Efficient synthesis of 1,4-dialkoxy and 1,4-dialkyl substituted 2,5-divinylbenzenes via the Stille reaction

Article abstract of DOI:10.1246/bcsj.78.367

An efficient palladium catalyzed cross coupling of tributyl(vinyl)stannane with dialkoxy and dialkyl substituted 1,4-dihalobenzenes is described. This single-step coupling provides an efficient synthesis of functionalized 2,5-divinylbenzenes, which are us

Full text of DOI:10.1246/bcsj.78.367

Short Articles
Bull. Chem. Soc. Jpn., 78, 367–369 (2005)
367
R1 R1
Ac
O
P
Efficient Synthesis of 1,4-Dialkoxy
and 1,4-Dialkyl Substituted 2,5-Di-
vinylbenzenes via the Stille Reaction
Pd
Pd
P
O
Ac
R1 R1
1
R
= o-Tolyl
Fig. 1. Chemical structure of palladacycle catalyst.
y
Walid A. Daoud and Michael L. Turneryy
ꢀ;
methyl group to the halide caused a steric hindrance, which re-
sulted in a lower yield. Herein we report on the use of the Stille
methodology in an efficient, yet simple, synthesis of 1,4-di-
alkoxy and 1,4-dialkyl substituted 2,5-divinylbenzenes in the
presence of trans-di(ꢀ-acetato)-bis[o-(di-o-tolylphosphino)-
benzyl]dipalladium(II) (Fig. 1) as a palladium catalyst and
without the use of any other additives.
Department of Chemistry, University of Sheffield,
Sheffield, S3 7HF, UK
Received July 20, 2004; E-mail: tcdaoud@polyu.edu.hk
1,4-Dialkylbenzene 1 (R1 ¼ R2 ¼ C16H33) was synthesized
in good yield (60%) by a nickel catalyzed cross-coupling of
a Grignard reagent with dibromobenzene (Scheme 1). The
corresponding 1,4-dialkoxybenzenes 1 (R1 ¼ R2 ¼ OC12H25
or OC16H33; R1 ¼ OC12H25, R2 ¼ OCH3) were obtained from
hydroquinone (67 and 64%, respectively) or 4-methoxyphenol
(82%) by a Williamson ether synthesis with an alkyl bromide.
The iodination of 1 with iodine and iodic acid gave 2 in 60%
after extensive purification.5
An efficient palladium catalyzed cross coupling of tri-
butyl(vinyl)stannane with dialkoxy and dialkyl substituted
1,4-dihalobenzenes is described. This single-step coupling
provides an efficient synthesis of functionalized 2,5-divinyl-
benzenes, which are useful precursors of 1,4-phenylenevi-
nylene copolymers.
The reaction of 2 with tributyl(vinyl)stannane12 in the
presence of a palladium catalyst required high temperatures
(>80 ꢁC) and extended reaction times. The products, 1,4-
dialkyl and 1,4-dialkoxy substituted 2,5-divinylbenzenes 3,
were isolated (55%) in the necessary purity for polymerization
reactions by column chromatography and recrystallization.
To ensure that the products are free of any organotiniodide
impurities, it was necessary to treat the reaction mixture with
potassium fluoride to precipitate insoluble tributyltinfluoride,
which may be removed by filtration through Celite.
Conjugated polymers, and in particular poly(1,4-phenylene-
vinylene) derivatives,1,2 have attracted considerable current
interest due to their processing ability and electroluminescent
properties. These polymers have been prepared by a number
of different methods, using a variety of precursors.3 Recently
synthetic methods employing transition metal catalyzed C–C
bond forming reactions, such as the Heck reaction, have been
reported. These methods have expanded the range of accessi-
ble polymer architectures.4 Suitable precursors include highly
functionalized 1,4-dihalobenzenes that may be condensed with
1,4-divinylbenzene in a palladium catalyzed Heck reaction
to give a wide range of substituted phenylenevinylene copoly-
mers.5,6 Dialkyl substituted divinylbenzenes undergo metathe-
sis polycondensation in the presence of a metal alkylidene
complex to give oligomeric all-trans phenylenevinylene
derivatives. These compounds were prepared in low overall
yield from the corresponding dicyanobenzenes using a five-
step procedure involving a Wittig reaction.7,8 The cross cou-
pling of tributyl(vinyl)stannane with various organic electro-
philes, such as aryl halides in the presence of a palladium
catalyst, has been demonstrated by Stille9 and others10 to be
a highly efficient method for the preparation of styrene deriv-
atives. However, the coupling of tributyl(vinyl)stannane with
aryl halides substituted with electron-donating groups is re-
ported to be not favored and gives a low yield of coupled prod-
ucts.11 Recently, Littke and Fu reported a successful cross cou-
pling of electron-rich monohaloaryls such as p-chloroanisole
and p-chloroaniline with organotin compounds in the presence
of PtBu3 as a ligand for palladium and CsF to activate the tin
reagent.10c According to these authors, the presence of an o-
A range of reaction conditions were employed to optimize
the yield of 3. The best conversions were obtained using a pal-
ladacycle catalyst, trans-di(ꢀ-acetato)-bis[o-(di-o-tolylphos-
phino)benzyl]dipalladium(II), prepared from palladium acetate
and tri(o-tolyl)phosphine in toluene at a temperature below re-
flux.13 This palladacycle catalyst was found to be more stable
at high temperatures than tetrakis(triphenylphosphine)palladi-
um. No reaction was detected at reaction temperatures below
ꢁ
80 C, and at temperatures close to toluene reflux (110 ꢁC)
the reaction time was much reduced, but the isolated yield
was very low (25%). The highest isolated yield (55%) of pure
product 3 was obtained after 40 h at 90 ꢁC. The cross coupling
of tributyl(vinyl)stannane with analogous substituted dibromo-
benzenes was also possible. However, a higher reaction tem-
perature (100 ꢁC) was required to achieve complete conversion
and it was necessary to add an extra equivalent of the catalyst
after 40 h in order to isolate 45% of the coupled product after
90 h.
To summarize, 1,4-dialkoxy and 1,4-dialkyl substituted 2,5-
divinylbenzenes can be prepared in good yield and high purity
by the palladium catalyzed cross-coupling of tributyl(vinyl)-
stannane and disubstituted dihalobenzenes. These compounds
are useful as monomers for 1,4-phenylenevinylene copoly-
mers; studies of their polymerization reactions are under inves-
tigation.
y Present address: Nanotechnology Centre, ITC, The Hong Kong
Polytechnic University, Hung Hom, Hong Kong
yy Present address: Department of Chemistry, University of
Manchester, M13 9PL, UK
Published on the web February 11, 2005; DOI 10.1246/bcsj.78.367

368 Bull. Chem. Soc. Jpn., 78, No. 2 (2005)
Ó 2005 The Chemical Society of Japan
R1
OH
OH
2RBr
K2CO3, DMF
RBr
K2CO3, DMF
MeO
HO
R2
1
NiCl2[(Ph2P)2propane)]
2RMgBr
R1 = C16H33, R2= C16H33
R1 = OC12H25, R2= OC12H25
R1 = OC16H33, R2= OC16H33
R1 = OC12H25, R2= OCH3
H2SO4
HIO3
CCl4
I2
Br
R1
R1
Br
Bu3SnCHCH2
"Pd" catalyst
I
I
R2
R2
2
3
Scheme 1. Preparation of divinyl substituted benzenes via the Stille reaction.
1-Dodecyloxy-4-methoxy-2,5-divinylbenzene.
1H NMR
(CDCl3) ꢁ 7.2 (m, 2H, –CH=CH2), 7.0 (s, 2H, arom.), 5.6 (dd,
2H, transJ ¼ 17:7 Hz, cisJ ¼ 1:36 Hz, cis-CH=CH2), 5.25 (dd,
2H, transJ ¼ 11:1 Hz, cisJ ¼ 1:4 Hz, trans-CH=CH2), 3.9 (t, 2H,
J ¼ 6:4 Hz, ꢂ-OCH2), 3.75 (s, 3H, –OCH3), 1.55–1.25 (m,
20H, aliph.), 0.8 (t, 3H, J ¼ 6:5 Hz, –CH3). 13C NMR (CDCl3)
ꢁ 151.8, 151.2, 131.5, 131.4, 127.1, 126.9, 114.3, 114, 110.7,
109.1, 69.4, 56.3, 31.9, 29.6, 29.4, 26.1, 22.7, 14.1. Analytical
data for C23H36O2: EI-MS m=z 344 (M+ 100%). Found (calcd):
C, 79.34 (79.73); H, 10.51 (10.46)%.
Experimental
Preparation of 2,5-Bis(dodecyloxy)-1,4-diiodobenzene.
A
250 mL flask was charged with iodine (1.14 g, 4.5 mmol), 1,4-
bis(dodecyloxy)benzene (2.23 g, 5 mmol), iodic acid (0.527 g, 3
mmol), CCl4 (4 mL), glacial acetic acid (18 mL), 0.65 mL H2SO4,
and 3 mL of deionized water. The resulting mixture was heated to
75 ꢁC for 3 h. After this time, a solution of sodium thiosulfate was
added to remove any unreacted iodine. The solution was extracted
with dichloromethane and washed three times with a 5% NaOH
solution, followed by washing three times with water. The organic
layer was dried over MgSO4 and the solvent removed under re-
duced pressure. The product, 2,5-bis(dodecyloxy)-1,4-diiodoben-
zene, was isolated by two recrystallization steps from ethanol
to give an overall yield of 60%. 1H NMR (CDCl3) ꢁ 7.28 (s,
2H, arom.), 3.92 (t, 4H, J ¼ 6:4 Hz, ꢂ-OCH2), 1.5–1.2 (m,
40H, aliph.), 0.8 (t, 6H, J ¼ 6:6 Hz, –CH3).
1,4-Dihexadecyl-2,5-divinylbenzene. 1H NMR (CDCl3) ꢁ
7.2 (s, 2H, arom.), 6.9 (dd, 2H, transJ ¼ 17:3 Hz, cisJ ¼ 11 Hz,
–CH=CH2), 5.6 (dd, 2H, transJ ¼ 17:3 Hz, cisJ ¼ 1:46 Hz, cis-
CH=CH2), 5.2 (dd, 2H, transJ ¼ 11 Hz, cisJ ¼ 1:46 Hz, trans-
CH=CH2), 2.5 (m, 4H, ꢂ-CH2), 1.55–1.25 (m, 56H, aliph.),
0.65 (t, 6H, J ¼ 6:6 Hz, –CH3). 13C NMR (CDCl3) ꢁ 138,
135.6, 134.4, 126.6, 114.6, 33, 31.9, 31.3, 29.7, 29.5, 22.7, 14.1.
Analytical data for C42H74: EI-MS m=z 579 (M+ 100%), 552.6
(12%). Found (calcd): C, 86.44 (86.69); H, 13.15 (12.8)%.
Preparation of 1,4-Bis(dodecyloxy)-2,5-divinylbenzene.
Two mole equivalents of tributyl(vinyl)stannane (0.6 mL, 1.93
mmol) were added to a solution of 2,5-bis(dodecyloxy)-1,4-di-
iodobenzene (0.64 g, 0.92 mmol) in 50 mL of toluene. To this,
(10 mg, 0.0094 mmol) of the isolated palladacycle catalyst was
added. The reaction mixture was stirred at 90 ꢁC for 3 h, after
which an additional amount (10 mg) of the catalyst was added,
and the mixture was heated at 90 ꢁC for 36 h. The reaction mixture
was allowed to cool to room temperature and a solution of potas-
sium fluoride and ether was added and stirred for 3 h. The result-
ing solution was filtered through Celite to remove solid tributyltin-
fluoride and the catalyst residues. The solvents were removed
under reduced pressure and the crude product was purified by
column chromatography on silica gel using hexane/DCM 6:1 as
the eluent. Recrystallization of the product from cold ethanol gave
0.25 g (55% yield) of 1,4-bis(dodecyloxy)-2,5-divinylbenzene.
1H NMR (CDCl3) ꢁ 7.0 (m, 2H, –CH=CH2), 6.9 (s, 2H, arom.),
5.65 (dd, 2H, transJ ¼ 17:8 Hz, cisJ ¼ 1:42 Hz, cis-CH=CH2),
5.2 (dd, 2H, transJ ¼ 11:3 Hz, cisJ ¼ 1:42 Hz, trans-CH=CH2),
3.9 (t, 4H, J ¼ 6:4 Hz, ꢂ-OCH2), 1.55–1.25 (m, 40H, aliph.),
0.8 (m, 6H, –CH3). 13C NMR (CDCl3) ꢁ 150.4, 131.5, 127.1,
114, 110.5, 69.3, 31.9, 29.6, 29.3, 26.1, 22.7, 14.1. Analytical data
for C34H58O2: EI-MS m=z 498 (M+ 100%), 330 (7%). Found
(calcd): C, 81.64 (81.86); H, 11.94 (11.72)%.
1,4-Bis(hexadecyloxy)-2,5-divinylbenzene.
1H NMR
(CDCl3) ꢁ 7.2 (s, 2H, arom.), 6.9 (m, 2H, –CH=CH2), 5.6 (dd,
2H, transJ ¼ 17:7 Hz, cisJ ¼ 1:46 Hz, cis-CH=CH2), 5.2 (dd,
2H, transJ ¼ 15 Hz, cisJ ¼ 1:46 Hz, trans-CH=CH2), 2.5 (t, 4H,
J ¼ 6:4 Hz, ꢂ-CH2), 1.55–1.25 (m, 56H, aliph.), 0.65 (t, 6H, J ¼
6:5 Hz, –CH3). 13C NMR (CDCl3) ꢁ 150.6, 131.6, 127.1, 113.9,
110.5, 69.3, 31.9, 29.7, 29.4, 29.4, 26.1, 22.7, 14.1. Analytical da-
ta for C42H74O2: EI-MS m=z 610 (M+ 100%). Found (calcd): C,
81.97 (82.22); H, 12.55 (12.13)%.
The University of Sheffield and Sheffield Hallam University
are gratefully thanked for the award of a research scholarship
to W. A. Daoud. Financial support from The Royal Society of
Chemistry is greatly appreciated.
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