Synthesis of mono- and bis-arylated 3,4-(ethylenedioxythiophenes) via direct palladium catalyzed arylation reactions

Article abstract of DOI:10.1016/j.tetlet.2006.11.138

The synthesis of arylated/heteroarylated 3,4-ethylenedioxythiophene derivatives is reported using a straightforward palladium mediated Heck coupling of 3,4-ethylenedioxythiophene with various aryl/heteroaryl halides.

Full text of DOI:10.1016/j.tetlet.2006.11.138

Tetrahedron Letters 48 (2007) 539–544
Synthesis of mono- and bis-arylated 3,4-(ethylenedioxythiophenes)
via direct palladium catalyzed arylation reactions
Arasambattu K. Mohanakrishnan,* P. Amaladass and J. Arul Clement
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India
Received 15 September 2006; revised 15 November 2006; accepted 22 November 2006
Abstract—The synthesis of arylated/heteroarylated 3,4-ethylenedioxythiophene derivatives is reported using a straightforward
palladium mediated Heck coupling of 3,4-ethylenedioxythiophene with various aryl/heteroaryl halides.
Ó 2006 Elsevier Ltd. All rights reserved.
In recent years, oligothiophenes, due to their physical
properties have received widespread attention as compo-
nents of molecular electronic and optical devices.1 Five-
membered heteroaromatics bearing substituents at the
2- and 5-positions have been explored as light emitting
and liquid crystalline materials.2 Oligothiophenes are
mostly prepared via palladium/nickel mediated cross-
coupling of either heteroaryl halides with arylmetals or
aryl halides with heteroaryl metals.3 However, it is
known that aryl halides/heteroaryl halides can couple
directly with thiophene at the reactive 2- and/or 5-posi-
tions.4 The latter is more advantageous since it does not
require the stoichiometric metallation of heterocycles.
The synthesis of 2-arylthiophenes via CuI or MnBr2 cat-
alyzed cross-coupling of 2-thienyltributylstannane with
aryl halides has been reported.5 Yokkoji et al. reported
a straightforward synthesis of 5,50-diarylated 2,20-bithio-
phene via a palladium catalyzed arylation.6 In addi-
tion, Mori and co-workers recently reported the
synthesis of donor–acceptor type 2,5-diarylthiophenes
via a palladium mediated sequential arylation reaction.7
reported, the synthesis of stable and soluble, end capped
oligo(3,4-ethylenedioxy)thiophenes11a and also the syn-
thesis of oligothienylenevinylenes incorporating EDOT
units.11b
The EDOT based thienyl oligomers 3 are mostly pre-
pared using either in situ prepared 3,4-ethylenedioxythio-
phenyl-2-magnesium bromide12 (Kumada) or 3,4-
ethylenedioxythiophenyl-2-zinc bromide12 (Negishi).
Additionally, the synthesis of EDOT based thienyl oligo-
mers was also achieved using stable 2-tributylstannyl-
3,4-ethylenedioxythiophene13 (Stille) and the 2-pinacol-
boronate ester of 3,4-ethylenedioxythiophene14 (Suzu-
ki), Scheme 1. Very recently, a direct C–H arylation of
heteroarenes was reported with aryl iodides using a rho-
dium catalyst where the arylation of various hetero-
cycles such as thiophene, furan, pyrrole and indole was
O
O
The syntheses of EDOT incorporated oligothiophenes
are well known.8 3,4-Ethylenedioxythiophene (EDOT)
has been used as a building block in several conjugated
systems that incorporate unique properties such as elec-
tro chromic behaviour9 and in low band gap polymers.10
Judicious choice of the number and position of EDOT
units in extended conjugated systems allows for the fine
tuning of electronic properties. Roncali and co-workers
S
1
O
O
O
O
Ni or Pd
Ar-X'
Ar
S
X
S
3 Ar = aryl (or) heteroaryl
2
X = MgBr, ZnCl
SnBu3, B(OR)2
Keywords: EDOT; Pd-catalyzed; Arylation; Heteroarylation.
*
Corresponding author. Tel.: +91 44 24451108; fax: +91 44
22352494; e-mail: mohan_67@hotmail.com
Scheme 1.
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.11.138

540
A. K. Mohanakrishnan et al. / Tetrahedron Letters 48 (2007) 539–544
OMe
I
O
O
O
O
5a
Pd(PPh3)4
S
7a
20%
O
6a
30%
OMe
B
S
K2CO3/DMF
MeO
O
80 o
C
4
OMe
I
O
O
O
O
5a
Pd(PPh3)4
S
K2CO3/DMF
80 oC, 42%
S
OMe
1
6a
Scheme 2.
achieved. In fact, mono- and bis-arylation of 3-meth-
oxythiophene was smoothly carried out in good yields.15
Nevertheless, to date, straightforward coupling reac-
tions with 3,4-ethylenedioxythiophene 1 are yet to be
explored.
ation of EDOT 1 with 4-iodoanisole 5a in the presence
of Pd(PPh3)4 and K2CO3 in DMF at 80 °C. Workup
led to the isolation of 6a in 42% yield.
Since thiophene oligomers have recently been explored
as push–pull type systems,17 we wanted to exploit the
high electron donating character of EDOT for such pur-
pose. Thus, we decided to explore the palladium medi-
ated coupling reaction of EDOT. The low yield
obtained during cross-coupling of EDOT–metals14 also
encouraged us to undertake the present investigation.
Hence, the coupling reaction of EDOT was carried out
with a variety of aryl/heteroaryl halides, 5a–m (1 equiv),
and the results are presented in Table 1.
In continuation of our work on thienyl oligomers,16 we
wanted to prepare 2-anisyl-3,4-ethylenedioxythiophene
6a via a palladium mediated Suzuki cross-coupling,
Scheme 2. However, workup of the reaction followed
by column chromatographic purification led to the isola-
tion of mono- and bis-anisyl EDOTs 6a and 7a in 30%
and 20% yields, respectively. Surprised by the formation
of bis-anisyl product 7a, we carried out a direct anisyl-
Table 1. Mono-arylation of 3,4-ethylenedioxythiophene
Entry
Ar–X18
Temperature (°C); time (h) Product19
Yielda (%); mp (°C)
O
O
I
OMe
1
80; 14
42; 75
OMe
S
5a
6a
O
O
O
I
NO2
2
3
4
65; 8
60; 8
60; 10
55; 158
NO2
5b
S
S
6b
O
NO2
50; 92
I
5c
6c
NO2
O
O
Br
CHO
50; 122
CHO
S
5d
6d

A. K. Mohanakrishnan et al. / Tetrahedron Letters 48 (2007) 539–544
541
Table 1 (continued)
Entry
Ar–X18
Temperature (°C); time (h) Product19
Yielda (%); mp (°C)
O
O
O
Br
5
65; 8
52; 118
O
Me
5e
5f
S
Me
6e
O
O
O
I
Me
6
7
8
80; 12
80; 12
80; 10
45; liquid
Me
S
S
6f
Br
O
40; 120
MeO
5g
OMe
6g
Br
O
O
O
N
35; 125
N
S
S
5h
6h
Br
O
9
60; 12
80; 10
80; 10
40; 192
6i
5i
O
O
10
11
34; 70
N
Br
S
N
5j
6j
O
O
O
O
O
Br
Br
Br
40; 190
S
S
S
S
S
S
S
5k
6k
O
O
O
Br
12
13
80; 12
45; 105
S
C6H13
C6H13
5l
C6H13
C6H13
6l
60; 24
No reaction
Br
Br
S
S
S
5m
a Isolated yield after column chromatography.
In general, the isolated yields of the mono-arylated
products 6a–l were low (34–55%; entries 1–12). A small
amount (ꢀ10%) of the starting material (EDOT) was
always recovered even on an extended reaction (more
than 24 h for entries 1 and 2) without any appreciable
change in the yield of arylated products 6a or 6b. The

542
A. K. Mohanakrishnan et al. / Tetrahedron Letters 48 (2007) 539–544
electron deficient aromatic halides (entries 2–5) affor-
ded the corresponding mono-arylated products 6b–e
in relatively better yields than the electron rich aro-
matic halides (entries 1, 6 and 7). The use of bromo
aryl or iodo aryl compounds did not have much effect
on the yield of the arylated products. The 5,50-di-
bromo-2,20-bithiophene 5k underwent a smooth bis-
Heck arylation with excess EDOT to afford the
coupled product 6k in 40% yield (entry 11). It should
be mentioned that the same product was obtained in
a relatively low yield (20%), via cross-coupling between
EDOT boronate ester 4 and 2,5-dibromothiophene.14
The fluorenyl dibromo compound 5l afforded coupled
product 6l in 45% yield (entry 12). All attempts to cou-
ple dibromo benzo[c]thiophene 5m (entry 13) were
unsuccessful.
the best. The yield of the coupling products was not sig-
nificantly altered by the use of different bases such as
Cs2CO3 or K3PO4 in place of K2CO3.
The bis-arylation of EDOT 1 was carried out with var-
ious aryl iodides and the results are described in Table 2.
4-Iodoanisole 5a (2 equiv) afforded the expected product
7a (entry 1) in a low yield (35%). The 4-iodo and 2-iodo
nitrobenzenes 5b and 5c afforded the corresponding bis-
arylated products 7b and 7c in 40% and 35% yields (en-
tries 2 and 3), respectively. 2-Iodobenzo[b]thiophene 5n
underwent a smooth cross-coupling with EDOT to af-
ford the respective coupled product 7d in 50% isolated
yield (entry 4).
Finally, the attempted bis-arylation of 2,20-bis(EDOT) 8
with 4-methoxyiodobenzene in dry DMF at 80 °C for
14 h led to the isolation of mono-anisylated product 9
in 30% yield, Scheme 3. All attempts to couple bis-
(EDOT) 8 with other aryl/heteroaryl halo compounds
proved to be unsuccessful.
The use of acetonitrile as a solvent in place of DMF did
not give any product. Among the three palladium cata-
lysts [Pd(PPh3)4, Pd(PPh3)2Cl2 and Pd(dba)3] employed
for the arylation of EDOT, Pd(PPh3)4 was found to be
Table 2. Bis-arylation of 3,4-ethylenedioxythiophene
Entry
1
Ar–X18
Temperature (°C); time (h)
Product19
Yielda (%); mp (°C)
O
O
I
OMe
80; 13
35; 160
MeO
OMe
S
5a
7a
O
O
I
NO2
2
80; 10
40; 155
O2N
NO2
5b
S
7b
O
O
NO2
3
4
80; 10
35; 166
I
S
5c
NO2
O2N
7c
O
O
I
S
70; 8
50; 165
S
s
S
5n
a Isolated yield after column chromatography.
7d
I
OMe
O
O O
O
O
O O
O
Pd(PPh3)4
S
K2CO3/DMF, 80 o
30%
C
S
S
S
8
9
OMe
Scheme 3.

A. K. Mohanakrishnan et al. / Tetrahedron Letters 48 (2007) 539–544
543
O
O
O
O
CH2CN
CN
DMF/POCl3
S
S
6a/6g
R
R
tBuOK/EtOH
S
CHO
S
10a/10g (72%, 80%)
11a/11g (62%, 65%)
10a/11a R = 4-methoxyphenyl
10g/11g R = 6-methoxynaphthalen-2-yl
Scheme 4.
3354; (d) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986,
25, 508–523; (e) Buerle, P.; Pfau, F.; Schlupp, H.;
As a model study, the formylation of mono-arylated
EDOTs 6a/6g was carried out under Vilsmeier formyl-
ation conditions to give mono aldehydes 10a/10g. The
latter on condensation with thiophene-2-acetonitrile
afforded the respective push-pull systems 11a/11g
(Scheme 4).
¨
Wurthner, F.; Gaudi, K.-U.; Caro, M. B.; Fischer, P. J.
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In summary, the synthesis of a variety of mono- and bis-
arylated EDOT analogs has been achieved in moderate
yields, involving direct Heck arylation of EDOT with
various aryl and heteroaryl halides. Extension of this
coupling procedure for other heteroaryl halides is in
progress and hopefully this new method will be applica-
ble to the synthesis of different types of EDOT analogs.
Investigations are underway to synthesize different types
of push-pull systems using mono-arylated EDOT
derivatives.
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Acknowledgements
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Roncali, J.; Blanchard, P.; Frere, P. J. Mater. Chem. 2005,
15, 1589–1610.
The authors thank DST, New Delhi (SR/S1/OC-37/
2005) and UGC-PFE for financial support. P.A. thanks
CSIR, for a CSIR-SRF fellowship. Financial support to
the Department by DST-FIST is also acknowledged.
Authors thank SAIF, IIT Madras, for high-resolution
NMR spectral data.
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18. Aryl halides are either commercially available or else were
prepared using known procedures.
19. All compounds gave satisfactory spectral and analytical
data.
(91), 120 (49), 82 (29). Anal. Calcd for C14H12SO3: C,
64.60; H, 4.65; S, 12.32. Found: C, 64.71; H, 4.56; S, 12.25.
Compound 6h: mp 125 °C; H NMR (400 MHz, CDCl3):
1
d 4.20 (d, J = 4 Hz, 2H), 4.28 (d, J = 3.6 Hz, 2H), 6.33 (s,
1H), 7.41 (t, J = 7.4 Hz, 1H), 7.61 (t, J = 7.6 Hz, 1H), 7.71
(d, J = 8 Hz, 1H), 8.05 (d, J = 8.40 Hz, 1H) 8.32 (s, 1H),
9.2 (d, J = 2 Hz, 1H). 13C NMR (100.6 MHz, CDCl3): d
64.4, 64.9, 99.1, 113.9, 126.7, 126.9, 127.8, 127.9, 128.9,
129.2, 131.1, 139.5, 142.4, 146.5, 148.7. MS (EI) m/z (%):
269 (M+, 100%), 210 (80), 191 (26), 113 (47). Anal. Calcd
for C15H11NO2S: C, 66.89; H, 4.12; N, 5.20, S, 11.91.
Found: C, 66.78; H, 4.20; N, 5.26, S, 12.01.
A representative procedure for mono-arylation:
A solution of 4-bromo acetophenone 5e (1 g, 5 mmol), 3,4-
ethylenedioxythiophene 1 (0.717 g, 5 mmol), Pd(PPh3)4
(583 mg, 0.5 mmol) and dry K2CO3 (0.83 g, 6.05 mmol) in
DMF (10 mL) was heated for 8 h at 65 °C under an N2
atmosphere. The mixture was poured into water and
extracted with CH2Cl2. The organic layer was washed
several times with brine, water and then dried (Na2SO4).
Removal of the solvent followed by a column chromato-
graphy of the residue (silica gel, hexane:EtOAc; 9:1)
afforded 6e as a colourless solid (0.682 g, 52%); mp 118 °C.
A representative procedure for diarylation:
Compound 6l: mp 105 °C; 1H NMR (400 MHz,
CD3COCD3): d 0.72 (t, J = 6.84 Hz, 6H), 1.02–1.20 (m,
16H), 2.90–2.93 (m, 4H), 4.26–4.37 (m, 8H), 6.43 (s, 2H),
7.71–7.80 (m, 6H). 13C NMR (100.6 MHz, CD3COCD3):
d 14.33, 23.22, 24.66, 30.74, 41.03, 56.07, 65.39, 65.92,
98.24, 118.38, 120.81, 120.93, 125.82, 133.33, 139.54,
140.34, 143.73, 152.15. MS (EI) m/z (%): 614 (M+,
100%), 500 (39), 499 (100), 344 (19). Anal. Calcd for
C37H42O4S2: C, 72.28; H, 6.89; S, 10.43. Found: C, 72.15;
H, 6.77; S, 10.52.
A solution of 4-iodoanisole 5a (1 g, 4.27 mmol), 3,4-
ethylenedioxythiophene 1 (0.30 g, 2.11 mmol), Pd(PPh3)4
(493 mg, 0.426 mmol) and dry K2CO3 (0.67 g, 4.85 mmol)
in DMF (10 mL) was heated for 13 h at 80 °C under an N2
atmosphere. The mixture was poured into water and
extracted with CH2Cl2. The organic layer was washed
several times with brine, water and then dried (Na2SO4).
Removal of the solvent followed by column chromato-
graphy of the residue (silica gel, hexane:EtOAc; 9:1)
afforded 7a as a colourless solid (0.53 g, 35%); mp 160 °C.
Spectral data of various mono- and bis-arylated 3,4-
ethylenedioxythiophenes:
1
Compound 7a: mp 160 °C; H NMR (400 MHz, CDCl3):
d 3.82 (s, 6H), 4.38 (s, 4H), 6.95 (d, J = 8.82 Hz, 4H), 7.65
(d, J = 8.82 Hz, 4H), MS (EI) m/z (%): 354 (M+, 100%),
151 (99), 119 (29), 108 (21) Anal. Calcd for C20H18O4S: C,
66.78; H, 5.12; S, 9.05. Found: C, 66.57; H, 4.98; S,
9.16.
Compound 9: mp 135 °C; 1H NMR (400 MHz,
CD3COCD3): d 3.81 (s, 3H), 4.26–4.37 (m, 8H), 6.31 (s,
1H), 6.90 (d, J = 9.28 Hz, 2H), 7.60 (d, J = 8.82 Hz, 2H),
MS (EI) m/z (%): 388 (M+, 10%), 213 (24), 150 (20), 116
(12). Anal. Calcd for C19H16O5S2: C, 58.75; H, 4.15; S,
16.51. Found: C, 58.67; H, 4.26; S, 16.60.
Compound 6a: mp 75 °C; 1H NMR (400 MHz,
CD3COCD3): d 3.71 (s, 3H), 4.22–4.31 (m, 4H), 6.33 (s,
1H), 6.61 (d, J = 8.8 Hz, 2H), 7.61 (d, J = 8.8 Hz, 2H).
MS (EI) m/z (%): 248 (M+, 87%), 15 (100), 81 (10), 69 (11).
Anal. Calcd for C13H12SO3: C, 62.88; H, 4.87; S, 12.90.
Found: C, 62.66; H, 4.96; S, 12.79.
Compound 10a: mp 158 °C; 1H NMR (400 MHz, CDCl3):
d 3.81 (s, 3H), 4.29–4.36 (m, 4H), 6.93 (d, J = 8.28 Hz,
2H), 7.73 (d, J = 8.38 Hz, 2H), 9.92 (s, 1H). 13C NMR
(100.6 MHz, CDCl3): d 55.3, 64.4, 65.1, 110.6, 114.8,
124.4, 128.4, 136.8, 141.7, 149.1, 160.1, 180.1. Anal. Calcd
for C14H12O4S: C, 60.86; H, 4.38; S, 11.60. Found: C,
60.72; H, 4.47; S, 16.67.
Compound 6c: mp 92 °C; 1H NMR (400 MHz, CD3-
COCD3): d 4.13–4.18 (m, 4H), 6.59 (s, 1H), 7.53 (m, 2H),
7.67–7.69 (m, 1H), 7.89 (d, J = 8.28 Hz, 1H). 13C NMR
(100.6 MHz, CDCl3): d 65.21, 65.31, 100.89, 111.84, 125.48,
127.03, 129.26, 132.71, 133.57, 140.22. 142.59, 149.98. MS
(EI) m/z (%): 263 (M+, 100%), 145 (66), 103 (22), 102 (19).
Anal. Calcd for C12H9NO4S: C, 54.75; H, 3.45; S, 12.18;
N, 5.32. Found: C, 54.66; H, 3.30; S, 12.29; N, 5.25.
Compound 6e: mp 118 °C; 1H NMR (400 MHz,
CD3COCD3): d 2.53 (s, 3H), 4.27–4.35 (m, 4H), 6.54 (s,
1H), 7.79 (d, J = 8.32 Hz, 2H), 7.95 (d, J = 8.32 Hz, 2H).
13C NMR (100.6 MHz, CDCl3): d 26.52, 65.13, 65.85,
100.32, 116.24, 125.92, 129.54, 135.65, 138.58, 141.0,
143.61, 197.16. MS (EI) m/z (%): 260 (M+, 100%), 245
Compound 11a: mp 165 °C; 1H NMR (400 MHz, CDCl3):
d 3.83 (s, 3H), 4.28–4.35 (m, 4H), 6.92 (d, J = 8.00 Hz,
2H), 7.02 (m, 2H), 7.21 (m, 1H), 7.54 (s, 1H), 7.74 (d,
J = 7.96 Hz, 2H), 13C NMR (100.6 MHz, CDCl3): d 55.3,
64.4, 65.1, 98.1, 110.5, 114.1, 117.8, 122.9, 124.7, 124.9,
125.5, 127.8, 128.0, 128.1, 136.7, 139.8, 144.9, 159.4.
Anal. Calcd for C20H15NO3S2: C, 62.97; H, 3.96; N,
3.67; S, 16.81. Found: C, 62.82; H, 4.05; N, 3.77; S,
16.75.