Efficient synthesis of functionalized 2,3-Di(alkenyl)benzothiophenes and dibenzothiophenes based on the first heck reactions of 2,3-Di- and 2,3,6-tribromobenzothiophene

Article abstract of DOI:10.1055/s-0029-1217975

Alkenyl-substituted benzothiophenes were prepared by the first Heck reactions of 2,3-di- and 2,3,6-tribromobenzo-thiophene. Functionalized dibenzothiophenes were prepared based on domino twofold Heck-6- electrocyclization reactions.

Full text of DOI:10.1055/s-0029-1217975

LETTER
2691
Efficient Synthesis of Functionalized 2,3-Di(alkenyl)benzothiophenes and
Dibenzothiophenes Based on the First Heck Reactions of 2,3-Di- and
2,3,6-Tribromobenzothiophene
2
, 3-Di(alkenyl)benzoth
u
iophene
s
and
n
D
ibenzothi
a
ophenes war Hussain,a Imran Malik,a Alexander Villinger,a Peter Langer*a,b
a
b
Received 31 March 2009
Actually, the standard route to 2a follows reference 18
where the bromination is carried out at 20 °C. During our
experiments related to the scale-up of this reaction we
have found that more vigorous conditions (reflux, 18 h)
were required to avoid the formation of monobrominated
byproducts. We have also prepared, for the first time,
2,3,6-tribromobenzothiophene (2b) by using an excess of
bromine.20
Abstract: Alkenyl-substituted benzothiophenes were prepared by
the first Heck reactions of 2,3-di- and 2,3,6-tribromobenzo-
thiophene. Functionalized dibenzothiophenes were prepared based
on domino ‘twofold Heck–6p-electrocyclization’ reactions.
Key words: catalysis, palladium, Heck reaction, electrocyclization,
benzothiophene
Benzothiophenes are of considerable pharmacological
relevance and are present in some natural products, such
as antiangiogenic bryoanthrathiophene.1 Dibenzo-
thiophenes have not yet been found in nature. However,
they have received considerable attention because of their
interesting pharmacological properties. This includes, for
example, antimicrobial,2 antileishmanial,3 antiprotozoal,4
antidiabetic,5 cytotoxic,6 and genotoxic activity.7 In addi-
tion, binding to the dopamine8 to the estrogen receptor9
and to neuroblastoma cells,10 inhibition of the human pro-
tein tyrosine phosphatase 1B,11 and of MAO A12 have
been studied.
Br
i
Br
S
S
1
ii
2a (84%)
Br
Br
S
Br
2b (70%)
Scheme 1 Bromination of benzothiophene (1). Reagents and condi-
tions: (i) Br2 (2.0 equiv), KOAc (2.0 equiv), CH2Cl2, reflux, 18 h; (ii)
Br2 (4.5 equiv), KOAc (4.5 equiv), CH2Cl2, reflux, 24 h.
Polyhalogenated heterocycles can be regioselectively
functionalized in palladium(0)-catalyzed cross-coupling
reactions. The regioselectivity is controlled by electronic
and steric parameters.13 Recently, we have reported Suzu-
ki and Heck reactions of tetrabromothiophene, tetrabro-
mo-N-methylpyrrole, tetrabromoselenophene, and other
polyhalogenated heterocycles.14 Eberbach and coworkers
reported that Sonogashira cross-coupling reactions of 2,3-
dibromobenzothiophene regioselectively occur at posi-
tion C-2.15 Suzuki16 and Stille17 reactions have also been
shown to occur selectively at the 2-position. Herein, we
report what are, to the best of our knowledge, the first
Heck reactions of 2,3-di- and 2,3,6-tribromoben-
zothiophene to give alkenyl-substituted benzothiophenes.
In addition, we report a new approach to functionalized
dibenzothiophenes based on domino ‘twofold Heck–
6p-electrocyclization’ reactions.18
The Heck reaction of 2a with acrylates 3b,e (2.5 equiv) af-
forded the 2,3-di(alkenyl)benzothiophenes 4b,e in good
yields (Scheme 2, Table 1). The best yields were obtained
when the reactions were carried out using Pd(OAc)2 (5
mol%) and the biaryl monophosphine ligand L1 (10
mol%) which was recently developed by Buchwald and
coworkers (Figure 1).21 The reactions were carried out in
DMF at 100 °C for 12 hours22 the employment of
Pd(PPh3)4 and other catalysts and ligands proved to be less
successful in terms of yield.
The Pd(OAc)2-catalyzed reaction of 2a with acrylates 3a–
c,e, carried out at 130 °C and using biaryl monophosphine
ligand L2, afforded the 1,2-dihydrodibenzothiophenes
5a–d as a mixture of two isomers. Their formation can be
explained by a domino ‘twofold Heck–thermal 6p-elec-
trocyclization’ cyclization and subsequent double-bond
migration. Heating of a xylene solution of crude 5a–d in
the presence of Pd/C resulted in the formation of diben-
zothiophenes 6a–d in 74–83% overall yields (based on
2a).22 The reaction of 2a with styrene 3f directly afforded
dibenzothiophene 6f in only one step.
The reaction of benzothiophene (1) with bromine (2.0
equiv) and KOAc (2.0 equiv) in CH2Cl2 (reflux, 18 h) re-
sulted in formation of (commercially available) 2,3-dibro-
mobenzothiophene (2a) in 84% yield (Scheme 1).15,16,19
SYNLETT 2009, No. 16, pp 2691–2695
x
x
.x
x
.2
0
0
9
Advanced online publication: 10.09.2009
DOI: 10.1055/s-0029-1217975; Art ID: D08509ST
© Georg Thieme Verlag Stuttgart · New York

2692
M. Hussain et al.
LETTER
R
of benzofuran and indole, carbon atom C-2 is much more
electron deficient than C-3. This effect is less pronounced
in the case of benzothiophene, and the rate of the oxida-
tive addition at C-2 and C-3 should be not too much dif-
ferent. On the other hand it has been pointed out in the
introduction, that palladium(0)-catalyzed reactions of
benzothiophene usually occur first at carbon C-2. A re-
duction of carbon C-2 in the first step is unlikely because
the 2,3-dialkenylbenzothiophenes 4b,e are cleanly formed
without any reduction. Therefore, the reason for the for-
mation of products 7 remains unclear at present.
R
S
i
Br
4b,e
R
Br
S
R
3a–f
R
ii
2
S
+
iii
R
R
R
R
R
S
Br
R
S
5a–d,f
3a,b,e,g,h
6a–d,f
Br
i
S
S
Scheme 2 Synthesis of 4b,e and 6a–d,f. Reagents and conditions:
(i) Pd(OAc)2 (5 mol%), L2 (structure see Figure 1, 10 mol%), 3 (2.5
equiv), Et3N (8.0 equiv), DMF, 100 °C, 12 h; (ii) Pd(OAc)2 (5 mol%),
L1 (structure see Figure 1, 10 mol%), 3 (2.5 equiv), Et3N, DMF,
130 °C, 48 h; (iii) Pd/C (10 mol%), xylene, reflux, 48 h.
7a–e
2a
Scheme 3 Synthesis of 7a–f. Reagents and conditions: i, Pd(OAc)2
(2.5–5 mol%), L1 (for 7a,b,d) or L2 (for 7c,e, 5–10 mol%), 3 (1.25
equiv), Et3N, DMF, 130 °C, 24 h.
Table 1 Synthesis of 4b,e and 6a–d,f
Table 2 Synthesis of 7a–f
3, 4, 6
R
Yielda (%) of 4
Yielda (%) of 6
3
7
R
Yielda (%) of 7
b
a
b
c
d
e
f
CO2Et
CO2n-Bu
CO2i-Bu
CO2n-Hex
Ph
–
76
81
74
77
3a
3b
3g
3e
3h
7a
7b
7c
7d
7e
CO2Et
CO2n-Bu
CN
81
65b
51
74
76
71
b
–
b
–
Ph
b
85
–
4-MeC6H4
b
4-ClC6H4
–
83c
a Yields of isolated products.
b Besides, 4b was isolated as a side product in 10% yield.
a Yields of isolated products based on 2a.
b Experiment was not carried out.
c Product was directly formed from 2a in one step.
PCy2
i-Pr
PCy2
i-Pr
OMe
L1
=
L2
=
MeO
Cy = cyclohexyl
i-Pr
Figure 1 Biaryl monophosphine ligands developed by Buchwald
and co-workers21
As mentioned above, the Sonogashira, Suzuki, and Stille
reactions of 2a regioselectively occurs at carbon atom C-
2. The Heck reaction of 2a with one equivalent of alkenes
3a,b,e,g,h afforded the 3-(alkenyl)benzothiophenes 7a–f
(Scheme 3, Table 2).23 The structure of 7d was indepen-
dently confirmed by X-ray crystal structure analysis
(Figure 2).24
Figure 2 Crystal structure of 7d
The Heck reaction of 2,3,6-tribromobenzothiophene (2b)
with n-butyl acrylate (3b) and styrene (3e) afforded the
2,3,6-tri(alkenyl)benzothiophenes 8a,b in good yields
(Scheme 4).25 The reaction was carried out in DMF at 100
°C for 12 hours using Pd(OAc)2/L1 as the catalyst. The
Pd(OAc)2/L1-catalyzed reaction of 2b with 3a,i, carried
out at 130 °C, afforded 9a,b as a mixture of two isomers.
The formation of products 7 can be explained by Heck
reaction, which occurs at carbon atom C-3, and reduction
of the bromide function located at carbon C-2. In the case
Synlett 2009, No. 16, 2691–2695 © Thieme Stuttgart · New York

LETTER
2,3-Di(alkenyl)benzothiophenes and Dibenzothiophenes
2693
Heating of a xylene solution of crude 9a,b in the presence
of Pd/C afforded the 5-alkenyldibenzothiophenes 10a,b.
References and Notes
(1) (a) Jeong, S.-J.; Higuchi, R.; Miyamoto, T.; Ono, M.;
Kuwano, M.; Mawatari, S. F. J. Nat. Prod. 2002, 65, 1344.
(b) Kelly, T. R.; Fu, Y.; Sieglen, J. T.; De Silva, H. Org. Lett.
2000, 2, 2351.
R
Br
R
(2) El-Naggar, A. M.; Ahmed, F. S. M.; Donia, S. G. J. Indian
Chem. Soc. 1983, 60, 479.
(3) Brendle, J. J.; Outlaw, A.; Kumar, A.; Boykin, D. W.;
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Agents Chemother. 2002, 46, 797.
(4) Patrick, D. A.; Hall, J. E.; Bender, B. C.; McCurdy, D. R.;
Wilson, W. D.; Tanious, F. A.; Saha, S.; Tidwell, R. R. Eur.
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(5) Wrobel, J.; Sredy, J.; Moxham, C.; Dietrich, A.; Li, Z.;
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(6) (a) Saulnier, M. G.; Balasubramanian, B. N.; Long, B. H.;
Frennesson, D. B.; Ruediger, E.; Zimmermann, K.;
Eummer, J. T.; Laurent, D. R. S.; Stoffan, K. M.; Naidu, B.
N.; Mahler, M. J. Med. Chem. 2005, 48, 2258. (b) Li, Z.;
Yang, Q.; Qian, X. Tetrahedron 2005, 61, 8711. (c)Durant,
J. L.; Busby, W. F.; Lafleur, A. L.; Penman, B. W.; Crespi,
C. L. Mutat. Res. 1996, 371, 123. (d) King, L. C.; Kohan,
M. J.; Brooks, L.; Nelson, G. B.; Ross, J. A.; Allison, J.;
Adams, L.; Desai, D.; Amin, S.; Padgett, W.; Lambert, G. R.
Chem. Res. Toxicol. 2001, 14, 661.
3b,e
Br
i
S
S
Br
R
2b
8a (R = CO2n-Bu, 68%)
8b (R = Ph, 73%)
3b,e
ii
R
R
R
R
S
S
R
+
iii
R
R
9a,b
R
S
R
10a (R = CO2n-Bu, 76%)
10b (R = Ph, 73%)
(7) Xu, Y.; Qian, X.; Yao, W.; Mao, P.; Cui, J. Bioorg. Med.
Chem. 2003, 11, 5427.
yields are based on 2b
(8) (a) Ellefson, C. R.; Prodan, K. A. J. Med. Chem. 1981, 24,
1107. (b) Arlt, M.; Boettcher, H.; Riethmueller, A.;
Schneider, G.; Bartoszyk, G. D. Bioorg. Med. Chem. Lett.
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(9) (a) Mori, Y.; Taneda, S.; Hayashi, H.; Sakushima, A.;
Kamata, K.; Suzuki, A. K.; Yoshino, S.; Sakata, M.; Sagai,
M.; Seki, K.-i. Biol. Pharm. Bull. 2002, 25, 145.
(b) Wallace, O. B.; Bryant, H. U.; Shetler, P. K.; Adrian, M.
D.; Geiser, A. G. Bioorg. Med. Chem. Lett. 2004, 14, 5103.
(10) Clark, R. D.; Jahangir, A.; Severance, D.; Salazar, R.;
Chang, T.; Chang, D.; Jett, M. F.; Smith, S.; Bley, K. Bioorg.
Med. Chem. Lett. 2004, 14, 1053.
Scheme 4 Synthesis of 8a,b, 9a,b, and 10a,b. Reagents and condi-
tions: (i) Pd(OAc)2 (5 mol%), L1 (10 mol%), 3 (3.75 equiv), Et3N (8.0
equiv), DMF, 100 °C, 12 h; (ii) Pd(OAc)2 (5 mol%), L1 (10 mol%), 3
(3.75 equiv), Et3N, DMF, 130 °C, 48 h; (iii) Pd/C (10 mol%), xylene,
reflux, 48 h.
The Heck reaction of 2b with two equivalents of acrylate
3a resulted in regioselective coupling of carbon atoms C-
2 and C-3 and reduction of C-6 to give the 2,3-dialkenyl-
benzothiophene 4a (Scheme 5).
(11) Shim, Y. S.; Kim, K. C.; Lee, K. A.; Shrestha, S.; Lee, K.-
H.; Kim, C. K.; Cho, H. Bioorg. Med. Chem. 2005, 13, 1325.
(12) Harfenist, M.; Joyner, C. T.; Mize, P. D.; White, H. L.
J. Med. Chem. 1994, 37, 2085.
(13) Review: Schröter, S.; Stock, C.; Bach, T. Tetrahedron 2005,
61, 2245.
CO2Et
Br
CO2Et
3a
CO2Et
Br
i
S
S
Br
(14) (a) Dang, T. T.; Dang, T. T.; Ahmad, R.; Reinke, H.; Langer,
P. Tetrahedron Lett. 2008, 49, 1698. (b) Dang, T. T.;
Villinger, A.; Langer, P. Adv. Synth. Catal. 2008, 350, 2109.
(c) Hussain, M.; Nguyen, T. H.; Langer, P. Tetrahedron Lett.
2009, 50, 3929. (d) Tengho Toguem, S.-M.; Hussain, M.;
Malik, I.; Villinger, A.; Langer, P. Tetrahedron Lett. 2009,
50, 4962. (e) Dang, T. T.; Dang, T. T.; Rasool, N.; Villinger,
A.; Langer, P. Adv. Synth. Catal. 2009, 351, 1595.
(15) Bussenius, J.; Laber, N.; Müller, T.; Eberbach, W. Chem.
Ber. 1994, 127, 247.
4a (64%)
2b
Scheme 5 Reaction of 2b with acrylate 3a (2 equiv). Reagents and
conditions: (i) Pd(OAc)2 (5 mol%), L1 (10 mol%), 3 (3.75 equiv),
Et3N (8.0 equiv), DMF, 70 °C, 12 h.
In conclusion, 2,3-di(alkenyl)benzothiophenes were pre-
pared by the first Heck reactions of 2,3-dibromoben-
zothiophene. Functionalized dibenzothiophenes were
prepared based on domino ‘twofold Heck–6p-electro-
cyclization’ reactions of 2,3-dibromobenzothiophene. In
addition, Heck reactions of 2,3,6-tribromoben-
zothiophene were reported, and the regioselectivity of the
reactions was studied.
(16) Heynderickx, A.; Samat, A.; Gugliemetti, R. Synthesis 2002,
213.
(17) Yamamura, K.; Houda, Y.; Hashimoto, M.; Kimura, T.;
Kamezawa, M.; Otani, T. Org. Biomol. Chem. 2004, 2, 1413.
(18) De Meijere and co-workers reported twofold Heck reactions
of 1,2-dibromocycloalk-1-enes and related substrates and
subsequent 6p-electrocyclization: Voigt, K.;
von Zezschwitz, P.; Rosauer, K.; Lansky, A.; Adams, A.;
Reiser, O.; de Meijere, A. Eur. J. Org. Chem. 1998, 1521;
and references cited therein.
Acknowledgment
Financial support by State of Pakistan (HEC scholarships for M.H.
and I.M.) and by the State of Mecklenburg-Vorpommern (scholar-
ship for M.H.) is gratefully acknowledged.
Synlett 2009, No. 16, 2691–2695 © Thieme Stuttgart · New York

2694
M. Hussain et al.
LETTER
211 (58), 185 (100). HRMS (EI, 70 eV): m/z calcd for
(19) Synthesis of 2,3-Dibromobenzothiophene (2a)
To a CH2Cl2 solution (50 mL) of benzo[b]thiophene (1, 5.00
g, 37.3 mmol) and KOAc (7.30 g, 74.6 mmol) was added Br2
(3.8 mL, 74.6 mmol) at 20 °C, and the solution was heated
under reflux for 24 h. To the solution was added a sat.
solution of Na2S2O3 and NaHCO3. The organic and the
aqueous layer were separated, and the latter was extracted
with CH2Cl2 (3 × 30 mL). The combined organic layers were
dried (Na2SO4), filtered, and concentrated in vacuo. The
residue was purified by flash silica column chromatography
(pure heptanes) to yield 2a as a white solid (8.30 g, 76%).
Depending on the scale of the reaction, inseparable mixtures
of bromo- and 2,3-dibromobenzothiophene were formed. In
this case, the mixture was reacted again with 1.0 equiv each
of Br2 and KOAc to give pure 2a.
(20) Synthesis of 2,3,6-Tribromobenzothiophene (2b)
To a CH2Cl2 solution (50 mL) of benzo[b]thiophene (1, 5.00
g, 37.3 mmol) and KOAc (16.5 g, 167.9 mmol) was added
Br2 (8.6 mL, 167.9 mmol) at 20 °C, and the solution was
heated under reflux for 24 h. To the solution was added a sat.
solution of Na2S2O3 and NaHCO3. The organic and the
aqueous layer were separated, and the latter was extracted
with CH2Cl2 (3 × 30 mL). The combined organic layers were
dried (Na2SO4), filtered, and concentrated in vacuo. The
residue was purified by flash silica column chromatography
(pure heptanes) to yield 2b as a white solid (9.7 g, 70%).
(21) Billingsley, K.; Buchwald, S. L. J. Am. Chem. Soc. 2007,
129, 3358; and references cited therein.
C18H18NO4S [M]+: 330.09203; found: 330.091818.
(23) General Procedure B for the Synthesis of 7
In a pressure tube (glass bomb) a suspension of Pd(OAc)2
(06 mg, 0.025 mmol) and dicyclohexyl(2¢,6¢-dimethoxy-
biphenyl-2-yl)phosphine (L1, 21 mg, 0.05 mmol) in DMF
(5 mL) was flushed with Ar and stirred at 20 °C to give a
yellowish or brownish transparent solution. To the stirred
solution were added the 2,3-dibromobenzothiophene (2a,
292 mg, 1.0 mmol), Et3N (1.1 mL, 8.0 mmol), and the
acrylate (1.25 mmol). The reaction mixture was stirred at
130 °C for 24 h. The solution was cooled to 20 °C, poured
into H2O and CH2Cl2 (25 mL each), and the organic and the
aqueous layer were separated. The latter was extracted with
CH2Cl2 (3 × 25 mL). The combined organic layers were
washed with H2O (3 × 20 mL), dried (Na2SO4), concentrated
in vacuo, and passed through a column (flash silica gel,
heptanes–EtOAc) to yield the product.
Analytical Data of (E)-3-Styrylbenzo[b]thiophene (7d)
Compound 7d was prepared starting with 2a (292 mg, 1.0
mmol) as a colorless crystalline solid (174 mg, 76%); mp
93–95 °C (CH2Cl2–EtOH). 1H NMR (300 MHz, CDCl3):
d = 7.12–7.23 (m, 2 H), 7.28–7.36 (m, 5 H), 7.46 (s, 1 H,
ArH), 7.46–7.49 (m, 2 H, ArH), 7.77–7.83 (m, 1 H, ArH),
7.91–7.94 (m, 1 H, ArH). 13C NMR (62 MHz, CDCl3):
d = 120.7, 121.8, 122.0, 123.0, 124.33, 124.6, 126.4, 127.7,
128.8, 130.3 (CH), 134.2, 137.4, 137.8, 140.5 (C). IR (KBr):
n = 2921, 2851 (s), 1667, 1598, 1492, 1454, 1446, 1434 (m),
1377, 1365, 1346, 1260, 1243, 1204, 1176, 1156, 1029,
1019, 948, 907, 887, 864 (w), 757, 748, 730, 696 (s), 623,
591, 555, 538 (w) cm–1. GC-MS (EI, 70 eV): m/z (%) = 236
(100) [M]+, 221 (18), 202 (16), 189 (05), 117 (08). HRMS
(EI, 70 eV): m/z calcd for C16H12S [M]+: 236.06542; found:
236.064490.
(22) General Procedure A for the Synthesis of
Dibenzo[b,d]thiophenes 6
In a pressure tube (glass bomb) a suspension of Pd(OAc)2
(12 mg, 0.05 mmol, 2.5 mol% per Br atom) and dicyclo-
hexyl(2¢,6¢-dimethoxybiphenyl-2-yl)phosphine (L1, 41 mg,
0.10 mmol) in DMF (5 mL) was flushed with Ar and stirred
at 20 °C to give a yellowish or brownish transparent
solution. To the stirred solution were added the 2,3-dibromo-
benzothiophene (2a, 292 mg, 1.0 mmol), Et3N (1.1 mL, 8.0
mmol), and the acrylate (1.25 equiv per Br). The reaction
mixture was stirred at 130 °C for 48 h. The solution was
cooled to 20 °C, poured into H2O and CH2Cl2 (25 mL each),
and the organic and the aqueous layer were separated. The
latter was extracted with CH2Cl2 (3 × 25 mL). The combined
organic layers were washed with H2O (3 × 20 mL), dried
(Na2SO4), concentrated in vacuo, and passed through a
column (silica gel). To a xylene solution (3 mL) of the crude
product was added Pd/C (30 mg, 10 mol%). The solution
was stirred under reflux for 48 h under argon atmosphere.
The reaction mixture was filtered, and the filtrate was
concentrated in vacuo. The residue was purified by
chromatography (flash silica gel, heptanes–EtOAc) to yield
the product.
(24) CCDC-746828 contains all crystallographic details of
this publication and is available free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html or can be
ordered from the following address: Cambridge
Crystallographic Data Centre, 12 Union Road, GB-
Cambridge CB21EZ; fax: +44 (1223)336033; or
deposit@ccdc.cam.ac.uk.
(25) General Procedure C for the Synthesis of
Dibenzo[b,d]thiophenes 10
In a pressure tube (glass bomb) a suspension of Pd(OAc)2
(12 mg, 0.05 mmol, 1.7 mol% per Br atom) and dicyclo-
hexyl-(2¢,6¢-dimethoxybiphenyl-2-yl)phosphine (L1, 41 mg,
0.10 mmol) in DMF (5 mL) was flushed with Ar and stirred
at 20 °C to give a yellowish or brownish transparent
solution. To the stirred solution were added the 2,3,6-
tribromobenzothiophene (2b, 371 mg, 1.0 mmol), Et3N (1.1
mL, 8.0 mmol), and the acrylate (1.25 equiv per Br). The
reaction mixture was stirred at 130 °C for 48 h. The solution
was cooled to 20 °C, poured into H2O and CH2Cl2 (25 mL
each), and the organic and the aqueous layers were
separated. The latter was extracted with CH2Cl2 (3 × 25
mL). The combined organic layers were washed with H2O
(3 × 20 mL), dried (Na2SO4), concentrated in vacuo, and
passed through a column (silica gel). To a xylene solution (3
mL) of the crude product was added Pd/C (30 mg, 10 mol%).
The solution was stirred under reflux for 48 h under argon
atmosphere. The reaction mixture was filtered, and the
filtrate was concentrated in vacuo. The residue was purified
by chromatography (flash silica gel, heptanes–EtOAc) to
yield the product.
Analytical Data of Diethyl Dibenzo[b,d]thiophene-2,3-
dicarboxylate (6a)
Compound 6a was prepared starting with 2a (292 mg, 1.0
mmol) as an amorphous white solid (249 mg, 76%); mp
118–119 °C. 1H NMR (300 MHz, CDCl3): d = 1.33 (t, 3 H,
J = 7.76 Hz, CH3), 1.35 (t, 6 H, J = 7.76 Hz, CH3), 4.31–4.40
(m, 4 H, 2 CH2O), 7.41–7.48 (m, 2 H, ArH), 7.79–7.82 (m,
2 H, ArH), 8.12 (s, 1 H, ArH), 8.13–8.15 (m, 1 H, ArH), 8.43
(s, 1 H, ArH). 13C NMR (62 MHz, CDCl3): d = 14.2 (2 CH3),
61.7, 61.8 (CH2O), 122.3, 122.4, 123.0, 123.6, 125.1, 128.0
(CH), 128.5, 130.4, 134.4, 137.1, 140.7, 141.9 (C), 167.5,
167.7 (CO). IR (KBr): n = 3053, 2975, 2931, 2896, 2867 (w),
1706 (s), 1632, 1603, 1540, 1483, 1469 (w), 1440, 1366,
1314 (m), 1247, 1229, 1098, 1021 (s), 913, 885, 873, 853
(w), 765, 757, 708 (s), 642, 583, 552 (w) cm–1. MS (EI, 70
eV): m/z (%) = 330 (17) [M]+, 284 (06), 257 (54), 229 (19),
Analytical Data of (E)-2,3-Diphenyl-7-styryldi-
benzo[b,d]thiophene (10b)
Compound 10b was prepared starting with 2b (371 mg, 1.0
Synlett 2009, No. 16, 2691–2695 © Thieme Stuttgart · New York

LETTER
mmol) as a brownish semisolid (319 mg, 73%). 1H NMR
2,3-Di(alkenyl)benzothiophenes and Dibenzothiophenes
2695
140.5, 141.2, 142.1 (C). IR (KBr): n = 3054, 3023, 291 (w),
1681, 1596, 1493, 1445 (m), 1178, 1155, 1072, 1026 (w),
956 (s), 908, 876, 812 (w), 747, 733, 688 (s) cm–1. MS (EI,
70 eV): m/z (%) = 438 (19) [M]+, 368 (31), 338 (100), 259
(20), 234 (16), 202 (10), 105 (15). HRMS (EI, 70 eV): m/z
calcd for C32H22S [M]+: 438.14422; found: 438.144012.
(300 MHz, CDCl3): d = 7.01–7.20 (m, 7 H), 7.24–7.34 (m, 7
H), 7.40–7.47 (m, 6 H), 7.75–7.86 (m, 2 H, ArH). 13C NMR
(62 MHz, CDCl3): d = 120.7, 121.3, 122.1, 122.3, 122.9,
125.6, 126.5, 126.6, 127.5, 128.6, 128.7, 128.8 (CH), 129.7,
130.3 (C), 130.4 (CH), 137.3, 137.4, 137.4, 137.5, 139.9,
Synlett 2009, No. 16, 2691–2695 © Thieme Stuttgart · New York