Synthesis of Fused 4-Iodoselenophene[2,3-b]thiophenes
CH2-CH3) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 132.5,
containing the previously prepared organozinc compound
131.5, 130.4, 128.2, 128.3, 128.2, 123.2, 104.2, 91.9, 86.2, 36.5, 24.8,
(1.5 mmol) was charged sequentially with 2a (0.5 mmol) and
13.3, 8.1 ppm. MS: m/z (%) = 370 (35), 312 (10), 184 (100), 139 Pd(PPh3)4 (0.057 g, 10 mol-%). The yellow mixture was stirred at
(49), 57 (9).
room temperature for 3 h. After this, the solution was diluted with
dichloromethane (20 mL) and washed with saturated aqueous
NH4Cl (3ϫ20 mL). The organic phase was separated, dried with
MgSO4, and concentrated under vacuum. The residue was purified
by flash chromatography (hexane).
General Procedure for the Cyclizations Reactions: To a solution of
the
appropriate
2-(alkylchalcogen)-3-(alkynyl)thiophene
(0.25 mmol) in CH2Cl2 (2 mL) was added gradually the electro-
philic source (1.1 equiv.) in CH2Cl2 (3 mL). The reaction mixture
was allowed to stir at room temperature for the desired time
showed in Table 2. The organic phase was extracted with CH2Cl2
(20 mL) and washed with saturated aqueous Na2S2O3. The com-
bined organic layer was dried with anhydrous Mg2SO4 and concen-
trated under vacuum to yield the crude product, which was purified
by flash chromatography on silica gel (hexane).
5-Phenyl-4-p-tolylselenopheno[2,3-b]thiophene (5a): Yield: 0.121 g
(69%). 1H NMR (200 MHz, CDCl3): δ = 7.62–7.11 (m, 11 H), 2.39
(s, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 149.1, 138.3,
136.6, 129.4, 128.9, 128.6, 127.8, 126.8, 126.1, 121.7, 118.3,
21.1 ppm. C19H14SSe (353.34): calcd. C 64.58, H 3.99; found C
64.71, H 4.20.
4-Iodo-5-phenylseleno[2,3-b]thiophene (2a): Yield: 0.074 g (76%). 1H
NMR (200 MHz, CDCl3, 25 °C): δ = 7.61–7.57 (m, 2 H, CH-Ar),
7.48–7.41 (m, 4 H, 3H-Ar, 1H-Th), 7.33 (d, JH,H = 5.3 Hz, 1 H,
CH-Th) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 151.8, 136.5,
129.7, 128.5, 128.5, 127.9, 124.2, 73.6 ppm. MS: m/z (%) = 385
(100), 260 (69), 216 (20), 169 (31), 137 (36), 86 (19), 50 (6).
C12H7ISSe (389.11): calcd. C 37.04, H 1.81; found C 37.29, H 2.12.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures, additional experimental details for
1
the preparation of all compounds, and H and 13C NMR spectra
for all reaction products.
Acknowledgments
General Procedure for the Copper-Catalyzed Coupling Reaction of
Intermediate 2a with 4-Chlorobenzenethiol: To a Schlenk tube, un-
der an argon atmosphere, containing 4-iodo-5-phenylsele-
nopheno[2,3-b]thiophene (2a; 0.5 mmol) in dry dioxane (3 mL) was
added the appropriate thiol (0.6 mmol). After this, Et3N (1 mmol)
was added dropwise, followed by CuI (0.0095 g, 10 mol-%). The
reaction mixture was stirred at reflux temperature for 6 h. After
this, the solution was cooled to room temperature, diluted with
dichloromethane (20 mL), and washed with saturated aqueous
NH4Cl (3ϫ20 mL). The organic phase was separated, dried with
MgSO4, and concentrated under vacuum. Purification was carried
out by flash chromatography on silica gel (hexane).
We are grateful to the Conselho Nacional de Desenvolvimento Ci-
entífico e Tecnológico (CNPq/INCT-catalise), Coordenação de Ap-
erfeiçoamento de Pessoal de Nível Superior (SAUX), and Fun-
dação de Amparo à Pesquisa do Estado do Rio Grande do Sul for
a fellowship and financial support.
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4-(4-Chlorophenylthio)-5-phenylselenopheno[2,3-b]thiophene
(3a):
Yield: 0.134 g (66%). 1H NMR (200 MHz, CDCl3, 25 °C): δ =
7.57–7.52 (m, 3 H, CH-Ar, CH-Th), 7.41–7.32 (m, 4 H, CH-Ar,
CH-Th), 7.14 (d, JH,H = 8.1 Hz, 2 H, CH-p-Cl-C6H4), 7.00 (d, JH,H
= 8.1 Hz, 2 H, CH-p-Cl-C6H4) ppm. 13C NMR (50 MHz, CDCl3,
25 °C): δ = 135.8, 135.1, 133.4, 131.2, 129.4, 129.0, 128.8, 128.6,
128.5, 127.9, 122.4 ppm. MS: m/z (%) = 408 (11), 406 (100), 326
(57), 290 (58), 171 (43), 145 (44), 89 (8), 45 (3).
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General Procedure for the Palladium-Catalyzed Coupling Reaction
of 2a with 4-Bromophenylboronic Acid: A solution of 4-iodo-5-
phenylselenopheno[2,3-b]thiophene (2a; 0.5 mmol) in DMF/H2O
(5:1, 5 mL) was added to Pd(PPh3)4 (2 mol-%) and K2CO3
(2 equiv.). After this, the boronic acid (1.5 equiv.) in DMF (0.5 mL)
was added dropwise, and the reaction mixture was stirred at reflux
temperature for 8 h. The organic phase was separated, dried with
MgSO4, and concentrated under vacuum. The residue was purified
by flash chromatography (hexane/ethyl acetate, 9:1).
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4-(4-Bromophenyl)-5-phenylselenopheno[2,3-b]thiophene (4a): Yield:
0.131 g (63%). 1H NMR (200 MHz, CDCl3, 25 °C): δ = 7.46 (d,
JH,H = 8.1 Hz, 2 H, CH-p-Br-C6H4), 7.39 (d, JH,H = 5.3 Hz, 1 H,
CH-Th), 7.27–7.17 (m, 7 H, CH-Ar, CH-p-Br-C6H4), 7.08 (d, JH,H
= 5.3 Hz, 1 H, CH-Th) ppm. 13C NMR (100 MHz, CDCl3, 25 °C):
δ = 149.7, 146.4, 135.9, 131.7, 131.3, 129.4, 128.5, 128.5, 127.6,
122.1, 121.3 ppm. MS: m/z (%) = 421 (15), 418 (100), 338 (24), 258
(70), 169 (30), 129 (58), 51 (2).
General Procedure for the Palladium-Catalyzed Negishi Coupling of
2a with p-Tolylzinc Chloride: A 10-mL Schlenk tube, equipped with
a magnetic bar and a rubber septum, under an argon atmosphere,
Eur. J. Org. Chem. 2010, 705–710
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