A receptor incorporating OH, NH and CH binding motifs for a fluoride selective chemosensor

Article abstract of DOI:10.1039/c2ob25304f

An anion receptor combined different types of hydrogen bond donors such as OH, NH and CH groups has been synthesized. By rotation of the sub methyl group, this receptor showed evident ¹H NMR response to both fluoride and sulfate, while colorimetric and fluorescent responses were only observed in the presence of fluoride.

Full text of DOI:10.1039/c2ob25304f

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PAPER
A receptor incorporating OH, NH and CH binding motifs for a fluoride
selective chemosensor†
Liang Xu,a,b Yongjun Li,*a Yanwen Yu,a,b Taifeng Liu,a,b Songhua Cheng,a,b Huibiao Liua and Yuliang Li*a
Received 11th February 2012, Accepted 12th April 2012
DOI: 10.1039/c2ob25304f
An anion receptor combined different types of hydrogen bond donors such as OH, NH and CH groups
has been synthesized. By rotation of the sub methyl group, this receptor showed evident 1H NMR
response to both fluoride and sulfate, while colorimetric and fluorescent responses were only observed in
the presence of fluoride.
Introduction
Anions play important roles in a wide range of chemical and bio-
logical processes. For example, the chloride anion is used by
living systems in cellular tasks.1 The fluoride anion shows ben-
eficial effects in dental health and the treatment of osteoporosis,2
however, it is accused of several human pathologies.3 Therefore,
Fig. 1 Schematic interpretation of the cavity formed by molecule 1.
the design of new types of anion receptors has attracted much
attention recently.4
to facilitate self-assembly.20 Highly sensitive and selective
The common binding subunits for anion receptors include
fluoride anion sensors have been constructed based on this
amide,5 pyrrole,6 urea,7 thiourea,8 azophenol,9 and imidazo-
motif.21
lium.10 In these motifs, O–H⋯X−, N–H⋯X−, (C–H)+⋯X− and
Recently, we have developed a urea like anion recognizing
motif, amidetriazole, which can be easily synthesized and
C–H⋯X− hydrogen bonding play very important roles for selec-
tive anion binding. The phenolic OH group is often introduced
derived. This molecular platform can be used extensively for the
as a strong donor and color-reporting unit,11 and it often under-
construction of numerous receptor systems with functional
goes deprotonation in the presence of basic anions such as
groups.22 Here we designed compound 1 based on amidetriazole,
fluoride, acetate, and dihydrogen phosphate. The amide NH
in which different types of hydrogen bond donors such as OH,
group is less susceptible to deprotonation than hydroxyl group,
NH and CH groups were linked covalently together for under-
and it is able to form strong hydrogen bonds. The (C–H)+⋯X−
standing their interactions with various anionic guests by rotation
of the sub methyl group (Fig. 1). The colorimetric and fluoro-
metric dual-modal response of this molecule towards fluoride
anion was also investigated. In this molecule, electron poor 2,2-
type ionic hydrogen bond is stronger, due to the charge–charge
electrostatic interaction.12 Compared to the OH hydrogen bond
donor and the NH hydrogen bond donor, the neutral CH hydro-
gen bond donor is rarely used in designing anion receptors,
dicyano-vinyl group was introduced to generate intramolecular
owing to its weak interactions.13 Interestingly, the click reac-
charge transfer from the electron rich hydroxide upon the depro-
tion14,15 assisted the driving of synthetic innovations in anion
tonation of the OH group.
receptor design. The 1,2,3-triazole with a 5-debye dipole is a
new motif which can result in multiple noncovalent interactions
such as anion recognition16 within flexible,17 shape-persistent
triazolophanes13,18 and in foldamers19 and they have the ability
Results and discussion
The compound 1 was synthesized starting from (5-bromo-3-
hydroxymethyl-2-methoxy-phenyl)-methanol 7,23 which was
converted to azide 6 in one step using Reddy’s procedure
(Scheme 1). A click chemistry coupling of 6 with propynoic
acid methyl ester gave 5 in 96% yield. Subsequent amination
with butylamine gave 1-(5-bromo-3-hydroxymethyl-2-methoxy-
benzyl)-1H-[1,2,3] triazole-4-carboxylic acid butylamide 4 in
94% yield. 2 was obtained through the oxidation of 4 with PCC
aCAS Key Laboratory of Organic Solid, Beijing National Laboratory for
Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy
of Sciences, Beijing, 100190, P. R. China. E-mail: ylli@iccas.ac.cn;
Fax: +86-10-82616576; Tel: +86-10-62588934
bGraduate University of Chinese Academy of Sciences, Beijing 100190,
P. R. China
†Electronic supplementary information (ESI) available: 1H NMR and
13C NMR of compounds 1–6. See DOI: 10.1039/c2ob25304f
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Scheme 1 Synthesis route for the receptor 1. Conditions: (a) NaN3,
Ph3P, DMF–CCl4 (4 : 1), (b) propynoic acid methyl ester, sodium ascor-
bate, CuSO4·5H2O, EtOH–H2O (1 : 1), (c) butylamine, (d) PCC, DCM,
(e) BBr3, (f) malononitrile.
(pyridinium chlorochromate) in DCM followed by the removal
of methyl group with the aid of BBr3. Coupling 2 with malono-
nitrile in the presence of base gave 1 in 79% isolated yield.
The 1H NMR titration of 1 with various anions provided struc-
tural information about the receptor and its complexes present in
1
solution. H NMR titration experiment in acetone-d6 was per-
formed to investigate the fluoride–1 interactions, as shown in
Fig. 2. The hydrogen bond donors exhibited two different reson-
ance signals at 8.78 (triazole-He) and 7.70 (amido-Hf) ppm. The
dicyanovinyl-Hc, the phenyl-Hb and phenyl-Ha showed signals
at 8.44, 8.11 and 7.94 ppm, respectively. Fluoride has a high
affinity to hydrogen and it could easily induce H–O bond clea-
vage. Upon addition of F− as tetrabutylammonium salt, the
signals of Ha and Hb on the phenyl ring gradually migrated to
upfield owing to charge delocalization on the entire phenyl ring
with the deprotonation of O–H. Upon addition of 2.0 equivalents
of F−, all of the signals associated with compound 1 completely
vanished, which indicated that the OH group had been deproto-
nation completely. The relative protons showed signals at 8.50
(triazole-He), 7.65 (amido-Hf), 8.44 (dicyanovinyl-Hc), 7.31
(phenyl-Hb) and 7.14 (phenyl-Ha). With the continuous addition
of F−, more complicated 1H NMR signal shifts were observed. It
was the combination of the F− anion binding process and the
intramolecular hydrogen bonding between the deprotonated O−
anion and the dicyanovinyl-Hc proton or triazole C–H. The
deprotonated O− anion can form intramolecular hydrogen bond
with the dicyanovinyl-Hc proton or triazole C–He. This may
account for the reason why the signal of dicyanovinyl-Hc
showed two sets of peaks upon addition of 4.0 equivalents of
F−. One signal showed at 8.60 ppm (c1) which is related to the
dicyanovinyl-Hc⋯O− hydrogen bonded species 1F-1, and the
other signal showed at 6.95 ppm (c2) which is due to the charge
delocalization on the dicyanovinyl group conjugated to the
phenyl ring with the deprotonation of O–H, while the deproto-
nated O− anion formed intramolecular hydrogen bond with the
triazole C–He (1F-2). The F− anion binding based on these two
species would lead to the splitting of the signal of amido-Hf.
One signal shifted to 8.70 ppm (f2) through the fluoride binding
by triazole-He and amido-Hf in 1F-1, and the other constant
Fig. 2 Top: The models of the fluoride complex of 1 before and after
the sub methyl group rotating. Bottom: Partial 1H NMR titration of 1
with F− ([d6] acetone, 298 K).
signal at 7.65 ppm (f1) which indicated that there is weak
fluoride binding in 1F-2.
As shown in Fig. 3, upon addition of 2.5 equivalents of SO4
2−
as tetrabutylammonium salt, the developments of the signals were
similar with that of F− titration, potentially indicating the occur-
2−
rence of O–H deprotonation. Upon addition of more SO4
,
there generated two sets of signals, which probably accounted
for the different chemical environments when binding with
sulfate anion (as the binding models shown in Fig. 3), that is, the
more negative charged sulfate binds with the proton Ha, triazole-
He and amido-Hf (top) or triazole-He and amido-Hf (down). The
triazole proton He preferred to bind with SO42− rather than to the
deprotonated O− anion. The two set of peaks of He at 9.59 and
9.60 ppm, those of Hf split and shifted downfield to 8.08 and
9.10 ppm, respectively. The two sets of peaks of Hc shifted to
the reversed directions, that is, one set of peak shifted upfield
to 8.50 ppm, while the other set of peak shifted downfield to
8.90 ppm. One set of peak of Hb remained nearly unchanged,
while the other set of peak of Hb shifted upfield from 7.30 ppm
to 7.25 ppm. The two sets of peaks of Ha located at 7.05 and
6.95 ppm, respectively.
The Cl− titration spectra exhibited totally different sets of
signals compared to F− and SO42−. Upon addition of 0.2 to 60.0
equivalents of Cl− (as tetrabutylammonium salt), the protons He,
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Fig. 4 Top: The models of the chloride complex of 1 before and after
the sub methyl group rotating. Bottom: Partial 1H NMR titration of 1
with Cl− ([d6] acetone, 298 K).
Fig. 3 Top: The models of the sulfate complex of 1 before and after
the sub methyl group rotating. Bottom: Partial 1H NMR titration of 1
with SO42− ([d6] acetone, 298 K).
Hc, Hb, Ha and Hf all shifted downfield, which indicated that no
O–H deprotonation occurred and the protons formed moderate
hydrogen bond interactions with Cl−. The signals of the protons
remained one set of peaks, potentially indicating that all the
hydrogen donor protons directed to Cl− and there is only one
conformation (Fig. 4).
Fig. 5 Visible color (a) and visual fluorescence color (b) changes of 1
(0.05 mM) in CH2Cl2 after the addition of 60 equiv. of various anions
(50 mM). From left to right: only 1, F−, Cl−, Br−, I−, PF6−, AcO−,
2−
H2PO4−, SO4
(TBA+ salts). The visual fluorescence color was
obtained with excitation at 365 nm using a hand-held UV lamp.
Color and fluorescence emission changes could be observed
by mixing the receptor and anions as shown in Fig. 5. Only
when fluoride ions were added, the color of the receptor solution
turned from colorless to yellow and the fluorescence color
became light green. However, a weak red color could be
observed when acetate, dihydrogen phosphate, and sulfate ions
were added, and a weak green color was observed for fluor-
escence color.
Fig. 6a and Fig. S5† showed the absorption and emission
spectral of compound 1 in the presence of various anions (60
equiv.). Significant UV-vis absorption changes were observed
only when F− was added. Meanwhile only F− caused a drastic
increase to the original emission peak at 408 nm and induced a
new strong emission peak at 580 nm. Only a slight increase for
−
emission was observed when H2PO4 was added, which is fol-
lowed by a weak charge transfer absorption band centered at
500 nm.
Fig. 6 Absorption spectra of compound 1 (5 × 10−5 M) upon addition
of 60 equivalents of tetrabutylammonium fluoride, chloride, bromide,
iodide, hexafluorophosphate, acetate, dihydrogen phosphate, and sulfate
in CH2Cl2.
The interaction of 1 with fluoride anion was investigated in
detail. Fig. 7a showed the absorption spectral changes of 1 with
the increase of the F− concentration in CH2Cl2 at room tempera-
ture. The UV-vis spectrum of 1 exhibited two absorption bands
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Table 1 Binding constants (K1) determined by UV-vis titrationa for the
interaction of 1 with various anionsb
Anion F−
Cl− Br− I−
PF6
OAc− H2PO4
SO4
1475
−
2−
2−
K1 21 721 477 399 321 140
968 1193
a The calculation is according to ref. 18. b Anions as
tetrabutylammonium salts in CH2Cl2.
continuing decrease in the absorption band at 294 nm and
352 nm and simultaneous growth of a new strong absorption
band at 448 nm. The binding stoichiometry of the 1–fluoride
interactions was confirmed to be 1 : 2 from the Job’s plot
(Fig. 7b). Fig. 7c showed the emission spectral changes of 1
with the increasing of the F− concentration in CH2Cl2 at room
temperature. The fluorescence responses of 1 with F− were
recorded with an excitation at the isosbestic point of 320 nm
from UV-vis titration experiment. The emission spectra of 1
showed one band at 408 nm. Upon addition of fluoride anion,
the emission band of 1 at 408 nm increased gradually and one
new strong emission band at 580 nm simultaneously grew,
which is ascribed to a twisted intramolecular charge-transfer
(TICT) state as internal rotation of the dicyanovinyl group with
respect to the benzene ring was limited upon the formation of
the intramolecular hydrogen bonding between the deprotonated
O− anion and the dicyanovinyl-Hc proton or triazole C–H.
The receptor–anion stoichiometry was determined via a con-
tinuous variation method (Job’s plots) and proved to be 1 : 2 for
fluoride anions. The association constant K1 between 1 and
various anions was determined by nonlinear curve fitting of the
titration curves obtained by plotting the absorbance changes at
352 nm (ΔA) against the concentration of anions added18
(Table 1). In the anions studied, 1 showed great selectivity
towards fluoride.
Conclusion
In summary, an anion receptor combining different types of
hydrogen bond donors such as OH, NH and CH groups had
been synthesized for the understanding of their interactions with
various anionic guests. With the help of the free rotation of the
sub methyl group, this receptor showed different binding behav-
ior towards fluoride, sulfate and other halides. This receptor
showed evident H NMR response to both fluoride and sulfate,
while colorimetric and fluorescent responses were only observed
in the presence of fluoride.
1
Fig. 7 (a) Changes in the UV-vis spectra of 1 (5 × 10−5 M in CH2Cl2)
upon titration with n-Bu4NF from 1 to 10, and 20, 30, 40, 50, 60 equiv.
(b) Absorption changes at 352 nm vs. concentrations of F−. Inset: Job’s
plot for fluoride–1 interactions. (c) Emission spectra of 1 (1 × 10−5 M in
CH2Cl2) upon titration with n-Bu4NF from 1 to 10, and 20, 30, 40, 50,
60 equiv. Excitation wavelength was 320 nm with 10.0 nm slit widths.
Experimental
(3-Azidomethyl-5-bromo-2-methoxy-phenyl)-methanol, 6
in dichloromethane. One moderately strong absorption band
appeared at 294 nm and the other relative weak absorption band
appeared at 352 nm. With the deprotonation of O–H, the UV-vis
spectra exhibited a red-shifted charge-transfer (CT) band from
electron rich hydroxide to electron poor dinitrile side. Addition
of tetrabutylammonium fluoride induced drastic color develop-
ment from colorless to yellow, which is associated with
Ph3P (2 mmol, 268 mg) and NaN3 (2.4 mmol, 160 mg) were
added into a solution of 723 (2 mmol, 492 mg), then 4 mL CCl4
were added. After a few minutes, the reaction was heated at
reflux with stirring for 6 hours, and then cooled to room temp-
erature. The resulting solution was poured into 125 mL of water,
and then extracted with Et2O (3 × 30 mL). The combined
organic layers were washed with brine (2 × 20 mL) and dried
4378 | Org. Biomol. Chem., 2012, 10, 4375–4380
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over MgSO4. Concentrated in vacuo and purified by flash chrom-
atography (7 : 1 hexanes–EtOAc) gave 6 (287 mg, 53%). Mp
139–141 °C. 1H NMR (CDCl3, 400 MHz), δ = 7.53 (s, 1 H), 7.4
(s, 1 H), 4.68 (s, 2 H), 4.36 (s, 2 H), 3.79 (s, 3 H), 2.36 (s, 1 H).
13C NMR (CDCl3, 100 MHz), δ = 155.06, 136.47, 132.11,
132.01, 130.93, 117.38, 62.29, 59.85, 49.02. MS (EI) Calcd for
C9H10BrN3O2 (M + H) 272.10; Found 272.2. Anal. Calcd for
C9H10BrN3O2: C, 39.73; H, 3.70; N, 15.44. Found: C, 39.81; H,
3.74; N, 15.49.
395.25; Found 395.3. Anal. Calcd for C16H19BrN4O3: C, 48.62;
H, 4.85; N, 14.18. Found: C, 48.69; H, 4.82; N, 14.22.
1-(5-Bromo-3-formyl-2-hydroxy-benzyl)-1H-[1,2,3]triazole-
4-carboxylic acid butylamide, 2
BBr3 (10 mmol, 10 mL, 1 M in DCM) was slowly added to a
solution of 3 (1 mmol, 394 mg) in dichloromethane (20 mL) and
the solution was stirred under argon at room temperature. After
4 hours, the mixture was poured slowly into a solution of satu-
rated sodium bicarbonate (100 mL) to obtain a precipitation of a
grey solid. After filtrated and washed with cold water and ether,
the crude product was further purified by column chromato-
graphy (CH2Cl2–MeOH, 4 : 1) to yield 2 (304 mg, 80%) as an
1-(5-Bromo-3-hydroxymethyl-2-methoxy-benzyl)-1H-[1,2,3]-
triazole-4-carboxylic acid methyl ester, 5
A solution of 6 (1 mmol, 127 mg), propynoic acid methyl ester
(2.2 mmol, 222 mg), sodium ascorbate (0.2 mmol, 44.6 mg),
and CuSO4 (0.02 mmol, 5.6 mg) in a 1 : 1 mixture of EtOH–
H2O (14 mL) was stirred at room temperature for 24 h. After
removal of the solvents in vacuo, the crude product was purified
by column chromatography (CH2Cl2–MeOH, 3 : 1) to afford 5
1
off-white solid. Mp 175–177 °C. H NMR (CDCl3, 400 MHz),
δ = 11.44 (s, 1 H), 9.87 (s, 1 H), 8.16 (s, 1 H), 7.73 (s, 1 H),
7.63 (s, 1 H), 7.11 (s, 1 H), 5.59 (s, 2 H), 3.44 (m, 2 H), 1.60
(m, 2 H), 1.40 (m, 2 H), 0.94 (t, 3 H, J = 7.2 Hz). 13C NMR
(CDCl3, 100 MHz), δ = 195.27, 159.77, 158.04, 143.65, 139.74,
136.54, 125.80, 125.06, 121.76, 111.59, 47.57, 38.77, 31.54,
19.95, 13.63. MS (EI) Calcd for C15H17BrN4O3 (M + H)
381.22; Found 381.3. Anal. Calcd for C15H17BrN4O3: C, 47.26;
H, 4.49; N, 14.70. Found: C, 47.34; H, 4.53; N, 14.64.
1
(309 mg, 94%). Mp 191–193 °C. H NMR (CDCl3, 400 MHz),
δ = 8.10 (s, 1 H), 7.65 (s, 1 H), 7.29 (s, 1 H), 5.56 (s, 2 H), 4.75
(s, 2 H), 3.92 (s, 3 H), 3.76(s, 3 H), 2.75 (s, 1 H). 13C NMR
(CDCl3, 100 MHz), δ = 160.92, 154.88, 140.11, 137.18, 133.21,
132.00, 128.94, 127.64, 117.68, 62.27, 59.40, 52.18, 48.71. MS
(EI) Calcd for C13H14BrN3O4 (M + H) 356.17; Found 356.2.
Anal. Calcd for C13H14BrN3O4: C, 43.84; H, 3.96; N, 11.80.
Found: C, 43.88; H, 3.99; N, 11.74.
1-[5-Bromo-3-(2,2-dicyano-vinyl)-2-hydroxy-benzyl]-1H-[1,2,3]-
triazole-4-carboxylic acid butylamide, 1
Piperidine (0.025 mmol, 25 μL) was added to a mixture of 2
(0.5 mmol, 190 mg) and malononitrile (0.5 mmol, 33 mg) in
ethanol (20 mL). The solution was stirred at room temperature
overnight and the resulting precipitate was collected by filtration.
The crude product was purified by column chromatography
(CH2Cl2–MeOH, 5 : 1) to yield compound 1 (169 mg, 79%) as a
1-(5-Bromo-3-hydroxymethyl-2-methoxy-benzyl)-1H-[1,2,3]-
triazole-4-carboxylic acid butylamide, 4
5 (1 mmol, 127 mg) in 4 mL butylamine was stirred at 70 °C for
4 h. After removal of butylamine in vacuo, the crude product
was purified by column chromatography (CH2Cl2–MeOH, 3 : 1)
1
1
to afford 4 (309 mg, 94%). Mp 187–189 °C. H NMR (CDCl3,
pale white solid. Mp 203–205 °C. H NMR (CDCl3, 400 MHz),
400 MHz), δ = 8.05 (s, 1 H), 7.63 (s, 1 H), 7.27 (s, 1 H), 7.16
(s, 1 H), 5.52 (s, 2 H), 4.72 (s, 2 H), 3.75 (s, 3 H), 3.42 (q, 2 H,
J = 7.2 Hz), 2.54 (s, 1 H), 1.58 (m, 2 H), 1.39 (m, 2 H), 0.93 (t,
3 H, J = 7.2 Hz), 13C NMR (CDCl3, 100 MHz), δ = 159.90,
154.93, 143.67, 137.15, 133.19, 132.07, 129.18, 125.41, 117.74,
62.30, 59.52, 48.69, 38.88, 31.58, 20.03, 13.70. MS (EI) Calcd
for C16H21BrN4O3 (M + H) 397.27; Found 397.3. Anal. Calcd
for C16H21BrN4O3: C, 48.37; H, 5.33; N, 14.10. Found: C,
48.41; H, 5.37; N, 14.06.
δ = 8.22 (s, 1 H), 8.18 (s, 1 H), 7.76 (s, 1 H), 7.62 (s, 1 H), 7.12
(s, 1 H), 5.79 (s, 2 H), 3.44 (d, 2 H, J = 8 Hz), 1.56 (t, 2 H, J =
4 Hz), 1.40 (m, 2H), 0.94 (t, 3 H, J = 8 Hz). 13C NMR (CDCl3,
100 MHz), δ = 162.87, 162.40, 139.83, 136.07, 133.78, 133.60,
133.53, 129.48, 129.15, 124.80, 123.50, 122.92, 40.97, 30.27,
20.35, 13.91, 1.156. MS (EI) Calcd for C18H17BrN6O2 (M + H)
429.27; Found: 429.3. Anal. Calcd for C18H17BrN6O2: C, 50.36;
H, 3.99; N, 19.58. Found: C, 50.46; H, 3.95; N, 19.49.
Acknowledgements
1-(5-Bromo-3-formyl-2-methoxy-benzyl)-1H-[1,2,3]triazole-4-
carboxylic acid butylamide, 3
This work was supported by the National Nature Science Foun-
dation of China (21031006), NSFC-DFG joint fund (TRR 61)
and the National Basic Research 973 Program of China.
Pyridinium chlorochromate (1.5 mmol, 322 mg) was added to a
solution of 4 (1 mmol, 396 mg) in CH2Cl2 under a nitrogen
atmosphere, and the mixture was stirred at room temperature
overnight. The crude product was purified by column chromato-
graphy (CH2Cl2) to afford 3 (355 mg, 90%). Mp 178–180 °C.
1H NMR (CDCl3, 400 MHz), δ = 10.26 (s, 1 H), 8.11 (s, 1 H),
7.97 (d, 1 H, J = 2.4 Hz), 7.60 (d, 1 H, J = 2.0 Hz), 7.12 (s, 1
H), 5.60 (s, 1 H), 3.92 (s, 1 H), 3.44 (q, 2 H, J = 6.8 Hz), 1.59
(m, 2 H), 1.41 (m, 2 H), 0.94 (t, 3 H, J = 7.2 Hz). 13C NMR
(CDCl3, 100 MHz), δ = 187.30, 159.80, 159.64, 143.91, 138.51,
133.40, 130.84, 130.77, 125.54, 118.11, 65.32, 47.95, 38.83,
31.55, 19.99, 13.66. MS (EI) Calcd for C16H19BrN4O3 (M + H)
Notes and references
1 R. Dutzler, E. B. Campbell, M. Cadene, B. T. Chait and R. MacKinnon,
Nature, 2002, 415, 287–294.
2 C. R. Wade, A. E. J. Broomsgrove, S. Aldridge and F. P. Gabbai, Chem.
Rev., 2010, 110, 3958–3984.
3 M. Cametti and K. Rissanen, Chem. Commun., 2009 (20), 2809–2829.
4 R. J. Brea, C. Reiriz and J. R. Granja, Chem. Soc. Rev., 2010, 39, 1448–
1456; S. E. Matthews and P. D. Beer, Supramol. Chem., 2005, 17, 411–
435; R. Martínez-Máñez and F. Sancenón, Chem. Rev., 2003, 103, 4419–
4476; P. D. Beer and P. A. Gale, Angew. Chem., Int. Ed., 2001, 40, 486–
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 4375–4380 | 4379

View Online
516; S. Rivadehi, E. F. Reid, C. F. Hogan, S. V. Bhosale and S.
J. Langford, Org. Biomol. Chem., 2012, 10, 705–709; K. Zhu, M. Zhang,
F. Wang, N. Li, S. Li and F. Huang, New J. Chem., 2008, 32, 1827–1830;
K. Zhu, S. Li, F. Wang and F. Huang, J. Org. Chem., 2009, 74, 1322–
1328; K. Zhu, L. Wu, X. Yan, B. Zheng, M. Zhang and F. Huang,
Chem.–Eur. J., 2010, 16, 6088–6098; G. Yu, Z. Zhang, C. Han, M. Xue,
Q. Zhou and F. Huang, Chem. Commun., 2012, 48, 2958–2960.
5 S. O. Kang, R. A. Begum and K. Bowman-James, Angew. Chem., Int.
Ed., 2006, 45, 7882–7894; K. Bowman-James, Acc. Chem. Res., 2005,
38, 671–678; S. O. Kang, D. Powell and K. Bowman-James, J. Am.
Chem. Soc., 2005, 127, 13478–13479.
15 H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem., Int. Ed.,
2001, 40, 2004–2021.
16 A. Kumar and P. S. Pandey, Org. Lett., 2008, 10, 165–168; H. Zheng,
W. Zhou, J. Lv, X. Yin, Y. Li, H. Liu and Y. Li, Chem.–Eur. J., 2009, 15,
13253–13262; Y. Zhao, Y. Li, Y. Li, H. Zheng, X. Yin and H. Liu, Chem.
Commun., 2010, 46, 5698–5700.
17 V. Haridas, K. Lal, Y. K. Sharma and S. Upreti, Org. Lett., 2008, 10,
1645–1647; Y. Zhao, Y. Li, Y. Li, C. Huang, H. Liu, S.-W. Lai, C.-
M. Che and D. Zhu, Org. Biomol. Chem., 2010, 8, 3923–3927; Y. J. Li,
Y. J. Zhao, A. H. Flood, C. Liu, H. B. Liu and Y. L. Li, Chem.–Eur. J.,
2011, 17, 7499–7505.
6 P. A. Gale, K. Navakhun, S. Camiolo, M. E. Light and M. B. Hursthouse,
J. Am. Chem. Soc., 2002, 124, 11228–11229.
18 Y. Li and A. H. Flood, Angew. Chem., Int. Ed., 2008, 47, 2649–2652;
Y. Li and A. H. Flood, J. Am. Chem. Soc., 2008, 130, 12111–12122; J.
R. Long and R. S. Drago, J. Chem. Educ., 1982, 59, 1037–1089; K.
A. Conors, Binding Constants, John Wiley & Sons, New York, 1987;
Y. Li, D. A. V. Griend and A. H. Flood, Supramol. Chem., 2009, 21,
111–117; Y. Li, M. Pink, J. A. Karty and A. H. Flood, J. Am. Chem. Soc.,
2008, 130, 17293–17295.
7 M. Boiocchi, L. Del Boca, D. E. Gómez, L. Fabbrizzi, M. Licchelli and
E. Monzani, J. Am. Chem. Soc., 2004, 126, 16507–16514; C. Jia, B. Wu,
S. Li, X. Huang, Q. Zhao, Q.-S. Li and X.-J. Yang, Angew. Chem., Int.
Ed., 2011, 50, 486–490; Y. Wu, X. Peng, J. Fan, S. Gao, M. Tian,
J. Zhao and S. Sun, J. Org. Chem., 2006, 72, 62–70.
8 S.-i. Sasaki, M. Mizuno, K. Naemura and Y. Tobe, J. Org. Chem., 2000,
65, 275–283; D. H. Lee, H. Y. Lee, K. H. Lee and J.-I. Hong, Chem.
Commun., 2001 (13), 1188–1189.
19 H. Juwarker, J. M. Lenhardt, D. M. Pham and S. L. Craig, Angew.
Chem., Int. Ed., 2008, 47, 3740–3743; R. M. Meudtner and S. Hecht,
Angew. Chem., Int. Ed., 2008, 47, 4926–4930.
9 D. H. Lee, J. H. Im, S. U. Son, Y. K. Chung and J.-I. Hong, J. Am.
Chem. Soc., 2003, 125, 7752–7753.
10 B. G. Zhang, P. Cai, C. Y. Duan, R. Miao, L. G. Zhu, T. Niitsu and
H. Inoue, Chem. Commun., 2004 (19), 2206–2207.
11 D. H. Lee, K. H. Lee and J.-I. Hong, Org. Lett., 2000, 3, 5–8.
12 J. Yoon, S. K. Kim, N. J. Singh and K. S. Kim, Chem. Soc. Rev., 2006,
35, 355–360.
20 W. S. Horne, M. K. Yadav, C. D. Stout and M. R. Ghadiri, J. Am. Chem.
Soc., 2004, 126, 15366–15367; W. Yang, Y. Li, J. Zhang, N. Chen,
S. Chen, H. Liu and Y. Li, J. Org. Chem., 2011, 76, 7750–7756.
21 E. J. Cho, B. J. Ryu, Y. J. Lee and K. C. Nam, Org. Lett., 2005, 7, 2607–
2609; V. Haridas, S. Sahu and P. P. Praveen Kumar, Tetrahedron Lett.,
2011, 52, 6930–6934; V. Haridas, S. Sahu and P. Venugopalan, Tetrahe-
dron, 2011, 67, 727–733.
13 Y. Hua and A. H. Flood, Chem. Soc. Rev., 2010, 39, 1262–1271.
14 V. V. Rostovtsev, L. G. Green, V. V. Fokin and K. B. Sharpless, Angew.
Chem., Int. Ed., 2002, 41, 2596–2599; C. W. Tornøe, C. Christensen and
M. Meldal, J. Org. Chem., 2002, 67, 3057–3064.
22 Y. J. Li, L. Xu, W. L. Yang, H. B. Liu, S. W. Lai, C. M. Che and Y. L. Li,
Chem.–Eur. J., 2012, 18, 4782–4790.
23 H. Sharghi, M. A. Nasseri and K. Niknam, J. Org. Chem., 2001, 66,
7287–7293.
4380 | Org. Biomol. Chem., 2012, 10, 4375–4380
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