenzothiazole (3e). The reacꢀ
tion of 2ꢀaminothiophenol (0.42 mL, 3.4 mmol) and 5ꢀbromoꢀ
2ꢀpyridinecarboxaldehyde (0.63 g, 3.4 mmol) in EtOH (10 mL)
gave compound 10 (0.68 g, 68%) as a white powder, m.p. 212 C.
1Н NMR (DMSOꢀd6), : 8.75 (d, 1 Н, J = 8.2 Hz); 8.53 (d, 1 Н,
J = 2.2 Hz); 8.12 (d, 1 Н, J = 8.2 Hz); 8.3 (t, 1 Н, J = 8.1 Hz);
7.97 (d, 1 Н, J = 7.9 Hz); 7.55 (d, 1 Н, J = 7.1 Hz); 7.45 (t, 1 Н,
J = 7.2 Hz). 13С NMR (DMSOꢀd6), : 153.89, 150.76, 149.72,
139.67, 136.02, 126.5, 125.94, 123.54, 122.58, 122.02, 121.91,
102.79. IR, /cm–1: 1575. Found (%): С, 49.54; Н, 2.59; N, 9.69;
S, 11.07. C12H7BrN2S. Calculated (%): С, 49.50; Н, 2.42;
N, 9.62; S, 11.01.
Scheme 3
Thus, we found that for all 2ꢀhetarylcarboxaldehydes
studied the reaction with 2ꢀaminothiophenol affords
2ꢀhetarylbenzothiazoles 3 rather than 2ꢀbenzothiazolines 2,
as it could be expected on the basis of published data.13
It is most likely that the hypothesis proposed earlier13 about
the key role of the electrostatic interaction between the
heterocyclic N atom and the NH group of the benzothiꢀ
azoline fragment in the determination of the rate of the
oxidation of the latter to benzothiazole is insufficient for
the unambiguous prediction of the result of the reaction of
2ꢀaminothiophenol with heteroaromatic aldehydes.
Experimental
The reaction course was monitored by thinꢀlayer chromatoꢀ
graphy in the fixed silica gel layer (Silufol plates). 1Н and 13С NMR
spectra were recorded on a Bruker Аvance instrument with workꢀ
ing frequencies of 400 and 100 MHz. IR spectra were measured
on a URꢀ20 instrument in Nujol. Aldehydes 1a—e and 2ꢀaminoꢀ
thiophenol (Aldrich) were used without additional purification.
2ꢀ(Pyridinꢀ2ꢀyl)ꢀ1,3ꢀbenzothiazole 3d (m.p. 132—133 C) was
synthesized according to described procedure8 (Ref. 8: m.p.
130 C).
Bis[2ꢀ(1ꢀmethylꢀ1Нꢀimidazolꢀ2ꢀyl)ꢀ1,3ꢀbenzothiazole]copꢀ
per(II) diperchlorate monohydrate (4). A solution of benzothiꢀ
azole 3b (0.11 g, 0.51 mmol) and Сu(СlO4)2•6H2O (0.095 g,
0.26 mmol) in EtOH (10 mL) was refluxed for 1 h and cooled.
The formed green precipitate was filtered off and dried in air.
Compound 4 was obtained in a yield of 0.159 g (86%),
m.p. > 250 C. IR, /cm–1: 3380 (br), 1565. Found (%): С, 37.23;
Н, 2.88; N, 11.60, S, 9.62. C22H18Cl2CuN6O8S2•H2O. Calcuꢀ
lated (%): С, 37.16; Н, 2.84; N, 11.82, S, 9.02.
Reaction of 2ꢀaminothiophenol with hetarylcarboxaldehydes
(general procedure). One—two droplets of glacial acetic acid were
added to a mixture of 2ꢀaminothiophenol (1 equiv.) and imidꢀ
azoleꢀ or pyridinecarboxaldehyde (1 equiv.) in ethanol. The reꢀ
action mixture was refluxed with stirring for 1.5 h. The precipiꢀ
tate formed after cooling was filtered off and dried in air.
2ꢀ(1НꢀImidazolꢀ2ꢀyl)ꢀ1,3ꢀbenzothiazole (3a). The reaction
of 2ꢀaminothiophenol (0.6 mL, 5 mmol) and 1Нꢀimidazoleꢀ2ꢀ
carboxaldehyde (0.48 g, 5 mmol) in EtOH (15 mL) gave comꢀ
pound 3a (0.49 g, 47%) as a black powder, m.p. 185 C. 1Н NMR
(DMSOꢀd6), : 13.5 (s, 1 Н, NH); 8.15 (d, 1 Н, J = 7.4 Hz); 8.02
(d, 1 Н, J = 8.2 Hz); 7.65 (t, 1 Н, J = 8.2 Hz); 7.47 (t, 1 Н,
J = 8.2 Hz); 7.42 (s, 1 Н); 7.18 (s, 1 Н). 13С NMR (DMSOꢀd6),
: 153.97, 139.85, 134.37, 129.80, 126.97, 126.95, 126.10, 123.33,
122.52. IR, /cm–1: 1575. Found (%): С, 59.92; Н, 3.71;
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 13ꢀ03ꢀ00399ꢀa).
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Received December 3, 2014;
in revised form February 27, 2015