Synthesis of new benzopyrano[2,3-c]pyrazoles and 3- triazolonyliminocoumarins from 3-cyano iminocoumarin derivatives

Article abstract of DOI:10.1080/00397911.2014.903422

Synthesis of benzopyrano[2,3-c]pyrazoles and 3-triazolonyliminocoumarins was successfully performed using heterocyclization of 3-cyano iminocoumarin or their N-ethoxycarbonylated derivatives with semicarbazide reagents. Elemental analysis, infrared, and <

Full text of DOI:10.1080/00397911.2014.903422

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Synthesis of New Benzopyrano[2,3-
c]pyrazoles and 3-
Triazolonyliminocoumarins from 3-Cyano
Iminocoumarin Derivatives
S. Trichili a , M. Kammoun a , S. Abid a & H. Ammar a
a Laboratoire de Chimie Appliquée: Hétérocycles, Corps Gras et
Polymères, Faculté des Sciences de Sfax , Université de Sfax , Sfax ,
Tunisia
Accepted author version posted online: 24 Apr 2014.Published
online: 28 Jul 2014.
To cite this article: S. Trichili , M. Kammoun , S. Abid & H. Ammar (2014) Synthesis of New
Benzopyrano[2,3-c]pyrazoles and 3-Triazolonyliminocoumarins from 3-Cyano Iminocoumarin
Derivatives, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 44:19, 2808-2817, DOI: 10.1080/00397911.2014.903422
To link to this article: http://dx.doi.org/10.1080/00397911.2014.903422
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Synthetic Communications1, 44: 2808–2817, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2014.903422
SYNTHESIS OF NEW
BENZOPYRANO[2,3-c]PYRAZOLES AND
3-TRIAZOLONYLIMINOCOUMARINS FROM 3-CYANO
IMINOCOUMARIN DERIVATIVES
S. Trichili, M. Kammoun, S. Abid, and H. Ammar
´
Laboratoire de Chimie Appliquee: Heterocycles, Corps Gras et Polymeres,
Faculte des Sciences de Sfax, Universite de Sfax, Sfax, Tunisia
´ ´
`
´
´
GRAPHICAL ABSTRACT
Abstract Synthesis of benzopyrano[2,3-c]pyrazoles and 3-triazolonyliminocoumarins was
successfully performed using heterocyclization of 3-cyano iminocoumarin or their N-
ethoxycarbonylated derivatives with semicarbazide reagents. Elemental analysis, infrared,
and 1H NMR spectral data confirmed the molecular structure of the newly synthesized
compounds.
Keywords Benzopyrano[2,3-c]pyrazole; iminocoumarin;
thiosemicarbazide; triazolonyliminocoumarin
4-phenylsemicarbazide;
INTRODUCTION
Iminocoumarins derivatives have attracted intense interest in the past few
decades. The growing interest is due to their chemical reactivity, biological compati-
bility, and number of applications associated with them. Several of these iminocou-
marins derivatives exhibit exceptional biological and pharmacological activities such
as antimicrobial,[1] antitumor,[2] and anticancer[3] activites. In addition, they serve as
Received January 21, 2014.
Address correspondence to Houcine Ammar, Laboratoire de Chimie Appliquee, Faculte des
´
Sciences de Sfax, Universite de Sfax, BP 1170, 3000 Sfax, Tunisia. E-mail: houcine_fss@yahoo.fr
´
´
2808

HETEROCYCLIC COMPOUNDS
2809
inhibitors of protein-tyrosine kinase[4] and they are also used as dyes in laser
technology.[5,6]
In recent years, some works have shown that iminocoumarins functionalized at
the 3-position can be used as starting materials to obtain novel heterocyclic com-
pounds consisting of a benzopyrane moiety fused with pyrazole,[7] naphthyridine,[8]
quinolone,[8] quinazoline,[9,10] and pyrimidine rings.[11–15] These modifications in
iminocoumarin backbones could significantly increase the antimicrobial efficiency,
broaden their antimicrobial spectrum, and improve their optical properties,[16,17]
leading to applications in the field of fluorescent sensors[18,19] and dye-sensitized
solar cells.[20]
In this work, we introduce triazolonyl and pyrazole ring into iminocoumarin
structure. As important aromatic nitrogen-containing heterocycles, triazole com-
pounds have aroused special interest because of their excellent pharmacokinetic
characteristics, favorable safety profile, and the latent ability for the formation of
hydrogen bonds with other active molecules. A number of triazole drugs including
fluconazole, itraconazole, and voriconazole have been prevalently used in anti-
infective therapy.[21,22] Recently, some triazole derivatives have been reported to
exhibit good anti-MRSA potency.[23] Although the extensively clinical use of triazole
anti-infective agents has revolutionized the treatment of many infectious diseases,
some of them are still limited by poor activities toward intractable fungi, high
frequency of renal toxicity, and several adverse effects.[24]
In the other hand, many previous studies have confirmed that pyrano[2,3-c]-
pyrazoles and their related derivatives are an important class of pharmaceutical
compounds and exhibit a broad spectrum of biological activities. In particular, these
compounds have been confirmed to possess antifungal, antibacterial, anticancer,
anti-inflammatory, analgesic, antiplatelet, and antioxidant activities.[25,26]
Over the past few years, we are particularly interested in synthesizing several
new 3-cyano iminocoumarins and their N-ethoxycarbonylated derivatives followed
by their transformation by N-nucleophilic reagents as amine, hydrazine, hydrazide,
and hydroxylamine to obtain respectively benzopyranopyrimidines,[15] 3-triazolony-
liminocoumarins,[27] benzopyranopyrazoles, and benzopyranoisoxazoles.[28] In
continuation of our research in the synthesis of heterocyclic compounds, we describe
in this article the reactivity of 3-cyano iminocoumarin with thiosemicarbazide. The
second part is devoted to their N-ethoxycarbonyl derivatives with 4-phenylsemi-
carbazide and thiosemicarbazide as nucleophilic reagents.
RESULTS AND DISCUSSION
3-Cyano iminocoumarins (1–7) were prepared using the Knoevenagel
procedure.[29] Their N-ethoxycarbonylated derivatives (8–10) were obtained in mod-
erate yields by N-ethoxyxarbonylation, as described previously[29,30] (Scheme 1).
1
Their structures were assigned by infrared (IR), H and 13C NMR, and elemental
analysis.
To prepare a variety of benzopyrano[2,3-c]pyrazoles derivatives, the starting
3-cyano iminocoumarins (1–7) were converted by thiosemicarbazide (a) as nucleo-
philic reagent. Reaction of 3-cyano iminocoumarins (1) with thiosemicarbazide (a)
was selected as a model system for a thorough study aimed at optimizing the

2810
S. TRICHILI ET AL.
Scheme 1. Synthetic route to 3-cyano iminocoumarins (1–10).
benzopyrano[2,3-c]pyrazoles (1a) yield. Three parameters were varied in this context,
namely the reaction temperature, the nature of the organic solvent, and the nature of
the catalyst. The best yield of the benzopyrano[2,3-c]pyrazoles (1a) was obtained
when acetic acid was utilized as a catalyst in chloroform at room temperature.
The benzopyrano[2,3-c]pyrazole (1a) was isolated by simple filtration after 16 days
in 85% yield with good selectivity (Scheme 2).
To explain the formation of benzopyrano[2,3-c]pyarazole (1a), we suggest in
Scheme 3 a possible mechanism involving in two steps: (i) a nucleophilic attack of
NH2 group on imidic carbon according to Schmidt reaction to give an amidrazone
(1a’) as intermediate and (ii) interaction of NH group with CꢀN function by an intra-
molecular heterocyclization process leading the corresponding benzopyrano[2,3-c]-
pyrazole (1a).
The infrared (IR) spectra showed absence of the absorption bands character-
istic of the CꢁN functions and the appearance of absorption bands at 1140 and
1
3325 cmꢂ1 corresponding to C S and NH2 groups respectively. Moreover, the H
=
NMR spectra were also in agreement with this structure. Particularly, the disappear-
ance of original peak arising from pyranic NH at 9.25 ppm and appearance of
peaks at 9.94 and 7.09 ppm corresponding of pyrazolic NH and thioamidic NH2
respectively, are clear indications that the cyclocondensation reaction had gone to
completion.
Encouraged by this success, we investigate the reactivity of other 3-cyano imi-
nocoumarins (2–7) in the same operating mode. We obtained the corresponding ben-
zopyrano[2,3-c]pyrazoles (2a–7a) in moderate to good yields 48–87% (Table 1). The
analytic spectra are in agreement with a model compound. The IR spectrum of these
compounds showed in each case, absorption bands at ((cmꢂ1): 1132–1163, 1574–
=
=
=
1618, 1642–1659, 3245–3322, and 3359–3372 corresponding to C S, C C, C N,
NH, and NH2 respectively. The 1H NMR spectra revealed a sharp singlet at
9.86–9.94 ppm assigned of pyrazolic NH and singlet from thioamidic NH2 at
6.98–7.09 ppm.
Scheme 2. Synthesis of benzopyrano[2,3-c]pyrazole (1a).

HETEROCYCLIC COMPOUNDS
2811
Scheme 3. Proposed mechanism of benzopyranopyrazole (1a).
We extended our study to the use of N-ethoxycarbonyl iminocoumarins (8–10)
as C-electrophile reagents with thiosemicarbaside (a) or 4-phenylsemicarbazide (b).
Herein we followed the same strategy. We first chose the heterocyclization reaction
Table 1. Synthesis of benzopyrano [2,3-c] pyrazoles 1a–7a
R5
R6
R7
H
R8
H
Time (days)
16
Yielda (%)
85
Mp (ꢀC)
252
1a
2a
3a
4a
5a
6a
7a
H
H
H
H
H
H
H
H
N(Et)2
OH
H
H
H
2
5
62
85
48
70
65
87
220
>260
188
Cl
OCH3
H
H
17
18
4
H
H
194
204
OCH3
H
H
OCH3
H
3,5
194
aIsolated yield.

2812
S. TRICHILI ET AL.
Scheme 4. Mechanistic pathways for the studied reaction.
of iminocoumarin (8) and 4-phenylsemicarbazide (b) as a model reaction system. To
optimize conditions for the reaction, a series of preliminary runs were conducted on
this system modifying solvents, time, and temperature. In the final protocol, triazo-
lonyl iminocoumarin (8b) were obtained in 76% with good selectivity by refluxing
absolute methanol for 2 h.
A literature survey indicates that two mechanistic pathways that can formally
be envisioned for this condensation leading the 3-triazolonyl iminocoumarin (8b) or
benzopyranopyrimidine (8b’) (Scheme 4).
Table 2. Synthesis of 3-triazolonyl iminocoumarin 8a–10a and 8b–10b
R5
R6
R7
R8
X
R
Time (h)
Yielda (%)
Mp (ꢀC)
8a
9a
H
H
H
H
H
H
H
H
H
H
H
H
N(Et)2
OCH3
H
H
H
S
S
H
H
24
3.5
24
2
74
78
80
76
83
87
230
>260
>260
>260
>260
250
10a
8b
OCH3
H
S
H
N(Et)2
OCH3
H
O
O
O
Ph
Ph
Ph
9b
10b
H
OCH3
2
8
aIsolated yield.

HETEROCYCLIC COMPOUNDS
2813
Scheme 5. Proposed mechanism of 3-triazolonyl iminocoumarin (8b).
The structure was defined by IR and 1H NMR spectral analysis involving com-
parison with literature data. In particular, the IR spectrum showed (i) the absence of
absorption at 2214 cmꢂ1, which confirmed the reactivity of the cyano group, (ii) the
absence of absorption at 1630 and 1640 cmꢂ1, and (iii) the appearance of band at
1718 cmꢂ1, which exclude the possibility of benzopyranopyrimidine product and
confirmed the triazolonic structure.[21,22]
The application of optimized conditions, used with the model system, to vari-
ous combinations gave corresponding 3-triazolonyl iminocoumarins with good yield
74–87% (Table 2). The chemical structures of the newly synthesized iminocoumarin
1
derivatives were characterized by FTIR and H NMR spectra.
The mechanism proposed for this condensation involved three steps: (i) the
nucleophilic attack of NH2 on the imidic function, giving the amidine intermediate,
(ii) the spontaneous cyclization between the iminocoumarin system and triazolonic
heterocycle, and (iii) the formation of triazolonic heterocycle following the interac-
tion between the carbonyl group and the carbazidic function (Scheme 5).
CONCLUSION
In conclusion, we have developed in this article a simple procedure for the
synthesis of benzopyranopyrazolic and 3-triazolonyliminocoumarinic compounds

2814
S. TRICHILI ET AL.
initiated by the condensation of different iminocoumarins with thiosemicarbazide
and 4-phenylsemicarbazide as nucleophilic reagents. These compounds are obtained
in moderate to good yields with high selectivity.
EXPERIMENTAL
Thiosemicarbazide and 4-phenylsemicarbazide were commercially available
from Aldrich. Ethanol, methanol, and chloroform (analytical grade) used for spec-
troscopic measurements were from VWR Prolabo and SDS, respectively. 3-Cyano
iminocoumarins (1–7) and N-ethoxycarbonylated derivatives (8–10) were prepared
as previously described.[29,30] The melting points were determined on an Electrother-
mal 9100 apparatus. Infrared spectra were registered on a Jasco FT-IR 420 spectro-
1
photometer apparatus using a Perkin-Elmer 100 instrument. H NMR spectra were
recorded on a Bruker WP 200 spectrometer operating at 300, in dimethylsulfoxide
(DMSO-d6) or CF3CO2D with tetramethylsilane (TMS) as internal standard
(chemical shifts in ppm).
General Procedure for the Synthesis of Benzopyrano[2,3-c]pyrazoles
1a–7a
A solution of 3-cyano-iminocoumarin (1–7) (5 mmol and thiosemicarbazide
(a) (5 mmol) was stirred in 30 ml of chloroform. After total dissolution, a catalytic
amount of glacial acetic acid was added, and the reaction mixture was stirred
at room temperature during the time indicated in Table 1. After completion of the
reaction, the simple benzopyrano[2,3-c]pyrazole obtained was separated by filtration
and washed with chloroform.
Benzopyrano[2,3-c]pyrazole (1a)
Orange solid, IR (cmꢂ1): n ¼ 1140 (C S), 1574 (C C), 1656 (C N), 3255=3322
=
=
=
(NH), 3372 (NH2). 1H NMR (DMSO-d6): d ¼ 7.09 (s, 2H, NH2), 7.60 (d,
J ¼ 8.40 Hz, 1H, H8), 7.67 (t, J ¼ 7.5 Hz, 1H, H6’’), 7.80 (t, J ¼ 7.50 Hz, 1H, H5’’)
,
8.08 (d, J ¼ 8.40 Hz, 1H, H5’), 8.26 (d, J ¼ 8.40 Hz, 1H, H6’), 8.83 (d, J ¼ 8.40 Hz,
1H, H7), 9.45 (s, 1H, H4), 9.94 (s, 1H, NH). Calculated for C15H10N4OS: C,
61.21%; H, 3.42; N, 19.04. Found: C, 61.46%; H, 3.13; N, 19.35.
General Procedure for the Synthesis of 3-Triazolonyliminocoumarin
(8a–10a) and (8b–10b)
A solution of 3-cyano-N-ethoxycarbonyl iminocoumarin 8–10 (5 mmol) and 4-
phenylsemicarbazid or thiosemicarbazide (5 mmol) in 30 ml of absolute methanol was
refluxed during the time indicated in Table 2. After complete reaction, the simple 3-tria-
zolonyl iminocoumarin obtained was separated by filtration and washed with methanol.
3-Triazolonyliminocoumarin (8a)
Orange solid, IR (cmꢂ1): n ¼ 1179 (C S), 1592 (C C), 1644 (C N), 1729
=
=
=
(C O), 3276 (NH). 1H NMR (CDCl3=CF3COOD): d ¼ 1.33 (t, J ¼ 6.9 Hz, 6H,
=

HETEROCYCLIC COMPOUNDS
2815
CH3), 3.59 (q, J ¼ 6.9 Hz, 4H, CH2N), 6.70 (s, 1H, H8), 6.94 (d, J ¼ 9.3 Hz, 1H, H6),
7.64 (d, J ¼ 9.3 Hz, 1H, H5), 8.05 (s, 1H, H4), 8.69 (s, 1H, NH), 9.47 (s, 1H, NH).
Calculated for C16H18N6O2S: C, 53.63%; H, 5.03; N, 23.46. Found: C, 53.59%; H,
5.08; N, 23.49.
3-Triazolonyliminocoumarin (8b)
Orange-brown solid, IR (cmꢂ1): n ¼ 1584 (C C), 1648 (C N), 1718= 1745
=
=
(C O), 3126 (NH). 1H NMR (CDCl3=CF3COOD): d ¼ 1.3 (t, J ¼ 7.2 Hz, 6H,
CH3), d ¼ 3.6 (q, J ¼ 7.2 Hz, 4H, CH2N), d ¼ 6.75 (d, J ¼ 2.4 Hz, 1H, H8), 6.99
(dd, J ¼ 2.4 Hz, J ¼ 9.3 Hz, 1H, H6), 7.29 (d, J ¼ 8.1 Hz, 1H, HAr), 7.43 (t, J ¼ 8.1 Hz,
Hz, 2H, HAr), 7.52 (d, J ¼ 8.1 Hz, 2H, HAr), 7.65 (d, J ¼ 9.3 Hz, 1H, H5), 8.52 (s, 1H,
H4). C22H22N6O3: C, 63.15%; H, 5.26; N, 20.09. Found: C, 63.22; H, 5.30; N, 19.99.
=
ACKNOWLEDGMENTS
The authors acknowledge Pr. Rachid El Gharbi for his useful discussions
about this work.
FUNDING
The authors thank the Ministry of Higher Education, Scientific Research, and
Technology in Tunisia for financial support.
SUPPORTING INFORMATION
Supplemental data for this article can be accessed on the publisher’s website.
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