Jul-Aug 2007
Synthesis of Thiophene/Phenylene Co-oligomers. V
859
(200 mL). The ethylacetate layer was separated from the water
layer in a separating funnel. The water layer was once again
extracted with ethyl acetate (200 mL) and the combined ethyl
acetate layers were washed with saturated aqueous sodium
chloride solution and dried with anhydrous magnesium sulfate.
After ethyl acetate was partly removed with a rotary evaporator,
the remaining ethyl acetate solution was cooled over an
ice/water bath to give 4'-butyl-4-biphenylboronic acid (2) after
filtration. The Hexane (100 mL) was added to the filtrated
solution to precipitate and recover from that solution 4'-butyl-4-
biphenylboronic acid (2). We obtained in total the crystals of
27.3 g (59%) of 4'-butyl-4-biphenylboronic acid (2), mp 157 °C;
1H nmr (deuteriotetrahydrofuran): ꢀ 0.94 (t, 3H, methyl protons,
J = 7.6 Hz), 1.38 (sextuplet, 2H, methylene protons, J = 7.6 Hz),
1.63 (quintuplet, 2H, methylene protons, J = 7.6 Hz), 2.64 (t,
2H, methylene protons, J = 7.6 Hz), 7.12 (s, 2H, hydroxyl
protons), 7.23 (d, 2H, phenylene protons, J = 8.0 Hz), 7.54 (d,
2H, phenylene protons), 7.56 (d, 2H, phenylene protons), 7.83
ppm (d, 2H, phenylene protons, J = 8.0 Hz).
Compound 2 (27.3 g, 107 mmoles) and 2,5-dibromothiophene
(3) (8.65 g, 36 mmoles) as well as tetrakis(triphenylphosphine)-
palladium(0) [abbreviated as Pd(PPh3)4 in the Schemes; 7.7 g,
6.7 mmoles] were dispersed and dissolved in a mixture of 1,2,4-
trichlorobenzene (1.15 L) and aqueous sodium carbonate (22.7
g, 214 mmoles in 532 mL of water). After being warmed at 85
°C for 8 hours, the reaction solution was cooled to 25 °C and
filtrated. The resulting precipitates were washed successively
with water (500 mL) and acetone (500 mL). These precipitates
were recrystallized from 1,2,4-trichlorobenzene to give 14.9 g
(84%) of BP1T-Bu as yellow crystals, mp 307 °C, lit [17] mp
321 °C; 1H nmr (deuteriotetrahydrofuran): ꢀ 0.95 (t, 6H, methyl
protons, J = 7.6 Hz), 1.39 (sextuplet, 4H, methylene protons, J =
7.6 Hz), 1.64 (quintuplet, 4H, methylene protons, J = 7.6 Hz),
2.65 (t, 4H, methylene protons, J = 7.6 Hz), 7.26 (d, 4H,
phenylene protons, J = 8.0 Hz), 7.44 (s, 2H, thienylene protons),
7.58 (d, 4H, phenylene protons, J = 8.0 Hz), 7.66 (d, 4H,
phenylene protons, J = 8.0 Hz), 7.74 ppm (d, 4H, phenylene
protons, J = 8.0 Hz). Anal. Calcd. for C36H36S: C, 86.35; H,
7.25; S, 6.40. Found: C, 86.12; H, 7.10; S, 6.14.
2,5-Bis(4'-methoxybiphenyl-4-yl)thiophene (BP1T-OMe).
4-Bromo-4'-hydroxybiphenyl (4) (151.4 g, 608 mmoles) was
dissolved in anhydrous N,N-dimethylformamide (1.5 L) and the
reaction solution was cooled at 5 °C. To this solution was added
sodium hydride (60%), and the reaction mixture was kept at 25
°C for 1 hour and at 50 °C for another hour. After the solution
was cooled at 30 °C, iodomethane (111.6 g, 786 mmoles) was
added dropwise to this solution. After being kept at that
temperature for 2 hours, the resulting solution was poured into
ice water (4.5 L) for crystallization to yield 157.9 g (99%) of 4-
bromo-4'-methoxybiphenyl (5), mp 143–144 °C, lit [18] mp
144.5 °C.
Compound (5) (53.0 g, 201 mmoles) was dissolved in
anhydrous tetrahydrofuran (1.55 L) with N,N,N',N'-tetra-
methylethylenediamine (abbreviated as TMEDA in the
Schemes; 23.1 g, 199 mmoles) and cooled at -65 °C. To this
solution was added dropwise 86 mL (224 mmoles) of 2.6 M n-
butyllithium and trimethyl borate (41.7 g, 401 mmoles)
dissolved in anhydrous tetrahydrofuran (120 mL) successively.
The reaction mixture was stirred at room temperature for 1
hour. The resulting solution was successively treated with (i)
10% sulfuric acid (111 g), (ii) washed with saturated aqueous
sodium chloride solution, (iii) extracted with ethyl acetate, and
(iv) dried with anhydrous magnesium sulfate as in the case of
the synthesis of BP1T-Bu. This solution was concentrated by
evaporation of ethyl acetate and successively cooled at 5 °C
for crystallization after addition of chloroform. The crystals
generated was collected and dried to give 36.7 g (80%) of (4'-
1
methoxybiphenyl-4-yl)boronic acid (6), mp 189–195 °C; H
nmr (deuteriotetrahydrofuran): ꢀ 3.80 (s, 3H, methyl protons),
6.96 (d, 2H, phenylene protons, J = 8.8 Hz), 7.10 (s, 2H,
hydroxyl protons), 7.53 (d, 2H, phenylene protons, J = 8.4 Hz),
7.56 (d, 2H, phenylene protons, J = 8.8 Hz), 7.81 ppm (d, 2H,
phenylene protons, J = 8.4 Hz).
Compound 6 (43.8 g, 192 mmoles) and 2,5-dibromothiophene
(15.6 g, 64 mmoles) as well as tetrakis(triphenylphosphine)-
palladium(0) (9.4 g, 8.1 mmoles) were dispersed and dissolved
in a mixture of 1,2,4-trichlorobenzene (2.9 L) and aqueous
sodium carbonate (56.5 g, 533 mmoles in 330 mL of water).
This reaction mixture was treated similarly as in the case of the
synthesis of BP1T-Bu. The resulting precipitates were
recrystallized from 1,2,4-trichlorobenzene to give 14.3 g (50%)
of BP1T-OMe as yellow crystals, mp 359 °C. Anal. Calcd. for
C30H24O2S: C, 80.33; H, 5.39; S, 7.15. Found: C, 80.55; H, 5.39;
S, 7.15.
2,5-Bis(4'-cyanobiphenyl-4-yl)thiophene (BP1T-CN). 4-
Biphenylcarbonitrile (7) (50.0 g, 279 mmoles) was mixed with
acetic acid (137 mL), water (28 mL), and 97% sulfuric acid (4.2
mL). To this reaction mixture were added iodine (36.4 g, 143
mmoles) and periodic acid (14.0 g, 61 mmoles), and the reaction
solution was warmed to 70 °C for 24 hours to yield precipitates.
The precipitates were washed with water and methanol
alternately and dissolved with chloroform (1 L). This solution
was washed with saturated aqueous sodium chloride solution
and dried with anhydrous magnesium sulfate. After chloroform
was evaporated, the remaining solid was dissolved in hot ethyl
acetate (500 mL). To the solution was added methanol (250 mL)
and cooled to 5 °C for crystallization. The precipitates generated
was filtrated and dried to give pale yellow crystals of 56.6 g
(67%) of 4'-iodo-biphenyl-4-carbonitrile (8), mp 178 °C, lit [19]
mp 166 °C; 1H nmr (deuteriochloroform): ꢀ 7.32 (d, 2H,
phenylene protons, J = 8.0 Hz), 7.65 (d, 2H, phenylene protons,
J = 8.4 Hz), 7.73 (d, 2H, phenylene protons, J = 8.4 Hz), 7.82
ppm (d, 2H, phenylene protons, J = 8.0 Hz).
Thiophene (9) (2.39 g, 28 mmoles) was dissolved in
dehydrated hexane (35 mL) with N,N,N',N'-tetramethylethyl-
enediamine (6.78 g, 58 mmoles). To this solution was added
dropwise at 0 °C 25 mL (65 mmoles) of 2.6 M n-butyllithium,
and the reaction mixture was refluxed for 30 min and
successively cooled to -10 °C. To the resulting solution was
further added dropwise anhydrous zinc chloride (8.52 g, 63
mmoles) dispersed in anhydrous tetrahydrofuran (100 mL), and
the solution was kept at 25 °C for 2 hours. To this solution were
added tetrakis(triphenylphosphine)-palladium(0) (1.0 g, 0.87
mmole) and subsequently 4'-iodo-biphenyl-4-carbonitrile (8)
(20.9 g, 68 mmoles) dissolved in anhydrous tetrahydrofuran
(200 mL). The reaction mixture was warmed to 50 °C for 16
hours and then cooled to 20 °C, yielding precipitates. These
precipitates were successively washed with tetrahydrofuran (100
mL), water (500 mL), a drop of 35% hydrochloric acid, water
(500 mL), and acetone (200 mL). These precipitates were
recrystallized from 1,2,4-trichlorobenzene to give 8.1 g (65%) of
BP1T-CN as yellow crystals, mp 300 °C. Anal. Calcd. for
C30H18N2S: C, 82.16; H, 4.14; N, 6.39; S, 7.31. Found: C, 82.39;
H, 4.17; N, 6.27; S, 7.46.