ZrOCl2·8H2O as a highly efficient, eco-friendly and recyclable Lewis acid catalyst for one-pot synthesis of N-substituted pyrroles under solvent-free conditions at room temperature

Article abstract of DOI:10.1002/aoc.1806

A new and efficient method for the synthesis of a variety of N-substituted pyrroles from condensation reactions of 2,5-hexanedione with amines or diamines using ZrOCl₂·8H₂O as a water-tolerant Lewis acid catalyst at room temperature is described.The use of nontoxic, inexpensive, easily available and reusable catalyst under solvent-free conditions make this protocol practical, environmentally friendly and economically attractive.

Full text of DOI:10.1002/aoc.1806

Full Paper
Received: 9 January 2011
Revised: 19 March 2011
Accepted: 7 April 2011
Published online in Wiley Online Library: 1 June 2011
(wileyonlinelibrary.com) DOI 10.1002/aoc.1806
ZrOCl2·8H2O as a highly efficient, eco-friendly
and recyclable Lewis acid catalyst for one-pot
synthesis of N-substituted pyrroles under
solvent-free conditions at room temperature
Ali Rahmatpour∗
A new and efficient method for the synthesis of a variety of N-substituted pyrroles from condensation reactions of 2,5-
hexanedione with amines or diamines using ZrOCl2·8H2O as a water-tolerant Lewis acid catalyst at room temperature is
described.The use of nontoxic, inexpensive, easily available and reusable catalyst under solvent-free conditions make this
c
protocol practical, environmentally friendly and economically attractive. Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Keywords: pyrroles; solventless reaction; ZrOCl2·8H2O; Paal–Knorr reaction; amine
Introduction
ity and simple work-up for the preparation of substituted pyrroles
by the Paal–Knorr condensation under neutral, mild and practical
conditions is of prime interest.
Pyrrole frameworks have attracted a plethora of research areas
owing to the broad applications as pharmaceutical agents,[1,2]
conducting polymers,[3] molecular optics,[4,5] electronics,[6] gas
sensors for organic compounds[7] and many physiologically inter-
esting natural products as building blocks, such as alkaloids.[8] In
particular,substitutedpyrrolespresentantibacterial,[9] antiviral,[10]
anti-inflammatory and antioxidant activities.[11] Owing to the mul-
tiple uses and varieties of biological activities, the synthesis of this
ring system has been the subject of intense investigation. The clas-
sical methods of constructing pyrrole ring systems include mainly
Hantzsch and Knorr or Paal–Knorr syntheses, which have been re-
ported in many research articles.[12–14] Among these methods, the
most reliable, commonly used and straightforward approach for
thepreparationofsubstitutedpyrrolederivativesisthePaal–Knorr
reaction, which consists the cyclocondensation of primary amines
with 1,4-dicarbonyl compounds and their masked equivalents. A
variety of acidic materials, such as zeolite,[15] Ti(OPri)4,[16] Al2O3,[17]
p-TSA,[18] H2SO4,[19] I2,[20] KSF, Fe+3-montmorillonite,[20] HCl,[21]
montmorillonite K10,[22] Sc(OTf)3,[23] Bi(NO3)3.5H2O,[24] RuCl3,[25]
InCl3,[26] SnCl2·2H2O,[27] layered zirconium phosphate and sul-
fophenyl phosphonate[28] and others[29] have been used to
promote these condensations. Additionally, the above cyclocon-
densationprocesscouldproceedinionicliquid[30] orultrasonicand
microwave irradiation.[31] However, despite the potential utility of
the aforementioned routes for the synthesis of substituted pyrrole
derivatives, some of them involve the use of excess amounts of
acids because they can be trapped by nitrogen in this condensa-
tion, or hazard organic solvents, tedious work-up leading to the
generationoflargeamountsoftoxicmetal-containingwaste, large
amounts of solid catalysts, and so they may not be the preferred
choices in view of the requirements of green chemistry. Moreover,
low yields, long reaction times, and the use of expensive reagents
are other disadvantages of some of the reported methods. There-
fore, to avoid these limitations, the discovery of a new and efficient
catalyst with high catalytic activity, short reaction time, recyclabil-
Lewis acid-catalyzed reactions receive great attention because
of their unique reactivity and selectivity, and the mild conditions
used.[32] Most zirconium (IV) compounds have relatively low
toxicity, are easy to handle, have low cost and possess good
stability. Zr4+ has a high charge-to-size ratio (Z2/r, 22.22 e2 m−10
)
and for this reason, zirconium (IV) compounds possess a high
coordinating ability that allows strong Lewis acid behavior and
high catalytic activity.[33] With increasing environmental concerns
and the need for efficient and green Lewis acid catalysts for
various useful organic transformations, the interest in zirconium
compounds has increased in the last decade. Among Zr (IV)
compounds, ZrOCl2·8H2O has been shown to be different from
traditional Lewis acids such as AlCl3, SnCl2 and BF3·OEt2, and is
also quite stable in water, nontoxic, reusable, readily available
and inexpensivem as well as highly effective in the case of many
nitrogen containing compounds such as nitriles and amines.[34]
ZrOCl2·8H2O is a oxysalt of Zr and its handling is easier in
comparison to that of the moisture-sensitive ZrCl4. In recent years,
several important organic transformations using this catalyst have
been reported in the literature.[35–41]
In continuation of our interest in the synthesis of organic
compounds from condensation of phenols with dialdehydes,
especially, 2,5-dimethoxytetrahydrofuran as a protected 1,4-
dicarbonyl compound,[42] and our ongoing research on the
application of heterogeneous solid acid catalysts for development
of useful synthetic methodology,[43] herein we wish to report an
efficient and eco-friendly method for the synthesis of pyrroles by
∗
Correspondenceto:Ali Rahmatpour,PolymerScienceandTechnologyDivision,
Research Institute of Petroleum Industry, 14665-1137 Tehran, Iran.
E-mail: rahmatpoura@ripi.ir
Polymer Science and Technology Division, Research Institute of Petroleum
Industry, 14665-1137 Tehran, Iran
c
Appl. Organometal. Chem. 2011, 25, 585–590
Copyright ꢀ 2011 John Wiley & Sons, Ltd.

A. Rahmatpour
O
O
Me
ZrOCl2.8H2O (2.5 mol%)
Solvent-free, r.t
Me
Me
H2NR
N
R +
2H2O
+
R= alkyl and aryl
Me
1
3
Scheme 1.
the condensation of 2,5-hexanedione with primary amines in the
presence of a catalytic amounts of ZrOCl2·8H2O as the catalyst
at ambient temperature under solvent-free conditions in good
to excellent yields with rather short reaction times (5–40 min;
Scheme 1).
Table 1. The condensation reaction of 2,5-hexanedione (2a) with
aniline (1a) under different reaction conditions at room temperature
Entry
Solventa
Time (min)
Yieldb (%)
1
CH2Cl2
35
35
45
35
40
35
6 h
30
25
15
15
70
69
2
CHCl3
3
THF
60
Experimental Section
4
CH3CN
73
5
CH3OH
62
Materials and Methods
6
EtOAc
68
All chemical reagents and ZrOCl2·8H2O were obtained from
Fluka and Merck Chemical Companies and were used without
further purification. Melting points were measured on an
Electrothermal 535 apparatus and were uncorrected. 1H, 13C
NMR spectra were recorded on a Bruker DPX-250 Avance
spectrometer at 250.13 MHz. IR spectra were recorded on a
Unicam Matteson 1000 spectrophotometer. Reaction monitoring
and purity determination of the products were accomplished by
TLC on silica gel polygram SILG/UV254 plates. All yields refer to
isolated products. Elemental analyses were performed using a
Heraeus CHN-O-Rapid analyzer by RIPI and the results agreed
favorably with calculated values.
7
None (no catalyst)
None (ZrOCl2·8H2O, 1 mol%)
None (ZrOCl2·8H2O, 2 mol%)
None (ZrOCl2·8H2O, 2.5 mol%)
None (ZrOCl2·8H2O, 3.5 mol%)
Trace
79
8
9
86
10
11
93
93
a The reaction was carried out using 2.5 mol% of ZrOCl2·8H2O in 3 ml
of solvent at room temperature.
b Isolated yield.
we also studied the influence of the amount of ZrOCl2·8H2O on
the reaction yields. We found that the yield was not significantly
affected by adding different amounts of ZrOCl2·8H2O catalyst, and
excessive amount of catalyst did not increase the yield remarkably
(Table 1, entry 11). To illustrate the need for ZrOCl2·8H2O for this
condensation, we examined the model reaction in the absence
of catalyst. In this case the reaction did not proceed even after
6 h (Table 1, entry 7). Obviously, ZrOCl2·8H2O is an important
component of the reaction. In the light of this, subsequent
studies were carried out in the following optimized conditions:
with 2.5 mol% catalyst at room temperature in the absence
of solvent (Table 1). Owing to the good results obtained, we
applied the optimal protocol to a variety of amines and the
results are summarized in Table 2. As indicated in Table 2, in
all cases, the ZrOCl2O·8H2O-catalyzed Paal–Knorr condensation
reaction proceeded smoothly, completed within 5–40 min, gave
the corresponding pyrrole products in good to excellent yields,
and also avoided the problems associated with solvent use, such
as cost, handling, safety and pollution. Different kinds of aromatic
amines bearing either electron-donating (Table 2, entries 2–4
and 6) or electron-withdrawing (Table 2, entries 5 and7) groups on
aromaticringswereconvertedtothecorrespondingN-substituted
pyrroles in the presence of ZrOCl2·8H2O. Both cyclic and acyclic
aliphatic amines gave excellent yields of the desired pyrroles
(Table 2, entries 12 and 8–11). It is well known that aliphatic
amines possess a greater reactivity compared with aromatic
amines; thus aliphatic amines give higher yields or shorter reaction
times than are generally observed in other systems.[44] Moreover,
we also examined the reactivity of less nucleophilic aromatic
amines such as 1-aminonaphthalene with 2a in the presence of
General Synthetic Procedure for the Preparation
of N-Substituted Pyrroles
Toamixtureofamine1(1 mmol)and2,5-hexanedione2a(1 mmol)
was added ZrOCl2·8H2O (2.5 mol%). The mixture was stirred at
room temperature for the appropriate time according to Table 2.
The progress of the reaction was monitored by TLC (eluent: n-
hexane–ethyl acetate, 3 : 1). After completion of the reaction,
EtOAc (10 ml) was added. The mixture was filtered and the catalyst
was washed with EtOAc (10 ml). The filtrate was evaporated under
reduced pressure and the residue was purified by short silica gel
column or by recrystallization to afford the pure product. All the
pyrrole products are known compounds and were characterized
by IR and NMR spectroscopies data and their melting points, which
agreed with reported values.[20,24,26,29,30,45,46]
Results and Discussion
At the onset of this work, we investigated a variety of conditions
with the model reaction involving aniline 1a (1 mmol) and 2,5-
hexanedione 2a (1 mmol) using ZrOCl2·8H2O as catalyst to afford
the pyrrole product 3a. The results are summarized in Table 1.
The best results were obtained by carrying out the model reaction
at room temperature for 15 min with 2.5 mol% of ZrOCl2·8H2O
catalyst without any solvent, and the reaction in the different
solvents examined, such as CH2Cl2, CHCl3, THF, CH3OH, EtOAc,
and CH3CN, took longer times than in neat conditions. In addition,
c
wileyonlinelibrary.com/journal/aoc
Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 585–590

Catalyst for one-pot synthesis of N-substituted pyrroles
Table 2. ZrOCl2·8H2O-catalyzed synthesis of pyrroles under solvent-free conditionsa
Entry
Amine (1)
Product (3)
Time (min)
Yieldb (%)
Reference
1
2
C6H5NH2
3a
3b
3c
3d
3e
3f
15
15
15
10
30
10
15
5
93
92
91
95
87
95
93
97
96
97
97
96
[24, 26]
[24,26]
[24,30]
[24,26]
[24,26]
[24,30]
[24,26]
[24,29]
[24,26]
[30]
p-(CH3)C6H4NH2
o-(CH3)C6H4NH2
p-(OCH3)C6H4NH2
p-(NO2)C6H4NH2
p-(OH)C6H4NH2
p-(Cl)C6H4NH2
C6H5CH2NH2
3
4
5
6
7
3g
3h
3i
8
9
p-(OCH3)C6H4CH2NH2
CH3CH2CH2NH2
CH3(CH2)3NH2
8
10
11
12
3j
5
3k
3l
6
[30]
8
[30]
NH2
NH2
13
14
3m
3n
40
89
[23,24]
60
660
660
30
85
83
83
89
[20]
[20]
[24]
[23,29]
NH2
N
CH3
N
H3C
(CH2)2
N
CH3
H3C
15
NH2(CH2)2NH2
3o
6
96
[26,29]
CH3
H3C
(CH2)4
N
N
H3C
CH3
16
17
18
19
20
NH2(CH2)4NH2
3p
3q
3r
8
40
25
85
80
95
86
90
83
85
[26,29]
[45]
C6H5CONH2
p-(OCH3)C6H4CONH2
C6H5SO2NH2
[45]
3s
3t
[46]
p-(OCH3)C6H4SO2NH2
[46]
a Reaction conditions: amine (1,1 mmol); 2,5-hexanedione (2a,1 mmol); ZrOCl2·8H2O (2.5 mol%); room temperature; solvent-free.
b Isolated yield.
ZrOCl2·8H2O (Table 2, entry 13). The results show that this catalyst
provides higher yields in shorter reaction times in comparison
to the previously reported methods using I2,[20] montmorillonite
KSF[20] and Bi(NO3)2·5H2O[24] (Table 2, entry 13). That means that
a better yield was obtained in a shorter time. Furthermore, the
reactivity of heteroaromatic amine (2-aminopyridine, 1n) with
2a was studied (Table 2, entry 14) and it exhibited analogous
behavior to the aromatic and aliphatic amines. Next, to extend
the scope of the ZrOCl2·8H2O-catalyzed method of pyrrole
synthesis, we investigated the reaction of diamines with 2a
in the same conditions (Table 2, entries 15 and 16). In this
reaction, 2 equivalents of 2a were required in order to obtain
a complete conversion of diamines. When aliphatic diamines such
as ethylene diamine and butylene diamine were examined, the
corresponding bis-pyrrole products (3o,3p) were obtained in 96
and 95% yields, respectively. This method was also applicable to
primary aromatic amides and primary aromatic sulfonamides such
as benzamide, 4-methoxybenzamide and benzenesulfonamide,
4-methoxybenzenesulfonamide (Table 2, entries 17–20) under
identical reaction conditions to afford the corresponding N-acyl
pyrroles and N-sulfonyl pyrroles (3q,3r and 3s,3t) in good yields,
respectively.
To further extend the scope and utility of this ZrOCl2·8H2O-
catalyzed procedure of pyrrole formation, other substituted
diketones such as 1-phenylpentane-1,4-dione (2b) and 1,4-
diphenylbutane-1,4-dione (2c) were used. Under identical con-
ditions, formation of pyrroles (3u, 3v) was observed with 2b, 2c as
the diketone components (Scheme 2). However, the formation of
3r from 2c required longer time.
The reusability of the catalyst is important from the large-scale
synthesis and industrial points of view. Therefore, the recovery
and reusability of ZrOCl2·8H2O were examined. The catalyst can
be separated and reused after washing with CHCl3 and drying
at 70 ◦C. The reusability of the catalyst was investigated in the
c
Appl. Organometal. Chem. 2011, 25, 585–590
Copyright ꢀ 2011 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

A. Rahmatpour
Ph
N
O
O
Ph
Ph
Me
ZrOCl2.8H2O , rt
Solvent-free
2b
2c
3u , 89 %, 55 min
O
O
1a
+
Ph
N
Ph
Ph
3v , 84 %, 75 min
Scheme 2.
H2O molecules and release of ZrOCl2·8H2O for the next catalytic
cycle.
Table 3. Reusability of ZrOCl2·8H2O catalyst in the reaction of aniline
(1a) with 2,5-hexanedione (2a) under solvent-free conditions
Finally, to show the efficiency of ZrOCl2·8H2O in comparison
with previously reported procedures in the literature, Table 4
compares our method with some other catalysts used in the
synthesis of (3h, 3a) from benzyl amine, aniline (1h), (1a) and
2,5-hexanedione (2a) with respect to reaction times and yields of
obtained products. It is clear from the results shown in Table 4 that
condensation reactions for the synthesis of 1-benzyl-2,5-dimethyl
pyrrole (3h) and 1-phenyl-2,5-dimethyl pyrrole (3a) carried out
with ZrOCl2·8H2O require shorter reaction times and give higher
yields.
Run
Time (min)
Yielda (%)
1
2
3
4
5
15
15
15
15
15
93
92
92
91
90
a Isolated yield.
reaction of aniline with 2,5-hexanedione (entry 1, Table 2) using
2.5 mol% ZrOCl2·8H2O. The results illustrated in Table 3 show that
the catalyst can be used at least five times without any appreciable
loss in its activity.
The actual mechanism of the reaction is unclear. However, the
proposed mechanism for the formation of N-substituted pyrroles
in the presence of ZrOCl2·8H2O as a catalyst is shown in Scheme 3.
The 2,5-hexanedione (2a, carbonyl groups) is first activated by
Zr(IV) as a Lewis acid to give 4 and then the primary amine
attacks 4, affording intermediate 5. Cyclization and dehydration-
aromatization of 5 afford the final product together with the two
Conclusion
In summary, a new, simple catalytic protocol to synthesize N-
substituted pyrroles by condensation of amines or diamine with
2,5-hexanedioneusingZrOCl2·8H2Oundersolvent-freeconditions
at room temperature has been developed. The short reaction
times, simple experimental procedure and product isolation, wide
applicability, good to excellent yields, mild reaction conditions,
and use of nontoxic, noncorrosive, inexpensive and readily
available Lewis acid catalyst are important features of this new
method. Recovery and reuse of catalyst is also satisfactory,
ZrOCl2.8H2O
Me
RNH2
O
O
O
O
Me
Me
4
Me
2a
OH
Me
ZrOCl2.8H2O
..
N
O
Me
R
H
ZrOCl2.8H2O
H
H
5
+
2H2O Me
Me
OH
Me
N
R
HO
Me
N
R
Scheme 3.
c
wileyonlinelibrary.com/journal/aoc
Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 585–590

Catalyst for one-pot synthesis of N-substituted pyrroles
Table 4. Comparison of some other procedures with the present method for the synthesis of 3h and 3a from 1h, 1a and 2a
Entry
Catalyst (loading)
Media
Time
Product/yielda (%)
Reference
1
2
I2 (0.1 mmol, 0.025 g)
Bi (NO3)3·5H2O (1 mmol)
Sc (OTf)3
THF, r.t.
9 h
3h (89)
3h (95)
3h (94)
3h (84)
3h (90)
3h (90)
3h (84)
3h (95)
3h (78)
3h (97)
3a (93)
3a (78)
3a (72)
3a (34)
3a (96)
3a(85)
[20]
[24]
CH2Cl2, r.t.
10 h
3
Solvent-free, 30 ◦C
CH2Cl2
30 min
1 h
[23]
4
InBr3 (5 mol%)
[26]
5
In(OTf)3 (5 mol%)
Microwave
CH2Cl2
0.5 h
0.5 h
1h
[26]
6
Ether
[31]
7
p-TSA
C6H6/80 ◦C
CH2Cl2, r.t.
[18b]
[20]
8
Montmorillonite, KSF (1 g)
α-Zr(KPO4)2
10 h
9
Solvent-free
Solvent-free, r.t.
Solvent-free, r.t.
Solvent-free, r.t.
Solvent-free, r.t.
Solvent-free, r.t.
CH2Cl2, r.t.
2 h
[47]
10
11
12
13
14
15
16
ZrOCl2·8H2O (2.5 mol%)
ZrOCl2·8H2O (2.5 mol%)
Cu(OTf)2 (5 mol%)
Bi(OTf)3 (5 mol%)
CuCl2 (40 mol%)
5 min
15 min
30 min
25 min
25 min
600 min
5 h
Table 2
Table 2
[23]
[23]
[23]
Bi(NO3)3·5H2O (1 mmol)
Cationic exchange resin
(Dowex 50 w, 1.63 g)
[24]
H2O/130 ◦C
[48]
a Isolated yields. r.t., Room temperature.
which demonstrates the cost efficiency and green aspect of our
methodology.
[14] a) R. A. Jones, G. P. Been, The Chemistry of Pyrroles, 1990, Academic
Press: New York, Chapter 3; b) P. K. Chiu, M. P. Sammes, Tetrahedron
1990, 46, 3439.
[15] R. Sreekumar, R. Padmakumar, Synth. Commun. 1998, 28, 1661.
[16] S. X. Yu, P. W. Le Quesne, Tetrahedron Lett. 1995, 36, 205.
[17] a) F. Tfxier-Boullet, B. Klein, J. Hamelin, Synthesis 1986, 409; b)
K. Kidwai, K. Singhal, S. Rastogi, J. Heterocycl. Chem. 2006, 43, 1231.
[18] a)S. Raghavan, K. Anuradha, Synlett 2003, 711;b)X. H. Zhu, G. Chen,
Z. L. Xu, ChinYouji Hauaxue 2008, 28, 115.
Acknowledgment
The author is grateful to RIPI for performing the elemental analysis.
[19] S. E. Drewes, C. J. Hogan, Synth. Commun. 1989, 19, 2101.
[20] B. K. Banik, S. Samajdar, I. Banik, J. Org. Chem. 2004, 69, 213.
[21] D. J. Shaw, W. F. Wood, J. Chem. Edu. 1992, 69, A313.
[22] a) S. Samajdar, F. F. Becker, B. K. Banik, Heterocycles 2001, 55, 1019;
b) M. Abid, A. Spaeth, B. To¨ro¨k, Adv. Synth. Catal. 2006, 348, 2191.
[23] J. Chen, H. Wu, Z. Zheng, C. Jin, X. Zhang, W. Su, Tetrahedron Lett.
2006, 47, 5383.
[24] B. K. Banik, I. Banik, M. Renteria, S. K. Dasgupta, Tetrahedron Lett.
2004, 45, 3417.
[25] K. De, K. Surya, Catal. Lett. 2008, 124, 174.
[26] J. X. Chen, M. C. Liu, X. L. Yang, J. C. Ding, H. Y. Wu, J.Braz.Chem.Soc.
2008, 19, 34.
[27] P. Armugam, P.T. Perumal, Chem. Lett. 2006, 35, 632.
[28] M. Curini, F. Montanari, O. Rosati, E. Lioy, R. Margarita, Tetrahedron
Lett. 2003, 44, 3923.
[29] a) H. Veisi, Tetrahedron Lett. 2010, 51, 2109; b) H. Luo, Y. Kang, Q. Li,
L. Yang, Heteroatom Chem. 2008, 19, 144.
[30] B. Wang, Y. Gu, C. Luo, T. Yang, L. Yang, J. Suo, Tetrahedron Lett.
2004, 45, 5873.
[31] a) H. S. P. Rao, S. Jothilingam, H. W. Scheeren, Tetrahedron 2004, 60,
1625; b) Z. H. Zhang, J. J. Li, T. S. Li, Ultrasonics Sonochemistry 2008,
15, 673; c) T. N. Danks, Tetrahedron Lett. 1999, 40, 3975.
[32] S. Kobayashi, K. Manabe, Pure Appl. Chem. 2000, 72, 1373.
[33] A. K. Chakraborti, R. Gulhane, Synlet 2004, 627.
[34] a) V. Mirkhani, I. Mohammadpoor-Baltork, M. Moghadam, S.
Tangestaninejad, M. S. Abdollahi-Alibeik, H. Kargar, Appl. Catal.
References
[1] a) M. V. Raimondi, S. Cascioferro, D. Schillaci, S. Petruso, Eur. J. Med.
Chem. 2006, 41, 1439; b) C. Rochais, V. Lisowski, P. Dallemagne,
S. Rault, Biorg. Med. Chem. 2006, 14, 8162.
[2] a) D. Lee, T. M. Swager, J. Am. Chem. Soc. 2003, 125, 6870; b)
J. V. Cooney, W. E. Mcewen, J. Org. Chem. 1981, 46, 2570.
[3] a) S. J. Higgins, J. Chem. Soc. Rev. 1997, 26, 247; b) C.-F. Lee, L.-
M. Yang, T.-Y. Hwu, A.-S. Feng, J.-C. Tseng, T.-Y. Luh, J. Am. Chem.
Soc. 2000, 122, 4992.
[4] a) R. E. Nizurski-Mann, M. P. Cava, Heterocycles 1992, 34, 2003; b)
S.-S. P. Chou, Y. H. Yeh, Tetrahedron Lett. 2001, 42, 1309.
[5] a) R. M. F. Batista, S. P. G. Costa, E. L. Malheiro, M. Belsley,
M. M. M. Raposo, Tetrahedron 2007, 63, 4258; b) M. M. M. Raposo,
M. R. C. Sousa, G. Kirsch, P. Cardoso, M. Belsley, E. M. Gomes,
A. M. C. Fonseca, Org. Lett. 2006, 8, 3681.
[6] C. D. Silva, D. A. Walker, J. Org. Chem. 1998, 63, 6715.
[7] B. P. J. De Lacy Costello, N. Guemion, N. M. Ratcliffe, P. S. Sivanand,
G. C. Teare, Synth. Met. 2000, 114, 181.
[8] G. Casiraghi, F. Zanardi, G. Rassu, L. Pinna, Org. Prep. Proced. Int.
1996, 28, 641.
[9] a) G. Dannhardt, W. Kiefer, G. Kramer, S. Maehrlein, U. Nowe,
B. Fiebich, J. Med. Chem. 2000, 35, 499; b) R. Ragno, G. R. Marshall,
R. D. Santo, R. Costi, S. Massa, R. Rompei, M. Artico, Bioorg. Med.
Chem. 2000, 8, 1423.
[10] Y. Harrak, G. Rosell, G. Daidone, S. Plescia, D. Schillaci, M. D. Pujol,
A
Gen. 2007, 325, 99; b) M. M. Hashemi, B. Eftekhari-Sis,
Bioorg. Med. Chem. 2007, 15, 4876.
[11] J. Lehuede, B. Fauconneau, L. Barrier, M. Ourakow, A. Piriou, J.-M.
Vierfonf, Eur. J. Med. Chem. 1999, 34, 991.
[12] a) A. Hantzsch, Ber.Dtsch.Chem.Ges. 1890, 23, 1474; b) V. F. Ferreira,
M. C. B. V. De Souza, A. C. Cunha, L. O. R. Pereira, M. L. G. Ferreira,
Org. Prep. Proced. Int. 2002, 33, 411.
[13] G. G. Kleinspehn, J. Am. Chem. Soc. 1955, 77, 1546; b) J. M. Hamby,
J. C. Hodges, Heterocycles 1993, 35, 843; c) A. Alberola, A. G. Ortega,
M. L. Sadaba, C. Sanudo, Tetrahedron 1999, 55, 6555; d) I. Elghamry,
Synth. Commun. 2002, 32, 897.
A. Abdollahifar, B. Khalili, Tetrahedron 2006, 62, 672.
[35] H. Firouzabadi, N. Iranpoor, M. Jafarpour, A. Ghaderi, J. Mol. Catal. A:
Chem. 2006, 252, 150.
[36] I. Mohammadpoor-Baltork, A. R. Khosropour, S. F. Hojati, Catal.
Commun. 2007, 8, 200; 2007, 8, 1865.
[37] R. Ghosh, S. Maiti, A. Chakraborty, Tetrahedron Lett. 2005, 46, 147.
[38] H.-Y. Lu, J.-J. Li, Z.-H. Zhang, Appl. Organometal. Chem. 2010, 23,
165.
[39] K. Mantri, K. Komura, Y. Sugi, Green Chem. 2005, 7, 677.
c
Appl. Organometal. Chem. 2011, 25, 585–590
Copyright ꢀ 2011 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

A. Rahmatpour
[40] A. R. S. Babu, R. Raghunathan, Tetrahedron Lett. 2007, 48, 305.
[41] W. Shen, L.-M. Wang, J.-J. Feng, H. Tian, Tetrahedron Lett. 2008, 49,
4047.
[42] a) A. Rahmatpour, J. Heterocycl. Chem. 2010, 47, 1011; b)
A. Rahmatpour, J. Chem. Res.(S) 2002, 2, 118; c) A. Rahmatpour,
A. Banihashemi, Tetrahedron 1999, 55, 7271.
[44] F. Texier-Boullet, B. Klein, J. Hamelin, Synthesis 1986, 409.
[45] A. R. Ekkati, D. K. Bates, Synthesis 2003, 1959.
[46] M. Abid, L. Texeira, B. Torok, Tetrahedron Lett. 2007, 4047.
[47] M. Curini, F. Montanari,O. Rosati, E. Lioy, R. Margarita, Tetrahedron
Lett. 2003, 44, 923.
[48] Y.-H. He, G.-Q. Wang, Z. Guan, J. Heterocycl. Chem. 2010, 47, 486.
[43] a) A. Rahmatpour, React. Funct. Polym, 2010, 70, 923; b)
A. Rahmatpour, Heteroatom Chem. 2011, 22, 51.
c
wileyonlinelibrary.com/journal/aoc
Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 585–590