Convenient synthesis and anion recognition properties of N-flurobenzoyl-N′-phenylthioureas in water-containing media

Article abstract of DOI:10.1016/j.jfluchem.2006.06.018

Novel artificial anionic receptors N-flurobenzoyl-N′-phenylthioureas were synthesized by simple steps in good yields. The binding properties for anions of these N-flurobenzoyl-N′-phenylthioureas and 2 N-benzoyl-N′-phenyl thiourea were examined by UV-vis and ¹H NMR spectroscopy. By fluorination of the benzoyl chromophore, the receptors had higher binding affinity for tested anions than the receptor 2. Especially, we studied the anion binding efficiency of the receptors 1 N-(3-flurobenzoyl)-N′-phenylthiourea and 2 in dimethyl and dimethyl sulfoxide-water binary solutions in detail respectively. In pure dimethyl sulfoxide, the receptors 1 and 2 had higher binding affinity for F^- over AcO^-. However, as the ratio of water to dimethyl sulfoxide increases, we found the binding properties for tested anions of 1 and 2 changed in dimethyl sulfoxide-water binary solutions. The receptor 1 showed high binding affinity and selective ability for AcO^- in dimethyl sulfoxide containing water with varied ratios.

Full text of DOI:10.1016/j.jfluchem.2006.06.018

Journal of Fluorine Chemistry 127 (2006) 1222–1227
www.elsevier.com/locate/fluor
Convenient synthesis and anion recognition properties of
N-flurobenzoyl-N0-phenylthioureas in water-containing media
*
Youming Zhang, Jingdong Qin, Qi Lin, Taibao Wei
College of Chemistry and Chemical Engineering, Gansu Key Laboratory of Polymer Materials, Northwest Normal University,
Lanzhou, Gansu 730070, People’s Republic of China
Received 31 March 2006; received in revised form 17 June 2006; accepted 23 June 2006
Available online 27 June 2006
Abstract
Novel artificial anionic receptors N-flurobenzoyl-N0-phenylthioureas were synthesized by simple steps in good yields. The binding properties
for anions of these N-flurobenzoyl-N0-phenylthioureas and 2 N-benzoyl-N0-phenyl thiourea were examined by UV–vis and 1H NMR spectroscopy.
By fluorination of the benzoyl chromophore, the receptors had higher binding affinity for tested anions than the receptor 2. Especially, we studied
the anion binding efficiency of the receptors 1 N-(3-flurobenzoyl)-N0-phenylthiourea and 2 in dimethyl and dimethyl sulfoxide–water binary
solutions in detail respectively. In pure dimethyl sulfoxide, the receptors 1 and 2 had higher binding affinity for Fꢀ over AcOꢀ. However, as the
ratio of water to dimethyl sulfoxide increases, we found the binding properties for tested anions of 1 and 2 changed in dimethyl sulfoxide–water
binary solutions. The receptor 1 showed high binding affinity and selective ability for AcOꢀ in dimethyl sulfoxide containing water with varied
ratios.
# 2006 Elsevier B.V. All rights reserved.
Keywords: Anion recognition; Hydrogen-bonding; Thiourea; Water-containing medium; Red shift; Isosbestic point
1. Introduction
N-benzoyl-N0-phenyl thiourea in dimethyl sulfoxide or dimethyl
sulfoxide–water binary solutionshadselective bindingability for
AcOꢀ. Since fluorine is the most electronegative element, the C–
F bond has dramatically different electronic properties when
compared with the C–H bond [18]. Therefore, the isosteric
replacement of hydrogen with fluorine in the benzoyl
chromophore as well as in their environment is expected to be
accompanied by various changes in their optical properties
[19,20]. Inview of theseandin continuationof ourpreviouswork
on the synthesis of anionic recognition properties of thiourea
derivatives [21,22], we report the synthesis of thiourea-based
receptors with flurobenzoyl units in this letter and show that the
stability of the receptor–anion complex can be significantly
improved by the fluorination of N-benzoyl-N0-phenyl thiourea 2.
In contrast to many papers describing the complexation
properties of various types of thiourea derivatives in 100%
organic media [13–17], the studies regarding the complexation
properties of thiourea in water-containing medium rather than
100% organic medium are scarce [23,24], especially with little
information available on anionic recognition in various ratio
water-containing media [25]. Here, we investigate the binding
efficiency of these receptors for AcOꢀ and Fꢀ in dimethyl
Anion recognition by artificial receptors has been growing in
the field of host–guest chemistry due to biological and
environmental significance [1–8]. Considerable attention has
been focused on the design and synthesis of anion receptors [7–
17], especially neutral receptors [12–17]. Among a variety of
possible H-bond donor groups, systems employing thiourea
moieties have been proven especially efficient in the design of
neutral anion binding receptors [13–17]. Moreover, it is well
demonstrated that phenyl substituted thiourea compounds
exhibit strong binding ability as compared with that of alkyl
substituted ones [17]. It appears to directly attach the thiourea
moiety to benzoyl to form N-benzoylthioureas, as that would be
expectedtodelivermoreefficientlythe anion-bindingmessageto
the benzoyl chromophore. Although the former literature
reported N-benzoyl-N0-phenyl thiourea had no selective
binding ability for AcOꢀ in acetonitrile [15], we found that
* Corresponding author. Tel.: +86 931 7970394; fax: +86 931 7971216.
E-mail address: weitaibao@126.com (T. Wei).
0022-1139/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2006.06.018

Y. Zhang et al. / Journal of Fluorine Chemistry 127 (2006) 1222–1227
1223
Scheme 1. The synthetic route of the compounds 1–4.
sulfoxide containing water with varied ratios as a useful
approach for some practical purpose in analytical chemistry
[24,26] and interpret the results based on the acidity of the
thioureido –NH protons and solvents [17]. In addition, it is
interesting that this molecule shows diagnostic binding
characteristics according to the basicity of the anions and
their charged shapes [27].
2. Results and discussion
The ionophores presented have the advantages of quick and
easy synthesis and purification [28]. These thiourea derivatives
have been synthesized according to previous papers (Scheme 1)
[29–31]. These compounds were characterized by IR, 1H NMR,
13C NMR, 19F NMR and elemental analysis.
Fig. 1. UV–vis absorption of receptor: (a) 1a and (b) 2b in the presence of
a
various anionsc. The concentration of the anion is 25 times as the receptor 1
b
(4.0 ꢁ 10ꢀ5 M). The concentration of the anion is 50 times as the receptor 2
c
(2.0 ꢁ 10ꢀ5 M). Anions exist in their n-Bu4N+ salt.
2.1. UV–vis absorption spectra
The associations of the receptors 1 and 2 with anions
(tetra(n-butyl) ammonium were used for counter cations) in
Me2SO and Me2SO–water binary solutions were studied by
using UV–vis absorption. As shown in Fig. 1, the receptors 1
and 2 exhibited selective recognition for CH3COOꢀ and Fꢀ iꢀn
Me2SO. However, addition of Clꢀ, Brꢀ, HSO4ꢀ, and NO3
scarcely showed spectral changes.
polarity of the solvent. As expected, the absorption spectra
response of 1 and 2 toward tested anions reduces as the ratio of
water to Me2SO increases, indicating that protic solvent H2O
competes with guest anions for hydrogen bonding sites of
receptor. But in contrast, the selective ability of 1 and 2 for
acetate enhances. In pure Me2SO, binding constants of the
receptors 1 and 2 for Fꢀ were larger than for AcOꢀ (Table 1).
However, as the ratio of water to Me2SO increases the situation
is different. As a result, 1 is found to show selective ability only
for acetate in 15% H2O–85% Me2SO (v/v) (Fig. 2(e) and (f)).
By gradually increasing the concentration of CH3COOꢀ to
the solution (5% H2O–95 %Me2SO (v/v)) of receptor 1,
The changes in the absorption spectra of receptor 1 upon
addition of CH3COOꢀ and Fꢀ observed in Me2SO–water
binary solvents were shown in Fig. 2. It should be considered
that the binding forces between a thiourea-based receptor and
anion species are mainly hydrogen bondings, so that the
binding strength ordinarily decreases with increasing in the
Table 1
Association constants Ka (mol/L)ꢀ1 and correlation coefficients R of 1 and 2 for CH3CO2 and Fꢀ in Me2SO and Me2SO–water binary solutionsa
ꢀ
Solvent
Receptor 1
Receptor 2
Ka (CH3CO2ꢀ) (R)b
Ka (Fꢀ) (R)b
Ka (CH3CO2ꢀ) (R)b
4.37 ꢁ 104 (0.9909)
Ka (Fꢀ) (R)b
Me2SO
4.53 ꢁ 105 (0.9978)
3.82 ꢁ 105 (0.9921)
1.96 ꢁ 105 (0.9924)
1.24 ꢁ 103 (0.9923)
3.13 ꢁ 106 (0.9920)
5.03 ꢁ 105 (0.9969)
6.62 ꢁ 104 (0.9984)
–
2.99 ꢁ 106 (0.9952)
5% H2O–95% Me2SO
10% H2O–90% Me2SO
15% H2O–85% Me2SO
1.59 ꢁ 103 (0.9964)
–
–
–
c
2.83 ꢁ 102 (0.9955)
a
Determined by UV–vis at 298 K. [1] = [2] = 4 ꢁ 10ꢀ5 M.
b
c
The values of R were obtained by the results of non-linear curve fitting.
Not determined.

1224
Y. Zhang et al. / Journal of Fluorine Chemistry 127 (2006) 1222–1227
Fig. 2. UV–vis spectral titration of 1 with AcOꢀ and Fꢀ (as their tetrabutylammonium salts) in Me2SO–water binary solutions (a and b in 5% H2O–95% Me2SO; c
and d in 10% H2O–90% Me2SO; e and f in 15% H2O–85% Me2SO (v/v)) at 298 K. [1] = 4.0 ꢁ 10ꢀ5 M. The non-linear fitting curve of change in absorbance of 1 at
269 nm with respect to amounts of anion was shown in the inset.
the intensity of absorption band at 269 nm was decreased
gradually with an unprecedented bathochromic shift occurred
from 269 to 283 nm, and a new absorption band appeared with a
maximum absorption at 312 nm (Fig. 2(a)). The absorbance at
312 nm was increased with increasing the concentration of
CH3COOꢀ, which represents the receptor–anion complex that
should be responsible for the new absorption band. And this new
peakproducedabathochromic shiftfrom312to316.5 nm, which
indicating that the receptor–anion complex could promote the
intramolecular charge transport further [21]. With the addition of
Fꢀ to the solution (5% H2O–95% Me2SO (v/v)) of receptor 1 the
absorption spectra showed similar tendencies. However, two
smaller bathochromic shifts occurred from 269 to 277 nm and
from 313 to 316 nm (Fig. 2(b)), respectively. As shown in
Fig. 2(c) and(d), inthesolution(10% H2O–90%Me2SO (v/v)) of
receptor 1, both similar red shift tendencies of 1-acetate anion
binding complex were obvious with increasing the concentration
of CH3COOꢀ, while the corresponding red shifts of 1-fluoride
anion binding complex were much smaller. The observations
showed that 1-acetate anion binding complex were more stable
than that of fluoride anion in aqueous media. These obvious red-
shifts of absorption band of 1-acetate anion binding complex in
aqueous media were possibly due to the stronger basicity of
acetate anion, and the planar shape of acetate anion, which was
easy to form coplanarity of the thiourea group with the guest
CH3COOꢀ so that the conjugation and stabilities of complex can
be enhanced and the complex was not easily affected by protic
solvent H2O (Scheme 2). At the same time, the complex of

Y. Zhang et al. / Journal of Fluorine Chemistry 127 (2006) 1222–1227
1225
Scheme 2. Molecular structure of 1 and its 1:1 hydrogen-bonding interaction with acetate anion and fluoride anion.
thiourea-based receptor and the spherical fluoride anions were
more easily affected by protic solvent H2O. It was therefore clear
that acetate anion binding to the thiourea moiety increases its
electron-donating ability in aqueous medium, which results in
more significant changes in the UV–vis spectra and larger red
shifts than fluoride anion does.
example, two corresponding red-shifts about 2 and 1 nm in the
presence of CH3COOꢀ for the absorption spectral titration
traces of 2 in the solution (5% H2O–95%Me2SO (v/v)) were
less obvious than that of 1, indicating that the magnitude of red-
shift of absorption band of N-benzoylthiourea-anion binding
complex was also subject to the substituent [15]. Binding
constants of 1 for AcOꢀ and Fꢀ in Me2SO or Me2SO–water
binary solutions were larger than those of 2, indicating that
fluorination of the benzoyl chromophore in the meta (3-F)
position enhanced the acidity of the thioureido –NH protons
and results in stronger bindings with guest anions respectively
accompanied by more significant changes in the UV–vis
spectra than those of 2. We found that 1 in Me2SO containing
10% water by volume showed a sensitive and a selective
binding to AcOꢀ with a binding constant of 1.96 ꢁ 105 (mol/
L)ꢀ1, which was even higher than that of 2 for binding AcOꢀ in
pure Me2SO (Table 1).
The appearance of an isosbestic point during the spectral
titrations suggests the formation of 1:1 hydrogen bonding
complexsbetweenthereceptors1, 2 andtheguestanions[13,14].
According to Fig. 2(b), in the low Fꢀ concentration range
(<5 equiv.), a clear isosbestic point at 283 nm can be observed.
However, the deviation from the clear isosbestic point at high
guest concentration indicated the formation of some amount of
1:2 complexes from one molecule of 1 and two Fꢀ beside the
dominant 1:1 complex [32]. A similar and larger deviation from
the isosbestic point at high fluoride anion concentration in 10%
H2O–90% Me2SO (v/v) was observed (Fig. 2(d)). As shown in
Fig. 2(f), with gradually increasing the concentration of Fꢀ,
changes of the absorption spectrum of 1 occurred. However, no
isosbestic point virtually existed, which demonstrated that 1 did
not form stable complex with Fꢀ in 15%H2O–85%Me2SO (v/v),
while the clear isosbestic points during the spectral titrations of
CH3COOꢀ in Me2SO and Me2SO–water binary solutions can be
observed (Fig. 2(a), (c) and (e)). These interesting observations
further showed the formation of 1:1 complex between 1 and
CH3COOꢀ were more stable than that of 1:1 complex between 1
and Fꢀ in aqueous media.
To further demonstrate that fluorination of the benzoyl
chromophore could enhance the acidity and anion binding
affinity of the thioureido –NH protons, we study the binding
properties for AcOꢀ and Fꢀ (tetra (n-butyl) ammonium were
used for counter cations) of the compounds 3 N-(4-
flurobenzoyl)-N0-phenylthiourea and 4 N-(4-trifluoromethyl-
benzoyl)-N0-phenylthiourea in Me2SO–water binary solutions
by UV–vis spectroscopy. As shown in Table 2, the receptors 3
and 4 have stronger bindings with guest anions respectively
than those of 2, indicating that the introduction of fluorine into
the molecule in the para (4-F) position of the benzoyl
chromophore also substantially enhanced the acidity of the
thioureido –NH protons.
The association constants and correlation coefficient of 1
and 2 for anionic species were calculated by non-linear curve
fitting of UV–vis titrations [33] and the results were
summarized in Table 1. All correlation coefficients (R)
obtained are larger than 0.99, which indicated the formation
of 1:1 stoichiometry complex between receptor 1 or 2 and the
two anions respectively [13,14,34].
2.2. 1H NMR spectra study
Evidence for the hydrogen-bonding nature of the thiourea-
anion interaction was further obtained from the 1H NMR
titration of 1 by Fꢀ in CDCl3. It was noticed in Fig. 3 that the
As shown in the inset of Fig. 2(a)–(e), the satisfactory non-
linear fitting curve further confirmed the formation of 1:1
complex between 1 and guest anions respectively [14].
However, the intramolecular six-membered-ring hydrogen
bond existed in the N-benzoylthioureas, which involving
carbonyl oxygen and the other thioureido –NH proton [35],
may prevent the formation of double hydrogen bonding with
oxoanions. On the basis of the known thiourea-guest anions
hydrogen-bonding mode [24,36], this may point to the
hydrogen-bonding interaction between thiourea moiety in 1
and guest anions, as indicated in Scheme 2.
Table 2
Association constants Ka (mol/L)ꢀ1 and correlation coefficients R of N-(4-
flurobenzoyl)-N0-phenylthiourea 3 and N-(4-trifluoromethylbenzoyl)-N0-phe-
nylthiourea 4 for CH3CO2ꢀ and Fꢀ in Me2SO containing 5% water by volumea
Anions
Receptor 3
Receptor 4
Ka
Rb
Ka
Rb
CH3COOꢀ
Fꢀ
5.55 ꢁ 105
0.9934
0.9906
8.77 ꢁ 105
0.9942
0.9911
2.07 ꢁ 105
7.37 ꢁ 105
Determined by UV–vis at 298 K. [3] = 2 ꢁ 10ꢀ5 M, [4] = 4 ꢁ 10ꢀ5 M.
The values of R were obtained by the results of non-linear curve fitting.
a
Under the identical conditions, the receptor 2 showed a
much weaker response to acetate or fluoride anion. For
b

1226
Y. Zhang et al. / Journal of Fluorine Chemistry 127 (2006) 1222–1227
were used without further purification. The tetrabutylammo-
nium salts were used as anionic substrates.
Melting points were measured on a X-4 digital melting-point
apparatus (uncorrected). The infrared spectra were performed
on a Digilab FTS-3000 FT-IR spectrophotometer. Elemental
analyses were determined by a PE-2400 CHN elemental
1
autoanalyzer. H NMR, 13C NMR and 19F NMR spectra were
recorded on a Varian Mercury plus-400 MHz spectrometer.
UV–vis spectra were taken on a Agilent-8453 spectrometer.
4.2. Synthesis for the title compound
4.2.1. N-(3-Flurobenzoyl)-N0-phenylthiourea (1)
3-Fluorobenzoyl chloride was first obtained from the
reaction of dried 3-fluorobenzoic acid (11 mmol) with freshly
distilled SOCl2 (20 mL) which was refluxed for 8 h, and then
SOCl2 was evaporated [35]. Powdered and dried NH4SCN
(13 mmol), PEG-400 (0.16 g, 3% with respect to NH4SCN),
AcOEt (15 mL) and 3-fluorobenzoyl chloride were placed in a
dried round-bottomed flask and stirred at room temperature for
1 h. Phenylamine (10 mmol) was then added, and the mixture
was stirred for 30 min. When the reaction finished, the mixture
was filtered off to remove inorganic salts and the solvent
distilled out. The resulting solid was recrystallized from EtOH
to give compound 1.
Yield, 82%; needle; mp 96–98 8C; IR (KBr); n 3221 (m) and
3141 (m) (N–H), 1674 (s) (carbonyl), 1267 (m) (thiocarbonyl),
1587 (m), 1526 (s) and 1439 (m) cmꢀ1 (Ph); 1H NMR
(400.1 MHz, CDCl3): d 12.47 (1H, s, NH-Ph), 9.12 (1H, s, NH-
carbonyl), 7.26–7.71 (9H, m, PhH); 13C NMR (100.6 MHz,
CDCl3): d 178.0 (s, C S), 165.6 (s, C O), 164.1 (s, C–F) and
161.6 (s, C–N); 19F NMR (TFA as external standard,
376.5 MHz, CDCl3) d ꢀ114.3 (m, 1F); Elemental analysis:
Anal. Calcd for C14H11O1N2S1F1: C, 61.3; H, 4.0; N, 10.2%.
Found: C, 61.4; H, 3.8; N 10.0%.
Fig. 3. The 1H NMR spectra of receptor 1 in the absence and presence of Fꢀ in
CDCl3 at 298 K. [1] = 0.2 M, (a) 1 only and (b) 1 and 1 equiv. of Fꢀ.
original signals of both thioureido –NH protons appearing at
12.47 and 9.12 ppm disappeared with 1 equiv. of Fꢀ. Similar
phenomena were observed in the 1H NMR spectra of the
receptor 1 in the presence of CH3COOꢀ and the receptor 2 in
the presence of Fꢀ or CH3COOꢀ. These observations clearly
confirmed the hydrogen bonding interaction between the
receptors and guest anions involving the thiourea NH group.
After addition of other anions, such as Clꢀ, Brꢀ, NO3 and
ꢀ
1
HSO4ꢀ, no similar variations were found in H NMR spectra.
3. Conclusions
In summary, we have synthesized a new series of thiourea-
based receptors by fluorination of the benzoyl chromophore for
anion sensing purposes, which are shown to be capable of
strongly binding AcOꢀ through hydrogen bonding interaction in
aqueous Me2SO. The appropriate introduction of fluorine into
the molecule may enhance anion binding affinities. We have
observed that the charge transfer (CT) absorption of the receptor
1 in co-solvent with different proportions of Me2SO and water
was shifted to the red upon binding to guest anions respectively,
therefore it can be concluded that the magnitude of red-shift of
absorption band of receptor-anion binding complex was possibly
subject to the mode of receptor-anion binding complex. But the
most striking finding in this research is that the change of
isosbestic point during theUV–vis spectral titrations of thetested
anions in aqueous medium may closely related to the stability of
anion-receptor binding complex. Moreover, this study provides a
promising methodology for designing optical sensors to
recognize anion species in aqueous medium. Further work to
modify N-benzoylthiourea-based receptor containing fluorine
for anion sensing purposes by naked-eyes is undergoing and will
be reported in the near future.
The compound 2 was synthesized according to literature
procedures [31] and its melting point was 146–147 8C. Its
melting point of the literature was 147–148 8C [29].
4.2.2. N-(4-Flurobenzoyl)-N0-phenylthiourea (3)
Host 3 was synthesized similarly to 1 by using 4-
fluorobenzoic acid. After the majority of SOCl2 was
evaporated, rude 4-fluorobenzoyl chloride was frozen and then
filtered to remove residual SOCl2 to get pure 4-fluorobenzoyl
chloride. When the reaction finished, the obtained solid
was recrystallized from EtOH to give the product as white
crystals.
Yield, 81%; needle; mp 144–146 8C; IR (KBr); n 3267 (m)
and 3029 (m) (N–H), 1662 (s) (carbonyl), 1258 (m)
(thiocarbonyl), 1598 (m), 1534 (s) and 1495 (s) cmꢀ1 (Ph);
1H NMR (400.1 MHz, CDCl3): d 12.52 (1H, s, NH-Ph), 9.13
(1H, s, NH-carbonyl), 7.17–7.93 (9H, m, PhH); 13C NMR
(100.6 MHz, CDCl3): d 178.2 (s, C S), 167.2 (s, C O), 165.8
(s, C–F) and 164.6 (s, C–N); 19F NMR (TFA as external
standard, 376.5 MHz, CDCl3) d ꢀ106.9 (m, 1F); Elemental
analysis: Anal. Calcd for C14H11O1N2S1F1: C, 61.3; H, 4.0; N,
10.2%. Found: C, 61.4; H, 3.9; N 10.0%.
4. Experimental
4.1. Materials and methods
Me2SO was dried and distilled before use according to
standard practice. All other commercially available reagents

Y. Zhang et al. / Journal of Fluorine Chemistry 127 (2006) 1222–1227
1227
4.2.3. N-(4-Trifluoromethylbenzoyl)-N0-phenylthiourea (4)
This compound was synthesized with the same way as 1 by
using 4-trifluoromethylbenzoic acid. It was recrystallized from
EtOH to give the product as light yellow crystals.
[12] S.I. Kondo, T. Suzuki, Y. Yano, Tetrahedron Lett. 43 (2002) 7059–
7061.
[13] D.H. Lee, H.Y. Lee, K.H. Lee, J.I. Hong, Chem. Commun. (2001) 1188–
1189.
[14] J.L. Wu, Y.B. He, Z.Y. Zeng, L.H. Wei, L.Z. Meng, T.X. Yang, Tetra-
hedron 60 (2004) 4309–4314.
Yield, 91%; needle; mp 145–146 8C; IR (KBr); n 3264 (m)
and 3030 (m) (N–H), 1672 (s) (carbonyl), 1261 (m)
(thiocarbonyl), 1600 (m), 1557 (s), and 1533 (s) cmꢀ1 (Ph);
1H NMR (400.1 MHz, CDCl3): d 12.44 (1H, s, NH-Ph), 9.19
(1H, s, NH-carbonyl), 7.25–8.01 (9H, m, PhH); 13C NMR
(100.6 MHz, CDCl3): d 177.9 (s, C S), 165.7 (s, C O), 137.4
(s, C–N), 134.9 (m, C–CF3) and 124.1 (s,CF3); 19F NMR (TFA
as external standard, 376.5 MHz, CDCl3) d ꢀ67.6 (s, 3F);
Elemental analysis: Anal. Calcd for C15H11O1N2S1F3: C, 55.6;
H, 3.4; N, 8.6%. Found: C, 55.5; H, 3.3; N 8.4%.
[15] L. Nie, Z. Li, J. Han, X. Zhang, R. Yang, W.X. Liu, F.Y. Wu, J.W. Xie, Y.F.
Zhao, Y.B. Jiang, J. Org. Chem. 69 (2004) 6449–6454.
[16] S.I. Kondo, M. Nagamine, Y. Yano, Tetrahedron Lett. 44 (2003) 8801–
8804.
[17] P. Bu¨hlmann, S. Nishizawa, K.P. Xiao, Y. Umezawa, Tetrahedron 53
(1997) 1647–1654.
[18] J.D. Dunitz, Chem. Biol. Chem. 5 (2004) 614–621.
[19] N. Budisa, P. Pal, S. Alefelder, P. Birle, T. Krywcun, M. Rubini, W.
Wenger, J.H. Bae, T. Steiner, Biol. Chem. 385 (2004) 191–202.
[20] P.P. Pal, J.H. Bae, M.K. Azim, P. Hess, R. Friedrich, R. Huber, L. Moroder,
N. Budisa, Biochemistry 44 (2005) 3663–3672.
[21] Y.M. Zhang, W.X. Xu, Y.Q. Zhou, H. Yao, T.B. Wei, Acta Chim. Sin. 64
(2006) 79–84.
Acknowledgements
[22] Y.M. Zhang, W.X. Xu, M.L. Li, T.B. Wei, Chinese J. Inorg. Chem. 21
(2005) 1815–1820.
We gratefully acknowledge the support of the National
Natural Science Foundation of China (No. 20371040), the
Natural Science Foundation of Gansu province (3YS051-A25-
01) and the Key Project of Chinese Ministry of Education (No.
205161).
[23] R. Kato, Y.Y. Cui, S. Nishizawa, T. Yokobori, N. Teramae, Tetrahedron
Lett. 45 (2004) 4273–4276.
[24] R. Kato, S. Nishizawa, T. Hayashita, N. Teramae, Tetrahedron Lett. 42
(2001) 5053–5056.
[25] L. Nie, X. Zhang, F.Y. Wu, Y.B. Jiang, Acta Chim. Sin. 62 (2004) 369–
372.
[26] N.R. Cha, S.Y. Moon, S.-K. Chang, Tetrahedron Lett. 44 (2003) 8265–
8268.
References
[27] P.D. Beer, P.A. Gale, Angew. Chem., Int. Ed. 40 (2001) 486–516.
[28] D.C. Schroeder, Chem. Rev. 50 (1955) 185–228.
[29] T.B. Wei, Q. Lin, Y.M. Zhang, W. Wei, Synth. Commun. 34 (2004) 181–
186.
[1] B.J. Calnan, B. Tidor, S. Biancalana, D. Hudson, A.D. Frankel, Science
252 (1991) 1167–1171.
[2] F.P. Schmidtchen, M. Berger, Chem. Rev. 97 (1997) 1609–1646.
[3] M.M.G. Antonisse, D.N. Reinhoudt, Chem. Commun. (1998) 443–447.
[4] P.A. Gale, Coord. Chem. Rev. 199 (2000) 181–233.
[5] J.K. Ray, S. Gupta, D. Pan, G.K. Kar, Tetrahedron 57 (2001) 7213–7219.
[6] B.D. Smith, T.N. Lambert, Chem. Commun. (2003) 2261–2268 (Feature
article).
[30] R. Rasmassen, F.J. Villani, L.E. Weaner, B.E. Reynolds, A.R. Hood, L.R.
Hecker, S.O. Nortey, A. Hanslin, J. Costanzo, E.T. Powell, A.J. Molinari,
Synthesis (1988) 456–459.
[31] Y.M. Zhang, T.B. Wei, L.M. Gao, Synth. Commun. 31 (2001) 3099–3105.
[32] W.S. Yeo, J.I. Hong, Tetrahedron Lett. 39 (1998) 8137–8140.
[33] Y. Liu, B. Li, B.H. Han, J. Chem. Soc., Perkin Trans. 2 (1999) 563–
568.
[7] P.D. Beer, E.J. Hayes, Coord. Chem. Rev. 240 (2003) 167–189.
[8] X.H. Qian, F.Y. Liu, Tetrahedron Lett. 44 (2003) 795–799.
[9] Y.J. Kubo, M. Tsukahara, S. Ishihara, S. Tokita, Chem. Commun. (2000)
653–654.
[34] J. Bourson, J. Pouget, B. Valeur, J. Phys. Chem. 97 (1993) 4552–4557.
´
[35] O.-S. Elena, P.-M. Leonel, E.-H. Osvaldo, R.-L. Susana, A.-C. Julian, J.
[10] Y.J. Kubo, M. Kato, Y. Misawa, S. Tokita, Tetrahedron Lett. 45 (2004)
3769–3773.
Chem. Soc., Perkin Trans. 2 (2001) 2211–2218.
[36] F.Y. Wu, Z. Li, Z.C. Wen, N. Zhou, Y.F. Zhao, Y.B. Jiang, Org. Lett. 4
(2002) 3203–3205.
[11] X.H. Hou, K. Kobiro, Tetrahedron 61 (2005) 5866–5875.