Synthesis of new substituted pyridopyrazolotriazines

Article abstract of DOI:10.1007/s10593-012-1101-4

Pyrazolo[3,4-b]pyridinediazonium chlorides react with a variety of active methylene-containing reagents (e.g., cyanoacetic acid arylidenehydrazide derivatives) to afford the corresponding 3-hydr-azonopyrazolo[3,4-b]pyridine derivatives. The diazonium chlo

Full text of DOI:10.1007/s10593-012-1101-4

Chemistry of Heterocyclic Compounds, Vol. 48, No. 7, October, 2012 (Russian Original Vol. 48, No. 7, July, 2012)
SYNTHESIS OF NEW SUBSTITUTED
PYRIDOPYRAZOLOTRIAZINES
M. A. Metwally1*, E. Abdel-Galil1, A. Metwally1, and F. A. Amer1
Pyrazolo[3,4-b]pyridinediazonium chlorides react with a variety of active methylene-containing
reagents (e.g., cyanoacetic acid arylidenehydrazide derivatives) to afford the corresponding 3-hydr-
azonopyrazolo[3,4-b]pyridine derivatives. The diazonium chlorides react with N'-acyl-2-cyanoaceto-
hydrazide derivatives to give the corresponding 3-hydrazonopyrazolopyridine derivatives. The latter
affords the corresponding 3-hydrazonopyrazolo[3,4-b]pyridine derivatives on reflux in acetic acid.
Diazo coupling of 2,4-dimethylpyrazolo[3,4-b]pyridinediazonium chloride with ketoester, e.g., ethyl
benzoylacetate, is followed by cyclization to afford pyrido[2',3':3,4]pyrazolo[5,1-c]triazine derivative.
Diazo coupling of the same dimethylpyrazolo[3,4-b]pyridinediazonium chloride with unsymmetrical
-diketone, e.g., benzoylacetone, was also studied to afford the corresponding hydrazono derivative,
which undergoes in situ cyclization to furnish the pyrido[2',3':3,4]pyrazolo[5,1-c]triazine derivative.
Keywords: 3-hydrazonopyrazolo[3,4-b]pyridines, pyrazolo[3,4-b]pyridinyldiazonium chlorides, pyri-
do[2',3':3,4]pyrazolo[5,1-c]triazines.
Due to the reported biological activities of triazines [1-5], as well as pyrazolopyridines [6], we were also
interested in the synthesis of molecules with the pyrido[2',3':3,4]pyrazolo[5,1-c]triazine heterocyclic system.
The latter has been used as disperse dyes (for polyester, polyamide, acrylic fibers) [7, 8], as antibacterial agents
[9], and as fungicides [10].
The highly versatile 3-aminopyrazolo[3,4-b]pyridine derivatives 1a,b have been reacted with sodium
nitrite and hydrochloric acid to afford the corresponding pyrazolo[3,4-b]pyridinediazonium chlorides 2a,b,
respectively. Their versatility derives from the easy accessibility of compounds 1a,b, which can be obtained
from acetylacetone, hydrazine, and cyanoacetamide [11, 12]. The synthetic potentiality of compounds 2a,b was
investigated through their reactions with a variety of active methylene-containing reagents.
+
Me
Me
N
N
NH2
N
X
X
–
NaNO2
HCl
Cl
N
N
N
N
N
1a,b
Me
Me
H
H
2a,b
1, 2 a X = H, b X = Br
_______
*To whom correspondence should be addressed, e-mail: mamegs@mans.edu.eg.
1Chemistry Department, Faculty of Science, Mansoura University, P. O. Box 23, Mansoura, Egypt.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1153-1159, July, 2012. Original
article submitted March 11, 2011; revision submitted November 8, 2011.
0009-3122/12/4807-1071©2012 Springer Science+Business Media New York
1071

The pyrazolopyridinediazonium chlorides 2a,b have been reacted with 2-cyano-N'-(4-methoxy-
benzylidene)acetohydrazide (3) to afford the corresponding 3-hydrazonopyrazolo[3,4-b]pyridine derivatives 4
and 5, respectively.
1
The structure of compounds 4 and 5 is confirmed by IR and H NMR spectroscopy, as well as by
1
elemental analysis. The H NMR spectra of compounds 4 and 5 include, in addition to the signals of both
pyrazolopyridine and cyanoacetic arylidenehydrazide fragments, two singlet signals at 10.80 and 12.25 ppm for
the three NH protons.
H
Me
N
O
CN
N
O
X
NaOAc
EtOH
NC
N
Ar
O
2a,b
+
N
NH
N
N
H
N
Me
N
Ar
O
H
3
4, 5
Ar
N
Me
N
N
Me
N
N
N
N
X
H
X
AcOH
CN
N
N
H
NH
N

Ar
N
NH2
N
Me
Me
N
4', 5'
6, 7
3, 4, 4', 5, 5', 6, 7 Ar = 4-MeOC6H4; 4, 4', 6 X = H; 5, 5', 7 X = Br
Further confirmation of the hydrazono structures 4 and 5 was given via their cyclization in boiling acetic
acid to give the corresponding pyrido[2',3':3,4]pyrazolo[5,1-c]triazine derivatives 6 and 7, respectively. The reaction
proceeds by nucleophilic attack of ring nitrogen to the cyano group in the tautomeric structures 4' and 5'.
The chemical structures of compounds 6 and 7 were confirmed by analytical and spectroscopic data.
The IR spectra of these derivatives clearly indicated the lack of the cyano group absorption band and revealed
the characteristic NH2 and NH group absorption bands in the region of 3380-3200 cm-1, in addition to the
carbonyl absorption band at 1652-1661 cm-1. The 1H NMR and mass spectra of compounds 6 and 7 also confirm
the proposed structure.
Furthermore, the diazonium chloride 2a was reacted with N'-acyl-2-cyanoacetohydrazide derivatives
8a,b to give the corresponding 3-hydrazonopyrazolopyridine derivatives 9a,b. The structures of compounds
9a,b were assigned on the basis of elemental analysis, IR, and 1H NMR spectral data.
H
Me
N
O
CN
N
O
H
NaOAc
EtOH
NC
N
R
2a
+
N
NH
N
H
N
Me
N
HN
R
O
O
H
8a,b
9a,b
O
Me
N
N
CN
NH
N
Me
N
N
H
AcOH
NH
N
O
N
N
N

H
Me
R
HN
R
NH2
N
Me
N
O
10a,b
9'a,b
O
8, 9, 9', 10 a R = Me, b R = Ph
1072

The IR spectrum of compound 9a (as an example) showed characteristic absorption bands at 3403,
3282, and 3201 cm-1 due to NH groups, 2192 cm-1 for the cyano group, and 1698 and 1657 cm-1 for the carbonyl
groups. The 1H NMR spectrum of the same compound revealed three singlet signals at 2.10, 2.50, and 2.60 ppm
for three methyl groups, a singlet signal at 7.00 ppm for the H-5 proton in addition to three singlet signals at
11.60, 12.85, and 14.25 ppm for the NH protons
When the hydrazono derivatives 9a,b were refluxed in acetic acid, they underwent cyclization to afford
the corresponding aminopyrido[2',3':3,4]pyrazolo[5,1-c]triazine derivatives 10a,b respectively. The structures
of the products were established based on the data of IR, 1H NMR, MS, and elemental analyses. As in the case
of cyclization of cyano derivatives 4, 5 to compounds 6, 7, the IR spectrum of compounds 10a,b showed the
absence of the nitrile absorption band and the presence of absorption bands of the NH2 and NH groups near
3380 and 3180 cm-1.
Diazo coupling of the dimethylpyrazolo[3,4-b]pyridinediazonium chloride 2a with a ketoester ethyl
benzoylacetate proceeded in ethanol solution of sodium acetate to furnish the corresponding hydrazono
derivative 11 which underwent cyclization in ethanol containing a catalytic amount of triethylamine to afford
the corresponding pyrido[2',3':3,4]pyrazolo[5,1-c]triazine derivative 12. The structures of the products 11 and
12 were confirmed based on the spectral and elemental analysis data.
H
Me
N
O
COOEt
Ph
N
O
O
NaOAc
EtOH
2a
+
N
Ph
OEt
N
Me
N
H
11
COOEt
Ph
N
Me
N
Me
N
N
N
N
COOEt
Et3N
EtOH
N
HO
NH
Ph
N
12
N
Me
Me
11'
The IR spectrum of compound 11 showed three bands at 3147, 1685, and 1667 cm-1 assigned to the
stretching frequency of the NH group and carbonyl groups of ester and phenyl ketone, respectively. The IR
spectrum of the corresponding cyclized derivative 12 indicated the absence of the carbonyl absorption frequency
(COPh) and displayed only the absorption band at 1737 cm-1 for the ester carbonyl group. The elemental
analysis and mass spectrum of compound 12 confirm molecular composition and molecular mass of the
proposed structure, indicating the loss of H2O molecule with respect to the molecular composition of compound
11.
The diazo coupling of dimethylpyrazolo[3,4-b]pyridinediazonium chloride 2a with an unsymmetrical
-diketone benzoylacetone was also studied. The diazo-coupling reaction proceeds upon stirring at 0-5°C in
ethanol solution of sodium acetate to afford the corresponding hydrazono derivative 13, which undergoes in situ
cyclization under the reaction conditions to furnish the pyrido[2',3':3,4]pyrazolo[5,1-c]triazine derivative 14
carrying the benzoyl group as substituent, instead of the other possible cyclization into the tricyclic system 15
carrying the acetyl group as substituent. Thus, it was suggested that the cyclization proceeds through water
elimination by the tautomeric form 13' rather than the other tautomeric from 13''. The structure of the isolated
product 14 is based on the spectral and elemental analysis data.
The IR spectrum of product 14 displayed the carbonyl absorption frequency at 1664 cm-1 assigned to
benzoyl carbonyl (COPh). The mass spectrum showed the molecular ion peak at m/z 316 (C18H15N5O); a
fragment ion at m/z 105, corresponding to the benzoyl group, was also observed, providing additional
confirmation of the structure 14.
1073

O
Me
N
N
N
Ph
Me
COPh
N
Me
N
N
N
Me
N
Me
HO
NH
14
N
Me
13'
O
H
Me
N
N
N
O
O
Ph
NaOAc
EtOH
2a
+
Ph
Me
N
Me
O
N
Me
H
13
O
Me
N
Me
Ph
N
N
Me
N
N
COMe
N
O
NH
Ph
N
Me
N
N
Me
15
13''
In conclusion, the synthesis of a new substituted pyridopyrazolotriazine from the reaction of pyrazolo-[3,4-
b]pyridinyldiazonium chlorides with a variety of active methylene-containing compounds (e g., cyanoacetic acid
arylidene hydrazide derivatives, N'-acyl-2-cyanoacetohydrazide derivatives, -ketoester and -diketone) was
described.
EXPERIMENTAL
1
IR spectra in KBr pellets were recorded with on a Mattson 5000 FTIR spectrometer. H NMR spectra
were measured on a Bruker WP 300 spectrometer (300 MHz), using TMS as internal standard. Mass spectra were
recorded on a Finnigan MAT 212 instrument, using the electron impact ionization method. Elemental analyses
were carried out in the Microanalytical Unit, Faculty of Science, University of Mansoura. Melting points
(uncorrected) were determined on a Weiss-Gallenkamp electric melting point apparatus.
Starting compounds 1a,b were prepared by method [11, 12]. Cyanoacetic acid hydrazides 3 and 8a,b
were obtained by the method described in [13-15].
Pyrazolopyridinediazonium Chlorides 2a,b (General Method). A solution of NaNO2 (0.69 g, 0.01
mol) was added dropwise with stirring during 15 min to an ice-cooled sample of compound 1a or 1b (0.01 mol)
at 0-5°C, dissolved in concentrated HCl (3 ml) and water (2 ml). After the addition, the stirring was continued for
a further 15 min, and then the solution was used in further reactions.
3-Hydrazonopyrazolo[3,4-b]pyridine Derivatives 4 and 5 (General Method). NaOAc (about 4 g, 0.05
mol) was added to a cold solution of 2-cyano-N'-(4-methoxybenzylidene)acetohydrazide (3) (0.01 mol) in EtOH
(50 ml). The solution was stirred and then the solution of diazonium salt 2a or 2b (0.01 mol) was added
dropwise with stirring. Stirring was continued for 2 h. The products so formed were collected by filtration and
washed with water, followed by cold EtOH. The isolated compounds were recrystallized from EtOH to give the
corresponding 3-hydrazonopyrazolo[3,4-b]pyridine derivatives 4 or 5.
1074

2-Cyano-2-[(4,6-dimethyl-1H-pyrazolo[3,4-b]pyridin-3-yl)hydrazono]-N'-(4-methoxybenzylidene)-
acetohydrazide (4). Yield 2.89 g (74%); mp 257-258°C. IR spectrum, , cm-1: 3314, 3163 (2NH), 2180 (CN),
1650 (CO). 1H NMR spectrum (DMSO-d6), , ppm (J, Hz): 2.40 (3H, s, CH3); 2.55 (3H, s, CH3); 3.90 (3H, s,
OCH3); 6.90 (2H, d, J = 8.2, H Ar); 7.20 (1H, s, H-5); 7.40 (2H, d, J = 8.2, H Ar); 8.20 (1H, s, N=CH); 10.80
(1H, s, NH); 12.25 (2H, s, 2NH). Found, %: C 58.37; H 4.71; N 28.66. C19H18N8O2. Calculated, %: C 58.45;
H 4.65; N 28.70.
2-[(5-Bromo-4,6-dimethyl-1H-pyrazolo[3,4-b]pyridin-3-yl)hydrazono]-2-cyano-N'-(4-methoxybenzyl-
idene)acetohydrazide (5). Yield 3.19 g (68%); mp 258-259°C. IR spectrum, , cm-1: 3325, 3214 (2NH), 2184
(CN), 1668 (CO). 1H NMR spectrum (DMSO-d6), , ppm (J, Hz): 2.40 (3H, s, CH3); 2.50 (3H, s, CH3); 3.85 (3H,
s, OCH3); 7.00 (2H, d, J = 8.0, H Ar); 7.40 (2H, d, J = 8.0, H Ar); 8.20 (1H, s, N=CH); 11.05 (1H, s, NH);
12.75 (2H, s, 2NH). Found, %: C 48.68; H 3.61; N 23.96. C19H17BrN8O2. Calculated, %: C 48.63; H 3.65;
N 23.88.
8-Aminopyrido[2',3':3,4]pyrazolo[5,1-c][1,2,4]triazine-7-benzylideneacetohydrazide Derivatives 6
and 7 (General Method). Compound 4 or 5 (0.005 mol) in acetic acid (20 ml) was heated under reflux for 30
min, and then allowed to cool. The solid product 6 or 7 was collected by filtration, washed with cold EtOH, and
recrystallized from EtOH–DMF mixture (1:1).
8-Amino-2,4-dimethylpyrido[2',3':3,4]pyrazolo[5,1-c][1,2,4]triazine-7-(4-methoxybenzylidene)-
acetohydrazide (6). Yield 1.78 g (91%); mp  300°C. IR spectrum, , cm-1: 3359, 3252, 3205 (NH2 and NH),
1660 (CO). 1H NMR spectrum (CDCl3–CF3COOD), , ppm (J, Hz): 2.90 (3H, s, CH3); 3.10 (3H, s, CH3); 3.85
(3H, s, OCH3); 7.00 (2H, d, J = 8.4, H Ar); 7.10 (1H, s, H-3); 7.40 (2H, d, J = 8.4, H Ar); 8.25 (1H, s, N=CH).
Found, %: C 58.54; H 4.70; N 28.78. C19H18N8O2. Calculated, %: C 58.45; H 4.65; N 28.70.
8-Amino-3-bromo-2,4-dimethylpyrido[2',3':3,4]pyrazolo[5,1-c][1,2,4]triazine-7-(4-methoxybenz-
ylidene)acetohydrazide (7). Yield 2.06 g (88%); mp  300°C. IR spectrum, , cm-1: 3386, 3277, 3204 (NH2 and
1
NH), 1661 (CO). H NMR spectrum (CDCl3–CF3COOD), , ppm (J, Hz): 2.90 (3H, s, CH3); 3.05 (3H, s, CH3);
3.85 (3H, s, OCH3); 7.00 (2H, d, J = 8.2, H Ar); 7.40 (2H, d, J = 8.2, H Ar); 8.30 (1H, s, N=CH). Found, %:
C 48.72; H 3.68; N 23.93. C19H17BrN8O2. Calculated, %: C 48.63; H 3.65; N 23.88.
3-Hydrazonopyrazolo[3,4-b]pyridine Derivatives 9a,b (General Method). A freshly prepared
solution of pyrazolopyridinediazonium chloride 2a (2.1 g, 0.01 mol) was added with continuous stirring to a
cold solution (0-5°C) of N'-acyl-2-cyanoacetohydrazide derivatives 8a or 8b (0.01 mol) and NaOAc (4.0 g, 0.05
mol) in EtOH (50 ml). The reaction mixture was allowed to stand in the cold for 2 h and then diluted with water.
The products so formed were collected by filtration and washed with water, followed by cold EtOH. The
isolated compounds were recrystallized from EtOH to give compounds 9a,b.
N'-Acetyl-2-cyano-2-[(4,6-dimethyl-1H-pyrazolo[3,4-b]pyridin-3-yl)hydrazono]acetohydrazide (9a).
Yield 2.17 g (69%); mp 285-286°C. IR spectrum, , cm-1: 3403, 3282, 3201 (3NH), 2192 (CN), 1698, 1657
(2CO). 1H NMR spectrum (DMSO-d6), , ppm: 2.10 (3H, s, COCH3); 2.50 (3H, s, CH3); 2.60 (3H, s, CH3); 7.00
(1H, s, H-5); 11.60 (2H, s, 2NH); 12.85 (1H, s, NH); 14.25 (1H, s, NH). Found, %: C 49.50; H 4.38; N 35.56.
C13H14N8O2. Calculated, %: C 49.68; H 4.49; N 35.56.
N'-Benzoyl-2-cyano-2-[(4,6-dimethyl-1H-pyrazolo[3,4-b]pyridin-3-yl)hydrazono]acetohydrazide
(9b). Yield 2.67 g (71%); mp 280-281°C. IR spectrum, , cm-1: 3416, 3284, 3199 (3NH), 2124 (CN), 1667,
1
1658 (2CO). H NMR spectrum (DMSO-d6), , ppm: 2.45 (3H, s, CH3); 2.60 (3H, s, CH3); 7.00 (1H, s, H-5);
7.30–7.50 (5H, m, H Ph); 10.35 (2H, s, 2NH); 12.20 (1H, s, NH); 13.75 (1H, s, NH). Found, %: C 57.59;
H 4.15; N 29.68. C18H16N8O2. Calculated, %: C 57.44; H 4.28; N 29.77.
8-Aminopyrido[2',3':3,4]pyrazolo[5,1-c]triazine-7-carboxylic Acid N'-acylhydrazide Derivatives
10a,b. Compound 9a,b (0.005 mol) in acetic acid (20 ml) was heated under reflux for 30 min and then allowed
to cool. The solid product 10a,b was collected by filtration, washed with cold EtOH, and recrystallized from
EtOH–DMF mixture (2:1).
8-Amino-2,4-dimethylpyrido[2',3':3,4]pyrazolo[5,1-c]triazine-7-carboxylic acid N'-Acetylhydra-
zide (10a). Yield 1.23 g (78%); mp 300°C. IR spectrum, , cm-1: 3378, 3180 (NH2 and NH), 1641 (br., CO).
1075

1H NMR spectrum (CDCl3–CF3COOD), , ppm: 2.10 (3H, s, COCH3); 2.80 (3H, s, CH3); 2.95 (3H, s, CH3); 7.10
(1H, s, H-3). Found, %: C 49.61; H 4.54; N 35.74. C13H14N8O2. Calculated, %: C 49.68; H 4.49; N 35.65.
8-Amino-2,4-dimethylpyrido[2',3':3,4]pyrazolo[5,1-c]triazine-7-carboxylic Acid N'-Benzoylhydrazide
(10b). Yield 1.58 g (84%); mp  300°C. IR spectrum, , cm-1: 3386, 3189 (NH2 and NH), 1638 (br., CO).
1H NMR spectrum (CDCl3–CF3COOD), , ppm: 2.80 (3H, s, CH3); 2.95 (3H, s, CH3); 7.10 (1H, s, H-3); 7.20-
7.50 (5H, m, H Ph). Found, %: C 57.40; H 4.35; N 29.81. C18H16N8O2. Calculated, %: C 57.44; H 4.28; N 29.77
Ethyl 2-[(4,6-Dimethyl-1H-pyrazolo[3,4-b]pyridin-3-yl)hydrazono]benzoyl Acetate (11). A freshly
prepared solution of pyrazolopyridinediazonium chloride 2a (2.1 g, 0.01 mol) was added with continuous stirring
to a cold solution (0-5°C) of ethyl benzoylacetate (1.92 g, 0.01 mol) and NaOAc (4.0 g, 0.05 mol) in EtOH (50
ml). The reaction mixture was allowed to stand in the cold for 2 h, and then diluted with water. The product so
formed was collected by filtration, washed with cold EtOH, and finally was recrystallized from EtOH to give
compound 11 as yellow crystals. Yield 2.78 g (76%); mp 165-166°C. IR spectrum, , cm-1: 3147 (NH), 1685
1
(COOEt), 1667 (COPh). H NMR spectrum (CDCl3), , ppm (J, Hz): 1.10 (3H, t, J = 7.2, COOCH2CH3); 2.60
(3H, s, CH3); 2.80 (3H, s, CH3); 4.25 (2H, q, J = 7.2, COOCH2CH3); 7.10 (1H, s, H-5); 7.40–7.70 (5H, m,
H Ph); 11.65 (1H, s, NH); 13.30 (1H, s, NH). Found, %: C 62.52; H 5.32; N 19.06. C19H19N5O3. Calculated, %:
C 62.46; H 5.24; N 19.17.
Ethyl 2,4-Dimethyl-8-phenylpyrido[2',3':3,4]pyrazolo[5,1-c][1,2,4]triazine-7-carboxylate (12). A
solution of compound 11 (1.83 g, 0.005 mol) in EtOH (30 ml) containing catalytic amounts of Et3N was heated
under reflux for 1 h. The product so formed on heating was collected by filtration, washed with cold EtOH, and
recrystallized from AcOH to afford 12 as yellowish green crystals. Yield 1.49 g (86%);mp 182-184°C. IR
1
spectrum, , cm-1: 1737 (CO, ester). H NMR spectrum (CDCl3), , ppm (J, Hz): 1.10 (3H, t, J = 7.2,
COOCH2CH3); 2.66 (3H, s, CH3); 3.00 (3H, s, CH3); 4.25 (2H, q, J = 7.2, COOCH2CH3); 7.12 (1H, s, H-3);
7.47-7.73 (5H, m, H Ph). Mass spectrum, m/z (Irel, %): 347 [M]+ (90). Found, %: C 65.72; H 4.87; N 20.12.
C19H17N5O2. Calculated, %: C 65.70; H 4.93; N 20.16.
7-Benzoyl-2,4,8-trimethylpyrido[2',3':3,4]pyrazolo[5,1-c][1,2,4]triazine (14). A freshly prepared
solution of pyrazolopyridinediazonium chloride 2a (2.1 g, 0.01 mol) was added with continuous stirring to a
cold solution (0-5°C) of benzoylacetone (1.62 g, 0.01 mol) and NaOAc (4.0 g, 0.05 mol) in EtOH (50 ml). The
reaction mixture was allowed to stand in the cold for 1 h and then diluted with water. The product so formed
was collected by filtration, washed with cold ethanol, and finally was recrystallized from ethanol to give
1
compound 14 as green crystals. Yield 2.35 g (74%); mp 170-172°C. IR spectrum, , cm-1: 1664 (COPh). H
NMR spectrum (DMSO-d6), , ppm: 2.35 (3H, s, CH3); 2.63 (3H, s, CH3); 2.75 (3H, s, CH3); 7.10 (1H, s, H-5);
7.12-7.89 (5H, m, H Ph). Mass spectrum, m/z (Irel, %): 317 [M]+ (18), 316 (31). Found, %: C 68.18; H 4.74;
N 22.03. C18H15N5O. Calculated, %: C 68.13; H 4.76; N 22.07.
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