Metal ion induced FRET On-Off in naphthyl-pyrenyl pendent tetrahomodioxacalix[4]arene

Article abstract of DOI:10.1016/j.tetlet.2009.02.083

A novel tetrahomodioxacalix[4]arene (7) bearing both naphthyl- and pyrenyl-amide pendants was synthesized as FRET-based fluorometric sensor for Cu²⁺ ion. Intramolecular FRET from the naphthalene emission to the pyrene absorption affords Cu

Full text of DOI:10.1016/j.tetlet.2009.02.083

Tetrahedron Letters 50 (2009) 2013–2016
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Metal ion induced FRET On–Off in naphthyl-pyrenyl pendent
tetrahomodioxacalix[4]arene
Ji Hee Jung a, Min Hee Lee a, Hyun Jung Kim a, Hyo Sung Jung a, Su Yeon Lee a,
a,
Na Ri Shin b, Kwanghyun No b, , Jong Seung Kim
*
*
a Department of Chemistry, Korea University, Seoul 136-701, Republic of Korea
b Department of Chemistry, Sookmyung Women’s University, Seoul 140-742, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel tetrahomodioxacalix[4]arene (7) bearing both naphthyl- and pyrenyl-amide pendants was syn-
thesized as FRET-based fluorometric sensor for Cu2+ ion. Intramolecular FRET from the naphthalene emis-
sion to the pyrene absorption affords Cu2+ ion selectivity over other metal ions. Upon addition of Cu2+ ion,
the complex solution of 7 gave a significantly decreased pyrene acceptor emission along with an
enhancement of naphthalene donor emission via FRET On–Off event.
Received 26 December 2008
Revised 10 February 2009
Accepted 12 February 2009
Available online 15 February 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
FRET
Fluorescence
Calixarenes
Homooxacalixarene
Copper
Many heavy and transition metal ions, such as Hg2+, Cu2+, Pb2+
,
step reaction starting from the bromination of p-tert-butylphenol.8
There have only been limited studies on the solution conforma-
tions, solid-state structures, and on complexation behavior of
homooxacalix[4]arenes.9–12 We also previously reported that there
are five conformations in tetrahomodioxacalix[4]arene with
appropriate nomenclature (cone, partial cone, C-1,2-alternate,
COC-1,2 alternate, and 1,3-alternate) as represented in Figure 1.13
Recently, we also reported a solid-state structure of C-1,2-alternate
N,N-diethyl tetrahomodioxacalix[4]arene tetraamide complexing
and Cd2+, have received considerable attention because of its wide-
spread use in agricultural, chemical and industrial processes,
which are becoming threats to living organisms.1 In particular,
Cu(II) is an essential element playing a fundamental role in the bio-
chemistry of the human nervous system, but is toxic with high
concentration.2 Thus, its accumulation in the human body affects
an oxidative stress and disorders associated with neurodegenera-
tive diseases, Menkes disease, Wilson disease, and Alzheimer’s dis-
ease.3 Therefore, development of the chemosensors specifically for
the Cu2+ has been greatly interesting in many fields.4
Many chemosensors were prepared by attachment of fluoro-
phore units to macrocyclic or chelating molecules. Among the
macrocyclic frameworks, a class of calix[4]arene is a good candi-
date for the chemosensor framework towards specific metal ion
because of their characteristic cavity size or geometrically re-
stricted conformation.5 However, homooxacalix[4]arenes, having
extra oxygen atoms in the macrocyclic ring, have received little
attention because they can only be synthesized in relatively low
yields.6–8 Tetrahomodioxa p-tert-butylcalix[4]arene was prepared
by Gutsche in 44% yield by dehydration of a bishydroxymethylated
dimer of p-tert-butylphenol, which was synthesized by a multi-
O
O
O
O
O
O
C-1,2-alternate
cone
partial cone
O
O
O
O
1,3-alternate
COC-1,2-alternate
* Corresponding authors. Tel.: +82 2 3290 3143; fax: +82 2 3290 3121 (J.S.K.).
E-mail addresses: hyun@sookmyung.ac.kr (K. No), jongskim@korea.ac.kr (J.S.
Kim).
Figure 1. Schematic representation of the five conformations of homooxacalix[4]-
arenes.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.02.083

2014
J. H. Jung et al. / Tetrahedron Letters 50 (2009) 2013–2016
Pb2+ proven by X-ray structure.14 For a corresponding monoalkyl
amide, the conformation changed to 1,3-alternate due to intramo-
lecular hydrogen bonding, resulting in weak binding of metal
ions.14
We also previously reported that a series of C-1,2-alternate tet-
rahomodioxacalix[4]arene pyreneamides were synthesized. Pb2+
coordination gave a quenched monomer and excimer fluorescence
emission, while upon Ca2+ ion binding the receptor provides an en-
hanced excimer and declined monomer emission with ratiometric
response. Upon Ca2+ binding, the efficient HOMO–LUMO interac-
tion between Py and Py* induces a formation of strong excimer
emission band, whereas there is no such interaction observed upon
Pb2+ complexation.15,16
Fluorescence chemosensors utilize photophysical changes pro-
duced by cation binding: photo-induced electron transfer
(PET);17 photo-induced charge transfer (PCT);18 excimer/exciplex
formation and extinction;19 or fluorescence resonance energy
transfer (FRET).20 The FRET is known to be sensitive, selective,
and adaptable to a wide variety of systems.21 However, reports
on FRET-based metal ion sensors are still at a modest number.
The FRET arises from a donor–acceptor (D–A) interaction between
a pair of fluorophores in their excited state. Excited state of the
fluorescent donor is then non-radiatively transferred to the accep-
tor, and the donor returns to its electronic ground state. Therefore,
the FRET is required to have a certain extent of spectral overlap be-
tween emission spectrum of the donor and absorption spectrum of
the acceptor.22 From this point of view, we herein report on syn-
thesis and the fluorescence properties of tetrahomodioxaca-
lix[4]arene bearing naphthyl- and pyrenyl-amides (7) able to
show the FRET On?Off by the Cu2+ ion.
The synthetic routes23 for tetrahomodioxacalix[4]arene deriva-
tives 6 and 7 are described in Scheme 1. Synthesis of 6 was per-
formed by the condensation of N-(1-naphthalenemethyl)
chloroacetamide (2) with tetrahomodioxacalix[4]arene (5)24 in
the presence of K2CO3 as a base and a catalytic amount of KI. Reac-
tion of 6 with N-(1-pyrenylmethyl)chloroacetamide (4)25 under
basic medium gave 7 in 72% yield.
There are two different shapes in 1,2-alternate conformations
on tetrahomooxacalixarene system. 1,2-alternate conformer in
which the adjacent syn aryl moieties are joined by a CH2 group is
designated as the C-1,2-alternate, while the 1,2-alternate con-
former in which the adjacent syn aryl moieties are joined by a
CH2–O–CH2 moiety is designated as the COC-1,2-alternate.14 The
dimethylenoxy protons of the ArCH2OCH2Ar bridge showed AB
NH
Cl
NH2
O
Cl
O
Cl
K2CO3
2
1
O
Cl
O
NH2
N
H
Cl
Cl
K2CO3
4
3
HN
O
HN
O
O
2
O
O
O
HO
K2CO3/KI
O
HO
O
OH
OH
OH
OH
5
6
4
HN
HN
O
O
O
O
O
O
O
O
O
O
HN
NH
7
Scheme 1. Synthetic pathways to 6 and 7.

J. H. Jung et al. / Tetrahedron Letters 50 (2009) 2013–2016
2015
1000
800
600
400
200
0
1.2
Sr2+, Cs+, Na+,
K+, Li+, Ca2+
Al3+, Ag+, Co2+,
Pb2+
Absorption
Fluorescence
0.8
Hg2+
7
7 + Cu2+
0.4
0.0
300
350
400
450
500
300
350
400
450
500
550 600
650
Wavelength (nm)
Wavelength (nm)
Figure 2. Fluorescence spectra of 7 (6.0
(100.0 equiv) in CH3CN/CHCl3 (40:1, v/v) with an excitation wavelength at 280 nm.
l
M) upon addition of various cations
3.5
2.8
2.1
1.4
0.7
0.0
doublets at d 4.86 and d 4.07 (Dm = 316 Hz) with a geminal coupling
7 + Cu2+
constant of 13.0 Hz. A doublet with peaks for the methylene pro-
tons of ArCH2Ar showed at d 3.75 and d 3.04 (Dm = 284 Hz) with
a geminal coupling constant of 11.4 Hz. The 13C NMR spectrum
showed one peak at 62.38 ppm for the ArCH2O bridge methylenoxy
carbons and one peak at 30.36 ppm for the ArCH2Ar bridge carbons
also indicating that two adjacent benzene rings are in a syn orien-
tation (C-1,2-alternate conformation).
7
For the detailed study of FRET occurring in 7, we examined its
fluorescence and UV/vis spectral behaviors upon addition of vari-
250
300
350
400
405
ous metal ions such as Li+, Na+, K+, Rb+, Cs+, Ag+, Cu2+, Co2+, Ba2+
,
Wavelength (nm)
Pb2+, Ca2+, Hg2+, Mg2+, Sr2+, Zn2+, and Al3+. As seen in Figure 2, 7
shows a weak naphthalene emission at 331 nm and strong pyrene
monomer and excimer emission bands at 382 and 470 nm, respec-
tively, with an excitation at 280 nm. Interestingly, we observed in-
crease in naphthalene emission shown at 331 nm along with
decreased pyrene excimer emission at 470 nm upon addition of
Cu2+ ion. We envisioned that these fluorescence changes may asso-
ciate with the FRET changes upon Cu2+ binding. In the solution of 7,
FRET-On occurs by overlapping of naphthalene emission (donor
fluorophore) with pyrene absorption (acceptor fluorophore) as
seen in Figure 3a. Thus, 7 exhibits a weak naphthalene emission
and strong pyrene emission bands although the excitation wave-
length is 280 nm which corresponds to the naphthalene absorption
band.
Figure 3. (a) Spectral overlap of naphthalene emission (FRET donor) and pyrene
absorption (FRET acceptor). (b) Absorption spectral changes of 7 in the absence and
in the presence of Cu2+ ion (100.0 equiv).
1000
50
40
30
800
20
7
10
600
0
300
320
340
360
7 + Cu2+
400
200
0
Upon addition of Cu2+ ion to a solution of 7, however, we noticed
that the naphthalene emission band at 331 nm increases, but the
pyrene emission concomitantly declines. This is attributable to the
fact that the pyrene absorption band of 7 decreases upon addition
of Cu2+ ion (Fig. 3b), then the spectral overlap between naphthalene
and pyrene is minimized to give the decline in FRET efficiency. With
respect to the extent of FRET changes, 7 indicates a high selectivity
toward Cu2+ ion over other metal cations.
To gain insight into the FRET efficiency in the energy transfer
process from naphthalene to pyrene, the photophysical property
of 6 in the absence of the pyrene units as an energy acceptor was
also studied. The FRET efficiency can be estimated by the following
equation:26
6
300
350
400
450
500
550
600
Wavelength (nm)
Figure 4. Fluorescence spectra of 6 and 7 (6.0
l
M, respectively) in the presence of
Cu2+ ion (100.0 equiv) in CH3CN/CHCl3 (40:1, v/v) with an excitation at 280 nm.
Inset: enlarged spectra of 6 and 7 between 300 and 365 nm.
Moreover, we observed a selective visual fluorescence change of
7 upon addition of Cu2+ ion over other various metal ions, which is
obviously due to the FRET-Off to give a decreased pyrene emission
of 7 (Fig. 5).
E ¼ 1 ꢀ ðF0 =FDÞ
D
where E denotes FRET efficiency; F0D and FD are the donor fluores-
cence intensity with and without an acceptor, respectively. As seen
in Figure 4, 7 without copper ion barely exhibits naphthalene emis-
sion band at 331 nm because of FRET occurring. However, addition
of Cu2+ ion to a solution of 7 increases the naphthalene emission
intensity due to the FRET-Off (inset). From the fluorescence
changes, E of 7 and 7ꢁCu2+ was calculated to be 0.58 and 0,
respectively.
Figure 5. Visual fluorescence changes of 7 (10.0 lM) upon addition of various
metal ions in CH3CN/CHCl3 (40:1, v/v). From left to right: free 7, Cu2+, K+, Li+, Na+,
Cs+, Rb+, Ag+, Co2+, Ba2+, Pb2+, Ca2+, Hg2+, Mg2+, Sr2+, Zn2+, and Al3+ (100.0 equiv,
respectively).

2016
J. H. Jung et al. / Tetrahedron Letters 50 (2009) 2013–2016
17. (a) Aoki, L.; Sakaki, T.; Shinkai, S. J. Chem. Soc., Chem. Commun. 1992, 730; (b)
Jin, T.; Ichikawa, K.; Koyama, T. J. Chem. Soc., Chem. Commun. 1992, 499; (c) Ji,
H.-F.; Brown, G. M.; Dabestani, R. Chem. Commun. 1999, 609; (d) Kim, J. S.; Noh,
K. H.; Lee, S. H.; Kim, S. K.; Kim, S. K.; Yoon, J. J. Org. Chem. 2003, 68, 597.
18. Leray, I.; Lefevre, J. P.; Delouis, J. F.; Delaire, J.; Valeur, B. Chem. Eur. J. 2001, 7,
4590.
19. (a) Birks, J. B. Photophysics of Aromatic Molecules; Wiley-Interscience: London,
1970; (b) Lee, S. H.; Kim, S. H.; Kim, S. K.; Jung, J. H.; Kim, J. S. J. Org. Chem. 2005,
70, 9288.
20. Hecht, S.; Vladimirov, N.; Fréchet, J. M. J. J. Am. Chem. Soc. 2001, 123, 18.
21. (a) Tsien, R. Y.; Miyawaki, A. Science 1998, 280, 1954–1955; (b) Weiss, S. Science
1999, 283, 1676.
22. Stryer, L.; Haugland, R. P. Proc. Natl. Acad. Sci. U.S.A. 1967, 58, 719.
23. Unless otherwise noted, reagents were obtained from commercial suppliers
and used without further purification. Melting points were taken in evacuated
and sealed capillary tubes with a Mel-Temp apparatus and were uncorrected.
IR spectra were recorded on a Nicolet Impact 400 FT-IR spectrometer. 1H and
13C NMR spectra were recorded with
Chemical shifts are recorded in parts per million relative to TMS as an
internal standard.
a Bruker AMX 400 spectrometer.
Figure 6. MALDI–TOF Mass spectrum of 7ꢁCu2+
.
N-(1-naphthalenemethyl)chloroacetamide (2). To
a suspension of 1-napht-
halenemethylamine (300 mg, 1.91 mmol) and potassium carbonate (1.10 g,
7.64 mmol) in a mixture of water (50 mL) and ethyl acetate (50 mL), a solution
of chloroacetyl chloride (0.25 mL, 3.14 mmol) in ethyl acetate (10 mL) was
added dropwise. After the reaction mixture was stirred at room temperature
for 2 h, organic phase was separated and dried over anhydrous magnesium
sulfate. The residue obtained by evaporation of solvent was triturated with
hexane to afford 440 mg (98%) as a colorless crystalline solid. mp 120 °C; 1H
NMR (400 MHz, CDCl3) d 8.00–7.44 (m, 7, ArH), 6,82 (br. s, 1, NH), 4.95 (d, 2,
CH2, J = 5.6 Hz), 4.11 (s, 2, CH2); 13C NMR (125 MHz, CDCl3) d 165.79 (C@O),
134.10, 132.73, 131.52, 129.17, 129.11, 127.06, 126.98, 126.34, 125.61, 123.40
(Ar), 42.80, 42.20 (CH2). Anal. Calcd for C13H12NOCl: C, 66.81; H, 5.18. Found. C,
66.89; H, 5.17.
For the binding mode between 7 and Cu2+ ion, MALDI-TOF Mass
analysis was carried out. A peak at 1789.6 m/z corresponding to
7ꢁCu2+ was observed by addition of excess Cu(ClO4)2 to 7 as seen
in (Fig. 6). We then noticed that the Cu2+ ion is coordinated by 7
with an 1:1 stoichiometry.
In conclusion, FRET-based fluorometric tetrahomodioxaca-
lix[4]arene 7 has been newly synthesized. Derivative 7 exhibits a
weak naphthalene emission and a strong pyrene emission to pro-
vide a FRET-On due to an energy transfer event from naphthalene
to pyrene unit. Complexation with Cu2+ increases the naphthalene
emission along with decreases in the excimer emission of 7 be-
cause of the FRET-Off. With respect to the extent of FRET changes,
we could observe the Cu2+ selectivity of 7 over other metal ions.
7,13,21,27-Tetraphenyl-29,31-bis[(N-(1-naphthalenylmethyl)aminocarbonyl)-
methoxy]-30,32-dihydroxy-2,4,16,18-tetraho-mo-3,17-dioxacalix[4]arene
(6).
Tetrahomodioxacalix[4]arene 5 (571 mg, 0.724 mmol), potassium carbonate
(100 mg, 0.726 mmol), potassium iodide (50 mg), and 2 (400 mg, 1.81 mmol)
in dried acetone (100 mL) was refluxed 80 h. After evaporation of solvent, the
residue was extracted with CH2Cl2. The organic layer was washed with water,
dried over MgSO4, and evaporated in vacuo. The residue was triturated with
MeOH to give the product mixture which was recrystallized from methanol to
afford 676 mg (80%) of the desired product as a pale yellow colored crystal. Mp
Acknowledgments
140–141 °C (decomposed); 1H NMR (400 MHz, CDCl3)
d 8.15 (d. 1, ArH,
The authors wish to acknowledge the financial support of the
SRC program (R11-2005-008-02001-0(2008) and the Sookmyung
Women’s University Research grant 2008 (1-0803-0137).
J = 6.6 Hz), 8.14 (d. 1, ArH, J = 6.6 Hz), 8.04 (d, 2, ArH, J = 8.8 Hz), 7.65–7.03 (m,
38, ArH, NH and OH), 6.90 (d, 4, ArH, J = 9.2 Hz), 5.29 (d, 1, NCH2Nap,
J = 14.4 Hz), 5.28 (d, 1, NCH2Nap, J = 14.4 Hz), 4.75 (d, 1, NCH2Nap, J = 14.4 Hz),
4.74 (d, 1, NCH2Nap, J = 14.4 Hz), 4.62 (s, 4, OCH2CO), 4.61 (d, 2, ArCH2O,
J = 14.8 Hz), 4.51 (d, 2, ArCH2O, J = 14.8 Hz), 4.39 (d, 2, ArCH2O, J = 10.4 Hz),
4.26 (d, 2, ArCH2O, J = 10.4 Hz), 3.87 (d, 2, ArCH2Ar, J = 14.0 Hz), 2.96 (d, 2,
ArCH2Ar, J = 14.0 Hz); 13C NMR (125 MHz, CDCl3) d 168.24 (C@O), 153.60,
153.41, 141.14, 140.25, 138.17, 134.36, 133.86, 133.03, 132.57, 131.51, 130.47,
130.07, 129.44, 129.07, 129.01, 128.83, 128.76, 128.21, 127.83, 127.37, 127.18,
127.13, 127.03, 126.93, 126.56, 125.84, 125.49, 125.25, 123.54, 122.56 (Ar),
73.32 (OCH2CO), 73.04, 71.02 (ArCH2O), 41.71 (NCH2Np), 28.88 (ArCH2Ar).
Anal. Calcd for C80H66O8N2: C, 81.20; H, 5.62. Found. C, 81.91; H, 5.66.
7,13,21,27-Tetraphenyl-29,31-bis[(N-(1-naphthalenylmethyl)amino-carbonyl)-
methoxy]-30,32-bis[N-(1-pyrenylmethyl)aminocarbonyl]-methoxy]-2,4,16,18-
tetrahomo-3,17-dioxacalix[4]arene (7). A mixture of 6 (421 mg, 0.316 mmol),
potassium carbonate (262 mg, 1.90 mmol), 4 (419 mg, 1.79 mmol) and a trace
catalytic amount of KI in dried CH3CN (120 mL) was refluxed for 120 h. The
solvent was evaporated and the residue was extracted with CH2Cl2. The
organic layer was washed two times with water, dried over anhydrous
magnesium sulfate, and evaporated in vacuo. The residue was triturated with
hexane to give the product mixture which was recrystallized from methylene
chloride and methanol to afford the pure product (393 mg, 72%) as a pale
yellow colored crystal. Mp 113–114 °C (decomposed); 1H NMR (400 MHz,
CDCl3) d 7.96–7.74 (m, 20, ArH and NH), 7.62–7.34 (m, 36, ArH), 7.19–6.62 (m,
8, ArH), 5.12 (d, 2, NCH2Ar, J = 12.0 Hz), 4.96 (d, 2, NCH2Ar, J = 12.0 Hz), 4.86 (d,
2, ArCH2O, J = 13.0 Hz), 4.83 (d, 4, OCH2CO, J = 10.8 Hz), 4.61 (d, 2, NCH2Ar,
J = 11.2. Hz), 4.07 (d, 2, ArCH2O, J = 13.0 Hz), 3.96 (d, 4, OCH2CO, J = 10.8 Hz),
3.75 (d, 2, ArCH2Ar, J = 12.4 Hz), 3.66 (d, 2, NCH2Ar, J = 11.2. Hz), 3.04 (d, 2,
ArCH2Ar, J = 12.4 Hz). 13C NMR (125 MHz, CDCl3) d 168.18 (C@O), 153.70,
139.44, 134.05, 133.08, 131.45, 131.16, 129.69, 129.0–129. 7, 129.00, 128.87,
127.99, 126.96, 126.90, 126.30, 126.21, 125.58, 125.37, 123.59, 123.40 (Ar),
71.26 (OCH2CO), 62.38 (ArCH2O), 41.28 (NCH2Np), 30.36 (ArCH2Ar). Anal. Calcd
for C118H92O10N4: C, 82.11; H, 5.37. Found. C, 81.29; H, 5.36.
References and notes
1. Senger, M. R.; Rico, E. P.; Arizi, M. D.; Frazzon, A. P. G.; Dias, R. D.; Bogo, M. R.;
Bonan, C. D. Toxicology 2006, 226, 229.
2. Hultberg, B.; Andersson, A.; Lsaksson, A. Toxicology 1997, 117, 89.
3. Barnham, K. J.; Masters, C. L.; Bush, A. I. Nat. Rev. Drug Discovery 2004, 3, 205.
4. (a) Zeng, L.; Miller, E. W.; Pralle, A.; Isacoff, E. Y.; Chang, C. J. J. Am. Chem. Soc.
2006, 128, 10; (b) Brunner, J.; Kraemer, R. J. Am. Chem. Soc. 2004, 126, 13626; (c)
Dujols, V.; Ford, F.; Czarnik, A. W. J. Am. Chem. Soc. 1997, 119, 7386.
5. (a) Kim, J. S.; Shon, O. J.; Rim, J. A.; Kim, S. K.; Yoon, J. J. Org. Chem. 2002, 67,
2348; (b) Kim, S. K.; Lee, S. H.; Lee, J. Y.; Lee, J. Y.; Bartsch, R. A.; Kim, J. S. J. Am.
Chem. Soc. 2004, 126, 16499; (c) Lee, M. H.; Quang, D. T.; Jung, H. S.; Yoon, J.;
Lee, C. H.; Kim, J. S. J. Org. Chem. 2007, 72, 4242.
6. (a) Gutsche, C. D.; Dhawan, B.; No, K. H.; Muthukrishnan, R. . J. Am. Chem. Soc.
1981, 103, 3782; (b) Masci, B.; Saccheo, S. Tetrahedron 1993, 49, 10739.
7. Bavoux, C.; Vocanson, F.; Perrin, M.; Lamartine, R. J. Incl. Phenom. Mol. Recogn.
Chem. 1995, 22, 119.
8. Dhawan, B.; Gutsche, C. D. J. Org. Chem. 1983, 48, 1536.
9. (a) Thuèry, P.; Nierlich, M.; Vicens, J.; Masci, B. Acta Crystallogr., Sect. C 2001, 57,
70; (b) Asfari, Z.; Harrowfield, J. M.; Ogden, M. I.; Vicens, J.; White, A. H. Angew.
Chem., Int. Ed. Engl. 1991, 30, 854.
10. Harrowfield, J. M.; Ogden, M. I.; White, A. H. J. Chem. Soc., Dalton Trans. 1991, 979.
11. Marcos, P. M.; Ascenso, J. R.; Lamartine, R.; Pereira, J. L. C. Tetrahedron 1997, 53,
11791.
12. Felix, S.; Ascenso, J. R.; Lamartine, R.; Pereira, J. L. C. Synth. Commun. 1998, 28,
1793.
13. No, K.; Lee, J. H.; Yang, S. H.; Kim, M. J.; Kim, J. S. J. Org. Chem. 2002, 67, 3165.
14. No, K.; Kim, J. S.; Shon, O. J.; Yang, S. H.; Suh, I. H.; Kim, J. G.; Bartsch, R. A.; Kim,
J. Y. J. Org. Chem. 2001, 66, 5976.
15. (a) Iasi, G. D.; Masci, B. Tetrahedron Lett. 1993, 34, 6635; (b) No, K.; Kim, J. S.;
Shon, O. J.; Yang, S. H.; Suh, I. H.; Kim, J. G.; Bartsch, R. A.; Kim, J. Y. J. Org. Chem.
2001, 66, 5976.
24. Thuery, P.; Nierlich, M.; Vicens, J.; Masci, B. Acta Crystallogr. 2001, C57, 70.
25. van der Veen, N. J.; Flink, S.; Deij, M. A.; Egberink, R. J. M.; van Veggel, F. C. J. M.;
Reinhoudt, D. N. J. Am. Chem. Soc. 2000, 122, 6112.
26. Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 2nd ed.; Plenum: New
York, 1999; Chapter 13..
16. Choi, J. K.; Lee, A.; Kim, S.; Ham, S.; No, K.; Kim, J. S. Org. Lett. 2006, 8, 1601.