Trichlorotriazine as a simple and efficient catalyst promoter for the synthesis of new generation of coumarins

Article abstract of DOI:10.4067/S0717-97072013000400073

The first synthesis of azo bearing coumarins from azo aldehydes and malononitrile in the presence of an efficient catalyst, trichlorotriazine under ultrasound irradiation in high yield and short reaction time is reported. In the other study, the first electrophilic substitution under ultrasound irradiation for the synthesis of azo bearing coumarins was developed. All of synthesized compounds were characterized by FTIR, NMR and elemental analysis.

Full text of DOI:10.4067/S0717-97072013000400073

J. Chil. Chem. Soc., 58, Nº 4 (2013)
TRICHLOROTRIAZINE AS A SIMPLE AND EFFICIENT CATALYST PROMOTER FOR THE SYNTHESIS OF
NEW GENERATION OF COUMARINS
MOHAMMAD NIKPASSAND*,a, LEILA ZARE FEKRIb, NARJES CHANGIZa, FOROUZAN IMANIa
aDepartment of Chemistry, Rasht Branch, Islamic Azad University, Rasht, Iran
bDepartment of Chemistry, Payame Noor University, PO Box 19395-3697 Tehran, Iran
(Received: June 20, 2013 - Accepted: July 8, 2013)
ABSTRACT
The first synthesis of azo bearing coumarins from azo aldehydes and malononitrile in the presence of an efficient catalyst, trichlorotriazine under ultrasound
irradiation in high yield and short reaction time is reported. In the other study, the first electrophilic substitution under ultrasound irradiation for the synthesis of
azo bearing coumarins was developed. All of synthesized compounds were characterized by FTIR, NMR and elemental analysis.
Keywords: Coumarins, trichlorotriazine, malononitrile, azo aldehydes
reaction times (5 min). The progress of the reaction was monitored by TLC
(EtOAc: petroleum ether 1:2). Then the reaction mixture was added in situ
dropwise to synthesized compound 7, and the reaction was irradiated for the
required reaction time (7-15 min) to produce compound 3a-j. Then the reaction
mixture was cooled to room temperature, and the product was filtered without
further purification.
INTRODUCTION
Coumarins are well known natural products for their diverse biological
activity such as photosensitizes 1, anti-HIV agents 2, antibiotics 3, rodenticides
and oral anticoagulants 4, inhibitor of platelet aggregation 5, antibacterial
,
6
anticancer 7 and inhibitor of steroid 5α- reductase . Coumarin derivatives
display a broad range of applications to the pharmaceutical, perfume, cosmetic,
food, agrochemical 9, sensors and sophisticated photophysical system 10-12, that
is, in organic light-emitting diodes 13 and molecular photonic devices 14 and in
the preparation of insecticides, optical brightening agents, dispersed fluorsent
and tunable dye lasers 15. Coumarins also act as intermediates for the synthesis
8
2-oxo-6-(phenyldiazenyl)-2H-chromene-4-carbonitrile
3a
(table
2, entry 1) brown solid, mp 263ºC dec. FT- IR (KBr): v 3055, 2231 (CN),
1
1733 (C=O), 1614, 1560, 1475, 1180 Cm-1. H NMR (CDCl , 400 MHz) d =
7.57-7.62 (m, 4H), 7.97-7.99 (m, 2H), 8.19 (d, J = 2.2 Hz, 13H), 8.33 (dd, JH=
8.8 Hz, J = 2.2 Hz, 1H), 8.41 (s, 1H) ppm. 13C NMR (DMSO- d6, 100 MHz)
d = 103.85, 114.90, 118.77, 122.51, 124.93, 128.94, 130.25, 137.11, 148.80,
1C49.09, 150.71, 153.65, 156.18, 167.98 ppm. Anal. Calcd. for C17H11N3O2: C,
70.58; H, 3.83; N, 14.53. Found: C, 70.44; H, 3.27; N, 14.45.
of fluorocoumarins, chromenes, coumarones and 2-acylresorcinols 16
1 Coumarins have been synthesized by several routes including Pechman
17, Knovenagel18, Reformatsky 19 and Wittig reaction 20
On the other hand, various procedures were used for the Perkin synthesis
of coumarins. The main disadvantages of the processes using these catalysts
are long reaction times, low yields, harsh reaction condition and temperature
above 150ºC, non reusability of the catalyst, use of excess amount of the re-
agent, strictly reactive condition(N atmosphere), special efforts required to
prepare the catalyst and tedious wor2k up and low selectivity.
11 However, to the best of our knowledge, no reports concerning couma-
rins conjugated with azo systems have appeared so far. Hence, synthesis of new
generation of coumarins in fast and environmentally benign synthetic routes
has created a lot of interest in organic chemistry.
.
.
2-oxo-6-(p-tolyldiazenyl)-2H-chromene-4-carbonitrile 3b (table 2,
entry 2) brown solid, mp 263ºC dec. FT- IR (KBr:) v 3049, 2225 (CN), 1737
(C=O), 1608, 1469, 1412, 1103 Cm-1. 1H NMR (CDCl , 400 MHz) d = 2.50 (s,
3H), 7.29 (d, J = 8.0 Hz, 2H), 7.55 (d, J = 8.8 Hz, 1H),37.87 (2H, d, JH= 8.0 Hz),
8.16 (1H, d, J = 2.2 Hz), 8.31 (1H, dd, J = 8.8 Hz, J = 2.2 Hz), 8.39 (s, 1H) ppm.
13C NMR (DMSO- d6,100 MHz) dC = 20.12, 105.63, 115.78, 119.09, 123.11,
124.73, 129.64, 130.16, 139.45, 148.34,149.87, 150.11, 152.45, 156.90, 166.08
ppm. Anal. Calcd. for C H11N3O2: C, 70.58; H, 3.83; N, 14.53. Found: C,
70.44; H, 3.27; N, 14.45. 17
6-((4-methoxyphenyl)diazenyl)-2-oxo-2H-chromene-4-carbonitrile 3c
(table 2, entry 3) brown solid, mp 263ºC dec. 1H NMR (CDCl3, 400 MHz) dH =
3.96 (s, 3H), 7.08 (d, J = 8.8 Hz, 2H), 7.53(d, J = 8.8 Hz, 1H), 7.98 (d, J = 8.8
Hz, 2H), 8.12 (d, J = 2.0 Hz, 1H), 8.28 (dd, J = 8.8 Hz, J = 2.0 Hz, 1H), 8.39
(s, 1H) ppm. 13C NMR (DMSO- d6, 100 MHz) dC = 71.00, 106.33, 118.91,
119.09, 124.01, 126.82, 128.93, 130.65, 138.53, 149.24, 149.87, 151.13,
154.46, 156.89, 167.61ppm. Anal. Calcd. for C17H11N3O3: C, 70.58; H, 3.83; N,
14.53. Found: C, 70.36; H, 3.78; N, 14.39.
6-((4-chlorophenyl)diazenyl)-2-oxo-2H-chromene-4-carbonitrile 3d
(table 2, entry 4) brown solid, mp 300ºC dec. FT- IR (KBr) v: 2933, 2233
(CN), 1737 (C=O), 1610, 1650, 1510, 1085 Cm-1. 1H NMR (CDCl3, 400 MHz)
d = 7.55 (d, J = 8.6 Hz, 2H), 7.59 (d, J = 8.4 Hz, 1H), 7.93 (d, J = 8.6 Hz, 2H),
8H.19 (d, J = 2.4 Hz, 1H), 8.32 (dd, J = 8.6 Hz, J = 2.4 Hz, 1H), 8.42 (s, 1H) ppm.
13C NMR (DMSO- d6, 100 MHz) dC = 103.85, 114.90, 118.77, 122.51, 124.93,
128.94, 130.25, 137.11, 148.80, 150.71, 153.65, 156.18, 156.98, 167.65ppm.
Anal. Calcd. for C16H8ClN3O2: C, 62.05; H, 2.60; N, 13.57. Found: C, 62.98;
H, 2.57; N, 13.53.
6-((4-bromophenyl)diazenyl)-2-oxo-2H-chromene-4-carbonitrile 3e
(table 2, entry 5) brown solid, mp 275ºC dec. FT- IR (KBr) v: 2929, 2237 (CN),
1739 (C=O), 1685, 1652, 1614, 1506 Cm-1. 1H NMR (CDCl , 400 MHz) dH =
7.57 (d, J = 8.8 Hz, 1H), 7.72 (d, J = 8.8 Hz, 2H), 7.88 (d, J =38.8 Hz, 2H), 8.19
(d, J = 2.0 Hz, 1H), 8.33 (dd, J = 8.8 Hz, J = 2.0 Hz, 1H), 8.42 (s, 1H) ppm.13C
NMR (DMSO- d6, 100 MHz) dC = 103.81, 114.88, 118.77, 124.98, 126.11,
128.91, 132.56, 132.98, 148.79, 150.98, 153.64, 156.16, 156.97, 167.78 ppm.
Anal. Calcd. For C16H8BrN3O2: C, 54.26; H, 2.28; N, 11.86. Found: C, 54.68;
H, 2.56; N, 11.09.
EXPERIMENTAL
Materials and measurements
Melting points were measured on an Electrothermal 9100 apparatus. IR
spectra were determined on a Shimadzo IR-470 spectrometer. 1H NMR spectra
were recorded on a 500 MHz Bruker DRX-500 and 13C NMR spectra were
recorded on a 250 MHz Bruker DRX-500 in DMSO-d6 as solvent. Chemicals
were purchased from Merck and Fluka. Elemental analyses were done on a
Carlo-Erba EA1110CNNO-S analyser and agreed with the calculated values.
All solvents used were dried and distilled according to standard procedures.
General Procedure for the synthesis of azo conjugated coumarins 3 in
pathway a under ultrasound irradiation
A mixture of azo aldehyde 1 (1 mmol), malononitrile (1 mmol) and TCT
(0.3mmol) in 5mL H2O were placed into Pyrex-glass open vessel and irradiated
in a water bath under silent condition by ultrasound (45kHz) at 60°C for the
required reaction times (5-9 min). The progress of the reaction was monitored
by TLC (EtOAc: petroleum ether 1:2). After completion of the reaction, as
indicated by TLC, the reaction mixture was filtered to separate the catalyst and
the organic compound was recrystallized by EtOH to produce azo coumarin
derivatives 3a-j as pure crystalline products.
General Procedure for the synthesis of azo conjugated coumarins 3 in
pathway b under ultrasound irradiation
A mixture of various aniline 4 (1 mmol), NaNO2 (1 mmol) and HCl (1mL)
were placed into Pyrex-glass open vessel and irradiated in a water bath under
silent condition by ultrasound (45 kHz) at room temperature for the required
e-mail: nikpassand@iaurasht.ac.ir
2239

J. Chil. Chem. Soc., 58, Nº 4 (2013)
6-((4-nitrophenyl)diazenyl)-2-oxo-2H-chromene-4-carbonitrile
3f
C16H8N4O4: C, 60.00; H, 2.52; N, 17.49; Found: C, 60.57; H, 2.43; N, 17.05.
(table 2, entry 6) brown solid, mp 274ºC dec. FT- IR (KBr) v: 3047, 2921,
2231 (CN), 1735 (C=O), 1610, 1562, 1463, 1182 Cm-1. 1H NMR (CDCl3, 400
MHz) dH = 7.57 (d, J = 8.8 Hz, 1H), 7.71 (d, J = 8.6 Hz, 2H), 7.94 (d, J = 8.4Hz,
2H), 8.19 (d, J = 2.0 Hz, 1H), 8.32 (dd, J = 8.8 Hz, J = 2.2 Hz), 8.40 (s, 1H)
ppm. 13C NMR (DMSO- d6, 100 MHz) dC = 107.23, 116.76, 118.56, 126.99,
127.09, 128.34, 132.06, 132.56, 148.45, 152.14, 153.67, 156.56, 156.97,
167.87 ppm. Anal. Calcd. For C16H8N4O4: C, 60.00; H, 2.52; N, 17.49. Found:
C, 60.23; H, 2.59; N, 17.88.
6-((2-methyl-4-nitrophenyl)diazenyl)-2-oxo-2H-chromene-4-
carbonitrile 3g (table 2, entry 7) brown solid, mp 265ºC dec. FT- IR (KBr)
v : 3053, 2229 (CN), 1733 (C=O), 1610, 1519, 1429, 1178 Cm-1. 1H NMR
(CDCl3, 400 MHz) dH = 2.86 (s, 3H), 7.61 (d, J = 8.8 Hz, 1H), 7.78 (d, J = 8.8
Hz, 1H), 8.18 (dd, J = 8.8 Hz, J = 2.0 Hz, 1H), 8.25 (d, J = 2.0 Hz, 1H), 8.30 (d,
J = 2.0 Hz, 1H), 8.35 (dd, J = 8.8 Hz, J = 2.0 Hz), 8.44 (s, 1H) ppm. 13C NMR
(DMSO- d6, 100 MHz) dC = 15.52, 103.86, 114.84, 117.34, 118.87, 122.69,
126.90, 128.89, 132.08, 137.53, 139.76, 149.00, 149.19, 153.51, 156.60,
156.92, 162.88 ppm. Anal. Calcd. For C17H10N4O4: C, 61.08; H, 3.02; N, 16.76.
Found: C, 61.35; H, 3.46; N, 16.90.
6-((2-chlorophenyl)diazenyl)-2-oxo-2H-chromene-4-carbonitrile
3i
(table 2, entry 9) brown solid, mp 275ºC dec. FT-IR (KBr) ν: 3043, 2231
1
(C≡N), 1733 (C=O), 1610, 1566, 1463, 1178 cm-1 . H NMR (CDCl , 400
MHz) dH = 7.41 (t, J = 7.2 Hz, 1H), 7.50 (t, J = 7.6 Hz, 1H), 7.58 (d, J = 83.8 Hz,
1H), 7.63 (d, J = 8.0 Hz, 1H), 7.77 (d, J = 8.0 Hz, 1H), 8.23 (d, J = 1.6 Hz, 1H),
8.37 (dd, J = 8.8, 1.6 Hz), 8.44 (s, 1H) ppm. 13C NMR (DMSO- d6, 100 MHz)
d : 106.56, 115.87, 117.81, 118.08, 118.23, 125.67, 129.07, 130.98, 133.22,
1C37.45, 142.63, 148.46, 154.31, 156.63, 156.94, 165.75ppm. Anal. Calcd. For
C16H8ClN O2: C, 62.05; H, 2.60; N, 13.57; Found: C, 62.45; H, 2.24; N, 13.41.
6-((43-iodophenyl)diazenyl)-2-oxo-2H-chromene-4-carbonitrile
3j (table 2, entry 10) brown solid, mp 288ºC dec. FT-IR (KBr) ν: 3080,
1
2231(C≡N), 1735 (C=O), 1610, 1560, 1461, 1182 cm-1. H NMR (400 MHz,
CDCl3) d = 7.57 (d, J = 8.8 Hz, 1H), 7.77 (d, J = 8.8 Hz, 2H), 7.94 (d, J = 8.8
Hz, 2H), H8.19 (d, J = 2.2 Hz, 1H), 8.32 (dd, J = 8.8, 2.2 Hz, 1H), 8.40 (s, 1H)
ppm. 13C NMR (DMSO- d6, 100 MHz) dC = 100.33, 103.38, 114.85, 118.85,
124.99, 129.14, 132.16, 139.05, 148.81, 151.41, 153.65, 156.14, 156.97,
167.49 ppm. Anal. Calcd. For C16H8IN3O2: C, 47.90; H, 2.01; N, 10.47; Found:
C, 47.57; H, 2.78; N, 10.23.
6-((2-nitrophenyl)diazenyl)-2-oxo-2H-chromene-4-carbonitrile
3h
(table 2, entry 8) brown solid, mp 265ºC dec. FT-IR (KBr) v: 3040, 2233,
RESULTS AND DISCUSSION
1
1731, 1608, 1566, 1461, 1178 Cm-1. H NMR (CDCl , 400 MHz) d = 7.42
(t, J = 8.0 Hz, 1H), 7.50 (t, J = 6.8 Hz, 1H), 7.59 (d, 3J = 8.9 Hz), 7H.64 (d, J
= 7.6 Hz, 1H), 7.77 (d, J = 2.0 Hz, 1H), 8.23 (d, J = 1.8 Hz, 1H), 8.38 (dd,
J = 8.9, J = 1.8 Hz), 8.44 (s, 1H) ppm. 13C NMR (DMSO- d6, 100 MHz)
d = 103.84, 114.76, 118.12, 118.68, 118.87, 125.56, 128.79, 131.38, 133.82,
1C34.79, 142.08, 149.04153.68, 156.36, 156.94, 165.98ppm. Anal. Calcd. For
In continuation of our studies on the synthesis of pharmaceutical and
heterocyclic compound 21-23, herein, we wish to report our preliminary efforts
for the synthesis of new azo containing coumarin moiety from synthesized
aldehydes and malononitrile using TCT under (i) reflux condition and (ii)
ultrasound irradiation and in electrophilic substitution reaction (Scheme 1).
Scheme1. Aqueous synthesis of coumarins using TCT.
Table 1. The optimization of amount of catalyst for the synthesis of 3a
at reflux.
Recently organic reactions in water without use of harmful organic
solvent have drawn much more attention, because water is a cheap, safe
and environmentally benign solvent. So, we prefer to use water as a green
solvent in this reaction. Initially, we carried out the reaction of 2-hydroxy-
5-(phenyldiazenyl)benzaldehyde (1a) and malononitrile (2) in the presence
of various amount of TCT at reflux condition. The results are summarized in
Table 1.
Amount of
catalyst
Time
(min)
Entry
catalyst
Yield(%)
1
2
3
4
none
TCT
TCT
TCT
none
240
75
57
67
76
74
0.1mmol
0.3mmol
0.5mmol
60
60
Based on the results above, the reaction condition was optimized to
improve the yield and reaction time by changing the amount of catalyst. As
shown in table 1, when the reaction was performed in the absence of catalyst,
57% yield of product was observed in 4 hours (entry 1, Table 1). However,
2240

J. Chil. Chem. Soc., 58, Nº 4 (2013)
a green and effective procedure to reach higher yield, shorter reaction time and
milder reaction condition, we concentrated to synthesize product 3a-j under
ultrasound irradiation. The results were summarized in Table 2. The higher
yield and less reaction time during ultrasonic irradiation in the presence of the
catalyst can be attributed to implosive collapse of the cavitations period of the
sound waves. When the formed bubbles burst, it results in high temperature and
high pressure which facilitate the intermolecular reaction. This is more useful
when the solid act as a catalyst.
The possible mechanism for the synthesis of 3a in the presence of TCT as a
promoter is shown in Scheme 2. On the basis of this mechanism, TCT catalyzes
the Pechman reaction by the activation of the aldehyde, making the carbonyl
group susceptible to nucleophilic attack by malononitrile by conversion to HCl
in situ. The intramolecular treatment of OH to nitrile group and hydrolysis of
intermediate 7 lead to product 3a.
when 0.3mmol of TCT was used, the yield was improved significantly (entry 3,
table 1). The reaction took much longer reaction time to give 3a when 0.1mmol
of TCT was involved as catalyst. Higher amount of catalyst did not further
improve the yield of 3a (entry4, Table 1).
To investigate the scope of this synthesis, different synthesized aldehydes
were reacted with malononitrile in the presence of 0.3mmol of TCT at reflux
condition and the results were listed in Table 2. The reaction preceded
smoothly giving 71-81% yield with various synthesized aldehydes bearing
different substituent. Moreover, azo linked aldehydes containing electron
withdrawing group provided better yields and times than those with electron
donating groups.
Ultrasound irradiation has been increasingly used in organic synthesis in
last three decades. Comparing with traditional methods, this method is more
conveniently and easily controlled. In the course of our investigation to develop
Table 2. Perkin synthesis of azo conjugated comarins 3a-j.
reflux
ultrasound
ultrasound
Time (min)
Yield (%)a
Time (min)
Yield (%)a
Time (min)
Yield (%)ab
1
2
3a
3b
3c
3d
3e
3f
60
75
75
60
60
45
75
75
75
60
76
73
79
75
80
81
77
71
75
80
7
9
8
5
5
5
7
8
7
5
89
92
90
95
96
98
86
88
87
96
12
15
10
8
87
90
90
94
97
95
82
86
88
97
3
4
5
7
6
9
7
3g
3h
3i
13
10
10
9
8
9
10
3j
a Isolated yield. b Identified by spectroscopic analysis (IR, 1H NMR, 13C NMR and elemental analysis)
All of the products were fully characterized by spectroscopic methods (IR
and 1H NMR, 13C NMR and elemental analysis). All of the products 3 exhib-
ited a singlet in their 1H NMR spectra at δ = 8.39 – 8.40 ppm for deshield Hβ
in coumarin ring and also a distinguishing peak at δ = 167 ppm for C=O in
their 13C NMR spectra. In IR spectra revealed C-O, N=N, CN and C=O peak at
1178-1182, 1566, 2225-2237 and 1731-1739 cm-1.
In the final research, we were interested to synthesize compound 3 via
electrophilic substitution. In this procedure, initially, the reaction between al-
dehyde and malononitrile was carried out, followed by drop-wise addition of
diazonium salt to synthesized coumarins under ultrasound irradiation. Various
derivatives of product 3 were synthesized in this pathway. The results are sum-
marized in table 2. It was interesting that the reaction time and yield in this new
pathway for the synthesis of azo containing coumarins were interesting as the
former pathway. On the other hand, this reaction in this new pathway can be
done at room temperature under ultrasound irradiation without any undesirable
by product.
ACKNOWLEDGEMENT
We thank the Research Committee of Islamic Azad University of Rasht
Branch for partial support given to this study.
CONCLUSION
TCT is an inexpensive, non corrosive and environmentally benign cata-
lyst. Finally, a convenient and efficient procedure for the preparation of azo
containing coumarins in high yield and short reaction time and mild condition
under ultrasound irradiation was reported. The electrophilic substitution reac-
tion reported in this work is mild and a wide range of functional groups can be
tolerated in the synthesis coumarins. In this pathway, the purification process is
much simplified. Generally, short reaction times and productivity, availability
of reactants, operational simplicity and easy workup are the notable advantages
of this methodology.
REFERENCES
1. Wulf, H. Rauer, H. During, T. Hanselmann, C. Ruff, K. Wrisch, A. Griss-
mer, S. Hansel,W. J. Med. Chem. 41, 4542, (1998).
2. Spino, C. Dodier, M. Sotheeswaren, S. Bioorg. Med. Chem. Lett. 8, 3475,
(1998).
3. Crow, F. W. Duholke, W. K. Farley, K. A. Hadden, C. E. Hahn D. A.
Scheme 2. Proposed pathway for the synthesis of azo containing coumarin.
2241

J. Chil. Chem. Soc., 58, Nº 4 (2013)
Kaluzny, B. D. Mallory, C. S. Martin, G. E. Smith, R. F. Thamann, T. J. J.
Heterocycl. Chem. 36, 365, (1999).
12. Jiao, C. Niu, C. Chen, L. Shen, G. Yu, R. Sens. Actuators B 94,176, (
2003).
4. Barker, W. M. Hermodson, M. A. Link. K. P. J. Med. Chem.14, 167,
(1971).
5. Cavettos, G. Nano, G. M. Palmisano, G. Tagliapietra, S. Tetrahedron: As-
ymmetry 12, 707, (2001).
6. Kayser, O. Kolodziej, H. Planta Med. 63, 508, (1997).
7. Wang, C. J. Hsieh, Y. J. Chu, C. Y. Lim, Y. L. Tseng, T. H. Cancer Lett.
183, 163, (2002).
8. Fan, G. J. Mar, W. Park, M. K. Choi, E. W. Kim, K. Kim, S. Bioorg. Med.
Chem. Lett. 11, 2361, (2001).
13. Mitsuya, M. Suzuki, T. Koyama, T. Appl. Phys. Lett. 77, 3272, (2000).
14. Adronov, A. Gilat, S. L. Frechet, J. M. J. Ohta, K. Neuwahl, F. V. R. Fle-
ming, G. R. J. Am. Chem. Soc.122, 1175, ( 2000).
15. Maeda, M. Laser Dyes, Academic Press, New York, 1984.
16. Sethna, S. M. Shah, N. M. Chem. Rev. 36, 1, (1945).
17. Murray, R. D. Mendez, J. Brown, S. A. The Natural Coumarins: Occurren-
ce, Chemistry and Biochemistry; John Wiley & Sons: New York, 1982.
18. Johnson. J. R. Org. React. 1, 210, (1942).
19. Jones, G. Org. React. 15, 204, (1967).
9. Kennedy, R. O. Thornes, R. D. Coumarins: Biology, Applications and
Mode of Action, John Wiley and Sons, Chichester, 1997.
10. Hara, K. Sayama, K. Ohga, Y. Shinpo, A. Suga, S. Arakawa, H. Chem.
Commun. 569, (2001).
20. Brafola, G; Fringuelli, F. Piermatti, O. Pizzo, F. Heterocycles 43, 1257,
(1996).
21. Nikpassand, M. Mamaghani M. Tabatabaeian, K. Kupaei Abiazi, M. Mol.
Diversity 389, (2009).
11. Hara, K. Tachibana, Y. Ohga, Y. Shinpo, A. Suga, S. Sayama, K.; Sugi-
hara, H. Arakawa, H. Sol. Energy Mater. Sol. Cells 77, 89, (2003).
22. Nikpassand, M. Zare, L. Shafaati, T. Chin. J. Chem. 30, 604, (2012).
23. Nikpassand, M. Zare, L. Saberi, M. Monatsh. Chem. 143, 289, (2012).
2242