Selective colorimetric and turn-on fluorimetric detection of cyanide using a chemodosimeter comprising salicylaldehyde and triphenylamine groups

Article abstract of DOI:10.1002/ejoc.201201085

Chemodosimeters S1 and S2 having salicylaldehyde and triphenylamine functionalities were synthesized, and the changes in their absorption and emission properties in the presence of anions were evaluated. S1 and S2 act as selective colorimetric and fluorimetric molecular probes for sensing and signalling cyanide. The signal transduction mechanism was investigated by UV/Vis absorption, emission, and NMR spectroscopy, and was supported by DFT calculations. The interaction between the receptors and cyanide ions causes large changes in both colour and emission intensity. A significant enhancement in fluorescence intensity was caused by the better nucleophilicity of the cyanide and by the carbonyl activation by the phenol proton of the salicylaldehyde group in the dosimeter through an intramolecular hydrogen bond. Intramolecular charge transfer from the negatively charged quinonoidal fragment to the triarylamine group was responsible for the colorimetric response. The detection limits were found to be 1.55 and 0.72 μM for S1 and S2, respectively, with fluorimetric enhancement factors of 350 and 25.

Full text of DOI:10.1002/ejoc.201201085

FULL PAPER
DOI: 10.1002/ejoc.201201085
Selective Colorimetric and “Turn-on” Fluorimetric Detection of Cyanide Using
a Chemodosimeter Comprising Salicylaldehyde and Triphenylamine Groups
Palas Baran Pati[a] and Sanjio S. Zade*[a]
Keywords: Sensors / Chromophores / Charge transfer / Anions / Cyanides
Chemodosimeters S1 and S2 having salicylaldehyde and tri-
phenylamine functionalities were synthesized, and the
changes in their absorption and emission properties in the
presence of anions were evaluated. S1 and S2 act as selective
colorimetric and fluorimetric molecular probes for sensing
and signalling cyanide. The signal transduction mechanism
was investigated by UV/Vis absorption, emission, and NMR
spectroscopy, and was supported by DFT calculations. The
interaction between the receptors and cyanide ions causes
large changes in both colour and emission intensity. A sig-
nificant enhancement in fluorescence intensity was caused
by the better nucleophilicity of the cyanide and by the carb-
onyl activation by the phenol proton of the salicylaldehyde
group in the dosimeter through an intramolecular hydrogen
bond. Intramolecular charge transfer from the negatively
charged quinonoidal fragment to the triarylamine group was
responsible for the colorimetric response. The detection lim-
its were found to be 1.55 and 0.72 μM for S1 and S2, respec-
tively, with fluorimetric enhancement factors of 350 and 25.
the most important methods for probing its presence. Ad-
dition of cyanide to an activated aldehyde group is one of
the important strategies used to develop probes that are se-
lective to cyanide only.[14] Colorimetric sensors are always
important because the presence of analyte can be rapidly
confirmed visually. There are several literature reports of
colorimetric probes for cyanide but colorimetric as well as
“turn-on” fluorimetric probes for cyanide are very few.[15]
Here we have designed and synthesized two compounds,
S1 and S2, as probes for cyanide comprising salicylaldehyde
and triphenylamine functionalities. The nucleophilic reac-
tivity of CN– towards the salicylaldehyde moiety was ex-
ploited to detect cyanide selectively. Triphenylamine func-
tionality is incorporated to generate colorimetric changes
through intramolecular charge transfer (ICT). The synthe-
sis of S1 and S2 was based on reported synthetic strategies
and was straightforward and high yielding. Anion recogni-
tion properties of S1 and S2 were studied in aqueous tetra-
hydrofuran (THF) solution towards several anions such as
Introduction
Anions play important roles in biology, medicine, cataly-
sis, and in the environment.[1] Recently, considerable atten-
tion has been paid to the development of selective optical
signalling systems for anionic species.[2] Among the various
anions, cyanide is one of the most concerning due to its
high toxicity to human and aquatic life.[3] The worldwide
production of cyanide in the various industries is
1,400,000 tons per year[4] due to its applications in the pro-
duction of nitriles, nylon, acrylic plastics and gold extrac-
tion processes.[5]
Several colorimetric and fluorimetric probes for cyanide
have been reported in recent literature,[6] and there are sev-
eral common approaches to the design of selective probes
for cyanide ions. Copper complexes have successfully been
used as a cyanide probe due to the affinity of CuII towards
cyanide.[7] Cyanide addition to ZnII–porphyrin,[8,6b] RuII–
complex,[9,6l] boronic acid derivatives,[10,6k] and CdSe quan-
tum dots[11] have also been exploited as detection methods.
Other strategies such as hydrogen-bonding interac-
tions,[12,6a] deprotonation,[13] and luminescence lifetime
measurements[7a] have also been used to design selective
probes for cyanide. Due to the exceptional nucleophilicity
of cyanide, nucleophilic substitution by cyanide is one of
–
–
–
CN–, AcO–, F–, Cl–, Br–, H2PO4 , NO2 , N3 , HS– and
–
ClO4 as their tetrabutylammonium salt. Both S1 and S2
showed selective colorimetric and “turn-on” fluorimetric
sensitivity towards CN–.
Results and Discussion
[a] Department of Chemical Sciences, Indian Institute of Science
Education and Research, Kolkata,
Synthesis of S1 and S2
PO: BCKV campus main office, Mohanpur 741252, Nadia,
West Bengal, India
Compounds S1 and S2 were synthesized in high yield by
the protocol shown in Scheme 1. Compound 1 was pre-
pared by following the reported procedure.[16] Stannylation
of 1 followed by Stille coupling between stannyl derivative
Fax: +91-33-25873020
E-mail: sanjiozade@iiserkol.ac.in
Homepage: http://www.iiserkol.ac.in/~sanjiozade/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201201085.
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P. B. Pati, S. S. Zade
FULL PAPER
2 and 5-bromosalicylaldehyde, afforded S1 with good yield.
Sonogashira coupling of 1 and ethynyltrimethylsilane in an-
hydrous THF afforded 3. Compound 5 was synthesized by
desilylation of 3 followed by stannylation of 4. Stille cou-
pling of 5 and 5-bromosalicylaldehyde afforded S2 in high
yield.
Figure 1. UV/Vis spectra of 0.1 mm solutions of (a) S1 and (b) S2
in THF/water mixture (95:5) upon addition of different anions
(5 equiv.).
Scheme 1. Synthetic routes to S1 and S2. Reagents and conditions:
(a) nBuLi (1.1 equiv.), Me3SnCl (1.1 equiv.), THF, –78 °C, 72%;
(b) 5-bromo-2-hydroxybenzaldehyde, [Pd(PPh3)4], toluene, reflux,
24 h, 68%; (c) CuI, [Pd(PPh3)2Cl2], Et3N, ethynyltrimethylsilane,
THF, 80%; (d) K2CO3, MeOH, room temp., overnight, 90%;
(e) nBuLi (1.1 equiv.), Me3SnCl (1.1 equiv.), –78 °C, THF, 78%;
(f) 5-bromo-2-hydroxybenzaldehyde, [Pd(PPh3)4], toluene, reflux,
24 h, 72%.
Colorimetric Detection
The anion-sensing properties of S1 and S2 were studied
in aqueous THF (THF/H2O = 95:5). S1 and S2 showed
absorption maxima at 326 and 346 nm, respectively; S2
showed a 20 nm redshift in absorption maxima due to ex-
tended conjugation by an extra acetylene group compared
with that of S1. The solution of S1 and S2 was treated
with a fixed amount of different anions (5 equiv., added as
tetrabutylammonium salts) and the absorption spectra were
recorded. Addition of CN– caused a marginal batho-
chromic shift of the high-intensity peak in the UV/Vis ab-
sorption spectra of S1 and S2 (Figure 1), however, an ad-
Figure 2. Colorimetric and fluoremetric responses of the dosimeter
(10 μm) in the presence of 5 equiv. of different anions: (a) colori-
–
metric and (c) fluorimetric for S1 (from left to right: H2PO4 ,
–
–
–
ClO4 , CN–, F–, AcO–, Br–, Cl–, NO2 , N3 , HS–); (b) colorimetric
–
and (d) fluorimetric for S2 (from left to right: H2PO4 , CN–, F–,
–
–
–
ditional low-intensity, broad peak appeared in the region ClO4 , AcO–, Br–, Cl–, NO2 , N3 , HS–).
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Detection of Cyanide with a Chemodosimeter
400–450 nm, which was responsible for the visible colour
change (from colourless to yellow; Figure 2, a and b). With
the addition of increasing amounts of tetrabutylammonium
cyanide (from 0.1 to 20 equiv.) to a solution of S1 and S2,
the intensity of both the peaks steadily enhanced (Figure 3).
Figure 3. Changes in the UV/Vis spectra of 3.3 μm solutions of S1
(a) and S2 (b) upon addition of increasing amounts of cyanide (0.1
to 20 equiv.) in THF/water.
To explain the origin of the colorimetric response, we
have performed DFT calculations on S1 and its product on
treatment with cyanide, S1-CN.[17] Geometry optimization
of S1 and S1-CN were performed at the B3LYP/6-31G(d)
level[18] and these optimized geometries were subsequently
considered for single point TD-DFT calculations at the
B3LYP/TZVP level.[19] Geometry optimization of S1-CN
from various probable structures converged on the same ge-
ometry, which corresponds to phenolic H transfer to formyl
oxygen, as shown in the structures of S1-CN. These results
Figure 4. DFT generated molecular orbital of S1 and S1-CN
(HOMO and LUMO+1) at B3LYP/6-31G(d).
1
were supported by H NMR spectroscopy studies. As a re-
sult, a negative charge moved on the phenolic oxygen, con-
verting it into a partial quinonoidal structure for which the
negative charge can be more effectively delocalized over the
Fluorimetric Detection
Compounds S1 and S2 showed emission maxima at 428
conjugated system. TD-DFT[20] calculations indicated the (λex = 326 nm) and 465 nm (λex = 346 nm), respectively,
origin of the broad low intensity peak in the region of 400– with very low quantum yields [S1 (0.08%) and S2 (0.9%)]
450 nm as a charge-transfer band from the negatively with respect to quinine sulfate. The large Stokes shifts of
charged quinone part to the triarylamine fragment 102 and 119 nm for S1 and S2, respectively, can be ascribed
(Figure 4). The calculated transition at 439 nm with an to excited state proton transfer (ESPT).[21] The ESPT pro-
oscillator strength
f
=
0.0272 corresponds to cess opens the ways for nonradiative deactivation and is re-
HOMOǞLUMO+1 (Table S1 in the Supporting Infor- sponsible for the very weak fluorescence of S1 and S2.[21]
mation).
By adding an excess of anions (5 equiv.) to the solutions of
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S1 and S2, emission spectra were recorded. Only the in-
clusion of cyanide ions led to emission with high intensity
at 534 and 516 nm for S1 and S2, respectively, whereas the
presence of other anions did not lead to any significant en-
hancement in emission intensity (Figure 5). The cyanoalk-
oxide anion (deprotonated cyanohydrins) generated after
addition of cyanide to the formyl group, exchanges the
phenolic proton. This process inhibits ESPT and leads to
strong emission after addition of cyanide ions to S1 and
S2. The change in emission spectra led to visible detection
under a 360 nm UV lamp with clear yellow fluorescence
(Figure 2, c and d). In cyanide titration experiments with
S1 and S2 and increasing amounts of cyanide (from 0.1 to
20 equiv.), the intensity of the peaks at 534 and 516 nm,
respectively, were gradually enhanced (Figure 6). According
to the previous theoretical study,[21] it is expected that local
excited states of S1-CN and S2-CN are not involved in the
ESPT process and thus strong fluorescence was obtained.
We note that after cyanide addition the emission peak for
S2 appeared at shorter wavelength than that of S1. This can
be ascribed to the contribution of allene-type structure S2-
CNЈ to the phenoxide ion S2-CN (formed by the proton
transfer of deprotonated cyanohydrins). The allene-type
structure restricts the conjugation and, as a result, the fluo-
rescent enhancement factor for S2 is less than that of S1.
To visualise the emission response of S1 to the different
ions, a bar diagram of F/F0 of different anions at 534 nm
Figure 5. Emission spectra of 3.3 μm solutions of (a) S1 and (b)
S2 in THF/water mixture (95:5) upon addition of different anions was plotted (Figure 7). The enhancement factor in the in-
(5 equiv.).
Figure 7. Fluorescence responses of (a) S1 (3.3 μm) upon addition
of various anions (5 equiv.) in THF/water solution, (b) S1 (3.3 μm)
Figure 6. Fluorescence titration spectra of 3.3 μm solutions of (a)
S1 and (b) S2 upon addition of cyanide from 0.1 to 20 equiv.
to CN– (1 equiv.) containing various anions (5 equiv.). λex
=
326 nm, Slit: 2.5 nm/2.5 nm.
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Detection of Cyanide with a Chemodosimeter
tensity of the emission peak of S1 at 534 nm on addition aldehyde proton of S1 and S2 at around δ = 10.3 ppm was
of cyanide is 350, whereas other anions did not show any shifted upfield to δ = 5.8 and 5.5 ppm, respectively, for S1
significant change in the emission intensity (Figure 7, a; for and S2 upon cyanide addition at room temperature. This
S2 see the Supporting Information, Figure S7). To check chemical shift was consistent with cyanohydrin formation
the detection dependence of CN– in the presence of other due to nucleophilic attack of the cyanide on the formyl
competitive anions, we carried out titration experiments group of the dosimeter. The detection limits obtained from
with S1, S2, cyanide (1 equiv.) and competitive anions the fluorimetric study were 1.55 (S1) and 0.72 μm (S2) (Fig-
(5 equiv.). It was clearly seen that there was no detectable ure S1 and S2).[22] Thus S1 and S2 are efficient probes for
change in the fluorimetric (Figure S3 and S4 in the Sup- very low concentrations of cyanide.
porting Information) or colorimetric (Figure S5 and S6 in
the Supporting Information) detection of cyanide in the
presence of other anions. From part b of Figure 7 it is clear
that emission intensity remains nearly unchanged in the
presence of competitive anions.
Conclusions
Chemodosimeters S1 and S2, comprising salicylaldehyde
and triphenylamine functionalities, act as a selective colori-
metric and “turn-on” fluorimetric sensor for cyanide in
1
aqueous THF with a very low detection limit (Ͻ2 μm) and
high fluorescence intensity enhancement factor (ca. 350-
fold). A significant enhancement in fluorescence intensity
was caused by the better nucleophilicity of the cyanide and
the carbonyl activation by the phenol proton of the salicyl-
aldehyde group in the dosimeter through an intramolecular
hydrogen bond. Intramolecular charge transfer from the
negatively charged quinone part to the triarylamine frag-
ment is responsible for the colorimetric response. The detec-
tion limits were 1.55 and 0.72 μm for S1 and S2, respec-
tively, with fluorimetric enhancement factors of 350 and 25.
Stoichiometry, H NMR Spectroscopic Studies, Selectivity,
and Detection Limits
Nucleophilic attack on the aldehyde group should also
satisfy 1:1 probe and cyanide stoichiometry. The result ob-
tained from a Job plot supports the formation of a 1:1 re-
ceptor–CN– adduct (for S1, see part a of Figure 8 and for
S2, see Figure S8). Furthermore, we investigated the 1H
NMR spectra of S1 (Figure 8, b) and S2 (Figure S19 in the
Supporting Information) in the presence of cyanide anions
and compared it with that of S1 and S2, respectively. The
Experimental Section
Materials and General Methods: All reactions were performed un-
der an argon atmosphere to maintain dry conditions. Anhydrous
toluene and THF were collected from Na and benzophenone. All
reagents were purchased from commercial sources and used with-
out further purification. Compounds S1 and S2 were readily pre-
pared by the synthetic protocol shown in Scheme 1. 1-(Hexyloxy)-
4-iodobenzene was synthesized from 4-iodophenol by following the
reported literature.[23] All the new compounds were characterised
by conventional methods (1H, 13C NMR, HRMS). Emission and
absorption spectra were recorded with Fluoromax-3 and HITACHI
U-4100 UV/Vis/NIR spectrophotometers, respectively. NMR spec-
troscopic data were recorded with Bruker Advance 500 MHz and
Jeol ECS 400 MHz spectrometers with either CDCl3 or [D6]DMSO
as solvent.
Compound 2: nBuLi (1.6 m in hexane, 2.8 mL) was added slowly to
a solution of 1 (2.1 g, 4 mmol) in THF (50 mL) at –78 °C under a
nitrogen atmosphere and the mixture was stirred for 2 h at the same
temperature. SnMe3Cl (1 m in hexane, 2.2 mL, 2.2 mmol) was
added slowly at –78 °C and stirred for 10 min at same temperature,
then stirred at room temp. overnight. The reaction was quenched
by adding water (50 mL) and the product was extracted with ethyl
ether. The organic layer was separated, dried with sodium sulfate,
and concentrated by using a rotary evaporator. The 1H NMR spec-
trum was recorded in CDCl3 and the crude product was used for
the next step without further purification. Conversion (72%) was
calculated on the basis of 1H NMR spectroscopy. 1H NMR
(400 MHz, CDCl3): δ = 0.37 (s, 9 H), 0.90 (t, J = 6.7 Hz, 6 H),
1.33 (m, 8 H), 1.41 (m, 4 H), 1.76 (m, 4 H), 3.92 (t, J = 6.7 Hz, 4
H), 6.80 (d, J = 9.1 Hz, 4 H), 6.90 (d, J = 8.5 Hz, 2 H), 7.05 (d, J
= 9.1 Hz, 4 H), 7.39 (d, J = 8.5 Hz, 2 H) ppm.
Figure 8. (a) Job plot of S1 with CN–; (b) 1H NMR spectral change
of the dosimeter upon addition of cyanide anions: (below) sensor
S1 only, and (above) sensor and CN– (10 equiv.) in [D6]DMSO.
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Compound S1: 5-Bromo-2-hydroxybenzaldehyde (202 mg, 1 mmol)
was dissolved in a dry three-necked round-bottomed flask and a
solution of 2 (1 g) in toluene (25 mL) was added, the solution was
purged with nitrogen for 10–15 min, then [Pd(PPh3)4] (100 mg) was
added. The reaction mixture was heated to 110 °C under nitrogen
for 24 h, then cooled to room temp. and toluene was evaporated
by rotary evaporator. The crude mixture was directly loaded onto
a column and the product was separated by flash column
chromatography (ethyl acetate/hexane); yield 384 mg (68%); pale-
yellow solid. 1H NMR (400 MHz, [D6]DMSO): δ = 0.86 (t, J =
6.7 Hz, 6 H), 1.30 (m, 8 H), 1.41 (m, 4 H), 1.67 (m, 4 H), 3.92 (t,
J = 6.7 Hz, 4 H), 6.81 (d, J = 8.5 Hz, 2 H), 6.89 (d, J = 9.1 Hz, 4
H), 7.00 (d, J = 9.1 Hz, 4 H), 7.04 (d, J = 8.5 Hz, 1 H), 7.44 (d, J
= 9.1 Hz, 2 H), 7.75–7.77 (m, 1 H), 7.83 (d, J = 1.8 Hz, 1 H), 10.29
(s, 1 H), 10.74 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
13.9, 22.1, 25.2, 28.7, 31.1, 67.5, 115.3, 117.8, 119.6, 123.3, 125.7,
126.5, 126.6, 130.4, 131.3, 133.9, 139.9, 147.6, 155.2, 159.6,
on the basis of 1H NMR spectroscopy. 1H NMR (400 MHz,
CDCl3): δ = 0.28 (s, 9 H), 0.86 (t, J = 6.8 Hz, 6 H), 1.30 (m, 8 H),
1.42–1.45 (m, 4 H), 1.72 (m, 4 H), 3.88 (t, J = 6.4 Hz, 4 H), 6.80–
6.84 (m, 6 H), 6.97 (d, J = 8.8 Hz, 4 H), 7.20 (d, J = 8.8 Hz, 2
H) ppm.
Compound S2: 5-Bromo-2 hydroxy benzaldehyde (202 mg, 1 mmol)
was taken in a dry three-necked round-bottomed flask and a solu-
tion of 5 (1.2 mg) in toluene (25 mL) was added. The solution was
purged with nitrogen for 10–15 min, then [Pd(PPh3)4] (100 mg) was
added. The reaction mixture was heated to 110 °C under nitrogen
for 24 h, then cooled to room temp. and toluene was evaporated
by rotary evaporator. The crude mixture was directly loaded onto
a column and the product was separated by flash column
chromatography (ethyl acetate/hexane); yield 384 mg (72%); pale-
yellow solid. 1H NMR (400 MHz, [D6]DMSO): δ = 0.87 (t, J =
6.8 Hz, 6 H), 1.30 (m, 8 H), 1.46 (m, 4 H), 1.69 (m, 4 H), 3.93 (t,
J = 6.4 Hz, 4 H), 6.67 (d, J = 8.5 Hz, 2 H), 6.92 (d, J = 9.1 Hz, 4
H), 7.00 (d, J = 8.5 Hz, 1 H), 7.05 (d, J = 9.1 Hz 4 H), 7.29 (d, J
= 8.5 Hz, 2 H), 7.59 (m, 1 H), 7.71 (d, J = 2.4 Hz, 1 H), 10.24 (s,
1 H), 11.09 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.0,
22.6, 25.7, 29.2, 31.6, 68.2, 86.0, 89.6, 113.1, 115.3, 115.8, 117.9,
118.9, 120.4, 127.15, 132.2, 136.5, 139.7, 139.8, 148.9, 155.9, 160.9,
+
191.5 ppm. HRMS (ESI): m/z calcd. for C37H43NO4 565.3192
[M+]; found 565.3184.
Compound 3: To a mixture of [PdCl2(PPh3)2] (70 mg, 0.10 mmol)
and CuI (38 mg, 0.2 mmol) in THF (40 mL) were added success-
ively
1 (2.10 g, 0.4 mmol), trimethylsilyl acetylene (624 μL,
+
196.2 ppm. HRMS (ESI): m/z calcd. for C39H43NO4 589.3192
4.4 mmol), and NEt3 (20 mL). The resulting mixture was stirred
for 18 h at room temp. The dark solution was evaporated under
reduced pressure and the resulting black solid was extracted with
CH2Cl2 and further purified by chromatography on silica gel (hex-
ane) to give 3; yield 1.75 g (80%); yellowish oil. 1H NMR
(400 MHz, CDCl3): δ = 0.23 (s, 9 H), 0.93 (t, J = 6.7 Hz, 6 H),
1.33 (m, 8 H), 1.41 (m, 4 H), 1.76 (m, 4 H), 3.93 (t, J = 6.4 Hz, 4
H), 6.80 (d, J = 8.5 Hz, 2 H), 6.82 (d, J = 8.8 Hz, 4 H), 7.05 (d, J
= 8.8 Hz, 4 H), 7.24 (d, J = 8.5 Hz, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 0.1, 14.0, 22.5, 25.7, 29.2, 31.5, 68.2, 92.1,
105.8, 113.6, 115.3, 118.9, 127.0, 132.7, 139.9, 148.9, 155.8 ppm.
HRMS (ESI): m/z calcd. for C35H47NO2Si+ 541.3376 [M+]; found
541.3371.
[M+]; found 589.3184.
Computational Details: All electronic structure calculations were
carried out using the Gaussian 09[17] program suite. Geometry opti-
misations were performed at the B3LYP/6-31G(d) level.[18] The
triple-ζ valence quality with one set of polarization functions
(TZVP)[19] was chosen as basis sets for single point TD-DFT[20]
calculations on the optimised geometries using the 6-31G(d) basis
set.
UV/Vis and Fluorescence Titration Procedure: In absorption and
emission titration experiments, the total volume of solution was
fixed to 3 mL. The response to cyanide anion is very fast, therefore,
spectra were recorded immediately after the addition of cyanide.
Supporting Information (see footnote on the first page of this arti-
cle): Graphs of detection limits for S1 and S2, sensitivity of cyanide
to S2, Jobs plot for S2; copies of the 1H and 13C NMR spectra
and computational details.
Compound 4: To a stirred solution of 3 (1.08 g, 2 mmol) in CH3OH
(30 mL) was added K2CO3 (28 mg, 0.2 mmol). The mixture was
stirred for 24 h at room temp., concentrated, and the residue was
diluted with Et2O and washed with water (3ϫ30 mL). The organic
phase was dried with Na2SO4, filtered, and concentrated by rotary
evaporator. The resulting organic compound was purified by fil-
tration through a silica gel column (hexane/CH2Cl2) to afford 4;
Acknowledgments
P. B. P. thanks the University Grants Commission (UGC) for his
fellowship. S. S. Z. is thankful to the Department of Science and
Technology (DST), India for funding.
1
yield 844 mg (90%). H NMR (400 MHz, CDCl3): δ = 0.90 (t, J =
6.8 Hz, 6 H), 1.33 (m, 8 H), 1.44–1.47 (m, 4 H), 1.78 (m, 4 H), 2.98
(s, 1 H), 3.92 (t, J = 6.4 Hz, 4 H), 6.80 (d, J = 8.5 Hz, 2 H), 6.83
(d, J = 9.1 Hz, 4 H), 7.05 (d, J = 8.5 Hz, 4 H), 7.24 (d, J = 9.1 Hz,
2 H) ppm. 13C NMR,(100 MHz, CDCl3): δ = 14.0, 22.5, 25.7, 29.2,
31.5, 68.2, 84.3, 112.3, 115.3, 118.7, 127.1, 132.8, 139.8, 149.2,
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+
155.9 ppm. HRMS (ESI): m/z calcd. for C32H39NO2 469.2981
[M+]; found 469.2974.
Compound 5: Compound 4 (940 mg, 2 mmol) and anhydrous THF
(40 mL) were taken in a 100 mL three-necked round-bottomed
flask. The reaction mixture was cooled to –78 °C and nBuLi (1.6 m
in hexane, 1.4 mL) was added slowly to the cold mixture and the
mixture was stirred for 1 h at the same temperature. SnMe3Cl (1 m
in hexane, 2.2 mL) was added slowly and the reaction mixture was
kept at room temp. overnight. The reaction was quenched by add-
ing water (25 mL) and the product was extracted with ethyl ether.
The organic layer was separated, dried with sodium sulfate, and
concentrated by using a rotary evaporator. The 1H NMR spectrum
was recorded in CDCl3 and crude product was used for the next
step without further purification. Conversion (78%) was calculated
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Received: August 10, 2012
Published Online: October 11, 2012
Eur. J. Org. Chem. 2012, 6555–6561
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6561