Dipolar cycloaddition reactions with thiazolonylhydrazones: A new route for the synthesis of several new thienyl- and furyl-thiazolonylpyrrolopyrazole derivatives of expected biological activities

Article abstract of DOI:10.1080/10426500307918

Several new pyrrolopyrazoles were synthesized via the reactions of each of 2-thiophenecarboxaldehyde thiazolonylhydrazone or 2-furaldehyde thiazolonylhydrazone with N-substituted maleimides followed by partial dehydogenation using bromobenzene and complete aromatization using nitrobenzene. Structures were established on the basis of elemental analyses and spectroscopic data studies.

Full text of DOI:10.1080/10426500307918

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Dipolar Cycloaddition Reactions with
Thiazolonylhydrazones: A New Route for the
Synthesis of Several New Thienyl- and Furyl-
Thiazolonylpyrrolopyrazole Derivatives of Expected
Biological Activities
Hatem M. Gaber a
a National Organization for Drug Control and Research , Cairo, Egypt
Published online: 27 Oct 2010.
To cite this article: Hatem M. Gaber (2003) Dipolar Cycloaddition Reactions with Thiazolonylhydrazones: A New Route for
the Synthesis of Several New Thienyl- and Furyl-Thiazolonylpyrrolopyrazole Derivatives of Expected Biological Activities,
Phosphorus, Sulfur, and Silicon and the Related Elements, 178:3, 417-424
To link to this article: http://dx.doi.org/10.1080/10426500307918
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Phosphorus, Sulfur and Silicon, 2003, Vol. 178:417–424
C
Copyright 2003 Taylor & Francis
1042-6507/03 $12.00 + .00
DOI: 10.1080/10426500390170552
DIPOLAR CYCLOADDITION REACTIONS
WITH THIAZOLONYLHYDRAZONES: A NEW ROUTE
FOR THE SYNTHESIS OF SEVERAL NEW THIENYL-
AND FURYL-THIAZOLONYLPYRROLOPYRAZOLE
DERIVATIVES OF EXPECTED
BIOLOGICAL ACTIVITIES
Hatem M. Gaber
National Organization for Drug Control and Research,
Cairo, Egypt
(Received February 17, 2002; accepted June 9, 2002)
Several new pyrrolopyrazoles were synthesized via the reactions of each
of 2-thiophenecarboxaldehyde thiazolonylhydrazone or 2-furaldehyde
thiazolonylhydrazone with N-substituted maleimides followed by par-
tial dehydogenation using bromobenzene and complete aromatization
using nitrobenzene. Structures were established on the basis of elem-
ental analyses and spectroscopic data studies.
Keywords: Cycloaddition reactions; furans; N-substituted maleimides;
pyrrolopyrazoles; thiazolinones; thiophenes
INTRODUCTION
Pyrazoles and their annelated derivatives have been widely investi-
gated for therapeutic uses, especially as antipyretic1,2 and active CNS
regulants;3,4 they also were reported to have hyptonic5 and herbicidal6
activities. Moreover, the thiophene, furan, and thiazolinone moieties
also are reported to be used in several pharmaceutical and medicinal
preparations.7–12 In view of these versatile benefits, it was important to
The author wishes to express his sincere thanks to Professor Sami S. Ghabrial
(NODCAR, Cairo, Egypt) and Professor Cyril Parkanyi (Florida Atlantic University,
Florida, USA) for their valuable discussions.
The author currently is a postdoctoral research fellow, Department of Chemistry and
Biochemistry, Florida Atlantic University, 777 Glades Road, PO Box 3091, Boca Raton,
FL 33431-0991.
Address correspondence to Hatem M. Gaber, National Organization for Drug Control
and Research, PO Box 29, Cairo, A. R. Egypt. E-mail: hatemgaber@yahoo.com
417

418
H. M. Gaber
incorporate these moieties with the pyrazole ring in a series of deriva-
tives. This would allow us obtain some new heterocyclic compounds
with expected wide spectrum of potential applications that were ex-
tensively required for our medicinal chemistry program.13–16 The re-
actions of each of 2-thiophenecarboxaldehyde thiazolonylhydrazone or
2-furaldehyde thiazolonylhydrazone with a variety of N-substituted
maleimides seemed to be an easy, logical, and unique route for using hy-
drazones and thiosemicarbazones of certain aldehydes as four-electron
three-atomic centers in dipolar cycloaddition reactions to synthesize
the desired heterocyclic derivatives.
RESULTS AND DISCUSSION
It has been found that the thiosemicarbazones of 2-thiophene-
carboxaldehyde and 2-furaldehyde 1a,b reacted with chloroacetic
acid to give the corresponding hydrazone derivatives 2a,b, which
were taken as the starting materials for the present study. Thus, it
has been found that 2-thiophenecarboxaldehyde N-(2-thiazolin-4-on-
2-yl)hydrazone (2a) reacted with N-phenylmaleimide (3a) to yield a
reaction product of molecular formula C18H14N4O3S2 resulting from
equimolecular addition of 2a to 3a. The IR spectrum of this reaction
product showed the presence of NH, CO NR0 CO,17 ring CO, and sat-
1
urated CH and CH2 groups. Its H NMR spectrum ( ppm) revealed
the signals at 3.49 (t, pyrrolidine H-4), 3.71 (s, thiazolonyl CH2), 3.98
(d, pyrrolidine H-3), 4.21 (d, pyrazolidine H-3), 4.58 (br, s, NH, D2O-
exchangeable), 6.55–6.92 (m, 3H, thiophene) in addition to aromatic
protons 7.16–7.77 (m, 5H, ArHs). In the light of the above findings,
this reaction product could be formulated as the 1-phenyl-5-thiazolonyl-
3-(2-thienyl)-pyrrolidino[3,4-c]pyrazolidin-2,6-dione derivative 4a (cf.
Experimental).
Analogously, 2a reacted with each of N-p-chlorophenylmaleimide
(3b), N-p-methylphenylmaleimide (3c), or N-ethylmaleimide (3d)
to give the corresponding 5-thiazolonyl-3-(2-thienyl)pyrrolidino[3,4-
c]pyrazolidin-2,6-dione derivatives 4b–d respectively. Structure of
4b–d also was established based on correct elemental analyses and
spectral data (cf. Experimental).
On the other hand, the 2-furaldehyde N-(2-thiazolin-4-on-2-
yl)hydrazone (2b) cycloadded to each of 3a–d to give good yields of the
pyrrolidino[3,4-c]pyrazolidin-2,6-dione derivatives 4e–h respectively.
1
IR and H NMR spectral data in addition to elemental analyses were
used to establish the structure of 4e–h as for 4a–d previously reported
(cf. Experimental).

Dipolar Cycloaddition Reactions with Thiazolonylhydrazones
419
The course of dehydrogenation of compounds 4a–h was taken as an
additional evidence for their assigned structure.
Thus, partial dehydrogenation of 4a–h using bromobenzene resulted
in the formation of products with two hydrogens less than the corre-
sponding startings 4a–h in each case. The absorption band of the NH
group was entirely absent in the IR spectra of these reaction products.
1
Moreover, their H NMR spectra did not reveal NH nor pyrazolidine
H-3 protons. Based on the above results, these reaction products could
be formulated as the 5-thiazolonylpyrrolidino[3,4-c]-12-pyrazolin-2,6-
dione derivatives 5a–h respectively (cf. Experimental).
CHART 1

420
H. M. Gaber
On the other hand, complete dehydrogenation of 5a–h was achieved
via boiling their solutions in nitrobenzene to give the corresponding
5-thiazolonylpyrrolo[3,4-c]pyrazol-2,6-dione derivatives 6a–h respec-
tively. 1H NMR spectra of 6a–h did not reveal any signals of pyrrolidine
or pyrazolidine or NH protons, thus supporting the assigned structure.
A further proof for the structure of 6a–h came from their alternative
syntheses via direct dehydrogenation of the corresponding 4a–h by boil-
ing their solutions in nitrobenzene. Compounds 6a–h prepared via this
route were found completely identical with 6a–h prepared via the first
route (cf. Experimental). The bioresponses of the newly synthesized
compounds are now under investigation.
EXPERIMENTAL
All melting points are uncorrected. IR (KBr discs) spectra were recorded
on Perkin Elmer FT-IR type 4 spectrophotometer. 1H NMR spectra were
recorded on Gemini 200 MHz spectrometer in CDCl3 using TMS as
an internal standard. Chemical shifts are expressed as ppm units.
Microanalyses were performed at the Microanalytical Center of Cairo
University.
Compounds 2a,18 2b,19 and 320 were prepared according to literature
procedures.
Synthesis of 4a–h
A solution of each of 2a,b (0.01 mol) in acetic acid (20 ml) was treated
with the appropriate 3a–d (0.01 mol) and the reaction mixture was
then heated under reflux for 4 h. Removal of the solvent gave a residue
which was crystallized from glacial acetic acid and identified as 4a–h
(cf. Tables I and II).
Partial Dehydrogenation of 4a–h
A solution of each of 4a-h (1.0 g) in bromobenzene (15 ml) was heated
under reflux for 3 h. Removal of the solvent left behind a residue which
was crystallized from the proper solvent and identified as 5a-h respec-
tively (cf. Tables I and II).
Complete Dehydrogenation of 4a–h or 5a–h
A solution of each of 4a–h or 5a–h in nitrobenzene (15 ml) was heated
under reflux for 3 h. The solvent was evaporated to dryness under

Dipolar Cycloaddition Reactions with Thiazolonylhydrazones
421
Cl
TABLE I Characterization data of the Newly Synthesized Compounds
Calcd./(Found)
Comp.
No.
m.p.
Color
C
Yield
(%)
M. Formula
(M. wt.)
C
H
N
S
4a
4b
4c
4d
4e
4f
257–258
Yellow
230–231
Yellow
90
85
87
91
77
87
93
84
76
73
81
83
74
82
89
78
80
72
83
75
79
77
81
78
C18H14N4O3S2
54.27
3.52
14.07
16.08
—
—
(54.4) (3.6) (14.2) (16.1)
C18H13N4O3S2Cl 49.94 3.01 12.95
(50.0) (3.1) (13.1) (14.7) (8.2)
14.80 8.21
209–210
Pale yellow
198–199
Orange
247–248
Brown
221–222
Pale yellow
203–204
Pale yellow
191–192
Yellow
251–252
Pale brown
262–263
Pale yellow
283–284
Yellow
215–216
Yellow
236–237
Pale brown
266–267
Brown
242–243
Yellow
226–227
Yellow
C
19H16N4O3S2
55.34
(55.2) (3.8) (13.6) (15.4)
48.00 4.00 16.00 18.29
(47.9) (4.0) (16.1) (18.3)
56.54
(56.8) (3.7) (14.5)
51.86 3.12 13.45
(52.0) (3.1) (13.6)
57.58 4.04 14.14
(57.7) (3.9) (14.0)
50.30 4.19 16.77
(50.4) (4.2) (16.9)
54.55 3.03 14.14
3.88
13.59
15.53
—
—
—
—
—
C14H14N4O3S2
C18H14N4O4S
3.66
14.66
8.38
(8.4)
7.68
(7.7)
8.08
(8.1)
9.58
(9.5)
16.16
—
C
18H13N4O4SCl
C19H16N4O4S
14H14N4O4S
C18H12N4O3S2
8.52
(8.4)
—
—
—
—
—
—
8.25
4g
4h
5a
5b
5c
5d
5e
5f
C
(54.7) (3.0) (14.2) (16.2)
18H11N4O3S2Cl 50.17 2.56 13.01 14.87
C
C
(50.4) (2.6) (13.2) (14.7) (8.2)
19H14N4O3S2
55.61
(55.7) (3.3) (13.8) (15.7)
48.28 3.45 16.09 18.39
(48.1) (3.4) (16.2) (18.5)
56.84
(56.8) (3.3) (14.6)
52.11 2.65 13.51
(52.1) (2.4) (13.6)
57.87 3.55 14.21
(57.7) (3.6) (14.3)
50.60 3.61 16.87
(50.8) (3.6) (16.9)
54.82 2.54 14.21
3.41
13.66
15.61
—
—
—
—
—
C14H12N4O3S2
C
C
18H12N4O4S
3.16
14.74
8.42
(8.5)
7.72
—
8.56
18H11N4O4SCl
(7.8) (8.6)
5g
5h
6a
6b
6c
6d
6e
6f
C19H14N4O4S
C14H12N4O4S
8.12
(8.1)
9.64
(9.5)
16.24
—
—
—
—
—
>300
Yellow
>300
Pale yellow
296–297
Brown
274–275
Brown
C
18H10N4O3S2
(55.0) (2.4) (14.2) (16.4)
50.41 2.10 13.07 14.94
(50.5) (2.1) (12.9) (15.1) (8.4)
—
8.28
C18H9N4O3S2Cl
C
C
C
C
19H12N4O3S2
14H10N4O3S2
18H10N4O4S
18H9N4O4SCl
55.88
(56.1) (3.0) (13.7) (15.8)
48.55 2.89 16.18 18.50
(48.5) (2.9) (16.0) (18.6)
57.14
(57.4) (2.5) (14.9)
52.36 2.18 13.58
(52.5) (2.2) (13.4)
58.16 3.06 14.29
(58.1) (3.1) (14.3)
50.91 3.03 16.97
(51.2) (3.0) (16.8)
2.94
13.73
15.69
—
—
—
—
—
>300
2.65
14.81
8.47
(8.4)
7.76
Orange
289–290
Brown
—
8.61
(7.8) (8.6)
6g
6h
>300
C19H12N4O4S
14H10N4O4S
8.16
(8.3)
9.70
(9.8)
—
—
—
—
Pale brown
270–271
Brown
C

422
H. M. Gaber
TABLE II IR and 1H NMR Data of the Synthesized Compounds
1
No.
IR ( cm
)
1H NMR (CDCl3/ ppm)
4a
3340 (NH), 2985 (sat. CH
and CH2), 1780, 1700
(CONR’CO) and 1676
(ring-CO).
3.49 (t, 1H, pyrrolidine H-4), 3.71 (s, 2H,
thiazolonyl-CH2), 3.98 (d, 1H, pyrrolidine
H-3), 4.21 (d, 1H, pyrazolidine H-3), 4.58 (br,
s, 1H, NH, D2O-exchangeable), 6.55–6.92
(m, 3H, thiophene) and 7.16–7.77 (m, 5H,
ArHs).
4b
4c
3330 (NH), 2980 (sat. CH
and CH2), 1770, 1705
(CONR’CO) and 1670
(ring-CO).
3350 (NH), 2976 (sat. CH
and CH2), 1780,
—
2.26 (s, 3H, CH3), 3.52 (t, 1H, pyrrolidine
H-4), 3.65 (s, 2H, thiazolonyl-CH2),
3.93 (d, 1H, pyrrolidine H-3), 4.17 (d, 1H,
pyrazolidine H-3), 4.70 (br, s, 1H, NH,
D2O-exchangeable), 6.43–6.85 (m, 3H,
thiophene) and 7.09–7.75 (m, 4H, ArHs).
1.15 (t, 3H, CH3), 3.41 (q, 2H, CH2), 3.63 (t,
1H, pyrrolidine H-4), 3.74 (s, 2H,
thiazolonyl-CH2), 3.92 (d, 1H, pyrrolidine
H-3), 4.15 (d, 1H, pyrazolidine H-3), 4.66 (br,
s, 1H, NH, D2O-exchangeable) and
6.69–7.04 (m, 3H, thiophene).
1710 (CONR’CO) and
1680 (ring-CO).
4d
3332 (NH), 2980 (sat. CH
and CH2), 1772, 1715
(CONR’CO) and 1680
(ring-CO).
4e
4f
3350 (NH), 2982 (sat. CH
and CH2), 1770, 1720
(CONR’CO) and 1680
(ring-CO).
3330 (NH), 2985 (sat. CH
and CH2), 1780, 1712
(CONR’CO) and
—
—
1684 (ring-CO).
4g
3344 (NH), 2975 (sat. CH
and CH2), 1770, 1710
(CONR’CO) and 1675
(ring-CO).
2.28 (s, 3H, CH3), 3.55 (t, 1H, pyrrolidine
H-4), 3.71 (s, 2H, thiazolonyl-CH2), 3.91
(d, 1H, pyrrolidine H-3), 4.16 (d, 1H,
pyrazolidine H-3), 4.85 (br, s, 1H, NH,
D2O-exchangeable), 6.02–7.10 (m, 3H,
furan) and 7.19–7.80 (m, 4H, ArHs).
1.15 (t, 3H, CH3), 3.43 (q, 2H, CH2), 3.61
(t, 1H, pyrrolidine H-4), 3.75 (s, 2H,
thiazolonyl-CH2), 3.89 (d, 1H, pyrrolidine
H-3), 4.20 (d, 1H, pyrazolidine H-3),
4.75 (br, s, 1H, NH, D2O-exchangeable)
and 6.12–7.20 (m, 3H, furan).
4h
3300 (NH), 2980 (sat. CH
and CH2), 1780, 1716
(CONR’CO) and 1680
(ring-CO).
5a
5b
2980 (sat. CH and CH2),
1780, 1710 (CONR’CO)
and 1682 (ring-CO).
2985 (sat. CH and CH2),
1775, 1710 (CONR’CO)
and 1685 (ring-CO).
—
3.53 (d, 1H, pyrrolidine H-4), 3.70 (s, 2H,
thiazolonyl-CH2), 3.95 (d, 1H, pyrrolidine
H-3), 6.49–6.86 (m, 3H, thiophene) and
7.15–7.70 (m, 4H, ArHs).
(Continued)

Dipolar Cycloaddition Reactions with Thiazolonylhydrazones
423
TABLE II IR and 1H NMR Data of the Synthesized Compounds (Continued)
1
No.
IR ( cm
)
1H NMR (CDCl3/ ppm)
5c
2985 (sat. CH and CH2),
1774, 1705 (CONR’CO)
and 1675 (ring-CO).
2.31 (s, 3H, CH3), 3.53 (d, 1H, pyrrolidine
H-4), 3.67 (s, 2H, thiazolonyl-CH2),
4.00 (d, 1H, pyrrolidine H-3),
6.51–6.88 (m, 3H, thiophene) and
7.09–7.74 (m, 4H, ArHs).
5d
5e
2980 (sat. CH and CH2),
1776, 1700 (CONR’CO)
and 1670 (ring-CO).
2985 (sat. CH and CH2),
1780, 1715 (CONR’CO)
and 1686 (ring-CO).
—
3.50 (d, 1H, pyrrolidine H-4), 3.69 (s, 2H,
thiazolonyl-CH2), 3.88 (d, 1H, pyrrolidine
H-3), 6.01–7.11 (m, 3H, furan) and
7.23–7.81 (m, 5H, ArHs).
5f
2975 (sat. CH and CH2),
1780, 1710 (CONR’CO)
and 1680 (ring-CO).
—
5g
5h
2985 (sat. CH and CH2),
1775, 1708 (CONR’CO)
and 1670 (ring-CO).
2980 (sat. CH and CH2),
1780, 1710 (CONR’CO)
and 1671 (ring-CO).
—
1.24 (t, 3H, CH3), 3.49 (q, 2H, CH2), 3.55 (d, 1H,
pyrrolidine H-4), 3.75 (s, 2H, thiazolonyl-
CH2), 3.93 (d, 1H, pyrrolidine H-3)
and 6.13–7.33 (m, 3H, furan).
—
6a
6b
6c
6d
6e
6f
2980 (sat. CH2), 1770, 1705
(CONR’CO) and 1680
(ring-CO).
2985 (sat. CH2), 1780, 1705
(CONR’CO) and 1685
(ring-CO).
2985 (sat. CH2), 1772, 1710
(CONR’CO) and 1670
(ring-CO).
2985 (sat. CH2), 1760, 1705
(CONR’CO) and 1675
(ring-CO).
2975 (sat. CH2), 1770, 1705
(CONR’CO) and 1673
(ring-CO).
2980 (sat. CH2), 1750, 1700
(CONR’CO) and 1675
(ring-CO).
3.80 (s, 2H, thiazolonyl-CH2), 6.50–6.88 (m, 3H,
thiophene) and 7.05–7.61 (m, 4H, ArHs).
—
1.31 (t, 3H, CH3), 3.60 (q, 2H, CH2), 3.82 (s, 2H,
thiazolonyl-CH2) and 6.63–7.00 (m, 3H,
thiophene).
—
—
6g
6h
2985 (sat. CH2), 1782, 1714
(CONR’CO) and 1680
(ring-CO).
2991 (sat. CH2), 1770, 1707
(CONR’CO) and 1675
(ring-CO).
2.40 (s, 3H, CH3), 3.75 (s, 2H, thiazolonyl-CH2),
6.00–7.09 (m, 3H, furan) and 7.18–7.80
(m, 4H, ArHs).
1.33 (t, 3H, CH3), 3.60 (q, 2H, CH2), 3.82 (s, 2H,
thiazolonyl-CH2) and 6.11–7.32 (m, 3H,
furan).

424
H. M. Gaber
reduced pressure and the residue obtained was triturated several times
with cold ethanol. Crystallization from the proper solvent gave 6a–h
respectively (cf. Tables I and II).
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