A selective fluorogenic chemodosimeter for Hg2+ based on the dimerization of desulfurized product

Article abstract of DOI:10.1016/j.tet.2013.10.024

A simple Hg²⁺-selective chemodosimetric system based on thiosemicarbazone was investigated. The transformation of thiosemicarbazone into semicarbazone selectively exerted by Hg²⁺ ions and the dimerization of semicarbazone resulted in a pronounced OFF-ON-type fluorescent signaling behavior. The coexistent metal ions, such as Fe³⁺, Ca²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb ²⁺, Zn²⁺, Cr³⁺, Mg²⁺, Na ⁺, K⁺, and Fe²⁺, had no obvious interference with the detection of Hg²⁺. In addition, S₁₂-Hg ²⁺ plays a high sensitivity for basic anions to form an 'OFF-ON-OFF' type signaling behavior, with the Hg²⁺-induced emission spectra can be quenched. Moreover, test strips based on S₁₂ exhibited a good selectivity to Hg²⁺. We believe the test strips could act as a convenient and efficient Hg²⁺ test kit.

Full text of DOI:10.1016/j.tet.2013.10.024

Tetrahedron 69 (2013) 10292e10298
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A selective fluorogenic chemodosimeter for Hg2þ based on the
dimerization of desulfurized product
,
,
,
,
,b
Peng Zhang a b, BingBing Shi a b, YouMing Zhang a b, Qi Lin a b, Hong Yao a
,
XingMei You a b, TaiBao Wei a
,
,b,
*
a Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, College of Chemistry and Chemical Engineering,
Northwest Normal University, Lanzhou, Gansu 730070, PR China
b Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou,
Gansu 730070, PR China
a r t i c l e i n f o
a b s t r a c t
A simple Hg2þ-selective chemodosimetric system based on thiosemicarbazone was investigated. The
transformation of thiosemicarbazone into semicarbazone selectively exerted by Hg2þ ions and the di-
merization of semicarbazone resulted in a pronounced OFFeON-type fluorescent signaling behavior. The
coexistent metal ions, such as Fe3þ, Ca2þ, Cu2þ, Co2þ, Ni2þ, Cd2þ, Pb2þ, Zn2þ, Cr3þ, Mg2þ, Naþ, Kþ, and
Fe2þ, had no obvious interference with the detection of Hg2þ. In addition, S12eHg2þ plays a high sen-
sitivity for basic anions to form an ‘OFFeONeOFF’ type signaling behavior, with the Hg2þ-induced
Article history:
Received 20 July 2013
Received in revised form 22 September 2013
Accepted 10 October 2013
Available online 17 October 2013
Keywords:
Mercury ions
Desulfurization
Dimerization
emission spectra can be quenched. Moreover, test strips based on S12 exhibited a good selectivity to Hg2þ
.
We believe the test strips could act as a convenient and efficient Hg2þ test kit.
Ó 2013 Published by Elsevier Ltd.
Fluorescence turn on
Thiosemicarbazone
Acetate anion
1. Introduction
Fluorescence spectroscopy has become a powerful tool for
sensing and imaging trace amounts of species, such as metal ions
because of its simplicity and high sensitivity.3 Many fluorescent
probes for mercury ions have been developed so far.4 A supramo-
lecular approach has received much attention, in which a binding
event between a mercury ion and an appropriate ligand attached to
a fluorophore leads to changes in the fluorescence property.5
However, the main disadvantage of such approach is the lack of
selectivity, other ionsdfor example, Cu2þ, Cd2þ, and Fe3þ ion-
sdoften interfere with such assays.6e8 To overcome this limitation,
many other detection methods for Hg2þ involve chemical reaction
of Hg2þ with sulfur-containing derivatives have been devised.9
These methods employ desulfurization or subsequent trans-
formation reactions of thioamide,10 thiourea,9a and thione.11 Most
of these traditional chemosensors contain a sulfur moiety and the
sensing process involves an intramolecular cyclic guanylation of
thiourea derivatives (Scheme 1).12 This kind of approach usually
Mercury is an indispensable element in the current chemical
industry, yet the highly poisonous nature of mercury and its de-
rivatives have drawn our keen concern regarding their environ-
mental contamination.1 The extreme toxicity of mercury results
from its high affinity for thiol groups in proteins and enzymes,
leading to the dysfunction of cells and consequently causing health
problems.2 Unfortunately, mercury contamination can occur
through a variety of natural and anthropogenic sources including
oceanic and volcanic emissions, gold mining, and combustion of
fossil fuels. Thus, the health concerns over exposure to mercury
have motivated the exploration of selective and efficient methods
for the monitoring of mercury in biological and environmental
samples.
displays
a localize change in fluorescence emission spectra.
Therefore, ‘OFFeON’ fluorimetric probes for Hg2þ based on de-
* Corresponding author. Tel.: þ86 931 7973191; e-mail address: weitaibao@126.
sulfurization are less common.
com (TaiBao Wei).
0040-4020/$ e see front matter Ó 2013 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.tet.2013.10.024

P. Zhang et al. / Tetrahedron 69 (2013) 10292e10298
10293
Scheme 1. Tactics for the sensing of Hg2þ
.
Furthermore, 5-aryl furfural derivatives have been synthe-
sized and used for biological activity for a long time,13 but they
have seldom been used in hosteguest chemistry, and there is no
report for sensing ions. 5-Aryl furfural derivatives are ideal
platforms for the development of cation, anion, and neutral
molecule recognition, because of its excellently photophysical
properties.
Our research group has a longstanding interest in molecular
recognition.14 Herein, we report a 5-aryl furfural-based Hg2þ che-
modosimeter (compound S12) as a new advance in Hg2þ recognition,
which was synthesized by the facile Schiff base condensation re-
action of 5-(4-nitro)phenyl-2-furaldehyde and thiosemicarbazide
(Scheme 2). Our design is based on the well-known reaction that
2. Experimental section
2.1. Materials and physical methods
All reagents and solvents were commercially available at ana-
lytical grade and were used without further purification. 1H NMR
and 13C NMR spectra were recorded on a Mercury-400BB spec-
trometer at 400 MHz and 100 MHz, respectively. Chemical shifts
are reported in parts per million downfield from tetramethylsilane
(TMS,
spectra were recorded on a Shimadzu UV-2550 spectrometer.
Photoluminescence spectra were performed on Shimadzu
RF-5301 fluorescence spectrophotometer. Melting points were
d scale with solvent resonances as internal standards) UVevis
a
Scheme 2. Synthetic procedures of sensor S12
.
thiosemicarbazone derivatives can be easily transformed into sem-
icarbazone derivatives with the promotion of the Hg2þ ion, and the
semicarbazone derivatives are very easy to self-assemble by in-
termolecular hydrogen bonding, as depicted in Scheme 1. First, we
chose the typically mercury-promoted desulfurization reaction as
the recognition event for its high selectivity (the strong thiophilic
affinity toward the Hg2þ ion).15 On the other hand, the 5-aryl furfural
group as the signaling moiety is attached to the recognition moiety
with a dissociated structure (nonfluorescent). When the Hg2þ-pro-
moted desulfurization reaction takes place, the emerging semi-
carbazone derivatives could dimerize by intermolecular hydrogen
bonding (strongly fluorescent). We are very gratifying to see that the
results go as we expect, sensor S12 could allow selectively recognition
of Hg2þ in DMSO. In addition, S12eHg2þ displays high sensitivity for
basic anions (such as, AcOꢀ, OHꢀ, Fꢀ, and H2PO4ꢀ) to form an
‘OFFeONeOFF’ type signaling behavior, with the Hg2þ-induced
emission spectra being quenched. To the best of our knowledge, this
is the first time to report an OFFeON fluorescent chemosensor with
high selectivity for Hg2þ, which based on the dimerization of the
Hg2þ-induced desulfurization product.
measured on an X-4 digital melting-point apparatus (uncorrected).
Infrared spectra were performed on a Digilab FTS-3000 FT-IR
spectrophotometer.
2.2. General procedure for UVevis experiments
UVevis spectroscopy was carried out just after the addition of
Hg2þ and AcOꢀ in DMSO solution, while keeping the ligand con-
centration constant (2.0ꢁ10ꢀ5 M) on a Shimadzu UV-2550 spec-
trometer. The solution of Hg2þ was prepared from the perchlorate
salt, the solution of anions was prepared from their tetrabuty-
lammonium salts.
2.3. General procedure for fluorescence spectra experiments
All fluorescence spectroscopy was carried out just after the
addition of perchlorate metal salts in DMSO solution, while keeping
the ligand concentration constant (2.0ꢁ10ꢀ5 M) on a Shimadzu
RF-5301spectrometer. The solution of metal ions were prepared

10294
P. Zhang et al. / Tetrahedron 69 (2013) 10292e10298
from the perchlorate salts of Fe3þ, Hg2þ, Ca2þ, Cu2þ, Co2þ, Ni2þ
Cd2þ, Pb2þ, Zn2þ, Cr3þ, Mg2þ, Naþ, Kþ, and Fe2þ
,
.
2.4. General procedure for test strips experiments
Test strips were prepared by immersing filter papers into
a DMSO solution of S12 (0.001 M) and then drying in air. The test
strips containing S12 were utilized to sense Hg2þ, when Hg2þ so-
lution (0.001 M) was added on the test kits, the fluorescence turn
on response can be observed under UV lamp. However, other ions,
such as Fe3þ, Ca2þ, Cu2þ, Co2þ, Ni2þ, Cd2þ, Pb2þ, Zn2þ, Cr3þ, Mg2þ
,
Naþ, Kþ, and Fe2þ, cannot induce obvious changes in color under UV
lamp.
2.5. Synthesis
2.5.1. Synthesis of 5-(4-nitro)phenyl-2-furaldehyde. 5-(4-Nitro)
phenyl-2-furaldehyde was synthesized according to literature
methods, yield 70%, mp 242e243 ꢂC.13
Fig. 1. Fluorescence spectra response of S12 (20
12 equiv of Hg2þ
lex¼410 nm). Inset: Photograph of S12 (20
of Hg2þ, which was observed under a UV-lamp (365 nm).
m
M) in DMSO upon addition of
(
m
M) upon adding 12 equiv
2.5.2. Synthesis of S12. The synthesis of chemosensor S12 is out-
lined in Scheme 2, by the facile Schiff base condensation reaction:
5-(4-nitro)phenyl-2-furaldehyde (0.587 g, 2.2 mmol), amino-
thiourea (0.130 g, 2 mmol) and a catalytic amount of acetic acid
(AcOH) were combined in absolute ethanol (60 ml). The solution
was stirred under reflux for 6 h. After cooling to room tempera-
ture, the black green precipitate was filtered, washed three times
with hot absolute ethanol, then recrystallized with EtOH/DMF to
give a celadon powder product S12 (0.488 g) in 85% yield (mp
>300 ꢂC), IR: (KBr, cmꢀ1) v: 3398, 3246 (NH), 3159 (C]NH), 1599
(C]C), 1539 (C]C), 1469 (C]C), 1332 (AreO), 1286 (C]S). 1H
NMR (DMSO-d6, 400 MHz):
d 11.64 (1H, s, NH), 8.41 (1H, s, NH2),
8.30 (2H, d, J¼8, ArH), 8.10 (2H, d, J¼8, ArH), 8.00 (1H, s, N]CH),
7.90 (1H, s, NH2), 7.46 (1H, d, J¼4, ArH), 7.18 (1H, d, J¼4, ArH); 13C
NMR (DMSO-d6, 100 MHz):
d 177.83, 152.16, 152.11, 151.02, 146.19,
135.25, 131.26, 124.59, 124.39, 115.36, 112.52, 112.48; Anal. Calcd
for C12H10N4SO3: C 49.66, H 3.45, N 19.31; found C, 49.65; H, 3.44;
N, 19.33. ESI-MS calcd for C12H10N4SO3, [MþH]þ¼291.0, found
[MþH]þ¼291.2.
Fig. 2. Fluorescence titrition spectra of S12 (20
creasing concentration of Hg2þ
lex¼410 nm).
mM) in DMSO upon adding of an in-
(
3. Results and discussion
A solution of probe S12 exhibits an absorption maximum at
410 nm, however, an obviously red shift takes place upon treated
with 12 equiv of Hg(ClO4)2 (Fig. S1). This behavior can be explained
by the Hg2þ-promoted displacement reaction, from the thio-
semicarbazone to semicarbazone, which leads to the change in the
absorption wavelengths.
The fluorescence spectral properties of probe S12 with Hg2þ
were also examined, compound S12 alone displayed none fluores-
cence emission band at 556 nm when it was excited at 410 nm. It
led to a prominent fluorescence enhancement, when 12 equiv of
Hg2þ was added to the DMSO solution of S12, indicating a Hg2þ
-
selective ‘OFFeON’ fluorescent signaling behavior (Fig. 1). The re-
action process completed as soon as the addition of Hg2þ, implying
that sensor S12 could be used for real-time detection of Hg2þ. The
increase of emission intensity may be attributed to the di-
merization of S12eHg2þ product by intermolecular hydrogen bond.
This was further confirmed by the appearance of a peak at m/z
549.0 assignable to S12eHg2þ dimer in the ESI-MS spectrum, while
the peak at m/z 275.2 assignable to the dissociated product of
S
12eHg2þ (Fig. S3).
The Hg2þ titration experiment with sensor S12 was then car-
Fig. 3. A plot of fluorescence spectra depending on the concentration of Hg2þ in the
ried out, as shown in Fig. 2, the fluorescent intensity remarkably
range from 0 to 1.0 equiv, the detection wavelength was 556 nm.

P. Zhang et al. / Tetrahedron 69 (2013) 10292e10298
10295
increased as the Hg2þ concentration increased from
0 to
1.0 equiv. Besides, it can be saw clearly form Fig. 3, while the
amount of Hg2þ ion is beyond 1.0 equiv, the emission at 556 nm
tends to saturation, which reveals the possible formation of
a 1:1 between S12 and Hg2þ. The detection limit that was cal-
culated on the basis of 3SB/S16 (see Supplementary data, Fig. S4)
showed a detection limit of approximately 1.67ꢁ10ꢀ6 M for Hg2þ
ion.
In order to verify the dimerization of S12eHg2þ product, basic
anions were added to the solution of S12þHg2þ, for they can
damage the hydrogen bonding of the dimer, for example, when
AcOꢀ was added to the solution of S12eHg2þ, it induced an obvi-
ous red shift from 412 nm to 506 nm in UVevis absorption
spectrum, and the color of the solution changes from yellow to
purple red, at the same time (Fig. 4a). The addition of AcOꢀ also
induced an ‘ONeOFF’ fluorescent response, the fluorescence
emission intensity returned to the levels observed for the free
compound S12 when 30 equiv of AcOꢀ were added, see Fig. 4b, and
the other basic anions, such as Fꢀ, OHꢀ, and H2PO4ꢀ, showed the
same properties with AcOꢀ (Figs. S5, S6, S7). From the AcOꢀ ti-
tration experiment with sensor S12eHg2þ (Fig. 4c), we can see that
the fluorescent intensity remarkably decreased as the AcOꢀ con-
centration increased. The decrease of emission intensity may be
attributed to that the intermolecular hydrogen bonding of
S
12eHg2þ product was damaged and the dimer disappeared when
AcOꢀ was added to the solution of S12eHg2þ. This shows that the
Hg2þ-induced dimer could therefore be used as a fluorescent
sensor for basic anions.
The recognition mechanism of the sensor S12 with Hg2þ was
investigated by FT-IR spectra (Fig. 5). Compared with S12
,
S
12eHg2þ product (1:1, solid complex, KBr) showed a peak dis-
appearance at 1286 cmꢀ1, while there came out a new peak at
1663 cmꢀ1, the changes of these peaks indicated that the C]S
bonding disappears and C]O bonding appears. Because of the
thiocarbonyl was replaced by carbonyl, and then the product
dimerized by hydrogen bonding, the peaks of NH2 and NH at
3398 cmꢀ1, 3246 cmꢀ1 and 3159 cmꢀ1 shifted to 3454 cmꢀ1
,
3356 cmꢀ1, and 3201 cmꢀ1
.
The signaling mechanism is based on Hg2þ-induced de-
sulfurization of the thio derivative and dimerization of S12eHg2þ
product by intermolecular hydrogen bonding (Scheme 3). The thi-
osemicarbazone group of S12 is readily transformed to its semi-
carbazone function by reaction with Hg2þ ions, the liberated sulfur
atom forms a stable species of HgS with Hg2þ ions and the oxygen
comes from the DMSO solvent (Fig. S8), at the same time, S12eHg2þ
product dimerized by intermolecular hydrogen bonding of NH and
NH2 with oxygen atoms. As a result of this transformation, none
fluorescent S12 is transformed into a strongly yellow emitting
dimer.
The proposed mechanism was also confirmed by 1H NMR ti-
tration, as shown in Fig. 6, sensor S12 showed three single peaks
at 11.63, 8.40, and 7.89 ppm in DMSO, we confirmed that which
correspond to the protons of eNHe and eNH2, respectively. With
the addition of Hg2þ, the thiocarbonyl was transformed to car-
bonyl and the intermolecular hydrogen bonding was formed
gradually, in the corresponding NMR spectra, the downfield shift
of NeHs (spectra aec) of S12 was according to the proposed di-
merization process through intermolecular hydrogen bonding,
while the upfield shift of protons Hb and Hc demonstrated by
spectra def was based on the
the concentration of the dimer increased, the
p
e
p
stacking of the dimer. When
interaction
Fig. 4. (a) UVevis spectra of S12 (20
m
M) upon addition of Hg2þ and AcOꢀ in DMSO. (b)
Fluorescence spectra of S12 (20 m
M) in the presence of Hg2þ (12 equiv) and AcOꢀ in
pep
between them appeared, which lead to the upfield shift of pro-
tons Hb and Hc. The change of 1H NMR spectra under variant
concentrations was also investigated (see Supplementary data,
Fig. S9), the signal at 12.88 ppm correspond to the proton of
Ha, which formated the intermolecular hydrogen bonding, and
DMSO (lex¼410 nm). (c) Fluorescence titrition spectra of S12þHg2þ(20
mM) in DMSO
upon adding of an increasing concentration of AcOꢀ
(
lex¼410 nm).

10296
P. Zhang et al. / Tetrahedron 69 (2013) 10292e10298
the signal at 10.48 ppm correspond to the proton of Ha without
the intermolecular hydrogen bonding, from Fig. S9, we can see
with the increasing concentration of S12eHg2þ, the peak at
10.48 ppm comes out, indicate that a part of S12eHg2þ product
cannot format the intermolecular hydrogen bonding.
To validate the selectivity of sensor S12, various ions including
Hg2þ, Fe3þ, Ca2þ, Cu2þ, Co2þ, Ni2þ, Cd2þ, Pb2þ, Zn2þ, Cr3þ, Mg2þ
,
Naþ, Kþ, and Fe2þ contacting with S12 were investigated by
fluorescence spectra. Among various ions, only the addition of
Hg2þ displayed an OFFeON response in fluorescence spectra, this
showed that S12 had a high selectivity for Hg2þ, other ions almost
caused no changes in fluorescence (Fig. 7a). The competition
experiments were also measured by addition of 12 equiv of Hg2þ
to the DMSO solution of S12 in the presence of 12 equiv of other
metal ions, such as, Fe3þ, Ca2þ, Cu2þ, Co2þ, Ni2þ, Cd2þ, Pb2þ, Zn2þ
,
Fig. 5. FT-IR spectra of S12 (the black line) and S12eHg2þ (the red line).
Scheme 3. Proposed sensing mechanism.
Fig. 6. Partial 1H NMR spectra of S12 (3 mM, DMSO-d6) and in the presence of varying amounts of Hg2þ. The mole ratio of Hg2þ to S12 is (a) 0, (b) 0.2, (c) 0.5, (d) 0.75, (e) 1.0, and
(f) 1.2, respectively.

P. Zhang et al. / Tetrahedron 69 (2013) 10292e10298
10297
Cr3þ, Mg2þ, Naþ, Kþ, and Fe2þ. As show in Fig. 7b, we find all the
coexistent metal ions had no obvious interference with the de-
tection of Hg2þ, which indicated that the system of Hg2þ-induced
dimerization was hardly affected by these coexistent ions. The
selectivity of Hg2þ over other ions, especially Cu2þ, Fe3þ, and
Cd2þ, is important because many reported Hg2þ sensors suffer
from deleterious interference of these ions. These results sug-
gested that sensor S12 displayed an excellent selectivity towards
Hg2þ
.
To investigate the practical application of chemosensor S12, test
strips were prepared by immersing filter papers into a DMSO so-
lution of S12 (0.001 M) and then drying in air. The test strips con-
taining S12 were utilized to sense Hg2þ. As shown in Fig. 8, when
Hg2þ solution was added on the test kits, the fluorescence turn on
response can be see under UV irradiation. Potentially competitive
anions exerted no influence on the detection of Hg2þ by the test
strips. Therefore, the test strips could conveniently detect Hg2þ in
solution.
4. Conclusion
In summary,
a
simple Hg2þ-selective chemodosimetric
system based on thiosemicarbazone was investigated. The sig-
naling is due to the dimerization of the Hg2þ-induced de-
sulfurization product. The transformation of the thiocarbonyl
function into a carbonyl group selectively exerted by Hg2þ ions
and the dimerization of semicarbazone resulted in a pro-
nounced OFFeON-type fluorescent signaling behavior. The pre-
pared compound may be utilized as a new chemodosimeter for
the analysis of Hg2þ ions in the micromolar concentration range.
In addition,
S
12eHg2þ displays a high sensitivity for basic
anions to form an ‘OFFeONeOFF’ type signaling behavior.
Moreover, test strips based on S12 were fabricated, which also
exhibited a good selectivity to Hg2þ as in solution. We believe
the test strips could act as a convenient and efficient Hg2þ test
kit.
Fig. 7. (a) Fluorescence spectra response of S12 (20 mM) in DMSO upon addition of
12 equiv of Hg2þ, Fe3þ, Ca2þ, Cu2þ, Co2þ, Ni2þ, Cd2þ, Pb2þ, Zn2þ, Cr3þ, Mg2þ, Naþ, Kþ
mM) upon adding 12 equiv of
various ions, which was observed under a UV-lamp (365 nm). (b) Fluorescence spectra
,
and Fe2þ ions (lex¼410 nm). Inset: Photograph of S12 (20
response of S12 (20 mM) in the presence of 12 equiv of various ions containing 12 equiv
of Hg2þ in DMSO.
Fig. 8. Photographs of test strips (A: only S12; B: S12þHg2þ; C: S12þother ions; D: S12þHg2þþother ions.), which was taken under a UV-lamp (365 nm).

10298
P. Zhang et al. / Tetrahedron 69 (2013) 10292e10298
Yuan, L.; Yu, Q. X. Org. Biomol. Chem. 2010, 8, 3618e3620; (h) Luca, P.; Carlotta,
Acknowledgements
B.; Marco, M.; Nelsi, Z.; Su, N.; Jerald, S. B.; Reed, M. I.; Paul, B. S. J. Am. Chem.
Soc. 2000, 122, 6769e6770.
This work was supported by the National Natural Science
Foundation of China (No. 21064006, 21262032 and 21161018), the
Program for Changjiang Scholars and Innovative Research Team in
University of Ministry of Education of China (No. IRT1177), the
Natural Science Foundation of Gansu Province (No. 1010RJZA018),
the Youth Foundation of Gansu Province (No. 2011GS04735) and
NWNU-LKQN-11-32.
5. (a) Dong, M.; Wang, Y. W.; Peng, Y. Org. Lett. 2010, 12, 5310e5313; (b) Yang, M.
H.; Thirupathi, P.; Lee, K. H. Org. Lett. 2011, 13, 5028e5031; (c) Lee, M. H.; Lee, S.
W.; Kim, S. H.; Kang, C.; Kim, J. S. Org. Lett. 2009, 11, 2101e2104; (d) Shi, B. B.;
Zhang, P.; Wei, T. B.; Yao, H.; Lin, Q.; Liu, J.; Zhang, Y. M. Tetrahedron 2013, 69,
7981e7987.
6. (a) Chen, X. Q.; Pradhan, T. H.; Wang, F.; Kim, J. S.; Yoon, J. Y. Chem. Rev. 2012,
112, 1910e1956; (b) Elizabeth, M. N.; Stephen, J. L. J. Am. Chem. Soc. 2003, 125,
14270e14271; (c) Guo, X. F.; Qian, X. H.; Jia, L. H. J. Am. Chem. Soc. 2004, 126,
2272e2273.
7. (a) Rao, A. S.; Kim, D. Y.; Wang, T. J.; Kim, K. H.; Hwang, S.; Ahn, K. H. Org. Lett.
2012, 14, 2598e2601; (b) Kaur, P.; Kaur, S.; Singh, K. Org. Biomol. Chem. 2012, 10,
1497e1501; (c) Chen, Y. T.; Jiang, J. Z. Org. Biomol. Chem. 2012, 10, 4782e4787.
8. Song, K. C.; Kim, J. S.; Park, S. M.; Chung, K. C.; Ahn, S.; Chang, S. K. Org. Lett.
2006, 8, 3413e3416.
9. (a) Wu, J. S.; Hwang, I. C.; Kim, K. S.; Kim, J. S. Org. Lett. 2007, 9, 907e910;
(b) Lee, M. H.; Cho, B. K.; Yoon, J.; Kim, J. S. Org. Lett. 2007, 9, 4515e4518;
(c) Yang, Y. K.; Ko, S. K.; Shin, I.; Tae, J. Org. Biomol. Chem. 2009, 7,
4590e4593; (d) Luxami, V.; Verma, M.; Rani, R.; Paul, K.; Kumar, S. Org.
Biomol. Chem. 2012, 10, 8076e8081; (e) Chen, Y.; Sun, Z. H.; Song, B. E.; Liu,
Y. Org. Biomol. Chem. 2011, 9, 5530e5534.
10. Zhang, G.; Zhang, D.; Yin, S.; Yang, X.; Shuai, Z.; Zhu, D. Chem. Commun. 2005,
2161e2163.
11. Rode, A. B.; Kim, J. K.; Kim, S. H.; Gupta, G.; Hong, I. S. Tetrahedron Lett. 2012, 53,
2571e2574.
12. Liu, Y. L.; Lv, X.; Zhao, Y.; Chen, M. L.; Liu, J.; Wang, P.; Guo, W. Dyes Pigm. 2012,
92, 909e915.
13. (a) Zhang, Y. M.; Lin, Q.; Wei, T. B.; Qin, X. P.; Li, Y. Chem. Commun. 2009,
6074e6076; (b) Wang, J. X.; Chen, J. C.; Li, Z. J. Chin. Sci. Bull. 1966, 419, 58e63.
14. (a) Zhang, Y. M.; Lin, Q.; Wei, T. B.; Wang, D. D.; Yao, H.; Wang, Y. L. Sens. Ac-
tuators, B 2009, 137, 447e453; (b) Wei, T. B.; Zhang, P.; Shi, B. B.; Chen, P.; Lin,
Q.; Liu, J.; Zhang, Y. M. Dyes Pigm. 2013, 97, 297e303; (c) Zhang, Y. M.; Shi, B. B.;
Zhang, P.; Huo, J. Q.; Chen, P.; Lin, Q.; Liu, J.; Wei, T. B. Sci. China. Chem. 2013, 56,
612e618; (d) Liu, M. X.; Wei, T. B.; Lin, Q.; Zhang, Y. M. Spectrochim. Acta A 2011,
79, 1837e1842; (e) Lin, Q.; Fu, Y. P.; Chen, P.; Wei, T. B.; Zhang, Y. M. Tetrahedron
Lett. 2013, 54, 5031e5034.
Supplementary data
These data include the Spectral data, MS data and copies of
1H/13C NMR of the compounds described in this article. Supple-
mentary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2013.10.024.
References and notes
1. (a) Patrick, L. Altern. Med. Rev. 2002, 7, 456e471; (b) US EPA. Final Report. EPA-
452/R-05e003; US EPA: Research Triangle Park, NC, 2005.
2. (a) Grandjean, P.; Weihe, P.; White, R. F.; Debes, F. Environ. Res. 1998, 77,
165e172; (b) Takeuchi, T.; Morikawa, N.; Matsumoto, H.; Shiraishi, Y. Acta
Neuropathol. 1962, 2, 40e57; (c) Harada, M. Crit. Rev. Toxicol. 1995, 25, 1e25.
3. (a) Callan, J. F.; Silva, A. P. D.; Magri, D. C. Tetrahedron 2005, 61,
ꢀ
8551e8588; (b) Martínez, M. R.; Sancanon, F. Chem. Rev. 2003, 103,
4419e4476; (c) Czarnik, A. W. Chem. Res. 1994, 27, 302e308; (d) Kim, J. S.;
Quang, D. T. Chem. Rev. 2007, 107, 3780e3799; (e) Zhou, Y.; You, X. Y.;
Fang, Y.; Li, J. Y.; Liu, K.; Yao, C. Org. Biomol. Chem. 2010, 8, 4819e4822.
4. (a) Nolan, E. M.; Lippard, S. J. Chem. Rev. 2008, 108, 3443e3480; (b) Jun, M. E.;
Roy, B.; Ahn, K. H. Chem. Commun. 2011, 7583e7601; (c) Joydev, H.; Suman, P.;
Gregor, P. J.; Subhajit, B. Inorg. Chem. 2012, 51, 10129e10135; (d) Lee, H. J.; Lee,
H. S.; Joseph, H. R.; Robert, D. H. Inorg. Chem. 2012, 51, 10904e10915; (e) Koner,
R. R.; Sinha, S.; Kumar, S.; Nandi, C. K.; Ghosh, S. Tetrahedron Lett. 2012, 53,
2302e2307; (f) Lu, H.; Xiong, L. Q.; Liu, H. Z.; Yu, M. X.; Shen, Z.; Li, F. Y.; You, X.
Z. Org. Biomol. Chem. 2009, 7, 2554e2558; (g) Lin, W. Y.; Cao, X. W.; Ding, Y. D.;
15. Namgoong, J. E.; Jeon, H. L.; Kim, Y. H.; Choi, M. G.; Chang, S. K. Tetrahedron Lett.
2010, 51, 167e169.
16. Analytical Methods Committee. Analyst 1987, 112, 199e204.