Syntheses of calix[4]pyrroles by amberlyst-15 catalyzed cyclocondensations of pyrrole with selected ketones

Article abstract of DOI:10.3390/12112458

A facile and efficient protocol is reported for the synthesis of calix[4]pyrroles and N-confused calix[4]pyrroles in moderate to excellent yields by reaction of dialkyl or cycloalkyl ketones with pyrrole catalyzed by reusable Amberlyst-15 under eco-friendly conditions.

Full text of DOI:10.3390/12112458

Molecules 2007, 12, 2458-2466
molecules
ISSN 1420-3049
© 2007 by MDPI
www.mdpi.org/molecules
Full Paper
Syntheses of Calix[4]Pyrroles by Amberlyst-15 Catalyzed
Cyclocondensations of Pyrrole with Selected Ketones
Shive Murat Singh Chauhan*, Bhaskar Garg and Tanuja Bisht
Bioorganic Research Laboratory, Department of Chemistry, University of Delhi, Delhi-110007, India;
Fax : (+91)-11-27666845
* Author to whom correspondence should be addressed. E-mail: smschauhan@chemistry.du.ac.in
Received: 1 October 2007; in revised form: 1 November 2007 / Accepted: 1 November 2007 /
Published: 9 November 2007
Abstract: A facile and efficient protocol is reported for the synthesis of calix[4]pyrroles
and N-confused calix[4]pyrroles in moderate to excellent yields by reaction of dialkyl or
cycloalkyl ketones with pyrrole catalyzed by reusable Amberlyst™-15 under eco-friendly
conditions.
Keywords: Calix[4]pyrrole; N-confused calix[4]pyrrole; Amberlyst™-15; Catalysis.
Introduction
The design and synthesis of receptors to recognize, sense and bind the anions is an important area
of supramolecular chemistry [1-5]. Calix[4]pyrroles are conformationally flexible macrocycles [6,7] of
significant importance due to their binding under different conditions with anions [8], neutral
substrates [9] and metal ions [10]. The complexation behavior of calix[4]pyrroles with anions and
cations has been widely studied using fluorescent [11], colorimetric [12] and electrochemical signaling
[13] devices. They find interesting applications as raw materials for transformation into novel
calix[4]pyridines and calix[4]pyridinopyrroles [14], as new solid supports capable of separating anion
mixtures [15], in optical recognition of organic vapors [16] and as biologically active species [17].
Porphyrinogens, bearing hydrogen atoms at meso positions, are key intermediates in biological and
chemical synthesis of porphyrins [18,19]. Various attempts have been made for the development of

Molecules 2007, 12
2459
milder methods for the synthesis of porphyrins [20-22], N-C isomerization [23, 24] and higher
homologues of porphyrins [25]. The meso-octamethylcalix[4]pyrrole 3a has been prepared by
condensation of pyrrole with acetone in the presence of aqueous hydrochloric acid or methanesulfonic
acid in methanol [26, 27]. The reaction of pyrrole and acetone in the presence of trifluoroacetic acid in
ethanol gave meso-octamethylcalix[4]pyrrole (3a) and the N-confused octamethylcalix[4]pyrrole (4b)
[28]. The reactions of pyrrole with dialkyl ketones in the presence of protic acids (HCl, H2SO4),
organic acids (CH3SO3H) and Lewis acids (BBr3 and BF3) have also been used in the synthesis of
calix[4]pyrroles [29-33]. The reaction of excess of pyrrole with dialkylketones in the presence of acid
gave 5,5-dialkyldipyrromethanes which on subsequent reaction with dialkylketones in the presence of
borontrifluoride-etherate formed strapped calix[4]pyrroles [34, 35]. These acids are considered
hazardous and corrosive and their removal from the reaction mixtures is difficult. Recently,
condensations in dichloromethane of pyrrole with dialkyl ketones in the presence of the molecular
sieve Al-MCM-41 and the zeolite HY afforded dipyrromethane, calix[4]pyrroles and other linear
products, but not the N-confused calix[4]pyrroles [36, 37].
Scheme 1.
R1 R2
R1 R2
H
2
18
12
18
2
4
N
1
1
19
19
20
3
20
3
7
17
16
17
16
NH
NH
24
HN
21
R2
R1
4
21
R1
R1
R2
R1
R2
R1
24
Amberlyst-15
DCM, rt
5
6
15
5
15
23
NH
22
HN
R2
22
HN
23
NH
R2
N
14
6
14
13
H
O
7
13
10
10
11
9
11
9
8
12
8
R1 R2
R1 R2
1
2
3
4
3a. R1 = R2 = CH3
4a. R1 = R2 = CH3
2a. R1 = R2 = CH3
3b. R1 = CH3, R2= C2H5
3c. R1 = R2 = C2H5
4b. R1 = CH3, R2= C2H5
2b. R1 = CH3, R2= C2H5
2c. R1 = R2 = C2H5
3d. R1-R2 = - (CH2)4 -
3e. R1-R2 = - (CH2)5 -
3f. R1-R2 = - (CH2)6 -
3g. R1-R2 = - (CH2)7 -
4d. R1-R2 = - (CH2)4 -
4e. R1-R2 = - (CH2)5 -
2d. R1-R2 = - (CH2)4 -
2e. R1-R2 = - (CH2)5 -
2f. R1-R2 = - (CH2)6 -
2g. R1-R2 = - (CH2)7 -
Amberlyst™-15 is an inexpensive and non-hazardous solid acid, useful as a catalyst. It can be
easily handled and is removed from reaction mixtures by simple filtration. In recent years
Amberlyst™-15 has been explored as a powerful catalyst for various organic transformations [38]. The
reaction of pyrrole with different aldehydes in dichloromethane in the presence of AmberlystTM-15
gave dipyrromethanes, which in the presence of excess aldehydes followed by oxidation with chloronil
[39] or DDQ [40] gave 5,10,15,20-tetraaryl porphyrins, whereas the reaction of pyrrole with aldehydes

Molecules 2007, 12
2460
in the absence of solvent followed by oxidation with DDQ gave 5,10,15-triarylcorroles [40]. Herein we
report an eco-friendly synthesis of calix[4]pyrroles and related products under mild reaction conditions
by the reaction between ketones and pyrrole catalyzed by Amberlyst™-15.
Results and Discussion
The reaction in dichoromethane of pyrrole (1) with acetone for 8 hrs in the presence of
Amberlyst™-15 (10 %, w/w) gave the calix[4]pyrrole 3a and the N-confused calix[4]pyrrole 4a in 83
and 14 % yield, respectively (Scheme 1, Table 1). On the other hand, an Amberlite™ IR-120 catalyzed
reaction of pyrrole with acetone afforded 3a and 4a in poorer yields (61.3 and 3.7 %). The same
reaction was examined using different solvents and the best yields were obtained in dichloromethane
(Table 1).
Table 1: Amberlyst™-15 catalyzed condensation of pyrrole and acetone in different solvents a.
Entry
Solvent
Isolated yield of 3a (%) Isolated yield of 4a (%)
1
2
3
4
5
6
7
8
EtOH (MeOH) [41]
CHCl3
75, (65 [28], 65 [41])
10, (26 [28], 15 [41])
65
8.6
C6H6
40
-
EtOAc
43
-
THF
60
-
DMF
33
-
Toluene
DCM
41
-
83, 77, 69 b , (70.3 [36])
14, 10, 5.8 b (0 [36])
a Reaction conditions: pyrrole (7.2 mmol) and acetone (7.2 mmol); solvent (10 mL); Amberlyst™-15
dried (10%, w/w); r.t.; 8 hrs; b Catalyst was reused over three runs.
This high yield formation of 3a and 4a in the presence of Amberlyst™-15 prompted us to examine
the reaction in dichloromethane of other ketones 3b-3g with pyrrole. The reaction products, yields and
physical data are given in Table 2.
Table 2: Reaction of different ketones (2a-2g) with pyrrole in DCM, catalyzed by Amberlyst™-15.
% yieldb/mp °C (lit. mp °C, [ref.])
%
Time
Conversion
Entry
2
Catalysta
(h)
3
4
of pyrrole
99.0
1
2
3
4
5
2a
Amberlyst™-15
8
12
83.0/295 (296 [27])
61.3/295 (296 [27])
78.0/144 (146 [42])
68.3 (71.1)c/222 (–)
79.7 /235 (236 [42])
83.5 (53.0 [43])/273
(271-272 [43])
14.0/ 185 (184 -185 [41])
3.7/185 (184 -185 [41])
9.0/121
2a Amberlite-IR-120
65.6
2b
2c
2d
Amberlyst™-15
Amberlyst™-15
Amberlyst™-15
10
87.0
48 (32)c
8
72.0
–
96.7
13.5 /198
11.3 (5.0 [43])/224
(223.2-223.6 [43])
6
2e
Amberlyst™-15
8
98.5
7
2f
Amberlyst™-15
Amberlyst™-15
60 (55)c
72 (64)c
33.0
24.9
30.2 (46.0)c/163 (–)
19.7 (40.0)c/223 (–)
–
–
8
2g
a
b
c
Amberlyst™-15, Amberlite™-IR-120 were dried before use; Isolated yields; Under reflux conditions in
absolute ethanol

Molecules 2007, 12
2461
Product Characterization
A strong N-H stretching peak appeared at 3450 cm-1 in the IR spectra of calix[4]pyrrole 3a in both
CHCl3 solution and KBr pellets. In the 1H-NMR spectrum of 3a a sharp singlet at δ 1.50 is assigned to
the eight bridge methyl groups, a doublet at δ 5.89 (J = 2.5 Hz) to the eight pyrrole ring β-protons and
a broad peak at δ 7.01 was assigned to the four N-H protons. The ratio of the integrated peak areas are
6:2:1, in agreement with the empirical formula and D4 symmetry of 3a. In the 1H-NMR spectrum of 4a
the appearance of a multiplet at δ 1.56-1.48 for the eight bridge methyl groups, signals at δ 6.30 and δ
5.50 corresponding to the α- and β-pyrrole hydrogens (1H each) of the 2,4-disubstituted pyrrole,
respectively, well apart from those of the 2,5-disubstituted pyrrole β-hydrogen atoms (δ 5.93-6.04, 6H)
and three broad peaks at δ 7.75 (1H), 7.41 (1H) and 7.26 (2H) for four N-H protons indicate the
reduction of symmetry as compared to 3a. Indeed, the higher polarity and non-zero dipole moment of
N-confused calix[4]pyrrole than calix[4]pyrrole have been attributed to this lower symmetry [50].
Calix[4]pyrrole 3a and N-confused calix[4]pyrrole 4a each gave a [M-H]- ion peak at 427.2860 and
427.2868, respectively, along with a peaks at 462.7863 and 462.7859 for the [M+Cl]- ion at 65V (cone
voltage) in negative ion ESI-MS. A detailed ESI-MS study of these macrocycles has been reported
recently [44]. The structures of calix[4]pyrroles 3a-3g and N-confused calix[4]pyrroles 4a, 4b, 4d and
4e were all confirmed by their physical and spectroscopic data (Tables 2, 3 and 4).
In the reactions of 2a, 2d and 2e with pyrrole, a third isomer (1-4 %) was also observed, but due to
small sample availability and poor solubility in organic solvents a detailed structural characterization
was not possible [28]. The reactions of cycloheptanone (2f) and cyclooctanone (2g) with pyrrole gave
the corresponding calix[4]pyrroles 3f and 3g in 30.2% and 19.7% yield at ambient temperature, but the
time required for the conversions was considered too long. By refluxing the reaction mixtures,
improved yields of 46.0 % (3f) and 40.0 % (3g) were obtained after shorter reaction times. In the
reactions of pyrrole with 2c, 2f and 2g, the corresponding N-confused calix[4]pyrroles could not be
isolated. This could be attributed to the steric hindrance encountered with these higher acyclic and
cyclic ketones. The C-2 and C-5 atoms are more reactive than the C-3 and C-4 positions in pyrrole,
hence the electrophilic reaction at C-2 and C-5 position of pyrrole with acetone in the presence of acid
gave calix[4]pyrrole in preference to N-confused calix[4]pyrrole [28, 43]. The data presented in Tables
1 and 2 indicates that Amberlyst™-15 is a more efficient and superior catalyst than other solid
catalysts for the formation of calix[4]pyrroles in DCM [36]. The recovered catalyst was recycled twice
with modest product yield loss being noted (Table 1). The catalytic activity of Amberlyst™-15 is
remarkable and it is environmentally benign. The ready commercial availability of this catalyst and its
superiority over the existing methods should make the present protocol an attractive addition to the
many conventional procedures.
Conclusions
A facile and efficient method has been developed for preparing a variety of calix[4]pyrroles and N-
confused calix[4]pyrroles in high yields by the reactions of various ketones with pyrrole in
dichloromethane in the presence of a catalytic amount of Amberlyst™-15.

Molecules 2007, 12
2462
Table 3: 1H-NMR and mass spectra of meso-octaalkyl and cycloalkyl calix[4]pyrroles 3a-3g.
Calix.
3a
1H-NMR spectra (298 K, δ = ppm)a
7.01 (4H, br s, NH), 5.89 (8H, d, J=2.5 Hz, β-pyrrole), 1.50 (24 H, s)
HRMS (ESI-MS)b
C28H36N4 [M-H]- : calcd :
427.2862, found : 427.2860.
3b
3c
3d
3e
3f
6.97 (4H, br s, NH), 5.80 (8H, d, J=2.5 Hz, β-pyrrole), 1.79-1.76 (8H, C32H44N4 [M-H]- : calcd :
q, -CH2-), 1.45-1.18 (12H, br s, CH3), 0.80-0.63 (12 H, t, CH3-)
7.05 (4H, br s, NH), 5.89 (8H, d, J=2.3 Hz, β-pyrrole), 1.79-1.57 C36H52N4 [M-H]- ; calcd :
(16H, q, -CH2-), 0.71-0.58 (24 H, t, CH3-) 539.4113, found : 539.4120.
7.03 (4H, br s, NH), 5.85 (8H, d, J=2.3 Hz, β-pyrrole), 2.21-2.00 C36H44N4 [M-H]- : calcd :
(16H, m), 1.68-1.44 (16H, m) 531.3488, found : 531.3486.
7.25 (4H, br s, NH), 5.89 (8H, d, J=2.5 Hz, β-pyrrole), 1.91-1.90 C40H52N4 [M-H]- : calcd :
(16H, m), 1.50-1.41 (24H, m), 587.4114, found : 587.4112.
6.88 (4H, br s, NH), 5.83 (8H, d, J=2.5 Hz, β-pyrrole), 2.01-1.94 C44H60N4 [M-H]- Calcd:
(16H, m), 1.72-1.52 (32H, m) 643.4817, Found: 643.4810.
6.99 (4H, br s, NH), 5.93 (8H, d, J=2.4 Hz, β-pyrrole), 1.97-1.95 C48H68N4 [M-H]- calcd :
(16H, m), 1.52-1.34 (32H, m), 1.23-1.21 (8H, m) 699.5443, Found : 699.5456.
483.3487, found : 483.3480.
3g
a
1
b
The H-NMR spectra of 3a-3g were in agreement with literature data [36]; The ESI-MS spectra were in
agreement with literature data [44].
Table 4: 1H-NMR and mass spectra of meso-octaalkyl and cycloalkyl N-confused calix[4]pyrroles 4a,
4b, 4d, 4e.
Calix. 1H-NMR spectra (298 K, δ = ppm)
HRMS (ESI-MS)
4a
4b
4d
4e
NH: 7.75 (1H, br), 7.41 (1H, br), 7.26 (2H, br); α-pyrrole: 6.30 C28H36N4 [M-H]- : calcd : 427.2862,
(1H, d, J= 2 Hz), β-pyrrole: 6.04 (2H, br), 5.97 (2H, br), 5.93 found : 427.2868
(2H, m), 5.50 (1H, br); 1.56-1.48 (24H, m) a
NH: 7.63 (1H, br), 7.53 (1H, br), 7.35 (2H, br); α-pyrrole: 6.40 C32H44N4 [M-H]- : calcd : 483.3487,
(1H, d, J= 2 Hz) ; β-pyrrole: 6.03 (2H, br), 5.88 (2H, br), 5.78 found : 483.3482.
(2H, m), 5.53 (1H, br); 1.92 (3H, s, -CH3), 1.83-1.12 (29H, m)
NH: 7.48 (1H, br), 7.29 (1H, br), 7.00 (2H, br); α-pyrrole: 6.42 C36H44N4 [M-H]- : calcd : 531.3488,
(1H, d, J=1.97 Hz); β-pyrrole: 6.00 (2H, br), 5.90 (2H, br), 5.88 found : 531.3480.
(2H, m), 5.58 (1H, br); 2.25-1.98 (16H, m), 1.50-1.20 (16H, m)
NH: 7.63 (1H, br), 7.44 (1H, br), 7.10 (2H, br); α-pyrrole: 6.42 C40H52N4 [M-H]- : calcd : 587.4114,
(1H, d, J= 1.98 Hz); β-pyrrole: 6.03 (2H, br), 5.97 (2H, br), 5.82 found : 587.4110.
(2H, m), 5.50 (1H, br); 2.70-2.10 (16H, m), 1.60-1.20 (24H, m)a
a 1H-NMR spectra of N-confused calix[4]pyrroles 4a and 4e are comparable to those reported in [43] and [28]
respectively.

Molecules 2007, 12
Experimental
General
2463
1
The infrared spectra (IR) were recorded on Perkin Elmer FT-1710 spectrophotometer. H-NMR
spectra were recorded in CDCl3 with TMS as internal standard on a Bruker Avance 300 MHz
spectrophotometer. ESI-MS spectra were recorded on KC ESI 455-TOF mass spectrometer
(Micromass, Manchester, UK). The starting materials such as pyrrole, ketones, Amberlyst™-15 and
Amberlite™ IR-120 were obtained from Acros USA. Pyrrole and ketones were distilled immediately
prior to use. The experimental operations were performed under ambient conditions. Neutral alumina
was used for all the chromatographic purifications.
Representative experimental procedure for the preparation of calix[4]pyrroles 3a-g and N-confused
calix[4]pyrroles 4a-g: synthesis of meso-octamethylcalix[4]pyrrole (3a) and N-confused octamethyl
calix[4]-pyrrole (4a)
Equimolar amount of pyrrole (0.5 mL, 7.2 mmol) and acetone (0.52 mL, 7.2 mmol) were taken up
in CH2Cl2 (5 mL). Dry Amberlyst™-15 (10% w/w) was added to the reaction mixture, which was
stirred at ambient temperature for the appropriate time (Table 2). The reaction progress was monitored
by thin layer chromatography (TLC). After the completion of reaction, the catalyst was removed by
filtration and washed thoroughly with CH2Cl2 to dissolve all the contents. The filtrate was concentrated
to give the crude product, which was subjected to column chromatography over neutral alumina
eluting with petroleum ether-chloroform (9:1, v/v) to afford pure meso-octamethylcalix[4]pyrrole (3a).
Further elution of the column with petroleum ether-chloroform (2:3, v/v) gave the N-confused isomer
of octametylcalix[4]pyrrole (4a). The above general method is used for the synthesis of different
calix[4]pyrroles 3b-3g and N-confused calix[4]pyrroles 4b, 4d and 4e.
Acknowledgements
The authors are thankful to the Department of Science and Technology (Govt. of India) for project
no. SR/S1/OC-54/2003 and the Council of Scientific and Industrial Research New Delhi for its
financial assistance.
References
1. Gale, P. A.; Sessler, J. L.; Král, V. Calixpyrroles. Chem. Commun. 1998, 1-8.
2. Suksai, C.; Tuntulani, T.; Chromogenic anion sensors. Chem. Soc. Rev., 2003, 32, 192–202.
3. Stibor, I.; Zlatuskova, P.; Chiral recognition of anions. Top. Curr. Chem. 2005, 255, 31-63.
4. Gale, P. A.; Quesada, R. Anion coordination and templated assembly: highlights from 2002-2004,
Coord. Chem. Rev. 2006, 250, 3219-3244.
5. Gale, P. A. Structural and molecular recognition studies with acyclic anion receptors. Acc. Chem.
Res. 2006, 39, 465-475.

Molecules 2007, 12
2464
6. Gale, P. A. Anion and ion-pair receptor chemistry: highlights from 2000 and 2001. Coord. Chem.
Rev. 2003, 240, 191-221.
7. Sessler, J. L.; Camiolo, S.; Gale, P. A. Pyrrolic and polypyrrolic anion binding agents. Coord.
Chem. Rev. 2003, 240, 17-55.
8. Gale, P. A.; Sessler, J. L.; Král, V.; Lynch, V. Calix[4]pyrroles: Old yet new anion-binding
agents. J. Am. Chem. Soc. 1996, 118, 5140-5141.
9. Allen, W. E.; Gale, P. A.; Brown, C. T.; Lynch, V. M.; Sessler, J. L. Binding of neutral substrates
by Calix[4]pyrroles. J. Am. Chem. Soc. 1996, 118, 12471-12472.
10. Bachmann, J.; Nocera, D. G. Multielectron redox chemistry of iron porphyrinogens J. Am. Chem.
Soc. 2005, 127, 4730-4743.
11. Miyaji, H.; Anzenbacher P.; Sessler, J. L.; Bleasdale E. R.; Gale P. A. Anthracene-linked
calix[4]pyrroles: fluorescent chemosensors for anions. Chem. Commun. 1999, 1723–1724.
12. Gale, P. A.; Twyman, L. J.; Handlin, C. I.; Sessler, J. L. A colourimetric calix[4]pyrrole–4-
nitrophenolate based anion sensor. Chem. Commun. 1999, 1851-1852.
13. Gale, P. A.; Hursthouse, M. B.; Light, M. E.; Sessler, J. L.; Warriner, C. N.; Zimmerman, R. S.
Ferrocene-substituted calix[4]pyrrole: a new electrochemical sensor for anions involving CH
anion hydrogen bonds. Tetrahedron Lett. 2001, 42, 6759-6762.
14. Král, V.; Gale, P. A.; Anzenbacher Jr. P.; Jursíková, K.; Lynch, V.; Sessler J. L.; Anzenbacher Jr.
P. Calix[4]pyridine: a new arrival in the heterocalixarene family. Chem. Commun. 1998, 9 – 10.
15. He, L. J.; Cai, Q. S.; Shao, S. J.; Jiang, S. X. Effect of calix[4]pyrrole as addition reagent on anion
separation in capillary zone electrophoresis (CZE). Chin. Chem. Lett. 2001, 12, 511-512.
16. Conoci, S.; Palumbo, M.; Pignataro, B.; Rella, R.; Valli, L.; Vasapollo, G. Optical recognition of
organic vapors through ultra thin calix[4]pyrrole films. Colloid. Surf. A: Physicochem. Eng. Asp.
2002, 198-200, 869-873.
17. Sessler, J. L.; Allen, W. E. Anion carriers: New tools for crossing membranes. Chemtech 1999,
29, 16-24.
18. Floriani, C. The porphyrinogen-porphyrin relationship: the discovery of artificial porphyrins.
Chem. Commun. 1996, 1257-1263.
19. Battersby, A. R.; Leeper, F. J. Biosynthesis of the pigments of life: mechanistic studies on the
conversion of porphobilinogen to uroporphyrinogen III. Chem. Rev. 1990, 90, 1261-1274.
20. Chauhan, S. M. S.; Singh, R.; Gulati, A. Clay catalyzed synthesis of 5,10,15,20-tetrakis-(2,6-
dichlorophenyl)porphyrin and related compounds. Ind. J. Heterocycl. Chem. 2000, 9, 231-232.
21. Chauhan, S. M. S.; Sahoo, B. B.; Sriniwas, K. A. Microwave assisted synthesis of 5,10,15,20-
tetraarylporphyrins. Synth. Commun. 2001, 31, 33-37.
22. Ghosh, A. A perspective of one pot pyrrole-aldehyde condensation as versatile self-assembly
processes. Angew. Chem. Int. Ed. 2004, 43, 1918-1931.
23. Maeda, H.; Furuta, H.; A dozen years of N-confused: from synthesis to supramolecular chemistry.
Pure Appl. Chem. 2006, 78, 29-44.
24. Geier, G. R.; Haynes, D. M.; Lindsey, J. S. An efficient one-flask synthesis of N-confused
tetraphenylporphyrin. Org. Lett. 1999, 1, 1455-1458.
25. Chandrashekar, T. K.; Venkatraman, S. Core-modified expanded porphyrins: new generation
organic materials. Acc. Chem. Res. 2003, 36, 676-691.

Molecules 2007, 12
2465
26. Baeyer, A.; Ueber ein condensation product von Pyrrol mit Aceton. Ber. Dtsch. Chem. Ges. 1886,
19, 2184-2185.
27. Rothenmund, P.; Gage, C. L. Concerning the structure of acetonepyrrole. J. Am. Chem. Soc. 1955,
77, 3340-3341.
28. Depraetere, S.; Smet, M.; Dehaen, W. N-confused calix[4]pyrroles. Angew. Chem. Int. Ed. 1999,
38, 3359-3361.
29. Shao, S.; Wang, A.; Yang, M.; Jiang, S.; Xianda Yu. Synthesis of meso-aryl-substituted
calix[4]pyrroles. Synth. Commun. 2001, 31, 1421–1426.
30. Chen, Q.; Wang, T.; Zhang, Y.; Wang, Q.; Ma, J. Doubly n-confused calix[4]pyrrole prepared by
rational synthesis. Synth. Commun. 2002, 32, 1051–1058.
31. Wu, Y.; Wang, D.; Sessler, J. L.; Conformational features and anion binding properties of
calix[4]pyrroles: A theoretical study. J. Org. Chem. 2001, 66, 3739-3746.
32. Anzenbacher Jr., P.; Jursíková, K.; Lynch, V. M.; Gale, P. A.; Sessler, J. L. Calix[4]pyrroles
containing deep cavities and fixed walls. Synthesis, structural studies, and anion binding
properties of the isomeric products derived from the condensation of p-hydroxyacetophenone and
Pyrrole. J. Am. Chem. Soc. 1999, 121, 11020-11021.
33. Camiolo, S.; Gale, P. A. Fluoride recognition in super-extended cavity calix[4]pyrroles. Chem.
Commun. 2000, 1129 – 1130.
34. Miyaji, H.; Hong, S.; Jeong, D.; Yoon, D.; Na, H.; Hong, J.; Ham, S.; Sesseler, J. L.; Lee, C. A
binol-strapped Calix[4]pyrrole as a model chirogenic receptor for the enantioselective recognition
of carboxylate anions. Angew.Chem.Int.Ed. 2007, 46, 2508-2511.
35. Jeong, S.; Yoo, J. Na, H.; Chi, D.; Lee, C. Strapped-calix[4]pyrroles bearing acridine moiety.
Supramolecular Chemistry 2007, 19, 271-275.
36. Radha Kishan, M.; Srinivas, N.; Raghavan, K. V.; Kulkarni, S. J.; Sarma, J. A. R. P.; Vairamani,
M. A novel, shape-selective, zeolite-catalyzed synthesis of calix[4]pyrroles. Chem. Commun.
2001, 2226 – 2227.
37. Radha Kishan, M.; Radha Rani, V. ; Murty, M.R.V.S.; Sita Devi, P.; Kulkarni, S. J.; Raghavan,
K.V. Synthesis of calixpyrroles and porphyrins over molecular sieve catalysts. J. Mol. Cat. A.
2004, 223, 263-267.
38. Harmer, M.A. Industrial processes using solid acid catalysts, in Handbook of Green Chemistry
and Technology; Clark, J. H.; Macquarris, D. J.; eds.; Blackwell Publishers: London, 2002; pp.
86-117.
39. Naik, R.; Joshi, P.; Kaiwar, S. P.; Deshpande, R. K. Facile synthesis of meso-substituted
dipyrromethanes and porphyrins using cation exchange resins. Tetrahedron, 2003, 59, 2207-2213.
40. Kumari, P. Synthesis of metallocorroles and their use in the oxidation of selected hydrocarbons.
Ph.D. Thesis, University of Delhi, 2007; Chapter 2, pp. 55-104.
41. Nishibayu, R.; Palacios, M. A.; Dehaen, W.; Anzenbacher, P. Jr. Synthesis, structure, anion
binding and sensing by calix[4]pyrrole isomers. J. Am. Chem. Soc. 2006, 128, 11496-11504.
42. Dey, S.; Pal, K.; Sarkar, S. An efficient and eco-friendly protocol to synthesize calix[4]pyrroles.
Tetrahedron Lett. 2006, 47, 5851-5854.
43. Anzenbacher Jr., P.; Nishibayu, R.; Palacios, M. A. N-confused calix[4]pyrrole. Coord. Chem.
Rev. 2006, 250, 2929-2938.

Molecules 2007, 12
2466
44. Bhaskar, G.; Prabhakar, S.; Ramanjaneyulu, G. S.; Vairamani, M.; Srinivasu, V. N. V.; Srinivas,
K. Mass spectral studies of meso-dialkyl, alkyl aryl and cycloalkyl calix[4]pyrroles under positive
and negative ion electrospray ionization conditions. J. Mass Spectrom. 2007, 42, 1194-1206.
Sample Availability: Limited samples of compounds 3a and 3e are available from the corresponding
author.
© 2007 by MDPI (http://www.mdpi.org). Reproduction is permitted for noncommercial purposes.