Facile synthesis of thiophene- and 1,3,4-thiadiazole-based heterocycles

Article abstract of DOI:10.1080/10426500903299919

Treatment of 3-cyanoacetylpyrazole derivative 1 with phenyl isothiocyanate in potassium hydroxide at room temperature followed by -haloketones 4a-d and hydrazonoyl halides 10a-e gave the corresponding pyrazolylthiophene 6a-d and pyrazolyl-1,3,4-thiadiazol

Full text of DOI:10.1080/10426500903299919

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Facile Synthesis of Thiophene- and
1,3,4-Thiadiazole-Based Heterocycles
Kamal M. Dawood a , Eman A. Ragab a & Ahmad M. Farag a
a Department of Chemistry, Faculty of Science , Cairo University ,
Giza, Egypt
Published online: 02 Aug 2010.
To cite this article: Kamal M. Dawood , Eman A. Ragab & Ahmad M. Farag (2010) Facile Synthesis of
Thiophene- and 1,3,4-Thiadiazole-Based Heterocycles, Phosphorus, Sulfur, and Silicon and the Related
Elements, 185:8, 1796-1802, DOI: 10.1080/10426500903299919
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Phosphorus, Sulfur, and Silicon, 185:1796–1802, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500903299919
FACILE SYNTHESIS OF THIOPHENE- AND
1,3,4-THIADIAZOLE-BASED HETEROCYCLES
Kamal M. Dawood, Eman A. Ragab, and Ahmad M. Farag
Department of Chemistry, Faculty of Science, Cairo University, Giza, Egypt
Treatment of 3-cyanoacetylpyrazole derivative 1 with phenyl isothiocyanate in potassium
hydroxide at room temperature followed by α-haloketones 4a–d and hydrazonoyl halides
10a–e gave the corresponding pyrazolylthiophene 6a–d and pyrazolyl-1,3,4-thiadiazole 12a–e
derivatives, respectively.
Keywords Hydrazonoyl halides; pyrazoles; 1,3,4-thiadiazoles; thiophenes
INTRODUCTION
Pyrazole derivatives are an interesting class of heterocycles because of their phar-
macological importance.1–3 In addition, 1,3,4-thiadiazoles recently have been reported
as highly anti-inflammatory,4–6 anticonvulsant,4,7,8 and antimicrobial9 agents. Further-
more, thiophene derivatives are known to have antiamoebic,10 molluscicidal,11 and anti-
inflammatory12,13 activity. Our research work recently has been aimed at the synthesis of
various biologically active heterocyclic systems;14–24 therefore we are concerned here with
the synthesis of heterocyclic skeletons having pyrazole, thiophene, and 1,3,4-thiadiazole
moieties starting with 3-cyanoacetylpyrazole derivative 1.
RESULTS AND DISCUSSION
3-Cyanoacetylpyrazole derivative 1 was recently reported by us.22 Treatment of a
solution of the 3-cyanoacetylpyrazole derivative 1 with phenyl isothiocyanate, in dimethyl-
formamide in the presence of potassium hydroxide, at room temperature afforded the
intermediate potassium salt 2, which was converted into the corresponding thioacetanilide
derivative 3 upon treatment with dilute hydrochloric acid (Scheme 1). The IR spectrum of
compound 3 showed a band at 3242 cm−1 due to NH group and two absorption bands at
2233 and 2216 cm−1 due to two nitrile functions. Its 1H NMR spectrum revealed two D2O-
exchangeable singlet signals at δ 4.13 and 14.10 due to SH and NH protons, respectively.
Moreover, the mass spectrum of the reaction product 3 exhibited a molecular ion peak at
m/z 447.
Treatment of compound 3 with chloroacetone (4a) in refluxing ethanol and in the
presence of a catalytic amount of triethylamine afforded a single product that was identified
Received 6 July 2009; accepted 27 August 2009.
Address correspondence to Prof. Dr. K. M. Dawood, Department of Chemistry, Faculty of Science, Cairo
University, Giza 12613, Egypt. E-mail: dr dawood@yahoo.com
1796

THIOPHENE- AND 1,3,4-THIADIAZOLE-BASED HETEROCYCLES
1797
CN
Ph
N
CN
Ph
Ph
Ph
CN
O
N
O
N
S
NHPh
N
CN
N
1
9
N
Ph
CN
PhNCS
KOH
Ph
Ph
CN
Ph
Ph
CN
Ph
Ph
CN
O
N
CN
Ph
N
Br
HCl
CN
N
N
S- K+
O
8
N
SH
N
O
HN Ph
2
3
HN Ph
Ph
Ph
O
N
RCOCH2X
4a-d
N
NH2
O
CN
O
Ph
O
CN
R
CN
S
PhHN
N
S
R
Ph
N
7
CN
HN
Ph
- H2O
Ph
5
N
CN
Ph
N
4-7
a
b
c
d
O
S
NHPh
R
CH3 C6H5 4-MeOC6H4 4-ClC6H4
R
6
Scheme 1
as 2-acetyl-3-(4-cyano-1,5-diphenyl-1H-pyrazol-3-yl)-5-phenylaminothiophene-4-carbo-
nitrile (6a), as shown in Scheme 1. Both elemental analysis and spectral data supported
the assigned structure 6a and excluded the other possible structure 7a. The IR spectrum of
the isolated product revealed bands at 2230, 2178, and 1668 cm−1, characteristic for two
1
nitrile and one carbonyl functions, respectively. Its H NMR spectrum revealed a singlet
signal at δ 2.25 due to CH3CO protons and a multiplet at δ 7.27–7.55 due to aromatic
protons, in addition to a broad (D2O exchangeable) signal at δ 10.73 due to NH proton.
The thioacetanilide derivative 3 reacted also with phenacyl bromides 4b–d under
similar reaction conditions to give the corresponding thiophene derivatives 6b–d but not
7b–d, as outlined in Scheme 1. The assignment of the latter structures was based on the
elemental analyses and spectral data of the reaction products. For example, the IR spectra
of the reaction products showed, in each case, two bands in the region 2200–2230 cm−1
characterstic for two nitrile functions and a band in the region 3210–3240 cm−1 due to NH
group. The 1H NMR of compound 6c, for example, revealed a singlet signal at δ 2.89 due
to OCH3 protons, and a multiplet at δ 6.80–7.55 due to aromatic protons, in addition to
a broad signal at δ 10.81 due to NH proton. Formation of compounds 6a–d proves that
reaction of the thioacetanilide derivative 3 with α-haloketones 4a–d proceeded via the loss
of hydrogen halide followed by elimination of a water molecule from the non-isolable
intermediate 5 (Scheme 1).
Furthermore, the 3-bromoacetylpyrazole 8 reacted with the thioacetanilide derivative
3, under the same reaction conditions above, to afford a single product that has the thiophene
structure 9 as depicted in Scheme 1. The elemental analyses and spectral data of the reaction

1798
K. M. DAWOOD ET AL.
product were compatible with structure 9. This assignment was supported by the appearance
of NH and carbonyl absorption bands at 3223 and 1680 cm−1, respectively, in addition to
two nitrile functions at 2223 and 2214 cm−1, in the IR spectrum of the isolated product.
Moreover, its mass spectrum exhibited a peak at m/z 714 corresponding to its molecular
ion.
When the thioacetanilide derivative 3 was treated with an equimolar amount of the
hydrazonoyl chloride 10a, it afforded only one isolable product as examined by TLC.
Scheme 2 represents the proposed two possible structures 12a and 13a for the reaction
products. However, the elemental analysis and spectral data are compatible only with the
Ph
CN
X
R
O
CN
+
N
SH
Ar
N
NH
Ph
N
10
X= Br, Cl
O
3
HN Ph
Ph
CN
O
CN
N
S
R
Ph
N
O
N
NH
Ph
HN
11
Ar
- PhNH2
- H2O
Ph
Ph
CN
O
CN
Ar
Ph
CN
O
N
S
Ar
CN
N
R
N
S
N
N
R
O
N
N
Ph
N
12
N
13
d
Ph
12
a
b
c
e
R
Me
Me
OEt
OEt NHPh
Ar 4-MePh 4-ClPh Ph 4-ClPh 4-MePh
Scheme 2
1,3,4-thiadiazole structure 12a. As outlined in the Experimental section, the IR spectrum of
the isolated product 12a revealed absorption bands at 2240 and 2214 cm−1 corresponding
to two nitrile functions, in addition to two conjugated carbonyl groups at 1689 and 1670
cm−1. The 1H NMR spectrum of compound 12a revealed two singlet signals at δ 2.41 and
2.63 characteristic for 4-tolyl and acetyl protons, respectively, in addition to a multiplet
in the region 7.39–7.61 due to aromatic protons. The mass spectrum of compound 12a
exhibited a molecular ion peak at m/z 528. These results indicated that the reaction of
the thioacetanilide derivative 3 with the hydrazonoyl bromide 10a proceeded via the loss
of hydrogen bromide followed by elimination of aniline molecule from the non-isolable
intermediate 11a (Scheme 2). Further reactions of the thioacetanilide derivative 3 with the

THIOPHENE- AND 1,3,4-THIADIAZOLE-BASED HETEROCYCLES
1799
NH2
SH
Ph
Ph
Ph
Ph
CN
O
CN
H
N
N
N
N
N
Br
S
14
8
Scheme 3
hydrazonoyl halides 10b–d, under typical reaction conditions as shown above, resulted in
the formation of the 1,3,4-thiadiazole structures 12b–d as shown in Scheme 2.
Reaction of 3-bromoacetyl-1,5-diphenyl-1H-pyrazole-4-carbonitrile (8) with
2-aminothiophenol in refluxing ethanol gave a product identified as 2-(4-cyano-1,5-
diphenyl-1H-pyrazol-3-yl)-4H-benzo[1,4]thiazine (14) (Scheme 3). Both elemental
analyses and spectral data confirmed the assigned structure 14 for the reaction product.
EXPERIMENTAL
Melting points were measured with a Gallenkamp apparatus. The IR spectra were
recorded on a Shimadzu FT-IR 8101 PC infrared spectrophotometer. The 1H NMR spectra
were determined in DMSO-d6 at 300 MHz on a Varian Mercury VX 300 NMR spectrometer
using TMS as an internal standard. Mass spectra were measured on a GCMS-QP1000 EX
spectrometer at 70 eV. Elemental analyses were carried out at the Microanalytical Center of
Cairo University. Cyanoacetylpyrazole 1,22 phenacyl bromides 4b–d,25 bromoacetylpyra-
zole 8,21 and hydrazonoyl bromides 10a,b,26 10c,d,27,28 and 10e29 were prepared according
to the procedures in the literature.
Synthesis of the Thioacetanilide Derivative 3
To a stirred solution of potassium hydroxide (0.11 g, 2 mmol) in dimethylformamide
(20 mL), the cyanoacetylpyrazole 1 (0.6 g, 2 mmol) was added. After stirring for 30 min,
phenyl isothiocyanate (0.27 g, 2 mmol) was added to the resulting mixture. Stirring was
continued for 6 h, then poured over crushed ice containing hydrochloric acid. The solid
product that formed was filtered off, washed with water, dried, and finally recrystallized
from acetic acid to afford 0.81 g (90%) of compound 3; mp 202–204◦C; IR (KBr) ν 3442
(NH), 2233, 2216 (2 C N), 1710 (C O) cm−1; 1H NMR (DMSO-d6) δ 4.13 (br.s, 1H, SH),
7.13–7.17 (m, 1H, ArH), 7.33–7.52 (m, 12H, ArH), 7.83–7.88 (m, 2H, ArH), 14.10 (br.s,
1H, D2O-exchangable, NH); MS m/z (%) 447 (M+, 4), 414 (8.2), 273 (98), 180 (12.9), 141
(20.8), 77 (100). Calcd. for C26H17N5OS: C, 69.78; H, 3.83; N, 15.65; S, 7.17. Found C,
69.70; H, 3.90; N, 15.76; S, 7.01%.
Reaction of Thioacetanilide Derivative 3 with α-Haloketones
To a solution of 3 (0.89 g, 2 mmol) in ethanol (20 mL), the appropriate α-bromoketone
4a–d or 8 (2 mmol) was added followed by few drops of triethylamine. The mixture was
refluxed for 2 h, then allowed to cool to room temperature. The formed solid was filtered
off, washed with ethanol, and recrystallized from EtOH/DMF to afford the corresponding
thiophene derivatives 6a–d and 9, respectively.

1800
K. M. DAWOOD ET AL.
2-Acetyl-3-(4-cyano-1,5-diphenylpyrazol-3-yl)-5-
phenylaminothiophene-4-carbonitrile (6a)
Yield (70%); mp 236–238◦C; IR (KBr) ν 3315 (NH), 2230, 2178 (2 C N), 1668
1
(C O) cm−1; H NMR (DMSO-d6) δ 2.25 (s, 3H, COCH3), 7.27–7.55 (m, 15H, ArH),
10.73 (br.s, 1H, NH); MS m/z (%) 485 (M+, 33.1), 244 (90.5), 198 (12.6), 144 (22.1), 77
(100). Calcd for C29H19N5OS: C, 71.73; H, 3.94; N, 14.42; S, 6.60. Found: C, 71.85; H,
4.08; N, 14.33; S, 6.87%.
2-Benzoyl-3-(4-cyano-1,5-diphenylpyrazol-3-yl)-5-
phenylaminothiophene-4-carbonitrile (6b). Yield (69%); mp 254–256◦C; IR
(KBr) ν 3219 (NH), 2226 (C N), 1688 (C O) cm−1; 1H NMR (DMSO-d6) δ 7.30–7.68
(m, 20H, ArH), 11.03 (br.s, 1H, NH); MS m/z (%) 547 (M+, 32.2), 470 (16.3), 443 (3.8),
295 (8), 180 (9.2), 105 (52.6), 77 (100). Calcd. for C34H21N5OS: C, 74.57; H, 3.87; N,
12.79; S, 5.86. Found: C, 74.79; H, 3.96; N, 12.94; S, 5.70%.
3-(4-Cyano-1,5-diphenylpyrazol-3-yl)-2-(4-methoxybenzoyl)-5-
phenylaminothiophene-4-carbonitrile (6c). Yield (76%); mp 220–222◦C; IR
(KBr) ν 3211 (NH), 2229, 2219 (2C N), 1670 (C O) cm−1; 1H NMR (DMSO-d6) δ 3.71
(s, 3H, OCH3), 6.79–6.89 (m, 2H, ArH), 7.05–7.27 (m, 3H, ArH), 7.37–7.55 (m, 14H,
ArH), 10.81 (br.s, 1H, D2O-exchangable, NH); MS m/z 577 (M+), 337, 244, 139, 98, 77.
Calcd. for C35H23N5O2S (577.65): C, 72.77; H, 4.01; N, 12.12; S, 5.55. Found: C, 72.89;
H, 3.84; N, 12.34; S, 5.78%.
3-(4-Cyano-1,5-diphenylpyrazol-3-yl)-2-(4-chlorobenzoyl)-5-
phenylaminothiophene-4-carbonitrile (6d). Yield (75%); mp 233–235◦C; IR
1
(KBr) ν 3240 (NH), 2220, 2198 (2 C N), 1635 (C O) cm−1; H NMR (DMSO-d6) δ
7.25–7.66 (m, 19H, ArH), 10.95 (br.s, 1H, D2O-exchangable, NH); MS m/z 582 (M+),
337, 244, 139, 98, 77. Calcd for C34H20ClN5OS (582.07): C, 70.16; H, 3.46; N, 12.03; S,
5.50. Found: C, 70.27; H, 3.40; N, 11.94; S, 5.74%.
2-(4-Cyano-1,5-diphenylpyrazol-3-carbonyl)-3-(4-cyano-1,5-
diphenylpyrazol-3-yl)-5-phenylaminothiophene-4-carbonitrile
(9). Yield
(74%); mp 278–280◦C; IR (KBr) ν 3223 (NH), 2223, 2214 (2 C N), 1680 (C O) cm−1
;
1H NMR (DMSO-d6) δ 7.15–7.27 (m, 10H, ArH), 7.30–7.57 (m, 15H, ArH), 10.85 (s, 1H,
NH); MS m/z 714 (M+), 444, 273, 180, 141, 77. Calcd. for C44H26N8OS (714.8): C, 73.93;
H, 3.67; N, 15.68; S, 4.49. Found: C, 74.06; H, 3.73; N, 15.74; S, 4.63%.
Synthesis of 1,3,4-Thiadiazole Derivatives 12a–e
To a solution of 3 (0.89 g, 2 mmol) in ethanol (20 mL), the appropriate hydrazonoyl
halide 10 (2 mmol) and few drops of triethylamine were added. The mixture was refluxed
for 1 h then allowed to cool. The solid product that formed was filtered off, washed
with ethanol, and recrystallized from DMF to afford the corresponding 1,3,4-thiadiazole
derivatives 12a–e.
5-Acetyl-2-(4-cyano-1,5-diphenylpyrazol-3-carbonyl)-3-(4-tolyl)
cyanomethylene-2,3-dihydro-1,3,4-thiadiazole (12a). Yield 74%; mp 277–279◦C;
IR (KBr) ν 2240, 2214 (2 C N), 1689, 1670 (2 C O) cm−1; 1H NMR (DMSO-d6) δ 2.41
(s, 3H, CH3), 2.63 (s, 3H, COCH3), 7.39–7.48 (m, 12H, ArH), 7.61 (d, 2H, ArH, J =
7.4 Hz); MS m/z 528 (M+), 311, 272, 144, 91, 77. Calcd. for C30H20N6O2S (528.54): C,
68.17; H, 3.81; N, 15.90; S, 6.07. Found: C, 68.29; H, 3.72; N, 16.01; S, 6.02%.

THIOPHENE- AND 1,3,4-THIADIAZOLE-BASED HETEROCYCLES
1801
5-Acetyl-2-(4-cyano-1,5-diphenylpyrazol-3-carbonyl)-3-(4-chlorophenyl)
cyanomethylene-2,3-dihydro-1,3,4-thiadiazole (12b). Yield 75%; mp 298–300◦C;
IR (KBr) ν 2281, 2208 (2 C N), 1687, 1668 (2 C O) cm−1; MS, m/z 550 (M+ +2), 548
(M+), 505, 276, 272, 244, 233, 77. Calcd. for C29H17N6O2SCl (549.01): C, 63.44; H, 3.12;
N, 15.31; S, 5.84. Found: C, 63.56; H, 3.25; N, 15.41; S, 5.91%.
Ethyl 2-(4-cyano-1,5-diphenylpyrazol-3-carbonyl)-3-phenylcyano-methy
lene-2,3-dihydro-1,3,4-thiadiazole-5-carboxylate (12c). Yield 69%; mp 254–
256◦C; IR (KBr) ν 2233, 2200 (2 C N), 1718, 1686 (2 C O) cm−1; 1H NMR (DMSO-d6)
δ 1.36–1.41 (t, 3H, CH3, J = 7.2 Hz), 4.47–4.52 (q, 2H, CH2, J = 7.2 Hz), 7.27–7.78 (m,
15H, ArH); MS m/z 544 (M+), 311, 272, 245, 131, 77. Calcd. for C30H20N6O3S (544.595):
C, 66.17; H, 3.70; N, 15.43; S, 5.89. Found: C, 66.00; H, 3.50; N, 15.31; S, 5.74%.
Ethyl 2-(4-cyano-1,5-diphenylpyrazol-3-carbonyl)-3-(4-chlorophenyl)cya
nomethylene-2,3-dihydro-1,3,4-thiadiazole-5-carboxylate (12d). Yield 73%; mp
261–263◦C; IR (KBr) ν cm−1 2232, 2205 (2 C N), 1740, 1689 (2 C O); MS, m/z 579
(%) (M+, 44.7), 549 (13.5), 306 (15), 272 (100), 180 (30.2), 141 (44), 77 (72). Calcd. for
C30H19N6O3SCl (579.04): C, 62.23; H, 3.31; N, 14.51; S, 5.54. Found: C, 62.05; H, 3.20;
N, 14.33; S, 5.46%.
2-(4-Cyano-1,5-diphenylpyrazol-3-carbonyl)-3-(4-tolyl)-5-(carboxamido-
N-phenyl)cyano-methylene-2,3-dihydro-1,3,4-thiadiazole (12e). Yield 78%; mp
282–284◦C; IR (KBr) ν 3180 (NH), 2239, 2208 (2 C N), 1665, 1679 (2 C O) cm−1
;
1H NMR (DMSO-d6) δ 2.42 (s, 3H, CH3), 7.17–7.49 (m, 15H, ArH), 7.67–7.80 (m, 4H,
ArH), 11.08 (br, s, 1H, D2O exchangable, NH); MS m/z (%) 605 (M+, 41.3), 500 (21.7),
334 (49.1), 191 (16.2), 141 (18.1), 77 (61). Calcd. for C35H23N7O2S (605.68): C, 69.41;
H, 3.83; N, 16.19; S, 5.30. Found: C, 69.32; H, 4.03; N, 16.35; S, 5.13%.
Synthesis of the Benzothiazine Derivative 14
A mixture of bromoacetylpyrazole 8 (0.73 g, 2 mmol) and 2-aminothiophenol (2.2
mmol) in ethanol (20 mL) was refluxed for 2 h, then allowed to cool. The precipitated
product was filtered off, washed with water, and dried. Recrystallization from dimethylfor-
mamide afforded 2-(4-cyano-1,5-diphenylpyrazol-3-yl)-4H-benzo[1,4]thiazine (14). Yield
(81%); mp > 300◦C; IR (KBr) ν 3310 (NH), 2230 (C N) cm−1; MS m/z (%) 392 (M+,
100), 359 (5.7), 229 (2.6), 121 (6.5), 77 (34.8). Calcd. for C24H16N4S: C, 73.45; H, 4.11;
N, 14.28; S, 8.17. Found: C, 73.48; H, 4.02; N, 14.47; S, 8.37%.
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