Friedel-Crafts alkylation of indoles with nitroolefins in the presence of β-cyclodextrin in water under neutral conditions

Article abstract of DOI:10.1139/V08-118

Various indolyl nitroalkanes were prepared by the reaction of indoles with nitroolefins in the presence of β-cyclodextrin in water under neutral conditions. β-Cyclodextrin can be recovered and re-used several times without loss of activity.

Full text of DOI:10.1139/V08-118

907
Friedel–Crafts alkylation of indoles with
nitroolefins in the presence of β-cyclodextrin in
water under neutral conditions
Vydyula Pavan Kumar, Regati Sridhar, Boga Srinivas, Mendu Narender, and
Kakulapati Rama Rao
Abstract: Various indolyl nitroalkanes were prepared by the reaction of indoles with nitroolefins in the presence of β-
cyclodextrin in water under neutral conditions. β-Cyclodextrin can be recovered and re-used several times without loss
of activity.
Key words: β-cyclodextrin, nitroolefins, indoles, neutral conditions, water.
Résumé : On a préparé divers nitroalcanes d’indolyle par réaction d’indoles avec des nitrooléfines, en présence de cy-
clodextrine, dans des conditions aqueuses neutres. On peut récupérer la β-cyclodextrine et la réutiliser un certain
nombre de fois sans perte d’activité.
Mots-clés : β-cyclodextrine, nitrooléfines, indoles, conditions neutres, eau.
[Traduit par la Rédaction] Kumar et al. 911
Introduction
there are reports in aqueous media with Lewis-acid catalysts
(9), there are no reports under neutral conditions in water.
The fundamental problem in performing these reactions in
water is that many organic substrates are hydrophobic and
are insoluble in water. Therefore, we made an attempt at the
Friedel–Crafts synthesis of 3-substituted indoles in water
through supramolecular catalysis using β-cyclodextrin (β-
CD) under neutral conditions.
The choice towards cyclodextrins was dictated by the fact
that many interactions are dominated by hydrogen bonding
in organocatalysis. Recently, metal-free hydrogen-bonding
based catalysts have been put on a rational basis (10). Hy-
drogen-bonding motif is becoming a powerful tool in
organocatalysis for the activation of carbonyl groups and re-
lated compounds through weak hydrogen-bond interactions
(11). It is well-known that substituents of aromatic rings ca-
pable of hydrogen bonding can bind the OH groups of the
cyclodextrin edges (12). Cyclodextrins, which are cyclic oli-
gosaccharides, exert micro-environmental effects leading to
selective reactions (13). They catalyze reactions by supramo-
lecular catalysis through noncovalent bonding as seen in en-
zymes. Complexation depends on the size, shape, and
hydrophobicity of the guest molecules. These attractive fea-
tures of cyclodextrins and our earlier expertise in the
biomimetic modeling of chemical reactions (14) prompted
us to examine their utility in Friedel–Crafts reaction of
indoles with nitroolefins.
Indoles are present in many biologically active and natu-
rally occurring compounds (1) and are also important inter-
mediates for the synthesis of drugs and pharmaceuticals (2).
Many indole alkaloids were synthesized utilizing the in-
creased nucleophilic reactivity of the 3-position of the indole
ring (3). The addition of indoles to electron-deficient alkenes,
which in many respects is considered as Friedel–Crafts reac-
tion (4), is a reaction of considerable synthetic utility, and
the adducts resulting from the reaction are key intermediates
for the synthesis of many biologically active compounds (5).
However, the synthesis of 3-substituted indoles in the classi-
cal methodologies utilized indolylgrignard reagent (6),
whereas the later reports involved either acid or base cata-
lysts (7). These methods suffer from various disadvantages,
such as drastic reaction conditions, longer reaction times,
lower yields, and undesirable side products due to polymer-
ization (8). Thus, there is a need to develop mild and envi-
ronmentally benign Friedel–Crafts synthesis of these high
value 3-substitued indoles in water under neutral conditions
with a recyclable catalyst. The use of aqueous medium as
solvent under neutral conditions reduces the harmful effects
of organic solvents and also precludes the use of either acid
or base. This becomes further sophisticated if these reactions
can be performed under supramolecular catalysis. Though
Received 18 February 2008. Accepted 21 May 2008.
Published on the NRC Research Press Web site at
canjchem.nrc.ca on 5 August 2008.
Results and discussion
V. Pavan Kumar, R. Sridhar, B. Srinivas, M. Narender,
and K. Rama Rao.1 Organic Chemistry Division-I, Indian
Institute of Chemical Technology, Uppal Road, Hyderabad
500–007 India.
In general, the reactions were carried out by the in situ
formation of the β-CD complex of the indole in water fol-
lowed by the addition of nitroolefin and stirring for 1–3 h at
50 °C to give the corresponding products (Scheme 1).
Alkylated indoles were formed as single products with high
1Corresponding author (e-mail: drkrrao@yahoo.com).
Can. J. Chem. 86: 907–911 (2008)
doi:10.1139/V08-118
© 2008 NRC Canada

908
Can. J. Chem. Vol. 86, 2008
Scheme 1.
The evidence for this mechanistic approach (Fig. 1) was
deduced from H NMR spectroscopy. The studies were car-
1
ried out with indole (1a) and 2-((E)-2-nitrovinyl)furan (2b)
as representative examples. NMR spectroscopy is one of the
most important techniques used for the characterization of
inclusion complexes. The formation of an inclusion complex
results in the shift changes in the resonances of the host
cyclodextrin and the guest protons (16). A comparison of the
1H NMR spectra (D2O) of β-CD, β-CD : indole complex, and
freeze-dried reaction mixture of β-CD : indole complex with
the nitroolefin 2b at 1 h were studied. It is observed from
Fig. 2 that there is an upfield shift of H3 (0.03 ppm) and H5
(0.05 ppm) protons of cyclodextrin in the β-CD : indole
complex as compared with β-CD, indicating the formation of
an inclusion complex of indole with β-CD from the second-
ary side of cyclodextrin. It is further observed from the spec-
tra of the reaction mixture of β-CD : indole complex with
the nitroolefin 2b at 1 h that there is also an upfield shift of
H6 proton by 0.06 ppm. This indicates the complexation of
the nitroolefin 2b from the primary side of cyclodextrin for
the reaction to proceed (Fig. 2). This clearly demonstrates
that the nitroolefin is elegantly set for the addition reaction
with the indole in the hydrophobic microenvironment of β-
cyclodextrin cavity.
Thus, we have demonstrated for the first time an opera-
tionally simple and efficient aqueous phase Friedel–Crafts
synthesis of indolyl nitroalkanes and pyrrolyl nitroalkanes
by using β-cyclodextrin under neutral conditions. β-
Cyclodextrin, apart from being nontoxic is also considered
metabolically safe (17). In contrast with the existing meth-
odologies using many acidic and basic catalysts, this method
is very simple, high-yielding, and environment-friendly. Fur-
ther potential applications of this reaction are under study.
degree of conversion (Table 1). This methodology is also
compatible with various substituted indoles and
nitroolefines. Several examples illustrating this simple and
practical methodology are summarized in Table 1. All the
1
products were characterized by H NMR, IR, mass spectros-
copy, and elemental analysis. No asymmetric induction was
observed in these reactions. The catalyst β-CD can be easily
recovered and re-used. To see the further application of this
reaction, it was also extended to pyrrole heterocycle (Ta-
ble 1, entries 17 and 18).
The reaction also occurs at room temperature, but longer
reaction times (48 h) are required and the isolated yields of
products obtained are also low (1%–15%). All compounds
listed in Table 1 failed to react with nitroolefins in water at
50 °C without the presence of β-cyclodextrin. Use of a cata-
lytic amount of β-CD (0.1 mmol per mole of the substrate) at
50 °C had no impact on the reaction. These experiments in-
dicate the substantial role of cyclodextrin. However, the re-
action did not proceed when substituents such as bromo and
nitro were present in the 5-position of indole ring, whereas
the presence of other functionalities improved the reaction,
which explains the important role of electron density on
heterocycle. It is observed that the reaction did not proceed
with alkyl substituted nitroolefins such as ((E)-2-
nitrovinyl)cyclohexane and (E)-1-nitrobut-1-ene. The impor-
tance of this methodology can be seen in the case of 5-
hydroxy indole (Table 1, entries 9 and 10), which reacts with
nitroolefins in very good yields, whereas the reported meth-
odologies utilize either acidic or basic catalysts leading to
low yields even after prolonged reaction times because of
the interaction of the indolyl hydroxyl group with the cata-
lyst (4d, 7f).
Inclusion complexes of indole with β-cyclodextrin have
been studied by Galian et al. (15). In this model, it was pro-
posed that the indole is included in the β-cyclodextrin cavity
in such a way that the pyrrole moiety of indole ring is di-
rected towards primary face of β-cyclodextrin and a hydro-
gen bonding formed between indolic proton and oxygen of
the primary hydroxyl (C6–O) of β-cyclodextrin. This hydro-
gen bonding enhances the nucleophilicity of indole. Under
the present reaction conditions of supramolecular catalysis,
this type of positioning of indole in the cyclodextrin cavity
facilitates the complexation of nitroolefin from the primary
side, which can be activated by hydrogen bonding with C6–
OH of cyclodextrin for further reaction with indole. This is
depicted in Fig. 1. However, in the case of N-substituted
indoles (Table 1, substrates 1g and 1h), longer reaction times
are required, since the hydrogen bonding is not possible in
these cases. This clearly explains the importance of the pres-
ence of free indolic NH group.
Experimental
General
Melting points were recorded on a Buchi R-535 apparatus
and are uncorrected. IR spectra were recorded on a
1
PerkinElmer FTIR 240-c spectrometer using KBr optics. H
NMR spectra were recorded on Gemini-200 spectrometer in
DMSO using TMS as internal standard. Mass spectra were
recorded on an Agilent 1200 spectrometer. Starting materials
were obtained commercially from Aldrich, Lancaster and
were used without purification.
General procedure for the synthesis of indolyl
nitroalkanes and pyrrolyl nitroalkanes
β-CD (1 mmol) was dissolved in water (20 mL) by warm-
ing to 50 °C until a clear solution was formed. Then,
indole/pyrrole (1 mmol) dissolved in methanol (0.5 mL) was
added dropwise, followed by nitroolefin (1 mmol), and the
mixture was stirred at 50 °C until the reaction was complete
(as monitored by TLC) (Table 1). The mixture was extracted
with ethyl acetate, and the extract was filtered. The organic
layer was dried over anhyd. Na2SO4, the solvent was removed
under reduced pressure, and the resulting product was further
purified by column chromatography. The aqueous layer was
cooled to 5 °C to recover β-CD by filtration.
© 2008 NRC Canada

Kumar et al.
Table 1. Freidel–Crafts reaction of indoles and pyrrole with nitroolefins in the presence of β-CD in water at 50 °C.
909
Entry
Substrate
R1
R2
R3
R4
Nitroolefin
R5
Producta
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1a
1a
1b
1b
1c
1c
1d
1d
1e
1e
1f
1f
1g
1g
1h
1h
H
H
H
H
H
H
H
H
H
H
OH
OH
H
H
H
H
H
H
—
—
H
H
H
H
H
H
H
H
H
H
Et
Et
H
H
H
H
—
—
H
H
H
H
H
H
H
H
H
H
H
H
Me
Me
Bn
Bn
—
—
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
Ph
2–Furyl
Ph
2-Furyl
Ph
2-Furyl
Ph
2-Furyl
Ph
2-Furyl
Ph
2-Furyl
Ph
2-Furyl
Ph
3ac
3bc
3cc
3dd
3ed
3f
3.0
3.2
2.1
2.4
2.5
3.0
2.4
2.5
3.4
3.5
2.2
2.4
5.3
5.5
6.2
6.3
3.3
3.4
88
86
92
93
90
89
85
86
91
90
93
94
82
84
81
80
89
92
Me
Me
Ph
Ph
COOH
COOH
H
H
H
H
H
H
H
H
—
—
3g
3h
3id
3j
3k
3l
3mc
3nc
3oe
3pe
3qc
3rc
2-Furyl
Ph
2-Furyl
Pyrrole
Pyrrole
1
aAll the products were characterized by H NMR, IR, and mass spectroscopy.
bIsolated yields after purification.
cRef. 7g.
dRef. 9b.
eRef. 7h.
1
Fig. 1.
Fig. 2. H NMR spectra of (a) β-CD, (b) β-CD : indole complex,
and (c) reaction mixture after 1 h. The spectra were obtained in
D2O at 25 °C.
Characterization data for new compounds
3-(1-(Furan-2-yl)-2-nitroethyl)-2-phenyl-1H-indole (3f)
Light yellow solid; mp 125–127 °C. IR: 3429, 3057,
1
2924, 1456 cm–1. H NMR (CDCl3, 300 MHz) δ: 8.13 (s,
1H), 7.59–7.04 (m, 10H), 6.35–6.27 (m, 1H), 6.14 (d, 1H, J
= 3.21 Hz), 5.35 (t, 1H, J = 7.74 Hz), 5.22 (dd, 1H, J =
12.46, 7.55 Hz), 4.93 (dd, 1H, J = 12.46, 7.93 Hz). 13C
NMR (CDCl3, 75 MHz) δ: 152.58, 142.16, 136.98, 135.97,
131.90, 129.08, 128.73, 126.72, 122.59, 120.25, 119.82,
111.32, 110.46, 107.37, 107.31, 77.12, 35.48. ESI-MS m/z:
333 (M + 1). Anal. calcd. for C20H16N2O3: C, 72.28; H,
4.85; N, 8.43. Found: C, 72.02; H, 4.98; N, 8.56.
C17H14N2O4: C, 65.80; H, 4.55; N, 9.03. Found: C, 66.04; H,
4.43; N, 9.12.
3-(1-(Furan-2-yl)-2-nitroethyl)-1H-indole-2-carboxylic
acid (3h)
Brown solid; mp 201–203 °C. IR: 3506, 2972, 1574 cm–1.
1H NMR (CDCl3 + DMSO-d6, 200MHz) δ: 11.44 (b s, 1H),
7.65–6.84 (m, 5H), 6.39–6.06 (m, 3H), 5.27 (dd, 1H, J =
12.50, 8.59 Hz), 5.02 (dd, 1H, J = 13.28, 7.03 Hz). 13C
NMR (CDCl3 + DMSO-d6, 75 MHz) δ: 168.16, 157.41,
146.52, 141.19, 130.93, 129.84, 129.67, 125.66, 125.10,
121.53, 117.76, 115.38, 111.79, 81.81, 39.48. ESI-MS m/z:
301 (M + 1). Anal. calcd. for C15H12N2O5: C, 60.0; H, 4.03;
N, 9.33. Found: C, 60.23; H, 4.11; N, 9.24.
3-(2-Nitro-1-phenylethyl)-1H-indole-2-carboxylic acid (3g)
White solid; mp 198–200 °C. IR: 3367, 2961, 1556 cm–1.
1H NMR (CDCl3 + DMSO-d6, 200 MHz) δ: 11.15 (s, 1H),
7.53–7.07 (m, 8H), 6.96 (t, 1H, J = 7.32 Hz), 6.08 (t, 1H, J
= 8.05 Hz), 5.47–5.12 (m, 2H). 13C NMR (CDCl3 + DMSO-
d6, 75 MHz) δ: 168.43, 156.72, 146.14, 141.83, 132.52,
130.65, 128.31, 125.64, 122.84, 122.31, 121.74, 121.43,
120.58, 80.74, 41.27. EI-MS m/z: 310 (M+). Anal. calcd. for
© 2008 NRC Canada

910
Can. J. Chem. Vol. 86, 2008
A. Giuliani, E. Marcantoni, L. Sambri, and E. Torregiani. J.
Org. Chem. 68, 4594 (2003).
3-(1-(Furan-2-yl)-2-nitroethyl)-1H-indol-5-ol (3j)
1
Oil. IR: 3419, 1550 cm–1. H NMR (CDCl3, 200MHz) δ:
10.18 (s, 1H), 7.21–6.95 (m, 2H), 6.88–6.80 (m, 1H), 6.76–
6.59 (m, 2H), 6.32–6.22 (m, 1H), 6.13 (d, 1H, J = 2.94 Hz),
5.16–4.78 (m, 3H). 13C NMR (CDCl3, 75 MHz) δ: 150.62,
141.04, 131.04, 126.19, 123.40, 113.62, 112.27, 112.0,
110.18, 109.47, 106.87, 102.43, 77.23, 35.57. ESI-MS m/z:
273 (M + 1). Anal. calcd. for C14H12N2O4: C, 61.76; H,
4.44; N, 10.29. Found: C, 61.51; H, 4.57; N, 10.17.
5. (a) H. Harada, Y. Hirokawa, K. Suzuki, Y. Hiyama, M. Oue,
H. Kawashima, H. Kato, N. Yoshida, Y. Furutani, and S. Kato.
Chem. Pharm. Bull. 53, 184 (2005); (b) E.D. Cox, H. Diaz-
Arauzo, Q. Huang, M.S. Reddy, C. Ma, B. Harris,
R. McKernan, P. Skolnick, and J.M. Cook. J. Med. Chem. 41,
2537 (1998).
6. W.E. Noland, G.M. Christensen, G.L. Sauer, and
G.G.S. Dutton, J. Am. Chem. Soc. 77, 456 (1955).
7. (a) T. Koike, M. Hagiwara, N. Takeuchi, and S. Tobinaga.
Heterocycles, 45, 1271 (1997); (b) S. Mahboobi, W. Wiegrebe,
and A. Popp. J. Nat. Prod. 62, 577 (1999); (c) T. Koike,
N. Takeuchi, M. Hagiwara, K. Yamazaki, and S. Tobinaga.
Heterocycles, 51, 1271 (1999); (d) M. Bandini, M. Fagioli, and
A.U. Ronchi. Adv. Synth. Catal. 346, 545 (2004); (e) C. Lin,
J. Hsu, M.N.V. Sastry, H. Fang, Z. Tu, J.-T. Liu, and Y.C. Fa.
Tetrahedron, 61, 11751 (2005); (f) R. Ballini, R.R. Clemente,
A. Palmieri, and M. Petrini. Adv. Synth. Catal. 348, 191 (2006);
(g) L.-T. An, J.-P. Zou, L.-L. Zhang, and Y. Zhang. Tetrahedron
Lett., 48, 4297 (2007); (h) G. Srihari, M. Nagaraju, and
M. M. Murthy. Synth. Commun. 38, 100 (2008).
7-Ethyl-3-(2-nitro-1-phenylethyl)-1H-indole (3k)
1
Oil. IR: 3422, 3058, 2965, 1550 cm–1. H NMR (CDCl3,
200 MHz) δ: 7.94 (b s, 1H), 7.41–7.17 (m, 6H), 7.06–6.87
(m, 3H), 5.25–4.77 (m, 3H), 2.83 (q, 2H, J = 7.39 Hz), 1.35
(t, 3H, J = 7.39 Hz). 13C NMR (CDCl3, 75 MHz) δ: 139.23,
135.36, 128.86, 127.74, 127.48, 126.77, 125.83, 121.23,
121.14, 120.23, 116.60, 114.83, 79.49, 41.63, 23.84. 13.68.
ESI-MS m/z: 295 (M + 1). Anal. calcd. for C18H18N2O2: C,
73.45; H, 6.16; N, 9.52. Found: C, 73.68; H, 6.29; N, 9.40.
7-Ethyl-3-(1-(furan-2-yl)-2-nitroethyl)-1H-indole (3l)
1
Oil. IR: 3417, 3018, 2929, 1552 cm–1. H NMR (CDCl3,
8. (a) M. Chakrabarty, R. Basak, and N. Ghosh. Tetrahedron Lett.
41, 8331 (2001); (b) I. Komoto and S. Kobayashi. Org. Lett. 4,
1115 (2002).
300 MHz) δ: 7.98 (b s, 1H), 7.39–7.31 (m, 2H), 7.08–6.95
(m, 3H), 6.29–6.24 (m, 1H), 6.13–6.09 (m, 1H), 5.19 (t, 1H,
J = 7.74 Hz), 4.99 (dd, 1H, J = 12.46, 7.93 Hz), 4.86 (dd,
1H, J = 12.46, 7.36 Hz), 2.81 (q, 2H, J = 7.74 Hz), 1.35 (t,
3H, J = 7.74 Hz). 13C NMR (CDCl3, 75 MHz) δ: 142.23,
140.56, 132.41, 129.71, 128.52, 123.47, 121.20, 120.43,
117.61, 116.46, 112.23, 107.36, 77.84, 35.81, 22.70, 13.73.
ESI-MS m/z: 285 (M + 1). Anal. calcd. for C16H16N2O3: C,
67.59; H, 5.67; N, 9.85. Found: C, 67.82; H, 5.78; N, 9.72.
9. (a) K. Manabe, N. Aoyama, and S. Kobayashi. Adv. Synth.
Catal. 343, 174 (2001); (b) M. Bandini, P. Melchiorre,
A. Melloni, and A. Umani-Ronchi. Synthesis, 1110 (2002);
(c) M. Bandini, P.G. Cozzi, M. Giacomini, P. Melchiorre,
S. Selva, and A. Umani-Ronchi. J. Org. Chem. 67, 3700
(2002); (d) H. Firouzabadi, N. Iranpoor, and F. Nowrouzi.
Chem. Commun. 789 (2005); (e) N. Azizi, F. Arynasab, and
M. R. Saidi. Org. Biomol. Chem. 4, 4275 (2006);
(f) R.S. Kumar and P.T. Perumal. J. Heterocycl. Chem. 43,
1383 (2006); (g) Y. Gu, C. Ogawa, and S. Kobayashi. Org.
Lett. 9, 175 (2007).
10. (a) P.R. Schreiner and A. Wittkopp. Org. Lett. 4, 217 (2002);
(b) A. Wittkopp and P. Schreiner. Chem. Eur. J. 9, 407 (2003);
(c) P.R. Schreiner. Chem. Soc. Rev. 32, 289 (2003);
(d) P.M. Pihko. Angew. Chem., Int. Ed. 43, 2062 (2004);
(e) C.S. Wilcox, E.-I. Kim, D. Romano. L.H. Kuo, A.L. Burt,
and D.P. Curran. Tetrahedron, 51, 621 (1995).
Acknowledgement
We thank Council of Scientific & Industrial Research
(CSIR), New Delhi, India, for fellowships to VPK, RS, BS,
and MN.
References
1. (a) R.J. Sunberg. The chemistry of indoles. Academic Press,
New York. 1969. p. 113; (b) L.G. Thomas. In Heterocyclic
chemistry. 3rd Ed. Vol. 11. Longman. England. 1997. Parts 1,
2, and 5.
2. (a) A. Kleeman, J. Engel, B. Kutscher, and D. Reichert. Phar-
maceutical substances. 4th Ed. Thieme, New York. 2001;
(b) J.F. Austin and D.W.C. MacMillan. J. Am. Chem. Soc.
124, 1172 (2002).
11. R.P. Herrera, V. Sgarzani, L. Bernardi, and A. Ricci. Angew.
Chem., Int. Ed. 44, 6576 (2005).
12. (a) G.G. Gaitano, P.R. Sainz-Rozas, J.R. Isasi, M. Sanchez, and
G. Tardajos. J. Phys. Chem. 108A, 392 (2004); (b) A. Sytnik
and C.D. Valle. J. Phys. Chem. 99, 13028 (1995); (c) T. Stalin
and N. Rajendiran. J. Photochem. Photobiol. A, 182, 137
(2006); (d) B. Manunza, S. Deiana, M. Pintora, and C. Gessa. J.
Mol. Graphics Mod. 15, 79 (1997).
3. (a) R.A. Moore, C. Cheuk, X.Q.G. Yang, G.M.L. Patterson,
R. Bonjoukalian, T.A. Smitka, J.S. Mynderse, R.S. Foster,
N.D. Jones, J.K. Skiartzendruber, and J.B. Deeter. J. Org.
Chem. 52, 1036 (1987); (b) R.L. Garnick, S.B. Levery, and
P.W. Le Quesne. J. Org. Chem. 43, 1226 (1978);
(c) R.E. Moore, C. Cheuk, and G.M.L. Patterson. J. Am.
Chem. Soc. 106, 6456 (1984).
4. (a) M. Bandini, A. Melloni, S. Tommasi, and A. Umani-
Ronchi. Synlett, 1199 (2005); (b) M. Bandini, M. Fagioli, and
A. Umani-Ronchi. Adv. Synth. Catal. 346, 545 (2004); (c) Z.-
P. Zhan and K. Lang. Synlett, 1551 (2005); (d) G. Bartoli,
M. Bosco, S. Giuli, A. Giuliani, L. Lucarelli, E. Marcantoni,
L. Sambri, and E. Torregiani. J. Org. Chem. 70, 1941 (2005);
(e) G. Bartoli, M. Bartolacci, M. Bosco, G. Foglia,
13. (a) V.B. Sheshanath and V.B. Sidhanath. Mini-Rev. Org.
Chem. 4, 231 (2007); (b) K. Liu, D. Haeussinger, and W.-
D. Woggon. Synlett, 14, 2298 (2007); (c) V. Ramamoorthy,
C. Meenakshi, S. Muthusubramanian, and S. Sivasubramanian.
J. Inclusion Phenom. Macrocyclic Chem. 36, 425 (2000).
14. (a) M. Narender, M.S. Reddy, V. Pavan Kumar, V.P. Reddy,
Y.V.D. Nageswar, and K.R. Rao. J. Org. Chem. 72, 1849
(2007); (b) K. Surendra, N.S. Krishnaveni, A. Mahesh, and
K.R. Rao. J. Org. Chem. 71, 2532 (2006); (c) N.S. Krishnaveni,
K. Surendra, and K.R. Rao. Chem. Commun. 669 (2005);
(d) K. Surendra, N.S. Krishnaveni, M.A. Reddy,
Y.V.D. Nageswar, and K.R. Rao. J. Org. Chem. 68, 2058 (2003).
15. R.E. Galian and A.V. Veglia. J. Photochem. Photobiol. A, 187,
356 (2007).
© 2008 NRC Canada

Kumar et al.
911
16. (a) S.-Y. Jia, Y.-Q. Hao, L.-N. Li, K. Chen, Y. Wu, J. Liu,
L. Wu, and Y.-H. Ding. Chem. Lett. 34, 1248 (2005);
(b) H.J. Schneider, F. Hacket, V. Rudiger, and H. Ikeda. Chem.
Rev. 98, 1755 (1998); (c) P.V. Demarco and A.L. Thakkar. J.
Chem. Soc. Chem. Commun. 2 (1970); (d) H. Yamamura,
Y. Yamada, R. Miyagi, K. Kano, S. Araki, and M. Kawai. J.
Inclusion Phenom. Macrocyclic Chem. 45, 211 (2003).
17. K. Uekama, F. Hirayama, and T. Irie. Chem. Rev. 98, 2045
(1998).
© 2008 NRC Canada