and methyl 2-bromothiophene-4-carboxylate (5) were
reaction mixture was cooled, diluted with CHCl to 50 mL,
and then filtered to remove the metal powder. The organic
phase was washed with water (3×30 mL) and dried over
3
obtained. 1H NMR (CDCl ) d 7.99 (d, J=1.5 Hz), 7.47 (d,
3
J=1.5 Hz), 7.36 (d, J=5 Hz), 7.24 (d, J=5 Hz), 3.89 (s),
3.86 (s).
MgSO . The CHCl was removed with a rotary evaporator.
4
3
Cold MeOH was added and the precipitate which formed was
filtered to give a brown–yellow crude solid product which was
purified as described below.
2-Bromothiophene-4-carboxylic acid. 2-Bromothiophene-4-
carboxylic acid was prepared essentially as described in the
literature.24 A solution of 23 g (0.14 mol) of bromine in
113 mL of glacial acetic acid was slowly added to a stirred
solution of 19 g (0.15 mol) of thiophene-3-carboxylic acid in
175 mL of glacial acetic acid at room temperature. The mixture
was stirred for 15 minutes and then poured into 1 L of cold
water (ice bath). The mixture was filtered and a light yellow
solid was obtained. The crude product was recrystallized from
1300 mL of water. 15 g (48%) of product 5 was obtained as
white needles: mp 140–141 °C (lit.,24 117–118 °C; lit.,25
139–140 °C); Anal. Calcd. for C H O SBr: C, 29.01; H, 1.46;
Dihexyl 2,2∞-bithiophene-4,4∞-dicarboxylate. The crude
product (0.21 g) was purified using column chromatography
(silica gel, 1×8 inch) with ethyl acetate–hexane (1550) as
eluent to give 0.18 g (43%) of a pale yellow solid product;
purity (HPLC) >99%; mp 60–61 °C. Anal. Calcd. for
C H O S : C, 62.53; H, 7.16; Found: C, 62.87; H, 7.22%;
22 30 4 2
1H NMR d 8.00 (d, J=1 Hz, 1H), 7.58 (d, J=1 Hz, 1H),
4.28 (t, J=7 Hz, 2H), 1.75 (quintet, J=7 Hz, 2H), 1.45–1.30
(m, 6H), 0.91 (t, J=7 Hz, 3H); 13C NMR (CDCl ) (1H
5
3 2
3
Found: C, 28.71; H, 1.13%; 1H NMR (CDCl ) d 10.27 (very
br s, 1H), 8.12 (d, J=1 Hz, 1H), 7.51 (d, J=1 Hz, 1H), 13C
NMR (CDCl ) (1H decoupled) d 166.8, 135.8, 133.1, 130.4,
113.4.
decoupled) d 162.4, 136.9, 134.6, 131.7, 124.6, 65.1, 31.4, 28.6,
3
25.6, 22.5, 14.0; IR (KBr) 3116, 3096, 3062, 2952, 2928, 2871,
2851, 1704, 1523, 1467, 1428, 1397, 1357, 1224, 1176, 1097,
1038, 984, 964, 908, 868, 844, 775, 751, 622, 467 cm−1;
3
UV–VIS (THF) l
9.9×103), two shoulders at 297 nm (e=9.7×103) and 312 nm
(e=9.4×103).
243 nm (e=1.4×104), 303 nm (e=
max
Alkyl 2-bromothiophene-4-carboxylates: general procedure.
8.28 g (40.0 mmol) of 2-bromothiophene-4-carboxylic acid
and 100 mL of SOCl were refluxed for 6 hours. The excess
2
SOCl was removed under vacuum (water aspirator) to pro-
2
Dioctyl 2,2∞-Bithiophene-4,4∞-dicarboxylate. The crude
product (0.28 g) was purified using column chromatography
(silica gel, 1×8 inch) with ethyl acetate–hexane (1550) as
eluent to give 0.24 g (50%) of a pale yellow solid product;
purity (HPLC) >99%; mp 69–70 °C. Anal. Calcd. for
duce a light yellow solid. Then, 0.40 mol of ROH and 8 mL
of dry pyridine were added to the flask dropwise through an
addition funnel. The mixture was stirred for 6 h at 80 °C,
cooled, poured into a 250 mL beaker with 60 g of ice and
80 mL of 1 M HCl, and stirred for a while. The solution was
washed with diethyl ether (4×300 mL) and the organic phase
was then washed with saturated NaHCO (3×300 mL) and
dried with K CO . The ethyl ether was removed with a rotary
evaporator and a light yellow crude product was obtained and
purified as described below.
C H O S : C, 65.24; H, 8.00; Found: C, 64.97; H, 7.78%;
26 38 4 2
1H NMR d 8.00 (d, J=1 Hz, 1H), 7.58 (d, J=1 Hz, 1H),
3
4.28 (t, J=7 Hz, 2H), 1.75 (quintet, J=7 Hz, 2H), 1.45–1.30
2
3
(m, 10H), 0.89 (t, J=7 Hz, 3H); 13C NMR (CDCl ) (1H
3
decoupled) d 162.4, 136.9, 134.6, 131.7, 124.6, 65.1, 31.8, 29.2,
28.7, 26.0, 22.6, 14.1; IR (KBr) 3121, 3060, 2953, 2915, 2870,
2847, 1709, 1523, 1475, 1403, 1363, 1228, 1173, 1102, 1035,
1018, 972, 941, 864, 845, 800, 772, 734, 621, 486 cm−1;
Hexyl 2-bromothiophene-3-carboxylate. The crude product
was distilled under vacuum to give 6.87 g (59%) of product as
UV–VIS (THF) l
9.7×103), two shoulders at 300 nm (e=9.6×103) and 310 nm
(e=9.3×103).
243 nm (e=1.4×104), 303 nm (e=
a
pale yellow liquid; purity (HPLC) about 99%; bp
max
75–76 °C/0.05 mm Hg. Anal. Calcd. for C H O SBr: C,
45.37; H, 5.19; Found: C, 45.41; H, 5.03%; 1H NMR d 7.98
11 15 2
(d, J=1 Hz, 1H), 7.46 (d, J=1 Hz, 1H), 4.25 (t, J=7 Hz,
2H), 1.72 (quintet, J=7 Hz, 2H), 1.45–1.30 (m, 6H), 0.90 (t,
Dialkyl 5,5∞-dibromo-2,2∞-bithiophene-4,4∞-dicarboxylates (6a
and 6b): general procedure. A solution of 0.144 g (0.90 mmol)
J=7 Hz, 3H); 13C NMR (CDCl ) (1H decoupled) d 161.6,
3
of bromine in 6 mL of CHCl was added slowly to a stirred
134.2, 133.6, 130.2, 112.8, 65.1, 31.4, 28.6, 25.6, 22.5, 14.0; IR
3
solution of 0.300 mmol of dihexyl or dioctyl 2,2∞-bithiophene-
(neat) 3108, 2959, 2929, 2858, 1719, 1528, 1467, 1422, 1378,
1227, 1175, 1094, 983, 927, 849, 735, 660 cm−1.
Octyl 2-bromothiophene-3-carboxylate. The crude product
was distilled under vacuum to give 8.29 g (65%) of product as
4,4∞-dicarboxylate and 6 mL of CHCl in a 25 mL round-
3
bottomed flask at room temperature. The mixture was warmed
to 60 °C for an additional 10 h and then poured into 50 mL
of cold water (ice bath), stirred for a while and Na SO was
2
3
added to react with excess bromine. The solution was washed
a
pale yellow liquid; purity (HPLC): >99%; bp
with CHCl (3×50 mL), and the organic phase was then
91–94 °C/0.05 mm Hg. Anal. Calcd. for C H O SBr: C,
3
13 19 2
washed with water (3×30 mL) followed by saturated NaCl
48.91; H, 6.00; Found: C, 48.74; H, 5.88; 1H NMR d 7.98 (d,
(2×50 mL) and dried over MgSO . The CHCl was removed
J=1 Hz, 1H), 7.46 (d, J=1 Hz, 1H), 4.25 (t, J=7 Hz, 2H),
1.72 (quintet, J=7 Hz, 2H), 1.45–1.30 (m, 10H), 0.88 (t, J=
4
3
with a rotary evaporator and a light yellow crude solid was
obtained and purified as described below.
7 Hz, 3H); 13C NMR (CDCl ) (1H decoupled) d 161.6, 134.2,
3
133.6, 130.2, 112.8, 65.1, 31.7, 29.2, 28.6, 26.0, 22.6, 14.0; IR
(neat) 3109, 2954, 2926, 2855, 1721, 1528, 1467, 1422, 1405,
Dihexyl
5,5∞-dibromo-2,2∞-bithiophene-4,4∞-dicarboxylate
1378, 1229, 1175, 1095, 983, 959, 923, 849, 735, 660 cm−1.
Dialkyl 2,2∞-bithiophene-4,4∞-dicarboxylates: general pro-
cedure. In a 10 mL one-necked flask were placed 22 mg
(6a). The crude product (0.12 g) was purified using column
chromatography (silica gel, 1×8 inch) with ethyl acetate–hex-
ane (15100) as eluent to give 0.104 g (60%) of a white solid
product; purity (HPLC) >99%; mp 87–88 °C. Anal. Calcd.
for C H O S Br : C, 45.53; H, 4.86; Found: C, 45.37; H,
(0.10 mmol) of NiBr , 0.20 g (0.76 mmol) of triphenylphos-
2
22 28 4 2
2
phine, 0.20 g (3.1 mmol) of zinc and 1 mL of DMF under
4.82%; 1H NMR d 7.36 (s, 1H), 4.30 (t, J=7 Hz, 2H), 1.76
argon and the mixture was stirred at 50 °C for 30 min. The
color of the reaction mixture changed from orange to reddish
brown and then 2.00 mmol of hexyl or octyl 2-bromothio-
phene-3-carboxylate in 1 mL of DMF was added via a syringe.
The mixture was warmed to 80 °C and stirred for 24 h. The
(quintet, J=7 Hz, 2H), 1.45–1.30 (m, 6H), 0.91 (t, J=7 Hz,
3H); 13C NMR (CDCl ) (1H decoupled) d 161.5, 135.2, 132.2,
3
125.9, 119.1, 65.5, 31.4, 28.6, 25.7, 22.5, 14.0; IR (KBr) 3095,
3066, 2954, 2927, 2890, 2869, 1729, 1522, 1479, 1423, 1318,
1221, 1159, 1060, 1017, 974, 919, 890, 852, 828, 766, 721, 553,
J. Mater. Chem., 1999, 9, 2155–2163
2161