Condensed imidazo-1,2,4-azines. 31*. Synthesis and chemical transformations of substituted 1,2,4-triazepino[2,3-a]benzimidazoles

Article abstract of DOI:10.1023/A:1019573532428

By reaction of 1,2-diaminobenzimidazole with 1,3-diketones, acetoacetic ester and its derivatives, we have synthesized substituted 1,2,4-triazepino[2,3-a]benzimidazole and 5H-1,2,4-triazepino[2,3-a]-benzimidazol-4-one. By reaction of 5H-2-methyl-1,2,4-triazepino[2,3-a] benzimidazol-4-one with aromatic aldehydes or phenyldiazonium chloride, we have obtained 3-arylidene(phenylazo) derivatives of this compound, and by reaction with P₂S₅ we have obtained 5H-2-methyl-1,2,4-triazepino[2,3-a]-benzimidazole-4-thione. We have shown that when reacted with ammonia, primary or secondary amines, the latter forms 4-amino-substituted 2methy-1,2,4-triazepino[2,3-a] benzimidazole.

Full text of DOI:10.1023/A:1019573532428

Chemistry of Heterocyclic Compounds, Vol. 38, No. 5, 2002
CONDENSED IMIDAZO-1,2,4-AZINES.
31*. SYNTHESIS AND CHEMICAL
TRANSFORMATIONS OF SUBSTITUTED
a
1,2,4-TRIAZEPINO[2,3- ]BENZIMIDAZOLES
V. P. Kruglenko1, V. P. Gnidets1, N. A. Klyuev2, and M. V. Povstyanoi1
By reaction of 1,2-diaminobenzimidazole with 1,3-diketones, acetoacetic ester and its derivatives, we
have synthesized substituted 1,2,4-triazepino[2,3-a]benzimidazole and 5H-1,2,4-triazepino[2,3-a]-
benzimidazol-4-one. By reaction of 5H-2-methyl-1,2,4-triazepino[2,3-a]benzimidazol-4-one with
aromatic aldehydes or phenyldiazonium chloride, we have obtained 3-arylidene(phenylazo) derivatives
of this compound, and by reaction with P2S5 we have obtained 5H-2-methyl-1,2,4-triazepino[2,3-a]-
benzimidazole-4-thione. We have shown that when reacted with ammonia, primary or secondary
amines, the latter forms 4-amino-substituted 2-methyl-1,2,4-triazepino[2,3-a]benzimidazole.
Keywords: 1,2-diaminobenzimidazole, dinucleophilic reagents, 1,2,4-triazepino[2,3-a]benzimidazole,
tautomerism.
Reaction of 1,2-diaminobenzimidazole (1) with chalcones in refluxing DMF occurs with elimination of
the amino group of the heterocycle, leading to formation of pyrimido[2,3-a]benzimidazoles [2]. Continuing a
study of reactions of 1 with dinucleophilic reagents [2-4], in this paper we present data on its condensation with
1,3-diketones, acetoacetic ester and its derivatives, and also on the behavior of the synthesized 5H-2-methyl-
1,2,4-triazepino[2,3-a]benzimidazol-4-one (4a) when treated with electrophilic and nucleophilic reagents.
R1
N
N
NH2
NH2
N
N
N
N
2
R
R1
O
2a–c
1
C6H5
N
N
N
R2
N
N
4a–c
N
H
N
Ph
3
2a,b, 4a,b R1 = Me, 2c R1 = Ph, 4c R1 = CH2CO2Et;
2a R2 = Me, 2b,c R2 = Ph, 4a,c R2 = H, 4b R2 = Et
_______
* For the previous communication, see [1].
__________________________________________________________________________________________
1
Kherson State Technical University, Kherson 73008, Ukraine; e-mail: lvi@tic.kherson.ua.
2 A. N. Severtsov Institute of Problems of Ecology and Evolution, Moscow 117071, Russia. Translated from
Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 683-691, May, 2002. Original article submitted
December 16, 1999.
598
0009-3122/02/3805-0598$27.00©2002 Plenum Publishing Corporation

In studying the conditions for condensation of 1 with pentane-2,4-dione, we found that of all the studied
solvents (refluxing in lower alcohols, dioxane, acetic acid, m-xylene, polyphosphoric acid (PPA)), the most
effective is 1-hexanol with additions of mineral acids. For example, the yield of 2,4-dimethyl-1,2,4-
triazepino[2,3-a]benzimidazole (2a) is 7% in boiling m-xylene, 20% in PPA, and 69% in 1-hexanol with
hydrochloric acid. In the absence of an acid catalyst, formation of a tricyclic heterosystem in trace amounts
(<1%) was observed only by chromatography, while when the reactions were carried out in lower alcohols or
dioxane, independent of the presence of mineral acid we recovered the starting compounds from the reaction
mixture.
Condensation of diaminobenzimidazole 1 with 4-phenylbutane-2,4-dione or dibenzoylmethane requires
more rigid conditions than for pentane-2,4-dione. Synthesis of triazepinobenzimidazoles 2b,c could be
accomplished only on heating the starting compounds in PPA at 110°C-115°C.
The spectral characteristics of the synthesized tricycles 2a-c are presented in Table 1.
In the mass spectra of triazepinobenzimidazoles 2b,c, we observe peaks for molecular [M+] ions of
intensity 100% (Table 2) and doubly charged ions [M2+], which suggests a condensed structure for compounds
1b,c [5]. Decomposition of M+ under electron impact conditions begins with cleavage of the bonds in the
triazepine ring, and proceeds in two main directions. The first direction is associated with successive
elimination of two nitrile molecules and formation of the ions [M-R1CN]+ (Φ) and [Φ-R2CN]+ (Φ1). The second
direction for decomposition of M+ is due to cleavage of the species NCR1CH2 (the Φ2 ion). Formation of Φ-Φ2
ions confirms the structure of the triazepine ring, and the fragmentary ions observed in the spectrum with m/z
118, 117, 103, 90, 77 confirm the structure of the benzimidazole moiety of compounds 2b,c.
The electronic spectra of compounds 2a-c, in contrast to the two-band spectrum of compound 1
(λmax 250 nm and 280 nm), are characterized by three absorption maxima (Table 1). The sensitivity of the
position of the long-wavelength band to substitution of the methyl radical at the C(4) atom by a phenyl group
suggests interaction of π-electrons of the aromatic ring and the multiple bonds of the tricycles 1b,c, leading to
lengthening of the main chromophore.
The reaction of compound 1 with β-diketones under high-temperature condensation conditions leads to
different results. Thus when compound 1 is refluxed with dibenzoylmethane in nitrobenzene or when it is heated
without a solvent (240°C-250°C) in the presence of ZnCl2, the compound 2,4-diphenylpyrimido[1,2-a]-
benzimidazole (3) is isolated [2, 6]. In this case, as for condensation of compound 1 with chalcones [2], the
reaction occurs with elimination of an amine group from the hydrazine moiety of the heterocycle.
When compound 1 is reacted with acetoacetic ester, its ethyl-substituted derivative,
or
1,3-diethoxycarbonylacetone, then the corresponding 2-substituted 5H-1,2,4-triazepino[2,3-a]benzimidazol-4-
ones (4a-c) are formed. The reaction proceeds smoothly in boiling acetic acid and, in contrast to synthesis of
analogous compounds from 1,2-diaminoimidazoles [7], does not require addition of sodium acetate.
Considering the possibility that lactam–lactim tautomerism exists for compounds 4a-c (forms A, B), we
used physical and chemical investigation methods to estimate the position of the tautomeric equilibrium A
in different aggregate states
.
B
R1
R1
N
N
N
N
N
R2
R2
N
N
H
N
X
XH
A
B
X = O, S, N
We showed earlier [8] that in the IR spectra (in KBr tablets) of tricycles 4a,c, we observe absorption
bands from carbonyl and imine groups of the triazepine ring, which are evidence that compounds 4a,c in
crystalline form exist predominantly in the lactam form A.
599

1
In the H NMR spectra of solutions of heterocycles 4a,b in DMSO-d6 (Table 1), in addition to signals
characterizing the structure of the substituents, we observe resonance from the proton of the imine group. The
absence of signals from the proton of the hydroxyl group in the spectra provides a basis for saying that in
solution, as in the crystalline state, form A is characteristic for compounds 4a,c.
Analysis of the mass spectra of lactams 4a,c showed that the fragmentation pattern under electron
impact conditions is somewhat different from that described above.
Me
Me
N
N
N
N
N
CHR1
R1
R2
N
N
5a–c
N
H
N
O
8a–d
4a
Me
Me
N
N
N
N
N
NPh
N
7
N
H
N
6
N
H
O
S
5 a R1 = Ph , b R1 = 4-MeOC6H4, c R1 = 4-O2NC6H4; 8 a R1 = R2 = H;
b R1 = H, R2 = CH2Ph; c R1+R2 = CH2(CH2)3CH2; d R1+R2 = (CH2)2O(CH2)2
Only in compound 4a, analogously to tricycles 2b,c and 5H-imidazo[1,2-c]-1,2,4-triazepin-4-ones [7],
do we observe cleavage of acetonitrile in the initial stages of decomposition of M+, leading to the Φ ion. The
lactams 4b,c initially lose a CO (the Φ ion), and only then the formation of the [Φ-R1CN]+ ion occurs.
Moreover, along with the fragmentation scheme for M+ of triazepinobenzimidazolones 4a,b on the whole is
general and is characterized by (in addition to the indicated ions) Φ1-[M-COH]+, Φ2-[M-HNCO]+,
Φ3-[M-CHR2CO]+, and Φ4-[M-NCR1CR2CO]+, which confirm the structure of the 1,2,4-triazepine ring. The
formation of the Φ-Φ4 ions directly from M+ is demonstrated by the mass spectra of the metastable ions (DADI
technique, "direct analysis of daughter ions") [9]. Additional confirmation of the nature and position of the
substituent R2 in the molecule of tricycle 4b comes from the ion peaks for Φ5-[Φ-C2H5]+, Φ6-[M-C2H5CHCO]+,
and Φ7-[(Φ-CH3CN)-C2H4]+ observed in the spectrum.
The presence of a labile ester group in the 2-ethoxycarbonylmethyl-substituted tricycle 4c results in
changes in the fragmentation scheme for its M+, where along with formation of Φ and Φ4 ions, there are charged
fragments illustrating the structure of the substituent at the C(2) atom: Φ5-[M-COOC2H4]+, Φ6-[M-COOC2H5]+,
and Φ7-[(M-COOC2H5)-H]+. Detection of ions with m/z 118, 117, 105, 104, 91, 90, and 77 confirms the
structure of the benzimidazole moiety of the molecule for lactams 4a-c.
A typical feature of the mass spectra of compounds 4a,b is elimination of a COH from M+. Formation of
[M-OH]+ ions indicates predominance of the lactim form B of tricycles 4a-c in the gas phase. Comparison of the
intensities of individual [M-CO]+ and [M-COH]+ ions of compounds 4a,b makes it possible to make a
quantitative estimate of the tautomeric forms A and B [9, 10]. According to these calculations, the fraction of
tautomeric form B in tricycles 4a,b is ~36% and 50% respectively.
Triazepinobenzimidazol-4-one 4a proved to be quite reactive. When lactam 4a and aromatic aldehydes
are reacted in boiling 1-butanol with addition of piperidine, then 5H-3-arylidene-2-methyl-1,2,4-triazepino-
[2,3-a]benzimidazol-4-ones 5a-c are synthesized; and upon azo coupling of lactam 4a with phenyldiazonium
chloride in dioxane, 3-phenylazo-substituted tricycle 6 is formed.
1
In the H NMR spectra of compounds 5a-c, 6, the signals for methylene protons are missing, which
together with the resonance for protons of the methyl group (Table 1) confirms that the methylene moiety of
tricycle 4a participates in the condensation and azo coupling.
600

TABLE 1. Characteristics of the Syntesized Compounds
Found, %
Calculated, %
1H NMR spectrum (CF3COOH),
——————
UV spectrum,
Com-
Empirical
formula
2
δ
mp, °С*
, ppm*
Yield, %
11
λmax
ε
pound
, nm (log )
С
3
Н
4
N
5
Нarom, m
СН2, s
8
СН3, s
9
1
2а
2
6
7
10
С12Н12N4
68.11
67.90
5.89
5.70
26.22
26.40
204-205
7.15
3.30
3.39
4.00
2.13
280 (4.45), 305 (3.95),
390 (2.84)
69
61
С17Н14N4
С22Н16N4
74.62
5.12
20.51
200-201
268-269
6.94
6.89
2.15
—
285 (4.40), 325 (3.85),
2b
2c
74.43
5.14
20.43
410 (2.92)
78.36
78.55
4.72
4.79
16.48
16.66
285 (4.40), 335 (3.90),
410 (2.98)
250 (4.32), 285 (4.05)
71
С11Н10N4O
С13Н14N4O
61.80
4.81
25.97
281-282
254-255
7.16*2
6.97*2
3.50
2.17
72
68
4а
61.67
4.71
26.0
64.62
64.45
5.66
5.82
23.22
23.20
3.55, t
2.17
250 (4.17), 282 (3.92)
4b
2.32, t
С14Н14N4O3
С18Н14N4O
58.84
4.83
19.42
227-228
258-259
260 (4.36), 290 (4.05)
278 (4.09), 320 (3.70)
64
67
4c
58.74
4.93
19.57
71.51
71.81
4.67
4.77
18.53
18.29
7.19
—
2.02
5а

TABLE 1 (continued)
1
2
3
4
5
6
7
8
9
10
11
65
С19Н16N4O
68.80
68.54
5.18
5.02
16.52
16.83
275-276
6.98
—
2.08
3.48
2.17
260 (4.08), 320 (4.20)
250 (4.13), 320 (4.11)
5b
С18Н13N5O3
С17Н13N6O
62.51
3.64
20.04
270-271
273-274
7.24
6.90
—
—
59
64
5с
62.25
3.77
20.16
64.42
64.36
4.34
4.13
26.37
26.49
2.22
240 (3.96), 275 (3.89),
387 (4.09)
6
С11Н10N4S
С11Н11N5
С18Н17N5
57.48
4.63
24.02
247-248
269-271
264-265
7.16
3.77
2.08
2.05
274 (4.22), 325 (4.33)
250 (4.31), 310 (4.53)
260 (4.64), 310 (4.55)
69
61
68
7
57.37
4.38
24.33
62.04
61.96
5.43
5.20
33.04
32.84
8а
8b
71.53
5.51
23.00
7.10
6.84
3.27
4.27
3.38
71.29
5.61
23.10
С16Н19N5
68.20
68.30
7.01
6.81
25.21
24.89
204-205
234-235
7.04*3
7.11*4
2.07
2.08
260 (4.54), 315 (4.51)
255 (4.27), 310 (4.42)
53
57
8с
С15Н17N5O
63.38
6.21
24.80
3.30
8d
63.59
6.05
24.72
_______
* The compounds were recrystallized as follows: 2a, 8b,d – from toluene; 2b,c, 4a,b, 5b, 6, 7 – from DMF; 4c, 8a – from
ethanol; 4a,b – from aqueous DMF; 7b – from 1-butanol.
2 1
δ
* H NMR spectrum (DMSO-d6), , ppm: 4a 8.84 (1H, br. s, NH); 7.39 (4H, m, Harom); 3.55 (2H, s, CH2); 2.41 (3H, s,
CH3); 4b – 8.92 (1H, br. s, NH); 7.42 (4H, m, Harom); 5.62 (1H, s, 4-CH); 8b – 8.68 (1H, br. s, NH); 7.19 (9H, m, Harom);
4.45 (2H, d, CH2–N); 2.18 (3H, s, CH3).
3
δ
* Signals from the piperidine moiety, , ppm: 3.56 (4H, m, (CH2)2N); 1.40 (6H, m, (CH2)3).
4
δ
* Signals from the morpholine moiety, , ppm: 3.94 (4H, br. m, (CH2)2O); 3.52 (4H, br. m, (CH2)2N).

TABLE 2. Mass Spectra of Compounds 2b,c, 4a-c (Ion Peaks with Intensity ≥10% Relative to Imax are Given)
Com-
pound
m/z (Irel, %)
[M+1]+
M+
other ions
Φ1
Φ2
Φ3
Φ4
—
Φ
275 (12)
274 (100)
233 (34)
130 (17)
130 (12)
185 (19)
219 (37)
219 (13)
171 (13)
—
—
М2+ – 137 (11), 129 (41), 118 (17), 117 (12),
2b
2с
4а
103 (20), 90 (11), 77 (24)
337 (13)
215 (14)
336 (100)
214 (100)
233 (31)
173 (12)
—
М2+ – 168 (14), 234 (62), 129 (35), 118 (11),
117 (28), 103 (31), 90 (10), 77 (51)
172 (21)
132 (25)
[М - СО]+ – 186 (34), [М-СОH]+ – 185 (19),
+
Φ
[
- СО] – 145 (26), 131 (27), 118 (82),
117 (28), 105 (39), 104 (38), 91 (14), 90 (59), 77 (41)
+
Φ5
Φ6
Φ
Φ
243 (15)
287 (11)
242 (100)
286 (68)
214 (13)
258 (10)
213 (13)
—
199 (16)
—
172 (23)
—
132 (24)
132 (25)
– 185 (20), [ - СН3СN] – 173 (15),
4b
4c
– 172 (23), 7 – 145 (10), 118 (52), 117 (23),
105 (14), 104 (20), 90 (43), 77 (21)
Φ5
Φ
Φ
– 214 (14), 6 – 213 (17), 7 – 212 (16),
+
1 +
Φ
Φ
[
5 - НСО] – 185 (28), [ - NСR ] –145 (12),
1 +
Φ
[
- НNСR ] – 144 (12), 118 (89), 117 (29),
105 (28), 104 (29), 91 (24), 90 (100),
77 (38), 67 (47)

A characteristic feature of the UV spectra of triazepinobenzimidazolones 4a-c, 6 is a bathochromic shift
of the long-wavelength maximum compared with the spectrum of lactam 4a; and in the case of azo compound 6,
we observe an additional band associated with absorption of the azo group. In subsequent experiments, we
observed that triazepinobenzimidazolone 4a enters into a thionylation reaction. When compound 4a is treated
with phosphorus pentasulfide in boiling dioxane or pyridine, its thio analog 7 is obtained. The reaction
proceeded most efficiently when lactam 4a was refluxed with a two-fold excess of P2S5 in dry dioxane.
1
The H NMR spectral data (Table 1) confirm the structure of the synthesized compound 6, and the
absorption bands observed in the IR spectrum for the C=S bond and the ring imine group (see the experimental
section) suggest predominance of the thione form A.
Thione 5 enters into a nucleophilic substitution reaction with ammonia and amines. When compound 7
is refluxed with ammonia, benzylamine, piperidine, or morpholine, we obtain 4-amino-substituted tricycles
8a-d.
Missing in the IR spectra of the substitution products of 8a-d is the absorption band for the C=S bond,
which is specific for the spectrum of the starting thione 7. The νNH absorption in the 3370-3390 cm-1 region is
characteristic for the IR spectra of compounds 8a,b and is observed in the spectrum of lactam 4a [8] and its thio
analog 7. Such a similarity shows that the considered compounds 8a,c are found in the imine A form.
The 1H NMR spectra of compounds 8b-d (Table 1) are consistent with the proposed structure.
An attempt to carry out the reaction of hydrazine hydrate with thione 6 led to decomposition of the
heterocycle, the major product of which was the diamine 1. The reason for such decomposition is not the
reducing properties of the hydrazine hydrate, but rather the alkaline medium created when it is present.
Confirmation of this comes from decomposition of thione 7 on refluxing in a 5% sodium hydroxide solution. In
this case, compound 1 is isolated in practically quantitative yield.
Thus when reactions of compound 7 are carried out using basic reagents, a preliminary estimate of their
destructive effect on the heterocycle is required. Investigations of biological activity showed that compounds
4a,b have slight muscle relaxant action, 4c has moderate anticonvulsive activity, 5c has antimicrobial properties,
while tricycles 7, 8a exhibit slight antiviral activity.
EXPERIMENTAL
The IR spectra were recorded on an IKS-22 in KBr tablets; the NMR spectra were recorded on Bruker
WH-90 (90 MHz) and Tesla BS-487C spectrometers in DMSO-d6 (TMS) and CF3COOH (HMDS). The electron
absorption spectra were taken on an SF-46 spectrophotometer in dioxane for a concentration of the compounds
equal to 0.2-0.4·10-4 mol/l. The mass spectra were obtained on a Finnigan HSQ-30 spectrometer with direct
injection of samples into the ion source.
2,4-Dimethyl-1,2,4-triazepino[2,3-a]benzimidazole (2a). A solution of 1,2-diaminobenzimidazole [11]
(0.45 g, 3 mmol), pentane-2,4-dione (0.4 g, 4 mmol), and conc. HCl (3 drops) in 1-hexanol (40 ml) was refluxed
for 4 h. The solution was evaporated down under vacuum to 1/2 volume; the residue formed was filtered out,
washed with cold toluene, and dried.
2-Methyl(phenyl)-4-phenyl-1,2,4-triazepino[2,3-a]benzimidazoles (2b,c). A mixture of compound 1
(0.6 g, 4 mmol), the corresponding β-diketone (4 mmol), and PPA (7 ml) was stirred for 1.5 h at 110-115°C.
The reaction mixture was cooled down and poured over ice (70 g); the precipitate was filtered out and
suspended in water (50 ml) and then a 10% NaHCO3 solution was added until pH ~8 was reached, and then it
was allowed to stand for 2 h. The suspension was filtered and the residue was washed with water and dried.
2,4-Diphenylpyrimido[1,2-a]benzimidazole (3). A. A mixture of compound 1 (0.9 g, 6 mmol),
dibenzoylmethane (1.46 g, 6.5 mmol), and anhydrous ZnCl2 (1.1 g) was heated for 1.5 h at 240-250°C. After
cooling the fusion cake was triturated, a 40% NaOH solution (20 ml) was added, and it was extracted with
604

benzene (6×50 ml). The benzene extracts were combined, evaporated down under vacuum until a precipitate
was obtained, then they were cooled down and the precipitate was filtered out and crystallized from DMF.
Yield 1.0 g (48%); mp 312-315°C.
B. A solution of dibenzoylmethane (0.6 g, 4 mmol) in nitrobenzene (5 ml) was refluxed for 5 h, and
after cooling the precipitate was filtered out. Yield 0.4 g (31%); mp 312-315°C (DMF), matches the data in [6].
Substituted 5H-1,2,4-triazepino[2,3-a]benzimidazol-4-one (4a-c). The corresponding acetoacetic
ester or 1,3-diethoxycarbonylacetone (6 mmol) were added to a solution of compound 1 (0.6 g, 4 mmol) in
acetic acid (30 ml), and then refluxed for 3 h. The reaction mixture was cooled; then the residue was filtered
out, washed with ethanol, and dried.
5H-3-Arylidene-2-methyl-1,2,4-triazepino[2,3-a]benzimidazol-4-one (5a-c). A solution of compound
4a (0.43 g, 2 mmol) and the corresponding aldehyde (2.1 mmol) in 1-butanol (40 ml) with 3 drops of piperidine
was refluxed for 30 min. The reaction mixture was evaporated down under vacuum until a precipitate appeared;
then it was cooled down and the precipitate was filtered out, washed with ethanol, and dried.
5H-2-Methyl-3-phenylazo-1,2,4-triazepino[2,3-a]benzimidazol-4-one
(6).
A
solution
of
phenyldiazonium salt (2.3 mmol) was added with stirring to a solution of triazepinobenzimidazolone 4a (0.43 g,
2 mmol) in DMF (75 ml) and then held for 3 h at a temperature of 18-20°C. The solution was diluted with water
(5 ml) and the precipitated orange crystals were filtered out and dried. IR spectrum, ν, cm-1: 3390-3415 (NH),
1710 (C=O), 1430 (N=N).
5H-2-Methyl-1,2,4-triazepino[2,3-a]benzimidazole-4-thione (7). A mixture of tricycle 4a (0.64 g,
3 mmol), P2S5 (0.67 g, 3 mmol) in dry pyridine (40 ml) was refluxed for 4 h. The solution was cooled down;
then the precipitate was filtered out, washed successively with water, dioxane, and water, and then dried. IR
spectrum, ν, cm-1: 3375-3400 (NH), 1155 (C=S).
4-Amino-substituted 2-Methyl-1,2,4-triazepino[2,3-a]benzimidazole (8a-d). Conc. ammonia (0.7 ml)
or the corresponding amine (0.3 mmol) was added to a solution of thione 7 (0.58 g, 2.5 mmol) in 2-propanol
(30 ml) and then was refluxed for 6 h. The solution was concentrated down at reduced pressure until a
precipitate appeared, and then was filtered.
Degradation of 5H-2-methyl-1,2,4-triazepino[2,3-a]benzimidazole-4-thione (7). A solution of thione
6 (0.64 g, 3 mmol) in a 5% solution of potassium hydroxide (15 ml) was refluxed for 1 h and cooled down; the
precipitate was filtered out and washed with water. Obtained 0.45 g (99%) of compound 1; mp 255-257°C
(water), which matches data in [11].
When compound 6 (3 mmol) was refluxed with 70% hydrazine hydrate (4 mmol) in 2-propanol (30 ml),
the yield of compound 1 was 0.37 g (81%).
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