Synthesis of new azocompounds and fused pyrazolo[5,1-c][1,2,4]triazines using heterocyclic components

Article abstract of DOI:10.1002/jhet.1533

Diazotization of 3-methyl-4-phenyl-1H-pyrazol-5-amine in hydrochloric acid has been reported to afford the corresponding diazonium salt 2. The latter underwent azocoupling with a variety of active methylene compounds (barbituric 3a and thiobarbituric 3d a

Full text of DOI:10.1002/jhet.1533

May 2013
Synthesis of New Azocompounds and Fused Pyrazolo[5,1-c][1,2,4]
573
triazines Using Heterocyclic Components
*
Irina V. Ledenyova, Vitaly V. Didenko, Alexander S. Shestakov, and Khidmet S. Shikhaliev
Department of Organic Chemistry, Voronezh State University, Universitetskaya pl. 1, Voronezh 394006, Russian
*
E-mail: irairachem@yandex.ru
Received May 31, 2011
DOI 10.1002/jhet.1533
Published online in Wiley Online Library (wileyonlinelibrary.com).
Diazotization of 3-methyl-4-phenyl-1H-pyrazol-5-amine 1 in hydrochloric acid has been reported to
afford the corresponding diazonium salt 2. The latter underwent azocoupling with a variety of active
methylene compounds (barbituric 3a and thiobarbituric 3b acid, 2-hetarylpyrimidine-4,6-dione 6a,b,
4-hydroxy-6-methylpyridin-2(1H)-one 10a, 4-hydroxy-6-methyl-2H-pyran-2-one 10b, 4-hydroxy-1-p-tolyl-
1H-pyrazole-3-carboxylic acid ethyl ester 14, 1,3-thiazolidine-2,4-dione 16a, 2-thioxo-1,3-thiazolidin-4-
one 16b) to yield new pyrazolylazo derivatives. Fused pyrazolo[5,1-c][1,2,4]triazines 5, 9a,b, 12, 13 were
obtained by heterocyclization reactions.
J Heterocyclic Chem., 50, 573 (2013).
INTRODUCTION
RESULTS AND DISCUSSION
Pyrazolediazonium salts are known as potential building
blocks for the synthesis of various heterocycles [1–6]. The
pyrazole-annelated nitrogen-containing structures can also
be referred to them. The pyrazolo[5,1-c][1,2,4]triazines
are the most important among them. The considerable
biological activity of these heterocycles as purine analogs
stimulated interest in the synthesis of derivatives of these
ring systems [7–12].
A direct procedure for obtaining pyrazolo[5,1-c][1,2,4]
triazines consists in azocoupling of pyrazole-3(5)-diazonium
salts with aliphatic compounds containing an active
methylene/methine followed by the cyclization of formed
hydrazones or azocompounds [13–18].
Nevertheless, there are only a few examples in which the
heterocyclic rings [19–21] are used as coupling components
in reactions with pyrazole-3(5)-diazonium salts.
In the previous article [22], we reported that the reac-
tion of pyrazolediazonium salts with alicyclic methylene
active reagents led to pyrazol-5-ylhydrazones, which
spontaneously cyclized to substituted pyrazolo[5,1-c]
[1,2,4]triazines.
3-Methyl-4-phenyl-1H-pyrazol-5-amine 1 reacted with so-
dium nitrite and hydrochloric acid to give the corresponding
pyrazole-3(5)-diazonium chloride 2. The latter was isolated
in pure form, and further, it was treated in situ (Scheme 1).
In the present study, the synthetic potential of compounds
2 was investigated through its reactions with heterocyclic
coupling components.
Thus, diazonium salt 2 reacted with barbituric acid 3a and
thiobarbituric acid 3b under the coupling conditions
(Scheme 2). For all interactions of this type, several
tautomeric forms of the products can be written. Spectral data
showed that linear derivatives exist in an azo tautomeric form.
According to the 1H NMR spectrum, there were no
signals in the range of d 11–12 ppm relating to NH-protons
of hydrazone form, as reported in the literature [23].
Besides, the analysis showed the hydroxyl group near d
14.5 ppm and the signals of NH-protons of pyrazole and
pyrimidine rings.
Subsequently, the attempts at heterocyclization of
derivatives 4a,b by heating with polyphosphoric acid
(PPA) for a few hours have been made. As a result, only
a new pyrazolo[5,1-c]pyrimido[4,5-e][1,2,4]triazine-4(3H)-
one 5 was obtained. Unfortunately, the cyclization of hetary-
lazocompound 4b both by heating with PPA and anhydrous
sodium acetate in acetic acid failed.
In the present work, we investigated the synthetic routes
to new azocompounds and tricyclic pyrazolo[5,1-c][1,2,4]
triazines using different heterocyclic components in the
azocoupling reaction with pyrazolediazonium salts.
© 2013 HeteroCorporation

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I. V. Ledenyova, V. V. Didenko, A. S. Shestakov, and K. S. Shikhaliev
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Scheme 1
showed the presence of amide NH-proton signal (d
11.80 ppm) of pyrimidine cycle and the absence of the analo-
gous signal of pyrazole ring in a low field.
Azocoupling of 4-hydroxy-6-methyl-1H-pyridine-2-one
10a and 4-hydroxy-6-methyl-2H-pyran-2-one (triacetic
acid) 10b with diazotized 3(5)-aminopyrazole resulted in
the formation of the pyrazolo[5,1-c][1,2,4]triazine deriva-
tives that were probably formed via intermediacy of the
azo form 11a,b (Scheme 4).
Similarly, diazonium salt 2 coupled smoothly with
In the case of compound 11a, the heterocyclization was
performed by heating the colored linear substrate with acetic
acid in ring-closure product 12. Such procedure is usable as a
novel route to obtain the pyrazolo[5,1-c]pyrido[4,3-e][1,2,4]
triazine derivative [24]. Differently, cyclocondensation of
intermediate 11b did not lead to the expected tricyclic structure
but gave a new 7-methyl-4-(2-oxopropyl)-8-phenylpyrazolo
[5,1-c][1,2,4]triazine-3-carboxylic acid 13. Probably, this was
due to the lactone ring opening under the action of water in acid
medium (Scheme 5).
2-hetarylpyrimidine-4,6-diones 6a,b in the presence of so-
1
dium acetate to yield the colored products (Scheme 3). H
NMR data of the compounds obtained showed the tautomeric
forms 7a,b only.
When the substances obtained were heated with PPA,
8-methyl-7-phenyl-2-hetaryl-pyrazolo[5,1-c]pyrimido[4,5-e]
[1,2,4]triazin-4(3H)-ones 9a,b were formed in satisfactory
yields (65–70%). Alternative structures 8a,b were excepted
1
on the basis of spectral data. The H NMR spectra of 9a,b
Scheme 2
Scheme 3
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Synthesis of New Azocompounds and Fused Pyrazolo[5,1-c][1,2,4]triazines
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Using Heterocyclic Components
Scheme 4
Scheme 5
Scheme 6
Moreover, the interaction of pyrazolediazonium salt 2
with 4-hydroxy-1-p-tolyl-1H-pyrazole-3-carboxylic acid
ethyl ester 14 yielded a linear bright red hetarylhydrazone
15 (Scheme 6). The spectral data were in good agreement
with the suggested structure. From the NMR data, the
broad signals of proton in the region of d 9.50 ppm proved
the presence of the linear C-NH-N═C fragment. The IR
spectrum revealed a strong absorption band at 1650 cmÀ1
for conjugated ketone. Neither heating of 15 with acetic
acid nor heating with PPA led to a new azoheterocycle.
This is, obviously, connected with the hindered nucleo-
philic attack at C(4)-position in pyrazole ring.
In addition, the synthetic possibilities of 1,3-thiazolidine-
2,4-dione and 2-thioxo-1,3-thiazolidin-4-one (rhodanin) as
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Scheme 7
(300 MHz) relative to SiMe4 as an internal standard (DMSO-d6
solutions). Mass spectra were measured on an LKB-9000
spectrometer (Shimadzu, Tokyo, Japan). Elemental analyses (C,
H, N) were conducted using the elemental analyzer Carlo Erba
NA 1500 (Heraeus, Hanau, Germany). Starting materials 3a,b,
10b, and 16a,b were commercially available.
2-Hetarylpyrimidine-4,6-diones 6a,b. A typical procedure
for the preparation of pyrimidine-4,6-dione derivatives was
described in paper [32].
4-Hydroxy-6-methyl-1H-pyridine-2-one 10a. The synthetic
procedure for obtaining 10a has been reported previously [33].
4-Hydroxy-1-p-tolyl-1H-pyrazole-3-carboxylic acid ethyl
ester 14. Compound 14 was prepared according to the literature
procedure [34].
methylene active components in reactions with diazonium
salt were considered. The aforementioned heterocycles were
found to be incorporated into natural subtracts and medicines
[25–28]. Therefore, the inclusion of these compounds in
synthetic polyheterocyclic systems made it possible to model
many potential drugs.
Azocoupling of pyrazole-(3)5-diazonium chloride 2 with
active methylene compounds 16a,b yielded colored linear
products 17a,b. On the basis of literature data, the tautomeric
forms of these compounds have been defined as azo-keto
forms [29–31]. The attempts at heterocyclization of azocom-
pounds 17a,b to pyrazolotriazine-containing structures
either by refluxing in acetic acid or by heating with PPA
for a few hours were unsuccessful because of the ring
destruction (Scheme 7).
Preparation of compounds 4a,b, 7a,b, 12, 13, 15.
A
solution of 3(5)-aminopyrazole [35] 1 (5.19 g, 0.03 mol) in
water (30 mL) and hydrochloric acid (9 mL, d = 1.19 gÁmLÀ1
)
was cooled to 0ꢀC. The mixture was treated with the water
solution of sodium nitrite (2.07 g, 0.03 mol) by stirring. Then,
the cooled (0–5ꢀC) pyrazolediazonium chloride 2 solution was
added with stirring to the active methylene compounds 3a,b,
6a,b, 10a,b, 14 (0.03 mol) with sodium acetate (30 g, 0.37 mol)
in acetic medium (30 mL). The reaction mixture was stirred at
room temperature for nearly 1 h and kept standing overnight.
The solid deposit was collected by filtration and washed well with
water. All colored products were recrystallized from acetic acid.
Synthesis of tricyclic pyrazolo[5,1-c][1,2,4]triazines 5,
CONCLUSION
Thus, the convincing examples of an effective synthesis of
earlier unknown pyrazol-5-yl-azocompounds and tricyclic
pyrazolo[5,1-c][1,2,4]triazines have demonstrated the
prospects for using different heterocycles as coupling com-
ponents in the reaction with pyrazolediazonium salts. In
addition, pyrazole-containing azocompounds can also find
application in industrial azo dyes and analytical indicators.
Finally, many pyrazolo[5,1-c][1,2,4]triazine derivatives
have been used as potential bioactive compounds because
they are structurally related to purines. The aforementioned
discussion makes it possible to consider all systems
obtained significant for the future research in the area of
heterocyclic and medicinal chemistry.
9a,b.
Dried up and crushed crystalline pyrazolylazo
compounds 4a, 7a,b were heated for 3 h with two-multiple
excess of solid PPA. The temperature of the reaction
mixture was kept between 140 and 160ꢀC. Then, water was
added to the cooled reaction mixture, and the latter was
neutralized with sodium bicarbonate. The solid deposit was
collected by filtration, washed with water, and recrystallized
from acetic acid, DMF, or the mixtures of them.
6-Hydroxy-5-[(3-methyl-4-phenyl-1H-pyrazol-5-yl)diazenyl]
pyrimidine-2,4(1H,3H)-dione 4a. Yield 93%; yellow crystals
1
(from AcOH); mp >300ꢀC; H NMR d 2.28 (3H, s, Me), 7.33
EXPERIMENTAL
(3H, m, HAr), 7.45 (2H, m, HAr), 12.38, 12.55 (2H, both br,
NH), 12.85 (1H, br, NHpyrazole), 14.49 (s, 1H, OH). ms, m/z
312 [M]+. Anal. Calcd for C14H12N6O3 (M 312.28): C, 53.85;
General procedures. Melting points were determined with
a Kofler apparatus (Heizbank, Reichert, Austria). Reaction
progress was monitored by an analytical thin-layer
chromatography on plates Silufol UV-254 (Merck, Darmstadt,
Germany) using the solvent systems of chloroform, ethyl
acetate, and isopropyl alcohol. The products were visualized
with UV light. Infrared spectrum was determined using a
Specord-82 M spectrometer, and the wave numbers are
expressed in cmÀ1. The 1 H NMR spectra were recorded on
Bruker AC-300 spectrometer (Bruker, Flawil, Switzerland)
H, 3.87; N, 26.91. Found: C, 53.92; H, 3.83; N, 26.88.
6-Hydroxy-5-[(3-methyl-4-phenyl-1H-pyrazol-5-yl)diazenyl]-2-
thioxo-2,3-dihydropyrimidin-4(1H)-one 4b. Yield 88%; yellow-
1
red crystal solid (from AcOH); mp 190–192ꢀC; H NMR d 2.30
(3H, s, Me), 7.10–7.30 (5H, m, HAr), 12.38, 12.49 (2H, both br,
NH), 12.80 (1H, br, NHpyrazole), 14.62 (1H, s, OH). MS, m/z 328
[M]+. Anal. Calcd for C14H12N6O2S (M 328.35):C, 51.21; H,
3.68; N, 25.59. Found: C, 51.30; H, 3.55; N, 25.61.
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Using Heterocyclic Components
2-Hydroxy-8-methyl-7-phenylpyrazolo[5,1-c]pyrimido[4,5-e]
Calcd for C23H22N6O3 (M 430.46): C, 64.17; H, 5.15; N, 19.52.
Found: C, 64.28; H, 5.10; N, 19.48.
Preparation of thiazolidine derivatives 17a,b. Azothiazolidines
17a,b were obtained according to the procedure described for the
analogous aryl derivatives [36].
A solution of 16a,b (0.03 mol in 30 mL water) was mixed with
2N aqueous NaOH (15 mL). The cooled solution was added
dropwise with stirring to a solution of the appropriate pyrazole-
diazonium chloride (prepared from 5.19 g, 0.03 mol of the amine
1 and the appropriate quantities of hydrochloric acid and sodium
nitrite). After addition, the mixture was stirred for 40 min at 0ꢀC
and then adjusted to pH ~3 with aqueous HCl. The precipitate
was filtered, washed with water, and dried.
[1,2,4]triazin-4(3H)-one 5.
Yield 67%; yellow crystal solid
(from AcOH–DMF); mp >300ꢀC; 1H NMR d 2.69 (3H, s,
Me), 7.50 (3H, s, HAr), 7.88 (2H, s, HAr), 11.79 (1H, br, NH).
ms, m/z 294 [M]+. Anal. Calcd for C14H10N6O2 (M
294.27): C, 57.14; H, 3.43; N, 28.56. Found: C, 57.39; H, 3.29;
N, 28.42.
6-Hydroxy-5-[(3-methyl-4-phenyl-1H-pyrazol-5-yl)diazenyl]-
2-piperidin-1-ylpyrimidin-4(3H)-one 7a.
Yield 87%; bright
1
yellow crystal solid (from AcOH); mp 182–184ꢀC; H NMR d
1.70 (6H, s, (CH2)3), 2.33 (3H, s, Me), 3.91 (4H, s, N(CH2)2),
7.30 (1H, s, HAr), 7.60 (4H, m, HAr), 11.56 (1H, br, NH), 12.80
(1H, br, NHpyrazole), 16.00 (1H, br, OH). ms, m/z 379 [M]+.
Anal. Calcd for C19H21N7O2 (M 379.42): C, 60.15; H, 5.58; N,
25.84. Found: C, 60.25; H, 5.51; N, 25.80.
5-[(3-Methyl-4-phenyl-1H-pyrazol-5-yl)diazenyl]-1,3-thiazoli-
dine-2,4-dione 17a.
Yield 62%; yellow crystal solid; mp
1
188ꢀC, decomp.; H NMR d 2.32 (3H, s, Me), 7.18–7.50 (5H,
m, HAr), 7.63 (1H, s, SCH), 12.46 (1H, br, NH), 13.22 (1H, br,
NHpyrazole). Anal. Calcd for C13H11N5O2S: C, 51.82; H, 3.68; N,
23.24. Found: C, 51.73; H, 3.60; N, 23.21.
2-(4-Benzylpiperidin-1-yl)-6-hydroxy-5-[(3-methyl-4-phenyl-
1H-pyrazol-5-yl)diazenyl]pyrimidin-4(3H)-one 7b.
Yield
79%; bright yellow crystal solid (from AcOH); mp 198–200ꢀC;
1H NMR d 1.26 (2H, m, CH2), 1.75 (2H, m, CH2), 1.90 (1H,
m, CH), 2.31 (3H, s, Me), 2.56 (2H, d, J = 13.0 Hz, CH2), 4.60
(4H, m, N(CH2)2), 7.10–7.50 (10H, m, HAr), 11.60 (1H, br,
NH), 12.89 (1H, br, NHpyrazole), 16.10 (1H, br, OH). ms, m/z
469 [M]+. Anal. Calcd for C26H27N7O2 (M 469.54): C, 66.51;
H, 5.80; N, 20.88. Found: C, 66.50; H, 5.74; N, 20.90.
5-[(3-Methyl-4-phenyl-1H-pyrazol-5-yl)diazenyl]-2-thioxo-
1,3-thiazolidin-4-one 17b. Yield 44%; orange crystal solid;
1
mp 150ꢀC, decomp.; H NMR d 2.31 (3H, s, Me), 7.20–7.45
(5H, m, HAr), 7.51 (1H, s, SCH), 10.63 (1H, br, NH), 13.40
(1H, br, NHpyrazole). Anal. Calcd for C13H11N5OS2: C, 49.19;
H, 3.49; N, 22.07. Found: C, 49.29; H, 3.40; N, 22.00.
8-Methyl-7-phenyl-2-piperidin-1-ylpyrazolo[5,1-c]pyrimido
[4,5-e][1,2,4]triazin-4(3H)-one 9a.
Yield 65%; brown
crystals (from AcOH–DMF); mp >300ꢀC; 1H NMR d 1.73
(6H, s, (CH2)3), 2.69 (3H, s, Me), 3.96 (4H, s, N(CH2)2), 7.39
(1H, s, HAr), 7.50 (2H, m, HAr), 7.86 (2H, m, HAr), 11.81
(1H, br, NH). ms, m/z 361 [M]+. Anal. Calcd for C19H19N7O
(M 361.40): C, 63.14; H, 5.30; N, 27.13. Found: C, 63.20; H,
5.40; N, 27.19.
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pyrimido[4,5-e][1,2,4]triazin-4(3H)-one 9b.
Yield 50%;
brown crystals (from AcOH–DMF); mp >300ꢀC; 1H NMR d
1.30 (2H, m, CH2), 1.76 (2H, m, CH2), 1.90 (1H, m, CH), 2.70
(3H, s, Me), 2.85 (2H, m, CH2), 4.23 (4H, s, N(CH2)2), 7.25–
7.80 (10H, m, HAr), 11.80 (1H, br, NH). ms, m/z 451 [M]+.
Anal. Calcd for C26H25N7O (M 451.52): C, 69.16; H, 5.58; N,
21.71. Found: C, 69.22; H, 5.55; N, 21.70.
2,8-Dimethyl-3-phenylpyrazolo[5,1-c]pyrido[4,3-e][1,2,4]
triazin-6(7H)-one 12.
Yield 45%; brown crystals (from
1
AcOH–DMF); mp >300ꢀC; H NMR d 2.43 (3H, s, Me), 2.67
(3H, s, Me), 6.94 (1H, c, CH), 7.44 (1H, t, J=7.4Hz, HAr), 7.57
(2H, t, J=7.6Hz, HAr), 7.85 (2H, d, J=7.6Hz, HAr), 12.39 (1H, br,
NH). ms, m/z 291 [M]+. Anal. Calcd for C16H13N5O (M 291.31): C,
65.97; H, 4.50; N, 24.04. Found: 66.06; H, 4.41; N, 24.00.
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triazine-3-carboxylic acid 13.
Yield 49%; orange
crystals (from AcOH); mp 187ꢀC, decomp.; 1H NMR d 1.92, 2.59
(6H, both s, Me), 3.05 (1H, d, J=8.9Hz, CH2), 3.24 (1H, d,
J=8.9Hz, CH2), 7.43 (1H, t, J=7.0Hz, HAr), 7.55 (2H, t,
J=7.8Hz, HAr), 7.78 (2H, d, J=7.7Hz, HAr), 8.28 (1H, s, COOH).
ms, m/z 310 [M]+. Anal. Calcd for C16H14N4O3 (M 310.31): C,
61.93; H, 4.55; N, 18.06. Found: 62.10; H, 4.46; N, 17.98.
Ethyl 1-(p-tolyl)-5-[(3-methyl-4-phenyl-1H-pyrazol-5-yl)hydra-
zono]-4-oxo-4,5-dihydro-1H-pyrazole-3-carboxylate 15.
Yield
66%; orange-red crystals (from AcOH); mp 167–169ꢀC,
1
decomp.; ir 1608, 1650 (C═O), 2961 (C-Halip). H NMR d 1.38
(3H, t, J = 2.8Hz, MeCH2O), 2.34 (3H, s, Me), 2.40 (3H, s, Me),
4.35 (2H, q, J = 5.0Hz, MeCH2O), 7.10–7.60 (9H, m, HAr), 9.50
(1H, br, NH), 13.20 (1H, br, NHpyrazole). ms, m/z 430 [M]+. Anal.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet