2258
A. S. Amarasekara, M. Pomerantz
SPECIAL TOPIC
Anal. Calcd for C11H14O2S: C, 62.83; H,, 6.71. Found: C, 62.75; H,
6.90.
an argon atmosphere. Then isopropyl magnesium bromide (1.0
mmol) in anhyd THF (5 mL) (freshly prepared from 1.0 mmol of
isopropyl bromide and 1.1 mg-atom of Mg) was added over a period
of 5 min. The mixture was stirred at –78 °C for 1 h and quenched
with H2O (1.0 mL). It was then diluted with CHCl3 (30 mL), washed
with aq HCl (10%; 20 mL), H2O (2 × 20 mL), dried (MgSO4) and
concentrated in vacuo to give the product as a pale yellow oil. The
composition of this mixture was analyzed by 1H NMR spectroscopy
[9 shows its thiophene hydrogens at = 7.46 (d, J = 1.5 Hz) and
GPC (THF; 1.0 mL/min): number average molecular weight
(Mn) = 6200 gmol–1; polydispersity (Mw/Mn) = 1.6.
H–T Regioregular Poly(octyl thiophene-3-carboxylate) (12)
Starting with octyl 2,5-dibromothiophene-3-carboxylate (1.592 g,
4.00 mmol) gave 12.
7.97 (d, J = 1.5 Hz)4 while 10 shows its thiophene hydrogens at
=
Yield: 495 mg (52%).
7.21 (d, J = 5.5 Hz) and 7.36 (d, J = 5.5 Hz)]. This experiment was
repeated at –40 and 25 C. In the fourth experiment the equivalent of
isopropylmagnesium bromide was added at –40 C and allowed to
stand at –40 C for 1 h, then the reaction mixture was slowly warmed
to room temperature (25 C) over a period of 1 h before quenching
with H2O. The 9:10 product ratios from four experiments are shown
in Table 1.
IR (KBr): 774, 827, 991, 1157, 1233, 1436, 1457, 1716, 2854, 2925
cm–1.
1H NMR (CDCl3): = 0.87 (br s, 3 H), 1.28 (br s, 10 H), 1.74 (br s,
2 H), 4.29 (br s, 2 H), 7.86(br s, 1 H).
13C NMR (CDCl3): = 14.2, 22.7, 26.1, 28.7, 29.3, 29.8, 31.9, 65.5,
128.2, 132.3, 132.4, 143.0, 162.8.
UV (THF): max = 410 nm.
UV (film cast from CHCl3): max = 405, 485 (sh) nm.
Acknowledgment
Anal. Calcd for C13H18O2S: C, 65.51; H, 7.61. Found: C, 65.38; H,
7.86.
We thank the Welch Foundation (Grant Y-1407) for financial sup-
port of this work.
GPC (THF; 1.0 mL/min): number average molecular weight
(Mn) = 5200 gmol–1; polydispersity (Mw/Mn) = 1.4.
References
Octyl 2-Bromothiophene-4-carboxylate (9)
(1) Pomerantz, M.; Yang, H.; Cheng, Y. Macromolecules 1995,
28, 5706.
This molecule was prepared as described previously.4,13
(2) Pomerantz, M.; Cheng, Y.; Kasim, R. K.; Elsenbaumer, R.
L. Synth. Met. 1997, 85, 1235.
(3) Pomerantz, M.; Cheng, Y. Tetrahedron Lett. 1999, 40, 3317.
(4) Pomerantz, M.; Chang, Y.; Kasim, R. K.; Elsenbaumer, R.
L. J. Mater. Chem. 1999, 2155.
Octyl 2-Bromothiophene-3-carboxylate (10)13
2-Bromothiophene-3-carboxylic acid5 (1.035g, 5.00 mmol) was
dissolved in thionyl chloride (1.0 mL; 1.63 g, 13.70 mmol) and the
mixture was refluxed for 1 h. The excess thionyl chloride was re-
moved under a stream of argon and the residue was treated with a
solution of 1-octanol (715 mg, 5.50 mmol) in pyridine (1.00 mL). It
was further refluxed for 2 h and allowed to cool. The resultant mix-
ture was dissolved in CH2Cl2 (50 mL) and washed with H2O (2 × 20
mL), dried (MgSO4) and concentrated to yield the crude product,
which was purified by column chromatography (silica gel; EtOAc–
hexane, 10%).
(5) Pomerantz, M.; Amarasekara, A. S.; Dias, H. V. R. J. Org.
Chem. 2002, 67, 6931.
(6) Pomerantz, M. Tetrahedron Lett. 2003, 44, 1563.
(7) Chen, T.; Rieke, R. D. J. Am. Chem. Soc. 1992, 114, 10087.
(8) Chen, T.; Rieke, R. D. Synth. Met. 1993, 60, 175.
(9) Chen, T.-A.; Wu, X.; Rieke, R. D. J. Am. Chem. Soc. 1995,
117, 233.
(10) Abarbri, M.; Thibonnet, J.; Bérillon, L.; Dehmel, F.;
Rottländer, M.; Knochel, P. J. Org. Chem. 2000, 65, 4618.
(11) Loewe, R. S.; Ewbank, P. C.; Liu, J.; Zhai, L.; McCullough,
R. D. Macromolecules 2001, 34, 4324.
(12) McCullough, R. D.; Ewbank, P. C. In Handbook of
Conducting Polymers, Chap. 9; Skotheim, T.; Elsenbaumer,
R. L.; Reynolds, J. R., Eds.; Dekker: New York, 1998, 225–
258.
(13) Although octyl 2-bromothiophene-3-carboxylate and hexyl
2-bromothiophene-3-carboxylate are said to be reported in a
reference,4 the compounds reported are actually octyl 2-
bromothiophene-4-carboxylate and hexyl 2-bromothio-
phene-4-carboxylate since there is a typographical error in
the experimental section of the paper.
Yield: 1.387g, 4.35 mmol (87%); colorless viscous oil.
IR (neat film): 708, 999, 1160, 1262, 1418, 1461, 1523, 1719, 2862,
2928 cm–1.
1H NMR (CDCl3): = 0.85 (t, J = 7.0 Hz, 3 H), 1.25 (m, 8 H), 1.27
(m, 2 H), 1.71 (m, 2 H), 4.24 (t, J = 6.8 Hz, 2 H), 7.17 (d, J = 5.8
Hz, 1 H), 7.33 (d, J = 5.8 Hz, 1 H).
13C NMR (CDCl3): = 14.2, 22.7, 26.1, 28.7, 29.3 (2 C), 31.9, 65.2,
119.6, 125.9, 129.5, 131.4, 162.0.
Anal. Calcd for C13H19BrO2S: C, 48.91; H, 6.00. Found: C, 49.16;
H, 5.89.
Temperature Effect on Selectivity of Br–Mg Exchange in Octyl
2,5-Dibromothiophene-3-carboxylate (4)
Octyl 2,5-dibromothiophene-3-carboxylate (4) (398 mg, 1.0 mmol)
was dissolved in anhyd THF (10 mL) and cooled to –78 °C under
Synthesis 2003, No. 14, 2255–2258 © Thieme Stuttgart · New York