Synthesis of new pyrazolopyrimidinedithiones and pyrazolopyrimidinephosphines from aminocyanopyrazoles

Article abstract of DOI:10.1080/00397911.2010.486516

A general, high-yielding synthetic protocol for the expedited synthesis of functionalized pyrazolopyrimidine dithione 2 and pyrazolodiazaphosphininethione 3 from amino-cyano pyrazole 1 precursors is presented.

Full text of DOI:10.1080/00397911.2010.486516

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Synthesis of New
Pyrazolopyrimidinedithiones and
Pyrazolopyrimidinephosphines from
Aminocyanopyrazoles
Fatma Allouche a , Fahker Chabchoub a , Mansour Salem a & Gilbert
Kirsch b
a Laboratoire de Chimie Appliquée, Hétérocycles, Corps Gras et
Polymères Faculté des Sciences de Sfax, Sfax, Tunisia
b Laboratoire d'Ingénierie Moléculaire et de Biochimie
Pharmacologique, Institut Jean Barriol, CNRS, Metz, France
Available online: 30 Mar 2011
To cite this article: Fatma Allouche, Fahker Chabchoub, Mansour Salem & Gilbert Kirsch
(2011): Synthesis of New Pyrazolopyrimidinedithiones and Pyrazolopyrimidinephosphines from
Aminocyanopyrazoles, Synthetic Communications: An International Journal for Rapid Communication
of Synthetic Organic Chemistry, 41:10, 1500-1507
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Synthetic Communications1, 41: 1500–1507, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.486516
SYNTHESIS OF NEW
PYRAZOLOPYRIMIDINEDITHIONES AND
PYRAZOLOPYRIMIDINEPHOSPHINES FROM
AMINOCYANOPYRAZOLES
Fatma Allouche,1 Fahker Chabchoub,1 Mansour Salem,1 and
Gilbert Kirsch2
1
´
Laboratoire de Chimie Appliquee, Heterocycles, Corps Gras et Polymeres
Faculte des Sciences de Sfax, Sfax, Tunisia
´ ´
`
´
2
´
´
Laboratoire d’Ingenierie Moleculaire et de Biochimie Pharmacologique,
Institut Jean Barriol, CNRS, Metz, France
GRAPHICAL ABSTRACT
Abstract A general, high-yielding synthetic protocol for the expedited synthesis of
functionalized pyrazolopyrimidine dithione 2 and pyrazolodiazaphosphininethione 3 from
amino-cyano pyrazole 1 precursors is presented.
Keywords Pyrazole; pyrazolopyrimidinedithione; pyrazolopyrimidinephosphine
INTRODUCTION
The pyrazole ring has attracted great attention[1–5] as it has become fairly
accessible, and it shows diverse properties. These heterocyclic compounds are not
only interesting because of their biological activities as potential inhibitors of
HIV[6] and herbicides,[7] but also they are important and useful as starting materials
for the synthesis of other fused heterocyclic pyrazolopyrimidine derivatives of
Received February 12, 2010.
Address correspondence to Fatma Allouche, Laboratoire de Chimie Appliquee, Heterocycles,
´ ´ ´
Corps Gras et Polymeres Faculte des Sciences de Sfax, 3018 Sfax, Tunisia. E-mail: fatma.
mallekallouch@yahoo.fr
`
´
1500

PYRAZOLOPYRIMIDINEDITHIONES
1501
considerable chemical and pharmacological importance.[8–14] In this work, a classical
method of pyrazole synthesis was applied for the preparation of compounds 1. These
aminocyanopyrazoles 1 possess two reactive sites, a cyano group and amine group,
which react with carbon disulfide and Lawesson reagent to yield a new class of con-
densed heterocycles 2 and 3.
RESULTS AND DISCUSSION
Synthesis of 5-Amino-4-cyano-1-substituted Pyrazoles 1
Several works mention the synthesis of the 5-amino-4-cyano pyrazoles.[15–16]
These products were prepared via a standard addition of hydrazine derivatives to
ketene ethoxymethylene compounds. To generalize the synthesis of 5-amino-4-
cyano-1-substituted pyrazoles 1, we have prepared a variety of ketene ethoxymethy-
lene compounds in good yields, and the corresponding pyrazoles as shown in Scheme 1.
Reaction of Carbon Disulfide on Compound 1
The formation of pyrazolopyrimidine dithione from pyrazoles derivatives is
well documented.[17–19] In this article, we report the synthesis of a variety of substi-
tuted pyrazolopyrimidine dithione obtained by refluxing aminocyanopyrazoles 1 with
carbon disulfide in anhydrous pyridine. Analysis of spectral and bibliographic data
shows that the reaction produced the corresponding substituted pyrazolopyrimidine.
The formation of these compounds is the result of Dimroth’s rearrangement. This
type of transposition has been already reported by other authors[20–22] (Scheme 2).
Synthesis of Pyrazolopyrimidinedithiones 2
1
The structures of compounds 2 were deduced by infrared (IR), H NMR, 13C
NMR, and mass spectra. Indeed, IR spectra of these compounds showed two bands
(3330 and 3200 cmꢀ1) due to the vibration of the amino group, and we report the
disparities of the CN band of aminocyanopyrazoles. 1H and 13C NMR of these com-
pounds confirm the structure of the obtained products.
Scheme 1. Reagents and conditions: EtOH=Hþ, reflux, 2 h.

1502
F. ALLOUCHE ET AL.
Scheme 2. Reagents and conditions: (i) CS2=pyridine, reflux, 7 h.
Synthesis of Pyrazolopyrimidines Phosphines 3
Lawesson’s reagent is known to react at both electrophilic and nucleophilic
sites.[23–26] The cyclization reaction between Lawesson’s reagent and aminocyano-
pyrazoles (1a–f) gave the corresponding pyrazolopyrimidine phosphine 3 from the
aminocyanopyrazole precursors. This condensation was carried out in boiling
toluene (Scheme 3).
1
The structures of compounds 3 were determined from their IR, H NMR, 13
C
NMR, 31P NMR, and mass spectra. IR spectra in particular revealed the absence of
the absorption band corresponding to the nitrile group (2200 cmꢀ1) while exhibiting
bands corresponding to C S and P S. 31P NMR of compound 3 gave as useful
information about the presence of phosphorus in this molecule; thus the signal at
=
=
1
55 ppm is indicative of the P S group. Similarly, H NMR spectra confirmed the
=
structure of compound 3 and revealed signals indicative for the NH and OCH3
groups.
In summary, we have used carbon disulfide and Lawesson’s reagent for the
preparation of pyrazolopyrimidine dithione 2 and pyrazolopyrimidine phosphine 3
from the amino pyrazoles precursors. In each case, reaction time and=or yield was
Scheme 3. Reagents and conditions: toluen, reflux, 7 h.

PYRAZOLOPYRIMIDINEDITHIONES
1503
dramatically improved under this protocol. Moreover, this new protocol was
employed for the rapid synthesis of 2 and 3. Biological data for these products will
be reported in due course.
EXPERIMENTAL
Spectra IR were determined for KBr on a Jasco Fourier transform (FT)–IR
ꢀ1
420 spectrometer with precision of 2 cmꢀ1 covering field 400–4000 cm
.
The spectra of 1 H NMR and 13C NMR were recorded in solution in CDCl3 or
in dimethylsulfoxide (DMSO-d6) on a Bruker spectrometer (1H at 300 MHz, 13C at
75 MHz). The chemical shifts are expressed in parts per million (ppm) by using
tetramethylsilane (TMS) as internal reference. The multiplicities of the signals are
indicated by the following abbreviations: s, singlet; d, doublet; t, triplet; q, quad-
ruplet; and m, multiplet, and coupling constants are expressed in hertz.
The melting points were determined in an Electrothermal 9100 apparatus and
are not corrected.
The reactions were monitored by thin-layer chromatography (TLC) using
aluminium sheets with silica gel 60 F254 from Merck.
The mass spectrometer was operated in electrospray ionization (EI) mode at
70 eV, and mass (MS) spectra were recorded from m=z 50 to 650.
General Procedure for Synthesis of Aminocyanopyrazoles (1)
A mixture of aryl hydrazine (33 mmol) and ethoxymethylene malononitrile
(33 mmol) was heated at reflux for 2 h in ethanol (30 mL). The product, which
precipitates, was filtered and recrystallized from ethanol (Scheme 4).
Data for Compounds 1
5-Amino-1-phenyl-1H-pyrazolo-4-carbonitrile (1a). Yield: 83%, white
solid. Mp 166 ꢁC (methanol). IR (cmꢀ1): n ¼ 1594, 1640, 2217 (CN), 2917, 3432,
1
3221. H NMR (DMSO-d6): d (ppm) 6.82 (s, 2H), 7.40–7.55 (m, 6H). 13C NMR
(DMSO-d6): d (ppm) C1 144.60; C2 73.48; C3 152.74; C4 114.17; C arom 117.08–
137.52.
5-Amino-3-methyl-1-phenyl-1H-pyrazolo-4-carbonitrile (1b). Yield: 85%,
white solid. Mp 133 ꢁC (methanol). IR (cm ꢀ1): n ¼ 1598, 1645, 2215 (CN), 3331,
3227. 1H NMR (DMSO-d6): d (ppm) 2.15 (s, 3H), 6.66 (s, 2H), 7.35–7.52
Scheme 4.

1504
F. ALLOUCHE ET AL.
(m, 5H).13C NMR (DMSO-d6): d (ppm): C1 151.96; C2 74.23; C3 150.56; C4 115.57;
C arom 124.40–138.03; MS: m=e ¼ 199 [M þ 1]þ, 100%.
5-Amino-3-ethyl-1-phenyl-1H-pyrazolo-4-carbonitrile (1c). Yield: 82%,
white solid. Mp 137 ꢁC (methanol). IR (cmꢀ1): n ¼ 1597, 1647, 2209 (CN), 3433,
3296. 1H NMR (DMSO-d6): d (ppm) 1.18 (t, 3H), 2.53 (q, 2H), 6.61 (s, 2H),
7.35–7.53 (m, 5H). 13C NMR (DMSO-d6): d (ppm) C7 12.88; C6 21.13; C1 155.58;
C2 73.22; C3 152.13; C4 115.47; C arom 124.43–138.11. MS: m=e ¼ 213 [M þ 1]þ,
100%; 158 [M ꢀ 54]þ, 5%.
5-Amino-1-tosyl-1H-pyrazolo-4-carbonitrile (1d). Yield: 70%, white solid.
Mp 192 ꢁC (methanol). IR (cmꢀ1): n ¼ 1527, 1616, 2211 (CN), 3347, 3225. 1H NMR
(DMSO-d6): d (ppm) 2.27 (s, 3H), 7.11 (s, 2H), 7.13–7.51 (m, 5H). 13C NMR
(DMSO-d6): d (ppm) C8 21.28; C1 138.58; C2 75.51; C3 145.55; C4 113.81; C arom
124.66–129.07.
5-Amino-3-methyl-1-tosyl-1H-pyrazolo-4-carbonitrile (1e). Yield: 72%,
white solid. Mp 185 ꢁC (methanol). IR (cmꢀ1): n ¼ 1534, 1628, 2216 (CN), 3381,
3227. 1H NMR (DMSO-d6): d (ppm) 2.04 (s, 3H); 2.39 (s, 3H), 7.63 (s, 2H),
7.47–7.87 (m, 4H). 13C NMR (DMSO-d6): d (ppm) C5 13.06; C8 21.53; C1 146.80;
C2 73.97; C3 154.87; C4 113.71; C arom 127.89–133.44.
5-Amino-3-ethyl-1-tosyl-1H-pyrazolo-4-carbonitrile (1f). Yield: 74%,
white solid. Mp 178 ꢁC (methanol). IR (cmꢀ1): n ¼ 1526, 1643, 2215 (CN), 3346,
3222. 1H NMR (DMSO-d6): d (ppm) 0.87 (t, 3H), 2.16 (q, 2H); 2.38 (s, 3H),
7.38–7.68 (m, 6H). 13C NMR (DMSO-d6): d (ppm) C7 10.81; C6 21.52; C8 23.30;
C1 143.49; C2 73.50; C3 144.26; C4 114.32; C arom 128.20–136.42.
Data for Compounds 2
General procedure for synthesis of pyrazolo-pyrimidine dithione (2). A
mixture of 5-amino-4-cyano-1-substituted pyrazole 1 (0.2 mol), disulfur of carbon
(0.25 mol), and anhydrous pyridine (10 mL) was heated under reflux for 7 h and
then evaporated under reduced pressure. The residue was treated with ethanol,
and the solid product so formed was collected by filtration and washed with ether
(Scheme 5).
1-Phenyl-1,7-dihydro-pyrazolo[3,4-d]pyrimidine-4,6-dithione
ꢀ1
(2a).
Yield: 79%, white solid. Mp 302 ꢁC (methanol). IR (cm ): n ¼ 1199, 1147 (C S),
=
1
=
1569, 1510 (C N), 3480 (N-H). H NMR (DMSO-d6): d (ppm): 2.70 (s, 1H), 2.86
Scheme 5.

PYRAZOLOPYRIMIDINEDITHIONES
1505
(s, 1H), 7.22–7.92 (m, 6H). 13C NMR (DMSO-d6): d (ppm), C1 153.15; C2 112.51; C3
142.12; C4 174.00; C5 162.26; C arom 124.44–136.49.
3-Methyl-1-phenyl-1,7-dihydro-pyrazolo[3,4-d]pyrimidine-4,6-dithione
(2b). Yield: 80%, white solid. Mp 305 ꢁC (methanol). IR (cmꢀ1): n ¼ 1193, 1162
(C S), 1562, 1515 (C N), 3472 (N-H). 1H NMR (DMSO-d6): d (ppm) 2.40(s,
3H), 7.43–7.68 (m, 7H); 13C NMR (DMSO-d6): d (ppm) C6 14.71; C1 148.74; C2
113.73; C3 129.33; C4 181.11; C5 163.36; C arom 121.80–137.66.
=
=
3-Ethyl-1-phenyl-1,7-dihydro-pyrazolo[3,4-d]pyrimidine-4,6-dithione
(2c). Yield: 76%, white solid. Mp 280 ꢁC (methanol). IR (cmꢀ1): n ¼ 1197, 1143
1
=
=
(C S), 1565, 1512 (C N), 3470 (N-H). H NMR (DMSO-d6): d (ppm) 1.23 (t,
3H), 2.71 (s, 1H), 2.87 (s, 1H), 3.01 (q, 2H), 7.43–7.93 (m, 5H); 13C NMR
(DMSO-d6): d (ppm) C8 13.05; C7 21.78; C1 153.94; C2 112.31; C3 137.84; C4
181.41; C5 162.25; C arom 121.90–129.42. MS: m=e ¼ 289 [M þ 1]þ, 100%; 272
[M ꢀ 16]þ, 7%; 255 [M ꢀ 33]þ, 5%, 230 [M ꢀ 58]þ, 9%.
1-Tosyl-1,7-dihydro-pyrazolo[3,4-d]pyrimꢀid1ine-4,6-dithione (2d). Yield:
73%, white solid. Mp 290 ꢁC (methanol). IR (cm ): n ¼ 1190, 1151 (C S), 1560,
=
1
=
1517 (C N), 3475 (N-H). H NMR (DMSO-d6): d (ppm) 2.28 (s, 3H); 6.90–7.53
(m, 7H); 13C NMR (DMSO-d6): d (ppm) C9 21.30; C1 145.59; C2 112.44; C3
134.83; C4 186.30; C5 162.26; C arom 125.43–137.60.
3-Methyl-1-tosyl-1,7-dihydro-pyrazolo[3,4-d]pyrimidine-4,6-dithione
(2e). Yield: 75% white solid. Mp 300 ꢁC (methanol). IR (cmꢀ1): n ¼ 1194, 1163
1
=
=
(C S), 1562, 1519 (C N), 3478 (N-H). H NMR (DMSO-d6): d (ppm) 2.28 (s,
3H); 2.87 (s, 3H), 6.99–7.50 (m, 6H); 13C NMR (DMSO-d6): d (ppm): C6 11.30;
C9 21.30; C1 145.59; C2 112.44; C3 134.83; C4 186.30; C5 162.26; C arom
125.43–137.60.
3-Ethyl-1-tosyl-1,7-dihydro-pyrazolo[3,4-d]pyrimidine-4,6-dithione (2f).
ꢀ1
Yield: 72%, white solid. Mp 306 ꢁC (methanol). IR (cm ): n ¼ 1191, 1142 (C S),
=
1
=
1567, 1510 (C N), 3481 (N-H). H NMR (DMSO-d6): d (ppm) 2.28 (s, 3H); 1.24
(t, 3H); 2.81 (q, 2H); 6.99–7.50 (m, 6H); 13C NMR (DMSO-d6): d (ppm) C7 21.30;
C8 21.30; C9 21.30; C1 145.59; C2 112.44; C3 134.83; C4 186.30; C5 162.26; C arom
125.43–137.60.
General Procedure for Synthesis of Pyrazolo-Diazaphosphinine
Thione (3)
A mixture of 5-amino-4-cyano-1-substituted pyrazole 1 (0.2 mol) and
Lawesson’s reagent (0.25 mol) in toluene (10 mL) was heated under reflux for 7 h
and then evaporated under reduced pressure. The solid product so formed was col-
lected by filtration and washed with ether (Scheme 6).
Data for Compounds 3
5-Methyl-2-(4-methoxyphenyl)-7-phenyl-2-thioxo-1,2,3,7-tetrahydro-
pyrazolo[3,4-d] [1,3,2]diazaphosphinine-4-thione (3a). Yield: 79%, white
ꢀ1
solid. Mp 174 ꢁC (methanol). IR (cm ): n ¼ 1226 (P S), 1190 (C S), 1594, 3231,
=
=

1506
F. ALLOUCHE ET AL.
Scheme 6.
1
3411. 31P NMR: 56, 28. H NMR (DMSO-d6): d (ppm) 2.48 (s, 3H), 3.77 (s, 3H),
6.92–7.82 (m, 9H), 10.13 (s, 2H). 13C NMR (DMSO-d6): d (ppm) C6 15.19; C5
55.70; C4 187.82; C2 113.93; C3 154.76; C arom 129.46–147.09.
5-Ethyl-2-(4-methoxyphenyl)-7-phenyl-2-thioxo-1,2,3,7-tetrahydro pyr-
azolo[3,4-d][1,3,2]diazaphosphinine-4-thione (3b). Yield: 75%, white solid.
ꢀ1
Mp 152 ꢁC (methanol). IR (cm ): n ¼ 1239 (P S), 1197 (C S), 1590, 3231, 3464.
=
=
31P NMR: 54, 72, H NMR (DMSO-d6): d (ppm) 1.22 (t, 3H), 3.07 (q, 2H), 3.81 (s,
1
3H), 7.09–7.88 (m, 9H), 10.29 (s, 1H), 10.90 (s, 1H). 13C NMR (DMSO-d6) d (ppm)
C1 139.89; 140.43; C8 12.79; C7 22.50; C5 56.11; C4 187.82; C2 114.30; C3 156.22; C
arom 125.31–140.42; 415 [M þ 1]þ, 100%; 381 [M ꢀ 33]þ, 25%; 213 [M ꢀ 201]þ, 40%.
2-(4-Methoxyphenyl)-7-phenyl-2-thioxo-1,2,3,7-tetrahydropyrazolo[3,4-
d][1,3,2]diazaphosphinine-4-thione (3c). Yield: 76%, white solid. Mp 179 ꢁC
1
(methanol). IR (cmꢀ1): n ¼ 1251 (P S), 1143 (C S), 1573, 3225, 3420. H NMR
(DMSO-d6): d (ppm) 4.42 (s, 3H), 7.06–7.89 (m, 9H), 10.29 (s, 1H), 10.69 (s, 1H).
13C NMR (DMSO-d6): d (ppm) C1 133.35; C5 55.61; C4 180.56; C2 113.79; C3
161.60; C arom 124.60–133.35.
=
=
2-(4-Methoxyphenyl)-7-tosyl-2-thioxo-1,2,3,7-tetrahydropyrazolo[3,4-d]-
[1,3,2]diazaphosphinine-4-thione (3d). Yield: 73%, white solid. Mp 160 ꢁC
1
(methanol). IR (cmꢀ1): n ¼ 1226 (P S), 1177 (C S), 1565, 3225, 3424. H NMR
(DMSO-d6): d (ppm) 2.20 (s, 3H), 4.40 (s, 3H), 7.06–7.89 (m, 9H), 10.29 (s, 1H),
10.69 (s, 1H). 13C NMR (DMSO-d6): d (ppm) C1 133.35; C5 55.61; C4 180.56; C2
113.79; C3 161.60; C arom 124.60–133.35.
=
=
2-(4-Methoxyphenyl)-7-tosyl-2-thioxo-1,2,3,7-tetrahydropyrazolo[3,4-d]-
[1,3,2]diazaphosphinine-4-thione (3e). Yield: 75%, white solid. Mp 170 ꢁC
1
(methanol). IR (cmꢀ1): n ¼ 1267 (P S), 1177 (C S) 1598, 3218, 3475. H NMR
(DMSO-d6): d (ppm) 2.25 (s, 3H), 2.77 (s, 3H), 3.93 (s, 3H), 7.09–7.88 (m, 9H),
10.25 (s, 1H), 10.93 (s, 1H). 13C NMR (DMSO-d6): d (ppm) C8 21.3; C1 139.89;
C5 56.11; C4 187.82; C2 114.30; C3 156.22; C arom 124.12–145.48.
=
=
5-Ethyl-2-(4-methoxyphenyl)-7-tosyl-2-thioxo-1,2,3,7-tetrahydropyra-
zolo[3,4-d][1,3,2] diazaphosphinine-4-thione (3f). Yield: 72%, white solid. Mp
ꢀ1
1
164 ꢁC (methanol). IR (cm ): n ¼ 1264 (P S), 1121 (C S), 1597, 3218, 3425. H
NMR (DMSO-d6): d (ppm) 1.25 (t, 3H), 3.10 (q, 2H), 2.22 (s, 3H), 3.97 (s, 3H),
7.10–7.76 (m, 9H), 10.26 (s, 1H), 10.87 (s, 1H). 13C NMR (DMSO-d6): d (ppm)
C8 21.7; C1 138.29; C5 56.22; C4 188.12; C2 115.13; C3 157.28; C arom 125.42–146.78.
=
=

PYRAZOLOPYRIMIDINEDITHIONES
1507
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