FeCl3-diorganyl dichalcogenides promoted cyclization of 2-organochalcogen-3-alkynylthiophenes: Synthesis of chalcogenophene[2,3-b] thiophenes

Article abstract of DOI:10.1039/c3ob27498e

We report here our results on the FeCl₃-diorganyl dichalcogenides intramolecular cyclization of 2-organochalcogen-3- alkynylthiophenes. The cyclization reaction proceeded cleanly under mild reaction conditions giving the (S)-Se-, (S)-S- and (S)-Te-heterocycles in good yields. In addition, the obtained chalcogenophenes were readily transformed into more complex products using the palladium cross-coupling reaction with boronic acids. Conversely, using a metal-halogen exchange reaction with n-BuLi, the chalcogenophenes produced the lithium-intermediate which was trapped with aldehyde furnishing the desired secondary alcohol in good yield. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ob27498e

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FeCl3–diorganyl dichalcogenides promoted cyclization
of 2-organochalcogen-3-alkynylthiophenes: synthesis
of chalcogenophene[2,3-b]thiophenes†
Cite this: DOI: 10.1039/c3ob27498e
André L. Stein, Filipe N. Bilheri, Alisson R. Rosário and Gilson Zeni*
We report here our results on the FeCl3–diorganyl dichalcogenides intramolecular cyclization of
2-organochalcogen-3-alkynylthiophenes. The cyclization reaction proceeded cleanly under mild reaction
conditions giving the (S)-Se-, (S)-S- and (S)-Te-heterocycles in good yields. In addition, the obtained
chalcogenophenes were readily transformed into more complex products using the palladium cross-
coupling reaction with boronic acids. Conversely, using a metal–halogen exchange reaction with n-BuLi,
the chalcogenophenes produced the lithium-intermediate which was trapped with aldehyde furnishing
the desired secondary alcohol in good yield.
Received 24th December 2012,
Accepted 1st March 2013
DOI: 10.1039/c3ob27498e
www.rsc.org/obc
alternative route to these heterocycles. This methodology takes
advantage, in the most of cases, of the presence of a halogen
Introduction
In recent years several research groups have reported hetero- atom suitable to suffer further transformations.12 During the
cyclization approaches to chalcogen-heterocycles.1 These types of past few years there has been an impressive increase of atten-
chalcogen-containing heterocycles have attracted much inter- tion in the development of environmentally benign protocols
est because of their potent biological and pharmacological and the great challenge for chemists is to apply cost effective,
activities,2 in addition to their role in the development of new green, mild and alternative methodologies.13 In this sense,
functional materials.3 Among these, many of them have been iron salts have appeared as versatile alternatives, due to their
used as organic electrode materials, semiconductor electrodes low price, low toxicity, and environmentally benign proper-
in electrocatalysis4 and for developing lightweight batteries.5 ties.14 Iron species proved to be effective in providing coupling
Besides, chalcogenophenes are widely studied agents with a reactions between Grignard species and various organic elec-
diverse array of pharmacological actions.6 These include trophiles as well as C–N15 and C–chalcogen16 bond formation.
potent antitumor and antiviral activities7 as well as an interest- Iron salts have also emerged as alternatives and promising cata-
ing profile of anti-inflammatory activity with significant lysts or promoters for the cyclization process.17 FeCl3/RSeSeR,
analgesic effects.8 With regard to synthetic strategies, synthetic due to the relatively easy access, offers an interesting synthetic
chemists have provided elegant examples of the utility of elec- alternative to IPy2BF4,18 halogens,19 NXS,20 trichloroisocyanu-
trophilic cyclization and transition metal catalyzed intramole- ric acid (TCCA),21 I(coll)2PF6/BF3·3OEt2,22 organoselenium,23
cular reactions for the preparation of a wide range of simple to organotellurium electrophiles24 metal-transition25 cyclization
complex chalcogenophenes.9 In this context, the transition- of functionalized alkynes. Given that the use of FeCl3/RSeSeR
metal catalyzed cyclization reaction of simple acyclic precur- in the cyclization procedures remains an intriguing chal-
sors is one of the most attractive ways to directly construct lenge,26 the above considerations led us to experiment this
chalcogen-heterocycles under mild conditions.10 In this way, system as a new and regioselective possibility to access chalco-
palladium is one of the most common transition metals used, genophene[2,3-b]thiophenes. Herein, we wish to report that
although it sometimes displays intolerance to some function- the cyclization reaction of 2-organochalcogen-3-alkynylthio-
alities or proceeds with a lack of regioselectivity.11 On the phenes 1 with an FeCl3–diorganyl dichalcogenides system gave
other hand, the electrophilic cyclization appears as an chalcogenophene[2,3-b]thiophene derivatives 2, in good to
high yields (Scheme 1).
Laboratório de Síntese, Reatividade, Avaliação Farmacológica e Toxicológica de
Results and discussion
Organocalcogênios, CCNE, UFSM, Santa Maria – Rio Grande do Sul, 97105-900,
Brazil. E-mail: gzeni@ufsm.br
The starting materials 2-organochalcogen-3-alkynylthiophenes
†Electronic supplementary information (ESI)
available. See DOI:
10.1039/c3ob27498e
1 were readily available applying the Sonogashira conditions in
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3-bromothiophene followed by the introduction of an organo- ratio (0.2 equiv.) to 2 equiv.; however, it did not offer any
chalcogen group via a reaction of 2-lithium thiophene inter- improvement in yields (Table 1, entries 7–9). Subsequently, the
mediate (prepared by a reaction with n-BuLi, in THF at −78 °C effects of employing various solvents were studied. We found
for 1 h), followed by the addition of elemental chalcogen and that MeCN and CHCl3 were also effective, but when THF and
alkylation with an appropriate alkylbromide.9 The feasibility of EtOH were used as solvents the reaction did not proceed
the cyclization started with a screening of iron trichloride (Table 1, entries 10–13). The cyclization of alkynylthiophenes
loading, diorganyl diselenides loading, solvent and tempera- 1a with diphenyl diselenide was examined under other iron
ture. Thus, a mixture of diphenyl diselenide (1 equiv.) and salts. Of these salts, FeCl3·6H2O was also effective giving the
FeCl3 (1 equiv.), using CH2Cl2 (3 mL) as a solvent, was reacted product in 68% yield. In contrast, Fe(acac)3 was not effective
with 1a (0.25 mmol) under an argon atmosphere at 40 °C for (Table 1, entries 14–15). We then examined the scope of the
2 h. As shown in Table 1, using these reaction conditions the reaction with a variety of 2-organochalcogen-3-alkynylthio-
desired product 2a was obtained in 73% yield (Table 1, phenes 1 and different diorganyl dichalcogenides (Table 2). In
entry 1). Regarding the influence of the diphenyl diselenide general, the appropriate 2-organochalcogen-3-alkynylthio-
loading, good results were achieved by using 1.5 equiv. of phenes 1 (0.25 mmol), FeCl3 (1.0 equiv.), diorganyl dichalco-
diphenyl diselenide (Table 1, entry 3), while 0.55 equiv. was genides (1 equiv.) in CH2Cl2 (3 mL) at room temperature and
less effective (Table 1, entry 2). Through control experiments, under an ambient atmosphere were used as standard
we found that the use of heating and more than 1 h, as the conditions.
reaction time, proved to be unnecessary for the proper
performance of the reaction (Table 1, entries 3–6). Next, the an easy access to chalcogenophene[2,3-b]thiophenes, we
amount of FeCl3 was investigated by varying from the catalytic prepared various 2-organochalcogen-3-alkynylthiophenes
In order to extend the scope of this methodology, allowing
and diorganyl diselenides bearing different substituents and
studied their cyclization under optimized conditions as
described in Table 1. The process was tolerant of a range of
functional groups on the diorganyl dichalcogenides, since no
significant differences in the yields were found with diaryl di-
selenides having a neutral, electron rich or electron poor sub-
stituent in the aromatic ring (Table 2, entries 1–4). Under the
same conditions, diaryl ditelluride reacted similarly and the
product 2e was obtained in good yield (Table 2, entry 5). Inter-
estingly, the cyclization reaction of 1a also proceeded smoothly
Scheme 1 General scheme.
Table 1 Optimization of cyclization conditionsa
Entry
[Fe] (equiv.)
PhSeSePh (equiv.)
Solvent
Temp. (°C)
Time (h)
Yieldb (%)
1c
2c
3c
4c
5
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (0.2)
FeCl3 (1.5)
FeCl3 (2.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3·6H2O (1.0)
Fe(acac)3 (1.0)
1.0
0.55
1.5
1.0
1.0
1.0
1.0
0.55
1.0
1.0
1.0
1.0
1.0
1.0
1.0
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
THF
40
40
40
25
25
25
25
25
25
25
25
25
25
25
25
2
4
2
3
2
1
24
1
1
12
12
6
3
3
73
45
76
72
82
83
Trace
57
69
Trace
Trace
64
55
68
6
7d
8
9
10
11
12
13
14
15
EtOH
MeCN
CHCl3
CH2Cl2
CH2Cl2
12
0
a Reaction conditions: 1a (0.25 mmol), diphenyl diselenide (0.25 mmol) in CH2Cl2 (3 mL), at room temperature, under an ambient atmosphere
for 1 h. b Yields of isolated products. c The reaction was carried out under an argon atmosphere. d 2-Organochalcogen-3-alkynylthiophenes 1a
were recovered.
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Table 2 FeCl3/RYYR-promoted cyclization of 2-organochalcogen-3-alkynylthio-
phenes 1a
Table 2 (Contd.)
Entry
10
Substrate
R1YYR1
Product/yieldb (%)
Entry
1
Substrate
R1YYR1
Product/yieldb (%)
2
1a
11
12
3
4
1a
1a
13
14
1f
5
6
1a
1a
n-BuSe)2
n-BuTe)2
15
16
7c
8
1a
17
9
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Table 2 (Contd.)
Scheme 2 Reactivity of 2a toward Suzuki cross-coupling with boronic acids.
Entry
18
Substrate
R1YYR1
Product/yieldb (%)
a Reaction performed in the presence of 1 (0.25 mmol), diorganoyl
dichalcogenide (0.25 mmol) in CH2Cl2 (3 mL), at room temperature,
under an ambient atmosphere for 1 h. b Yields of 2a–r are given for
isolated products. c 57% yield of 2g was obtained by using FeCl3 (2
equiv.) and (BuTe)2 (2 equiv.).
Scheme 3 Reaction of lithium intermediate 4a’ with 4-chlorobenzaldehyde.
study reported by Larock who showed that if the substrate has
the selenium and oxygen atoms competing, the Se-cyclization
is predominant.27
with dialkyl diselenides and dialkyl ditellurides; however,
noticeably lower yields were obtained compared to the use of
aryl derivatives. Since a butyl group directly bonded to the
chalcogen atom has a beta-hydrogen, the structure could
suffer decomposition via a telluro/selenoxide syn-elimination
reaction, during the purification or work-up process, giving
the products in reduced yields. In an attempt to broaden the
scope of our methodology, the possibility of performing the
reaction with other 3-alkynylthiophene derivatives, which have
Me 1b, OMe 1c and Cl 1d groups in the aromatic ring, was also
investigated. Both the electron-donating (Me and OMe) and
the electron-withdrawing (Cl) groups delivered products in
good yields (Table 2, entries 8–10). In addition to aromatic
rings, the reactions with alkyl directly bonded to the alkyne,
such as a hexyl group, also led to the formation of the desired
product (Table 2, entry 11). We have found that benzothio-
phene derivatives 1f–1h, which have an aryl group bonded to
the thiophene ring, had a little influence on the cyclization
reaction since polyheterocyclic rings 2l–2o were obtained in
lower yields than thiophene derivatives (Table 2, entries
12–15). The reaction of 1i–k, possessing the sulfur and tellur-
ium atoms as latent nucleophiles, was also examined.
Although the yield was not high for tellurium derivatives (42%
yield in entry 17), the desired products were produced in 68%
and 64% yields by the reaction with thiol derivatives (Table 2,
entries 16 and 18). We performed a competitive cyclization
reaction between nucleophilic oxygen from a methoxyl substi-
tuent at the ortho position of an aryl group and a selenium
nucleophile directly bonded to the thiophene ring, to deter-
mine how the nucleophilicity of the competing functional
groups affects the cyclization. Therefore, we were pleased to
find out that the cyclization with 1h smoothly afforded the
corresponding selenophene 2o via an Se-cyclization, in the
complete absence of furan derivatives (Table 2, entry 15).
We observed that this result is in complete agreement with the
In order to complete our investigation and to further prove
the potential of chalcogenophene[2,3-b]thiophene derivatives
as precursors for increasing molecular complexity, we tested
the reactivity of these compounds toward Suzuki28 palladium-
catalyzed reactions and Li–Se exchange reactions. Recently, a
new application of organotellurium compounds employing
palladium catalyzed cross-coupling was described.29 In this
case, they behave as aryl or vinyl carbocation equivalents. This
led us to explore the possibility to use these chalcogenophene
[2,3-b]thiophenes as substrates in palladium cross-coupling
reactions, under the classical Suzuki protocol. Under the
Suzuki reaction conditions 4-butyltelluro-selenophene[2,3-b]-
thiophene 2g underwent smooth cross-coupling upon ex-
posure to boronic acids affording 4-p-tolylselenophene[2,3-b]-
thiophene 3a and 4-(4-bromo phenyl)selenophene[2,3-b]thio-
phene 3b in good yields (Scheme 2).
We have also carried out the selenium–lithium exchange
reaction of 4-butyltelluro-selenophene[2,3-b]thiophene 2 with
n-butyllithium. The selenium–lithium exchange is a very attrac-
tive transformation of selenides, since it affords the corre-
sponding organolithium species,30 which could react with a
wide range of electrophiles generating directly polyfunctiona-
lized molecules.31 The generation of the organolithium
reagent from selenide 2l with n-butyllithium (1.0 equiv.), THF
(3 mL), at −78 °C gave the lithium intermediate 4a’ which was
trapped with 4-chlorobenzaldehyde (1.5 equiv.) affording the
secondary alcohol 4a in 63% yield (Scheme 3).
Conclusion
In conclusion, we have described a simple and efficient FeCl3–
diorganoyl dichalcogenide cyclization of alkynyl thiophenes as
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well as established a route to obtain substituted heterocycles 13C NMR (CDCl3, 50 MHz): δ 153.9, 151.9, 136.0, 133.8, 132.5,
in good yields. The cyclization was carried out at room temp- 129.8, 129.5, 129.2, 128.4, 128.3, 128.2, 126.1, 123.4, 113.6. MS
erature, under an air atmosphere affording 4-(organochalco- (relative intensity) m/z: 419 (99), 339 (91), 260 (75), 218 (43),
gen) heterocycles exclusively via
a 5-endo-dig cyclization 171 (100), 139 (61), 77 (21). HRMS calcd for C18H12SSe2:
process. The best condition worked well with a broad range of 419.8990. Found: 719.9005.
2-organochalcogen-3-alkynylthiophenes and diorganoyl dichalco-
5-Phenyl-4-(4-tolylphenylseleno)selenophene[2,3-b]thiophene
genides. In addition, when we applied the Suzuki conditions (2b). Yield: 0.081 g, 75%. 1H NMR (CDCl3, 400 MHz):
to the obtained product, we were able to convert 2-telluro- δ 7.54–7.51 (m, 2H, ArH), 7.36–7.27 (m, 4H, ArH), 7.14–7.10
chalcogenophenes to Suzuki-type products in good yields. For (m, 3H, ArH), 6.93 (d, J = 7.89 Hz, 2H, ArH), 2.22 (s, 3H, CH3).
instance, the selenide 2l was treated under selenium–lithium 13C NMR (CDCl3, 50 MHz): δ 153.3, 152.0, 136.0, 135.9, 133.7,
exchange conditions followed by trapping the lithium inter- 129.9, 129.8, 129.7, 128.5, 128.3, 128.2, 128.1, 123.4, 114.0,
mediates with 4-chlorobenzaldeyde providing the correspond- 20.9. MS (relative intensity) m/z: 432 (74), 354 (95), 274 (53),
ing secondary alcohol in good yield. We believe that this 218 (41), 171 (100), 139 (63), 91 (37), 65 (10). Anal. calcd for
approach to chalcogenophenes should prove quite useful in C19H14SSe2: C, 52.79; H, 3.26. Found: C, 52.90; H, 3.31.
synthesis, particularly when one considers that there are many
4-(Butylseleno)-5-phenylselenophene[2,3-b]thiophene (2f).
ways to transform the resulting tellurium and selenium func- Yield: 0.065 g, 65%. 1H NMR (CDCl3, 200 MHz): δ 7.61–7.35
tionalities into other substituents.
(m, 7H, ArH), 2.66 (t, J = 7.3 Hz, 2H, SeCH2CH2), 1.44 (quint,
J = 7.3 Hz, 2H, CH2CH2CH2), 1.20 (sext, J = 7.3 Hz, 2H,
CH2CH2CH3), 0.74 (t, J = 7.3 Hz, 3H, CH2CH3). 13C NMR
(CDCl3, 100 MHz): δ 152.8, 151.6, 136.6, 133.2, 129.9, 128.2,
128.1, 127.9, 123.4, 114.7, 32.2, 28.6, 22.5, 13.3. MS (relative
intensity) m/z: 399 (44), 341 (57), 263 (100), 183 (64), 170 (32),
138 (59), 57 (11). HRMS calcd for C16H16SSe2: 399.9303.
Found: 399.9317.
4-(Butyltelluro)-5-(phenylseleno)selenophene[2,3-b]thiophene
(2g). Yield: 0.060 g, 54%. 1H NMR (CDCl3, 200 MHz):
δ 7.55–7.37 (m, 7H, ArH), 2.66 (t, J = 7.3 Hz, 2H, TeCH2CH2),
1.54 (quint, J = 7.3 Hz, 2H, CH2CH2CH2), 1.19 (sext, J = 7.3 Hz,
2H CH2CH2CH3), 0.76 (t, J = 7.3 Hz, 3H, CH2CH3). 13C NMR
(CDCl3, 50 MHz): δ 155.5, 154.2, 137.8, 133.9, 130.2, 128.2,
128.1, 127.3, 124.9, 97.1, 33.5, 24.7, 13.3, 9.1. MS (relative
intensity) m/z: 447 (7), 281 (18), 264 (68), 207 (48), 184 (100),
139 (55), 73 (40). HRMS calcd for C16H16ClSSeTe: 449.9200.
Found: 449.9213.
Experimental section
1H NMR spectra were obtained at 200 MHz with a DPX-200
NMR spectrometer or at 400 MHz with a DPX-400 NMR spec-
trometer. Spectra were recorded in CDCl3 solutions. 13C NMR
spectra were obtained either at 50 MHz with a DPX-200 NMR
spectrometer or at 100 MHz with
a
DPX-400 NMR
spectrometer. Spectra were recorded in CDCl3 solutions.
Column chromatography was performed using Merck Silica
Gel (230–400 mesh). Thin layer chromatography (TLC) was per-
formed using Merck Silica Gel GF254 (0.25 mm thickness). For
visualization, TLC plates were either placed under UV light, or
stained with iodine vapour, or acidic vanillin. Most reactions
were monitored by TLC for disappearance of starting material.
MS spectra were recorded with a Shimadzu GC-MS-2010P.
Elemental analyses were performed with a Vario EL III elemen-
tal analysis instrument. HRMS were recorded with a Shimadzu
LC-MS-IT-TOF spectrometer.
4-(Phenylseleno)-5-(4-tolyl)selenophene[2,3-b]thiophene (2h).
Yield: 0.082 g, 76%. 1H NMR (CDCl3, 200 MHz): δ 7.44–7.40
(m, 2H, ArH), 7.30–7.09 (m, 9H, ArH), 2.35 (s, 3H, CH3). 13C
NMR (CDCl3, 100 MHz): δ 154.2, 151.9, 138.4, 132.6, 131.4,
129.6, 129.5, 129.1, 129.0, 128.1, 126.0, 123.4, 113.3, 99.5, 21.2.
MS (relative intensity) m/z: 433 (59), 353 (82), 275 (60), 261 (42),
197 (100), 151 (51), 77 (32). HRMS calcd for C19H14SSe2:
General procedure for iron-promoted cyclization of
2-butylchalcogen-3-alkynylthiophenes and diorganoyl
dichalcogenides
To a Schlenk tube, under an air atmosphere, containing a 433.9147. Found: 433.9163.
mixture of FeCl3 (0.25 mmol) in dry CH2Cl2 (2 mL) was added
5-(4-Methoxyphenyl)-4-(phenylseleno)selenophene[2,3-b]-
the appropriate diorganoyl dichalcogenide (0.55 equiv.). The thiophene (2i). Yield: 0.091 g, 81%. 1H NMR (CDCl3,
resulting solution was stirred for 5 min at room temperature. 200 MHz): δ 7.46 (d, J = 8.8 Hz, 2H, ArH), 7.32–7.08 (m, 7H,
After this 2-butylchalcogen-3-alkynylthiophenes (0.25 mmol) ArH), 6.90 (d, J = 8.8 Hz, 2H, ArH), 3.81 (s, 3H, OCH3). 13C
in CH2Cl2 (1 mL) were added and the resulting solution was NMR (CDCl3, 50 MHz): δ 159.8, 154.1, 151.9, 132.9, 132.7,
stirred under room temperature for 1 hour. After this the solu- 130.9, 129.3, 129.1, 128.5, 128.0, 126.0, 123.4, 113.9, 133.7,
tion was diluted with dichloromethane (10 mL), and washed 55.3. MS (relative intensity) m/z: 448 (83), 370 (100), 293 (65),
with saturated aq. NH4Cl (3 × 10 mL). The organic phase was 277 (62), 250 (36), 184 (26), 169 (45), 77 (14). Anal. calcd for
separated, dried over MgSO4, and concentrated under vacuum. C19H14OSSe2: C, 50.90; H, 3.15. Found: C, 51.09; H, 3.19.
The residue was purified by flash chromatography on silica gel
using hexane as the eluent.
2-Phenyl-3-(phenylseleno)benzo[d]thieno[2,3-b]thiophene (2r).
Yield: 0.067 g, 64%. 1H NMR (CDCl3, 200 MHz): δ 8.61–8.56
5-Phenyl-4-(phenylseleno)selenophene[2,3-b]thiophene (2a). (m, 1H, ArH), 7.80–7.76 (m, 1H, ArH), 7.58–7.53 (m, 2H, ArH),
Yield: 0.087 g, 83%. 1H NMR (CDCl3, 200 MHz): δ 7.56–7.49 7.39–7.06 (m, 10H, ArH). 13C NMR (CDCl3, 50 MHz): δ 150.6,
(m, 2H, ArH), 7.41–4.31 (m, 4H, ArH), 7.24–7.12 (m, 6H, ArH). 143.6, 142.5, 137.4, 134.0, 133.2, 133.2, 130.1, 129.4, 128.5,
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128.3, 125.9, 124.5, 124.3, 122.8, 122.2, 112.2. MS (relative
intensity) m/z: 422 (55), 342 (100), 264 (61), 221 (92), 77 (12).
Anal. calcd for C22H14S2Se: C, 62.70; H, 3.35. Found: C, 62.81;
H, 3.39.
Notes and references
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General procedure for a palladium-catalyzed coupling reaction
of 2g with boronic acid
The solution of 4-(butyltelluro)-5-(phenylseleno)selenophene
[2,3-b]thiophene 2g (0.25 mmol) in MeOH (3 mL) was added to
appropriate boronic acid (1.3 equiv.), Pd(PPh3)4 (10 mol%) and
Ag2O (2 equiv.). After this Et3N (4 equiv.) was added, and the
reaction mixture was stirred at reflux temperature for 3 h. The
organic phase was separated, dried over MgSO4, and concen-
trated under vacuum. The residue was purified by flash chrom-
atography and eluted with hexane.
4-(4-Bromophenyl)-5-phenylselenophene[2,3-b]thiophene (3a).
Yield: 0.066 g, 63%. 1H NMR (CDCl3, 200 MHz): δ 7.48–7.38
(m, 3H), 7.27–7.38 (m, 7H, ArH), 7.08 (d, J = 5.3 Hz, 2H, ThH).
13C NMR (CDCl3, 50 MHz): δ 149.7, 146.4, 135.9, 135.8, 131.7,
131.3, 129.4, 128.9, 128.6, 128.5, 127.6, 126.1, 122.1, 121.3. MS
(relative intensity) m/z: 417 (100), 337 (26), 258 (95), 213 (25),
169 (30), 129 (67), 106 (8). Anal. calcd for C18H11BrSSe: C,
51.69; H, 2.65. Found: C, 51.73; H, 3.10.
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Procedure for the reactions of intermediate 3-lithio-benzo[b]-
selenopheno[3,2-d]thiophene with 4-chorobenzaldehyde
To a two-neck round-bottomed flask, under argon, containing
a solution of 2-phenyl-3-(phenylseleno)benzo[b]selenopheno-
[3,2-d]thiophene (0.25 mmol) in THF (3 mL) at −78 °C was
added n-BuLi (0.25 mmol) in one portion. The reaction
mixture was stirred for 15 minutes, and then a solution of
4-chlorobenzaldehyde (0.3 mmol) in THF (1 mL) at −78 °C was
added. The reaction mixture was allowed to stir at room temp-
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with ethyl acetate (20 mL) and washed with saturated aq.
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(4-Chorophenyl)(2-phenylbenzo[b]selenophene[3,2-d]thiophene-
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200 MHz): δ 7.94–7.90 (m, 1H, ArH), 7.75–7.71 (m, 1H, ArH),
7.58–7.22 (m, 11H, ArH), 6.48 (s, 1H, ArCH(OH)Ar), 2.99 (s, 1H,
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455 (5), 374 (29), 338 (28), 281 (37), 207 (37), 171 (72), 139 (57),
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Acknowledgements
The financial support by UFSM, CAPES, FAPERGS and CNPq
(PRONEX) research grant # 10/0005-1 is gratefully acknowl- 14 (a) T. Wang, W. Zhou, H. Yin, J.-A. Ma and N. Jiao,
edged. We also thank CNPq for fellowships.
Angew. Chem., Int. Ed., 2012, 51, 10823; (b) Y. Su, W. Jia and
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