Oligothiophene S,S-Dioxides. Synthesis and Electronic Properties in Relation to the Parent Oligothiophenes

Article abstract of DOI:10.1021/jo980507g

Oligothiophene S,S-dioxides from dimers to pentamers were obtained in good yields by reaction of mono- and dibrominated thiophene S,S-dioxides with the appropriate thienyl stannanes in the presence of Pd(AsPh₃)₄ generated in situ. The reaction rate with brominated thiophene S,S-dioxides is greatly accelerated compared to that employing thienyl bromides to obtain the parent oligothiophenes. HF/6-31G*ab initio calculations on 2,2′-bithiophene and the corresponding monoand bis-S,S-dioxides show that the functionalization of the thienyl sulfur to the S,S-dioxide does not affect the π,π* nature of the frontier orbitals, decreases the energy of the LUMO much more than that of the HOMO, increases the degree of planarity of the molecular skeleton, and leads to higher syn anti rotation barriers about the carbon-carbon bond.

Full text of DOI:10.1021/jo980507g

J . Org. Chem. 1998, 63, 5497-5506
5497
Oligoth iop h en e S,S-Dioxid es. Syn th esis a n d Electr on ic P r op er ties
in Rela tion to th e P a r en t Oligoth iop h en es
G. Barbarella,*,† L. Favaretto,† G. Sotgiu,† M. Zambianchi,† L. Antolini,*,‡ O. Pudova,*,§ and
A. Bongini*,
I.Co.C.E.A., Area Ricerca CNR, Via Gobetti 101, 40129 Bologna, Italy, Dipartimento di Chimica,
Universita’ di Modena, Via Campi 183, 41100 Modena, Italy, Latvian Institute of Organic Synthesis,
Aizkraukles str. 21, Riga, LV-1006, Latvia, and Dipartimento di Chimica G. Ciamician, Universita’ di
Bologna, Via Selmi 2, 40126 Bologna, Italy
Received March 17, 1998
Oligothiophene S,S-dioxides from dimers to pentamers were obtained in good yields by reaction of
mono- and dibrominated thiophene S,S-dioxides with the appropriate thienyl stannanes in the
presence of Pd(AsPh3)4 generated in situ. The reaction rate with brominated thiophene S,S-dioxides
is greatly accelerated compared to that employing thienyl bromides to obtain the parent
oligothiophenes. HF/6-31G*ab initio calculations on 2,2′-bithiophene and the corresponding mono-
and bis-S,S-dioxides show that the functionalization of the thienyl sulfur to the S,S-dioxide does
not affect the π,π* nature of the frontier orbitals, decreases the energy of the LUMO much more
than that of the HOMO, increases the degree of planarity of the molecular skeleton, and leads to
higher syn anti rotation barriers about the carbon-carbon bond.
It is well-known that di- or higher alkylated thiophenes
are oxidized to the corresponding thiophene S,S-dioxides
by peroxides such as m-chloroperoxybenzoic acid (m-
CPBA) or dimethyldioxirane.1 Recently, it has been
reported that thiophenes substituted with electron-
withdrawing groups can be efficiently oxidized to S,S-
dioxides using the complex HOF‚CH3CN, obtained by
passing F2 through a mixture of CH3CN and H2O.2 Even
more recently, the synthesis and the low-temperature
characterization of unsubstituted thiophene S,S-dioxide,
which dimerizes at ambient temperature, has been
described.3 The interest in polysubstituted thiophene
S,S-dioxides stems from the fact that they are useful
synthetic intermediates for the preparation of various
types of organic compounds, since they may undergo
Diels-Alder or other diene reactions.1b
We have extended the oxidation with m-CPBA to R,ω-
bissilylated oligothiophenes from bi- to quaterthiophene
and showed that incorporation of a thiophene S,S-dioxide
moiety into an oligothiophene increases dramatically the
electron delocalization and the electron affinity of the
molecule.4a,b This result was encouraging in relation to
the possibility of transforming oligothiophenesswhich
are p-type (hole-transporting) semiconducting materials
applied in a variety of organic based devices5sinto n-type
(electron-transporting) semiconductors.
However, in the course of our study of oxidation of
oligothiophenes with m-CPBA, we observed an accentu-
ated decrease of the rate of formation of the S,S-dioxides
upon increasing the length of the oligomer, probably due
to increasing aromatic stabilization. Moreover, with the
longer oligothiophenes, mixtures of partially oxidized
oligothiophenes were obtained, which became difficult to
separate by chromatography or crystallization.4a As a
consequence, we decided to explore different synthetic
pathways to obtain oligothiophene S,S-dioxides.
We report here results showing that the coupling of
brominated thiophene S,S-dioxides with thienyl stan-
nanes in the presence of a palladium(0) catalyst (Stille
reaction6) allows for the easy and selective insertion of
thiophene S,S-dioxide moieties into the skeleton of bi-,
ter-, quater- and quinquethiophenes. We also report an
ab initio HF/6-31G* study of the changes caused by this
chemical modification in the HOMO and LUMO frontier
orbitals compared to those of the parent oligothiophenes
and in the energy barriers to rotation around the inter-
ring carbon-carbon bonds.
† I.Co.C.E.A.
‡ Universita’ di Modena.
§ Latvian Institute of Organic Synthesis.
Resu lts
Universita’ di Bologna.
(1) (a) Vorontsova, L. G. J . Struct. Chem. 1966, 7, 234. (b) Gronowitz,
S. Phosphorus, Sulfur Silicon 1993, 74, 113. (c) Gronowitz, S.;
Ho¨rnfeldt, A. B.; Lukevics, E.; Pudova, O. Synthesis 1994, 40. (d)
Furukawa, N.; Hoshiai, H.; Shibutani, T.; Higaki, M.; Iwasaki, F.;
Fujihara, H. Heterocycles 1992, 34, 1085. (e) O’Donovan, A. R. M.;
Shepherd, M. K. Tetrahedron Lett. 1994, 35, 4425. (f) Miyahara, Y.;
Inazu, T. Tetrahedron Lett. 1990, 31, 5955.
(2) Rozen, S.; Bareket, Y. J . Org. Chem. 1997, 62, 1457.
(3) Nakayama, J .; Nagasawa, H.; Sugihara, Y.; Ishii, A. J . Am.
Chem. Soc. 1997, 119, 9077.
(4) (a) Barbarella, G.; Pudova, O.; Arbizzani, C.; Mastragostino, M.;
Bongini, A. J . Org. Chem. 1998, 63, 1742. (b) Barbarella, G.; Favaretto,
L.; Zambianchi, M.; Pudova, O.; Arbizzani, C.; Bongini, A.; Mastra-
gostino, M. Adv. Mater. 1998, 10, 551. (c) Barbarella, G.; Zambianchi,
M.; Sotgiu, G.; Bongini, A. Tetrahedron 1997, 53, 9401. (d) Barbarella,
G.; Zambianchi, M.; del Fresno, M.; Marimon, I.; Antolini, L.; Bongini,
A. Adv. Mater. 1997, 9, 484.
Syn th esis of th e Ma ter ia ls. The pattern followed
to synthesize dimers, trimers, tetramers, and pentamers
(5) (a) Hajlaoui, R.; Horowitz, G.; Garnier, F.; Arce-Brouchet, A.;
Laigre, L.; El Kassmi, A.; Demanze, F.; Kouki, F. Adv. Mater. 1997, 9,
389. (b) Garnier, F.; Hajlaoui, R.; Yassar, A.; Srivastava, P. Science
1994, 265, 1684. (c) Dodabalapur, A.; Torsi, L.; Katz, H. E. Science
1995, 268, 270. (d) Swager, T. M.; Marsella, M. J . Adv. Mater. 1994,
6, 595. (e) Fichou, D.; Nunzi, J . M.; Charra, F.; Pfeffer, N. Adv. Mater.
1994, 6, 64. (f) Arbizzani, C.; Bongini, A.; Mastragostino, M.; Zanelli,
A.; Barbarella, G.; Zambianchi, M. Adv. Mater. 1995, 7, 571. (g) Geiger,
F.; Stoldt, M.; Schweitzer, H.; Ba¨uerle, P.; Umbach, E. Adv. Mater.
1993, 5, 922. (h) Tsivgoulis, G. M.; Lehn, J . M. Adv. Mater. 1997, 9,
39.
(6) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
S0022-3263(98)00507-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/17/1998

5498 J . Org. Chem., Vol. 63, No. 16, 1998
Barbarella et al.
Sch em e 1
Sch em e 2
containing from one to three thiophene S,S-dioxide units
is illustrated in Schemes 1-3. Scheme 3 also gives the
synthetic pathway followed to obtain some oligothio-
phenes never described so far and useful to compare their
electronic properties to those of the corresponding S,S-
dioxides. Most products were R,ω-functionalized to pre-
vent reactivity at the terminal positions. Dimethyl-tert-
butylsilyl and n-hexyl were chosen as end-capping groups
on the grounds that they favor a very ordered molecular
arrangement in the solid state.7
2-(Dimethyl-tert-butylsilyl)-5-bromothiophene 1,1-di-
oxide (3), the corresponding 2-(n-hexyl) derivative (4), and
(7) (a) Yassar, A.; Garnier, F.; Deloffre, F.; Horowitz, G.; Ricard, L.
Adv. Mater. 1994, 6, 660. (b) Garnier, F.; Yassar, A.; Hajlaoui, R.;
Horowitz, G.; Deloffre, F.; Servet, B.; Ries, S.; Alnot, P. J . Am. Chem.
Soc. 1993, 15, 8716.

Oligothiophene S,S-Dioxides
J . Org. Chem., Vol. 63, No. 16, 1998 5499
Sch em e 3
2,4-dibromothiophene 1,1-dioxide (15) were used for the
Stille coupling with the appropriate thienylstannanes in
the presence of Pd(AsPh3)4 generated in situ. The choice
of Pd(AsPh3)4 was motivated by the fact that this is the
catalyst leading to the best reaction yields in the syn-
thesis of oligothiophenes.4c
Thiophene S,S-dioxides 3 and 4 were obtained by
action of 2 molar equiv of m-CPBA on the 2-bromothie-
nyls 1 and 2. The yield of the reaction depends largely
on the ability to separate the mixture of unreacted
m-CPBA and m-chlorobenzoic acid from the S,S-dioxide
that is formed. In our case, the bissilylated compound 3
(59% yield) was more easily separated than its dialky-
lated counterpart 4 (37% yield).
oligothiophenes, whereas the coupling of dibrominated
dioxide 15 with thienylmonostannanes allows the inser-
tion of a thiophene S,S-dioxide unit in the central position
of the molecular skeleton. It is worth noting that the
coupling of 15 with stannanes 13 and 14, which already
contained a thiophene S,S-dioxide moiety, allowed the
preparation of quinquethiophenes 16 and 17 character-
ized by alternating aromatic and nonaromatic units
(Scheme 1). The yield of formation of stannanes 13 and
14 depends largely on the reaction conditions and in
particular on the rate of addition of thienyldistannane
10. When 10 was added very slowly (dropwise, in more
than 1 h), a yield increase from 13% to 52% was observed
for compound 14.
Scheme 3 gives the synthetic pathways to obtain a few
oligothiophenes and thiophene S,S-dioxides bearing n-
hexyl groups at the terminal positions. Bis(n-hexyl) bi-
and quaterthiophenes 37 and 40 were obtained in high
yield by coupling of lithiated 2-(n-hexyl)thiophene and
2-(n-hexyl)-2,2′-bithiophene in the presence of iron acetil-
acetonate, Fe(acac)3. As we have already found in other
cases,4d this reaction8 affords highly pure compounds in
rather good yields and appears a very useful way to
obtain even-numbered R,ω-substituted oligothiophenes.
The oxidation of 2,5-bis(n-hexyl)thiophene (43) with
m-CPBA affords the corresponding S,S-dioxide (44) in
70% yield. On the contrary, the oxidation of 2,5′-bis(n-
hexyl)-2,2′-bithiophene (37) is difficult, the monodioxide
(38) is obtained in low yield (10%), and no bis-S,S-dioxide
is formed. It is worth noting that the oxidation of 2,5′-
bis(dimethyl-tert-butylsilyl)-2,2′-bithiophene with m-CP-
BA is easier and that the 1,1,1′,1′-tetraoxide derivative
can be prepared in this way.4a
Table 1 gives the UV-vis maximum wavelength ab-
sorption (λmax) of oligothiophene S,S-dioxides of Schemes
1-3, compared to that of the parent oligothiophenes. The
table shows that both 2-(n-hexyl)- and 2-(dimethyl-tert-
butylsilyl)thiophene S,S-dioxide are red shifted (by 69
and 46 nm) with respect to the parent thiophenes and
that this trend is mantained with the oligomers up to
the pentamers. The insertion of the S,S-dioxide moieties
2,5-Dibromothiophene 1,1-dioxide 15 was prepared
from 2,5-bis(trimethylsilyl)thiophene 1,1-dioxide by ac-
tion of bromine in the presence of AgBF4, according to
the procedure described by Furukawa et al.1d This
reaction affords compound 15 in high yield (70%). We
were able to identify one of the byproducts of this reaction
(∼5% yield), namely 2,3,5-tribromothiophene 1,1-dioxide,
which was obtained in the form of colorless crystals
suitable for X-ray structure determination (see below).
Brominated thiophene S,S-dioxides 3, 4, and 15 re-
acted with thienylstannanes in the presence of Pd-
(AsPh3)4 generated in situ to form carbon-carbon bonds
in yields up to 65%. The reaction rate was much faster
than that between thienyl bromides and thienylstan-
nanes in the presence of the same catalyst.4c,6 Carrying
out detailed kinetic measurements was beyond the aim
of the present work, but, qualitatively, we estimated the
reaction rate of brominated thiophene S,S-dioxides with
thienyl stannanes as being of about 2 orders of magnitude
greater than that of thienyl bromides with thienylstan-
nanes. This decreases from hours to minutes the reaction
time required for the formation of the C-C bond and
makes oligothiophene S,S-dioxides easier to prepare than
some of the parent oligothiophenes, particularlly the
longer ones.
As shown in Schemes 1 and 2, the reaction of mono-
brominated thiophene S,S-dioxides 3 and 4 with thie-
nylmono- and -distannanes allows the insertion of
thiophene S,S-dioxide units at the terminal positions of
(8) Higuchi, H.; Nakayama, T.; Koyama, H.; Ojima, J .; Wada, T.;
Sasabe, H. Bull. Chem. Soc. J pn. 1995, 68, 2363.

5500 J . Org. Chem., Vol. 63, No. 16, 1998
Barbarella et al.
Ta ble 1. Ma xim u m Wa velen gth Absor p tion (λm a x, n m )a
of S,S-Dioxid es a n d of th e P a r en t Oligoth iop h en es
Rb
H
Sil
Hex
T
O
TT
OT
OO
TTT
231
2454a
254 (43)
300 (44)
340 (37)
402 (38)
3144a
302
3444a
4084a
4064a
352
3704a
380 (35)
TOT
OTT
OTO
426 (32)
440 (33)
460 (20)
460 (11)
4124a
430 (21)
442 (12)
400 (40)
448 (29)
F igu r e 1. Molecular structure of 2,3,5-tribromothiophene 1,1-
dioxide with atom numbering scheme. Thermal ellepsoids for
non-H atoms enclose 60% probability. Bond lengths (Å): S1-
O1, 1.414(8); S1-O2, 1.415(9); S1-C2, 1.752(12); S1-C5,
1.773(12); C2-C3, 1.30(2); C2-Br1, 1.838(10); C3-C4, 1.48-
(2); C3-Br2, 1.866(10); C4-C5, 1.25(2); C5-Br3, 1.864(12).
Bond angles (deg): O1-S1-O2, 116.8(6); O1-S1-C2, 110.5-
(6); O2-S1-C2, 112.3(6); O2-S1-C2, 112.3(6); O1-S1-C5,
111.4(6); O2-S1-C5, 111.8(6); C2-S1-C5, 91.3(5); C3-C2-
S1, 109.6(8); C3-C2-Br1, 130.3(9); S1-C2-Br1, 119.9(6);
C2-C3-C4, 114.0(10); C2-C3-Br2, 125.8(9); C4-C3-Br2,
120.2(9); C5-C4-C3, 114.2(11); C4-C5-S1, 110.9(10); C4-
C5-Br3, 131.3(10); S1-C5-Br3, 117.7(7).
TTTT
OTTT
TOTT
OTTO
TTTTT
OTTTT
TTOTT
OTTTO
OTOTO
390
416
470 (28)
4804a
492 (24)
420
470 (9)
512 (30)
520 (25)
542 (16)
480 (26)
526 (17)
a
b
In CHCl3. R ) R,ω substituents. Sil ) SiMe2(t-Bu). Hex )
(CH2)5CH3.
affects more the λmax of the longer oligomers, which in
turn depends on the position and on the number of
sulfonyl groups present in the molecular skeleton. Re-
gioisomers such as trimers 33 and 20 or pentamers 9 and
30 display different λmax values. The pentamer contain-
ing one terminal thiophene S,S-dioxide moiety (OTTTT,
9) is red shifted by 50 nm with respect to quin-
quethiophene TTTTT, whereas the pentamer containing
alternate aromatic and nonaromatic units (OTOTO, 16)
is red shifted by 122 nm with respect to TTTTT. As far
as we know, 16 has the largest value of the maximum
wavelength absorption (λmax ) 542 nm) ever measured
for short thiophene-based oligomers.
note that the dimensions of the molecule are in close
agreement with those previously found for the 2,5-di-tert-
butyl analogue.1a The molecular packing is characterized
by a number of extremely short van der Waals separa-
tions, all involving sulfonic O atoms. There are seven
contacts less than 3.60 Å, four of them being less than
3.20 Å.
Th eor etica l Ca lcu la tion s. To have an idea of the
effects caused by the functionalization of the thienyl
sulfur on the frontier orbitals and on the energy barriers
to rotation around the inter-ring C-C bonds, we carried
out ab initio HF/6-31G* calculations11 on 2,2′-bithiophene
(TT), 2,2′-bithiophene 1,1-dioxide (OT), and 2,2′-bithio-
phene 1,1,1′,1′-tetraoxide (OO).
In agreement with the results of other authors for
thiophene S,S-dioxide,12 we found that the oxygen lone
pairs of the SO2 group do not interact with the adjacent
unsaturated system and that the frontier orbitals of the
dioxide and of the tetraoxide mantain the π,π* character.
Figure 2 gives the HOMO and LUMO energies and the
coefficients pattern of TT, TO, and OO. It is seen that
the sulfur atoms are strongly involved in the LUMO (but
not in the HOMO) of 2,2′-bithiophene. Thus, as shown
in Figure 2, the transformation of the thienyl sulfur into
the corresponding dioxide, which decreases the energy
of both the HOMO and the LUMO, affects the energy of
the latter much more than that of the former.
Sin gle-Cr ysta l X-r a y Str u ctu r e of 2,3,5-Tr ibr o-
m oth iop h en e 1,1-Dioxid e.9 This compound was ob-
tained as a byproduct of the reaction of 2,5-bis(trimeth-
1d
ylsilyl)thiophene with bromine in the presence of AgBF4
in the form of colorless crystals suitable for X-ray
structure determination (see above). Since only very few
structural data on thiophene S,S-dioxides are available
so far,1a we report in Figure 1 the molecular structure of
this compound together with the values of the bond
angles and bond lengths.
The molecule is characterized by close coplanarity of
all atoms of the five-membered ring (the maximum
atomic deviation from mean plane is 0.005(8) Å). The
oxygen atoms of the SO2 moiety lie, roughly at the same
distance, above and below the pentaatomic ring, and the
plane through the O-S-O atoms is nearly pependicular
(89.5(4)°) to that through the ring atoms. The Br atoms
deviate slightly (maximum 0.11 Å) from such a plane.
Despite the limited accuracy due to the presence of
three heavy Br atoms, C-C and C-S bond distances are
consistent with two fully localized double bonds between
C2-C3 and C4-C5 atoms (1.30(2) and 1.25(2) Å, respec-
tively). With respect to the thiophene molecule, the loss
of the aromatic conjugation by the S atom implies C-S
and C3-C4 bond lengthening. Their values (1.75(1),
1.77(1), and 1.48(2) Å, respectively) in the present
compound compare well with the reported mean single-
bond length in parent derivatives.10 It is of interest to
(9) The authors have deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK.
(10) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, J .; Guy
Orpen, A.; Taylor, R. J . Chem. Soc. Perkin Trans. 2 1987, S1-S19.
(11) Gaussian 94, Revision E.2: Frisch, M. J .; Trucks, G. W.;
Schlegel, H. B.; Gill, P. M. W.; J ohnson, B. G.; Robb, M. A.; Cheeseman,
J . R.; Keith, T.; Petersson, G. A.; Montgomery, J . A.; Raghavachari,
K.; Al-Laham, M. A.; Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.;
Cioslowski, J .; Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.;
Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.;
Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.;
Defrees, D. J .; Baker, J .; Stewart, J . P.; Head-Gordon, M.; Gonzalez,
C.; Pople, J . A. Gaussian, Inc., Pittsburgh, PA, 1995.
(12) (a) J ursic, B. S. J . Heterocyclic Chem. 1995, 32, 1445. (b) Rozas,
I. J . Phys. Org. Chem. 1992, 5, 74.

Oligothiophene S,S-Dioxides
J . Org. Chem., Vol. 63, No. 16, 1998 5501
tions of TT is smaller than that of OT. In particular,
the energy of the anti conformation of TT is only 3.14 kJ
mol-1 smaller than the corresponding syn one.
When both thienyl sulfurs of bithiophene are converted
to the S,S-dioxide, the energy of the syn forms increases
to a such extent that no energy minimum is found
between 0° and 90°. Indeed, only a single energy
minimum at φ ) 169.6° is found for OO, indicating also
in this case that the molecule is forced to exist entirely
in the anti-quasiplanar conformation.
Discu ssion
The present results show that the palladium(0)-
catalyzed reaction of brominated thiophene S,S-dioxides
with thienylstannanes leads to the formation of new
carbon-carbon bonds in relatively high yields. This
reaction, which is a particular case of the well-known
Stille reaction,6 allows for the synthesis of oligoth-
iophenes containing a variable number of dearomatized
thiophene S,S-dioxide moieties in different positions of
the molecular skeleton. Indeed, as shown in Schemes
1-3, depending on whether a mono- or a bisthienylstan-
nane is used, thiophene S,S-dioxide moieties can be
inserted in the external or in the internal position of a
given oligomer. The appropriate choice of the stannanes
and of the bromides makes also possible to vary the
length of the aromatic residue between two adjacent
nonaromatic thiophene S,S-dioxide moieties and even the
synthesis of compounds having alternating aromatic and
nonaromatic rings. This versatility is interesting in view
of the fact that the redox properties4a,b and the optical
gaps (see Table 1) of oligothiophene S,S-dioxides depend
on the number and on the position of the dearomatized
units and that in this way a fine modulation of the
properties of this new class of compounds can be achieved.
The coupling reaction between thienylstannanes and
thienyl bromides requires extreme conditions such as use
of refluxing toluene as the solvent.4c On the basis of our
previous experience with the synthesis of oligothiophenes,
we employed extreme conditions also for the preparation
of oligothiophene S,S-dioxides. However, the much
greater reaction rate of brominated thiophene S,S-
dioxides compared to the corresponding thienyl bromides
suggests that these compounds could be synthesized in
much milder conditions, such as refluxing or even room-
temperature THF, as in the case of the coupling of
arylstannanes with vinyl triflates.14b
F igu r e 2. Coefficient patterns and energies (eV) of frontier
orbitals of 2,2′-bithiophene, 2,2′-bithiophene-1,1-dioxide and
2,2′-bithiophene-1,1,1′,1′-tetraoxide as calculated at the HF/
6-31G* level.
F igu r e 3. HF/6-31G* ab initio calculated torsional potential
energies (kJ mol-1) of 2,2′-bithiophene (TT), 2,2′-bithiophene-
1,1-dioxide (TO), and 2,2′-bithiophene-1,1,1′,1′-tetraoxide (OO)
vs inter-ring torsional angles (deg).
According to the calculations, there is a progressive
decrease of the inter-ring bond distance on passing from
TT (1.464 Å) to TO (1.453 Å) to OO (1.448 Å).
Figure 3 gives the ab initio HF/6-31G* calculated
potential energies (kJ mol-1) of TO and OO as a function
of the torsional inter-ring angle φ (°) for φ varying from
0° (fully planar syn conformation) to 180° (fully planar
anti conformation). For comparison, the potential ener-
gies of TT, calculated with the same basis set,13 are also
reported.
Fully relaxed geometry minimization of syn-like and
anti-like TO forms leads to two minima at φ ) 46.3° and
160.8°, with the latter being 10.46 kJ mol-1 lower in
energy than the former. Qualitatively, the energy profile
of TO is similar to that of TT, for which also two minima
are found at φ ) 43.9° and 147.4°.13 However, the energy
difference between the preferred syn and anti conforma-
There is much experimental evidence that thiophene
S,S-dioxide and its polysubstituted counterparts are very
reactive compounds that afford a variety of derivatives
in the presence of Grignard reagents, organolithium
compounds, amines, etc. through ring opening and sub-
sequent rearrangements.1b Thus, the question arises
whether and to what extent the reactivity of a thiophene
S,S-dioxide moiety is changed upon insertion within the
aromatic skeleton of an oligothiophene. In our experi-
ence, oligothiophene S,S-dioxides are very stable micro-
crystalline compounds. Their higher oxidation poten-
tials4a,b make them less sensitive than the parent
oligothiophenes to attack by moisture or oxygen.15 They
(14) (a) Farina, V. J . Am. Chem. Soc. 1991, 113, 9585. (b) Farina,
V.; Roth, G. P. Tetrahedron Lett. 1991, 32, 4243. (c) Farina, V.;
Krishnan, B.; Marshall, D. R.; Roth, G. P. J . Org. Chem. 1993, 58,
5434. (d) Roth, G. P.; Farina, V.; Liebeskind, L. S.; Pen˜a-Cabrera, E.
Tetrahedron Lett. 1995, 36, 2191.
(13) (a) Samdal, S.; Samuelsen, E. J .; Volden, H. V. Synth. Met. 1993,
59, 259. (b) Ort´ı, E.; Viruela, P. M.; Sanchez-Marin, J .; Tomes, F. J .
Phys. Chem. 1995, 99, 4955. (c) Hernandez, V.; Lopez Navarrete, J . T.
J . Chem. Phys. 1994, 101, 1373.

5502 J . Org. Chem., Vol. 63, No. 16, 1998
Barbarella et al.
are apparently also less sensitive than oligo- and poly-
thiophenes to photodegradation.16
1.84 V. Electrochemical data also show that the trend
is maintained with the longer oligothiophene S,S-
dioxides. For example, while quinquethiophene TTTTT
has Ec,p ) -2.13 V and Ea,p ) 0.92 V, pentamer OTOTO
(16) characterized by alternating aromatic and nonaro-
matic units has Ec,p ) -0.82 V and Ea,p ) 1.46 V. In
general, the selective insertion of a variable number of
thiophene S,S-dioxide units according to the synthetic
pathways described in Schemes 1-3 allows a fine-tuning
of the redox properties of oligothiophenes, and the
electron affinity can be increased to the point that the
compounds are more easily reduced than oxidized.4a,b
Oligothiophene S,S-dioxides display smaller optical
energy gaps than the parent oligothiophenes. Table 1
shows that their λmax values are red shifted by 50 to 122
nm, depending on the number and on the position of the
sulfonyl moieties. Pentamers 16 and 17, having alter-
nating aromatic and nonaromatic units, display unusu-
ally high λmax values in chloroform (542 and 526 nm,
respectively), even larger than those observed for regio-
regular functionalized polythiophenes.17 The results of
ab initio calculations on 2,2′-bithiophene and its mono-
and bis-S,S-dioxides indicate that a contribution to such
large λmax values also comes from the more planar
conformations of the bithiophene subsystems containing
thiophene S,S-dioxide moieties and from the smallerr
inter-ring carbon-carbon distances.
Figure 3 shows that the energy difference between the
more stable anti conformation and the less stable, more
puckered, syn conformation of 2,2′-bithiophene (TT)
amounts to only 3.14 kJ mol-1. Thus, in solution, TT
exists as a family of syn and anti conformers of very
similar energies. On the contrary, for 2,2′-bithiophene
1,1-dioxide (TO) and a fortiori for 2,2′-bithiophene 1,1,1′,1′-
tetraoxide (OO), the difference in energy between the syn
and anti conformation is such that only the latter is
populated. These results indicate that the functional-
ization of the thienyl sulfur to the corresponding S,S-
dioxide leads to the rigidification of the molecular skel-
eton. The rigidification of the backbone of oligo- and
polythiophenes through the insertion of ethylene bonds
is a strategy that has been pursued by several authors,
since it leads to the lowering of the optical gap by
decreasing the rotational disorder.18 Clearly, the oxida-
tion of the thienyl sulfur is an alternative way to achieve
the same result, since the structural data reported in
Figure 1 indicate that, in the end, this amounts to the
insertion of a butadiene moiety rigidly held in the cis
configuration by the sulfonyl group.
Con clu sion
We have shown that brominated thiophene S,S-
dioxides can be successfully coupled to thienylstannanes
in the presence of palladium(0) catalysts to afford oligo-
mers bearing a variable number of thiophene S,S-dioxide
moieties in different positions of the molecular skeleton.
The regioselective insertion of such units into the
backbone of oligothiophenes permits us to achieve a
continuous modulation of the electronic and redox prop-
erties of the system. The possibility for the thienyl sulfur
atom to deconnect its lone pair from the aromatic system
through the formation of the dioxide leads to smaller
optical gaps, as shown by the large red shifts of the
maximum wavelength absorption of oligothiophene S,S-
dioxides with respect to that of the parent oligoth-
iophenes. This also leads to a dramatic decrease of the
LUMO energy and to the consequent increase of the
electron affinity. In this way, it is possible to go from
easily oxidized oligothiophenes to easily reduced oligoth-
iophene S,S-dioxides containing alternating aromatic and
non aromatic moieties.
Exp er im en ta l Section
Gen er a l Meth od s. Pd2dba3, AsPh3, BuLi, 2-(tributylstan-
nyl)thiophene, 2,2′-bithiophene, n-hexyl bromide, and Bu3SnCl
were purchased from Aldrich. m-Chloroperoxybenzoic acid (m-
CPBA) and 2-(n-hexyl)thiophene were purchased from Fluka
and Lancaster, respectively. All solvents used in reactions and
chromatographies were dried by standard procedures. Flash
chromatographies were carried out using silica gel (230-400
mesh ASTM) and analytical thin-layer chromatographies
(TLCs) using 0.2 mm silica gel plates (Merck). The visualiza-
tion in TLC was accomplished by UV light.
The synthesis of 2,5-bis(tributylstannyl)thiophene (10),19
2,5-dibromothiophene 1,1-dioxide 15),1d 2,5′-bis(tributylstan-
nyl)-2,2′-bithiophene (22),19 and 2,5′′-bis(tributylstannyl)-2,2′:
5′,2′′-terthiophene (23),19 has already been described.
Theoretical calculations show (Figure 2) that on pass-
ing from TT to TO to OO there is a progressive decrease
of the energy of both frontier orbitals and that the energy
of the LUMO is decreased much more than that of the
HOMO. Figure 2 shows that the latter effect is a
consequence of the much greater contribution of sulfur
lone pair to the LUMO of 2,2′-bithiophene. Thus, the
calculations predict that the insertion of a thiophene S,S-
dioxide moiety into the skeleton of an oligothiophene
should lead to the increase of the electron affinity of the
system.
2,3,5-Tribromothiophene 1,1-dioxide (Figure 1) was obtained
as a byproduct of the preparation of compound 15 according
to ref 1d. The product was isolated as a colorless crystalline
compound (from pentane): mp 120-122 °C; MS m/e 350 (M•+);
The trend predicted by the calculations has been
confirmed experimentally through the electrochemical
determination of the reduction (Ec,p) and oxidation (Ea,p
)
potentials of 2,5′-bis(dimethyl-tert-butyl)-2,2′-bithiophene
(SiTT) and of the corresponding mono- (SiTO) and bis-
S,S-dioxides (SiOO).4b On going from SiTT to SiTO to
SiOO, there is a progressive increase of the electron
affinity of the system, as shown by the reduction potential
that changes from <-2.1 V to -1.34 V to -0.85 V while
the oxidation potential increases from 1.29 V to 1.6 V to
λ
max(CHCl3) 330 nm; 1H NMR (CDCl3, TMS/ppm) 6.95 (s, 1H);
13C NMR (CDCl3, TMS/ppm) 131.2, 124.2, 120.5, 118.8. The
crystals were suitable for X-ray structure determination.
2-(Dim eth yl-ter t-bu tylsilyl)-5-br om oth iop h en e, 1. To
a solution of 4.95 g (0.025 mol) of 2-(dimethyl-tert-butylsilyl)-
thiophene4a in 15 mL of DMF at room temperature were added
4.37 g (0.025 mol) of N-bromosuccinimide.The mixture was
stirred for 12 h at 80 °C. Then 50 mL of distilled water was
added, followed by 50 mL of ethyl ether. The organic phase
(15) De Leew, D. M.; Simenon, M. M. J .; Brown, A. R.; Einerhand,
R. E. F. Synth. Met. 1997, 87, 53-59.
(16) Caronna, T.; Forte, M.; Catellani, M.; Meille, S. V. Chem. Mater.
1997, 9, 991.
(17) McCullogh, R. D. Adv. Mater. 1998, 10, 93.
(18) Roncali, J . Chem. Rev. 1997, 97, 173.
(19) Miller, L. L.; Yu, Y. J . Org. Chem. 1995, 60, 6813.
(20) Van Pham, C.; Burkhardt, A.; Nkansah, A.; Shabana, R.;
Cunnigham, D. D.; Mark, H. B., J r.; Zimmer, H. Phosphorus, Sulfur,
Silicon Relat. Elem. 1989, 46, 153.

Oligothiophene S,S-Dioxides
J . Org. Chem., Vol. 63, No. 16, 1998 5503
was separated, dried over MgSO4, and evaporated. After
distillation (95 °C, 18 mmHg), 4.1 g (59% yield) of a mixture
of two products, identified as 1 and the isomeric 2-(dimethyl-
tert-butylsilyl)-3-bromothiophene 1′, was obtained. GC mea-
surements gave a ratio 9:1 for 1:1′. Further attempts to
separate the isomers by distillation were unsuccessful, and the
mixture was used as such in the subsequent steps.
heating at 80 °C, the mixture was cooled at room temperature,
hydrolyzed with a saturated solution of NH4Cl, extracted with
ethyl ether, dried over MgSO4, and evaporated. The residue
was chromatographed on silica gel using petroleum ether/
methylene chloride 5:1 as the eluent, and 0.142 g (36% yield)
of 7 as a yellow oil was recovered: MS m/e 390 (M•+); 1H NMR
3
3
(CDCl3, TMS/ppm) 7.36 (d, J ) 3.9 Hz, 1H), 7.08 (d, J ) 3.9
1
3
3
1: MS m/e 276 (M•+); H NMR (CDCl3, TMS/ppm) 7.09 (d,
Hz, 1H), 6.94 (d, J ) 4.5 Hz, 1H), 6.55 (d, J ) 4.5 Hz, 1H),
1.00 (s, 9H), 0.33 (s, 6H); 13C NMR (CDCl3, TMS/ppm) 143.1,
139.6, 138.5, 131.6, 129.4, 127.7, 123.7, 117.2, 26.2, 17.2. Anal.
Calcd for C14H19BrO2S2Si: C, 42.96; H, 4.89. Found: C, 43.02;
H, 4.91.
3
3J ) 3.5 Hz, 1H), 6.99 (d, J ) 3.5 Hz, 1H), 0.92 (s, 9H), 0.28
(s, 6H).
1
1′: MS m/e 276 (M•+); H NMR (CDCl3, TMS/ppm) 7.22 (d,
3J ) 4.5 Hz, 1H), 6.90 (d, J ) 4.5 Hz, 1H), 0.92 (s, 9H), 0.36
(s, 6H).
3
5-(Dim et h yl-ter t-b u t ylsilyl)-5′′-(t r ib u t ylst a n n yl)-2,2′:
5′,2′′-ter th iop h en e, 8. To a solution containing 0.28 g (0.773
mmol) of 5-(dimethyl-tert-butylsilyl)-2,2′:5′,2′′-terthiophene4a
was added 0.31 mL (0.773 mmol) of a 2.5 M solution of BuLi
in hexane. After 1 h, 0.21 mL (0.773 mmol) of Bu3SnCl was
added dropwise. The reaction mixture was stirred overnight,
hydrolyzed with a saturated solution of NH4Cl, extracted with
ethyl ether, dried over MgSO4, and evaporated. A total of
0.471 g (94% yield) of pure 8 as a dark green oil was
recovered: MS m/e 650 (M•+): 1H NMR (CDCl3, TMS/ppm) 7.28
2-(n -Hexyl)-5-br om oth iop h en e, 2. To a solution of 2.9 g
(0.017 mol) of 2-n-hexylthiophene 36 in 10 mL of DMF was
added stepwise 3.03 g (0.017 mol) of N-bromosuccinimide. The
mixture was stirred at room temperature for 4 h, 30 mL of
distilled water was added, and then the organic compounds
were extracted twice with 25 mL of methylene chloride. After
the usual workup, the crude product was distilled (110 °C, 760
mmHg), and 2.53 g (84% yield) of pure 2 as a white oil was
obtained: MS m/e 247 (M•+); λmax(CHCl3) 246 nm; 1H NMR
3
3
3
3
(CDCl3, TMS/ppm) 6.84 (d, J ) 3.6 Hz, 1H), 6.53 (doublet of
(d, J ) 3.8 Hz, 1H), 7.22 (d, J ) 3.6 Hz, 1H), 7.14 (d, J )
3
4
3
triplets, J ) 3.6 Hz, J ) 1.8 Hz, 1H), 2.75 (t, 2H), 1.65 (m,
2H), 1.30 (m, 6H), 0.90 (m, 3H); 13C NMR (CDCl3, TMS/ppm)
147.8, 129.4, 124.3, 108.5, 31.5, 31.4, 30.3, 28.7, 22.5, 14.0.
Anal. Calcd for C10H15BrS: C, 48.59; H, 6.12. Found: C,
48.69; H, 6.11.
3.6 Hz, 1H), 7.08 (s, 2H), 7.07 (d, J ) 3.8 Hz, 1H), 1.56 (m,
6H), 1.33 (m, 6H), 1.12 (t, 6H), 0.98 (s, 9H), 0.86 (t, 9H), 0.3
(s, 6H); 13C NMR (CDCl3, TMS/ppm) 142.9, 142.5, 136.8, 136.7,
136.5, 136.3, 136.0, 135.9, 124.8, 124.5, 124.3, 124.2, 29.0, 27.2,
26.4, 16.9, 13.7, 10.9.
2-(Dim eth yl-ter t-bu tylsilyl)-5-br om oth iop h en e 1,1-Di-
oxid e, 3. A 3.34 g (0.012 mol) portion of the 9:1 mixture of 1
and 1′ dissolved in 30 mL of CH2Cl2 was added dropwise to a
suspension of 7.41 g (0.03 mol) of m-CPBA 70% in CH2Cl2.
After being stirred for 2 days at room temperature, the mixture
was cooled to -50 °C, and the precipitate containing unreacted
m-CPBA and m-chlorobenzoic acid was filtered. After evapo-
ration of the solvent, the residue was crystallized from pentane
to yield 2.19 g (59% yield) of 3 as a white solid: mp 94 °C; MS
5,5′′′′-Bis(dim eth yl-ter t-bu tylsilyl)-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-
qu in qu eth iop h en e 1,1-Dioxid e, 9. To a 10 mL toluene
solution containing 0.006 mmol of Pd(AsPh3)4 prepared in situ4c
was added 0.138 g (0.212 mmol) of 8 and 0.081 g (0.212 mmol)
of 7, and the solution was refluxed during 4 h. The reaction
mixture was then hydrolyzed with a saturated solution of NH4-
Cl, and after usual workup the residue was washed with ethyl
ether. A total of 0.069 g (47% yield) of 9 as a red polycrys-
talline solid, mp 216-217 °C, was recovered: MS m/e 672
(M•+); λmax(CHCl3) 470 nm; H NMR (CDCl3, TMS/ppm) 7.56
3
1
m/e 308 (M•+); 1H NMR (CDCl3, TMS/ppm) δ 6.88 (d, J ) 4.8
3
3
3
3
Hz, 1H), 6.73 (d, J ) 4.8 Hz, 1H), 0.98 (s, 9H), 0.31 (s, 6H);
(d, J ) 4.0 Hz, 1H), 7.26 (d, J ) 4.0 Hz, 1H), 7.19 (d, J )
13C NMR (CDCl3, TMS/ppm) δ 147.7, 138.5, 126.7, 125.5, 26.2,
17.3. Anal. Calcd for C10H17BrO2SSi: C, 38.83; H, 5.54.
Found: C, 38.71; H, 5.52.
4.0 Hz, 1H), 7.16 (d, 3J ) 3.5 Hz, 1H), 7.15 (d, 3J ) 3.5 Hz,
3
3
1H), 7.11 (s, 2H), 7.10 (d, J ) 4.0 Hz, 1H), 6.99 (d, J ) 4.6
3
Hz, 1H), 5.57 (d, J ) 4.6 Hz, 1H), 1.02 (s, 9H), 0.97 (s, 9H),
2-(n -Hexyl)-5-br om oth iop h en e 1,1-Dioxid e, 4. A 2.05
g (8.3 mmol) portion of 2 was dissolved in 10 mL of methylene
chloride and the solution added to a mixture of 5.1 g (21.0
mmol) of m-CPBA (70%) in 20 mL of methylene chloride. The
mixture was stirred overnight at room temperature and then
filtered and washed twice with a 10% solution of NaHCO3, and
the product was crystallized from pentane. A total of 0.85 g
(37%) of a white crystalline product, mp 48 °C, was obtained:
MS m/e 278 (M•+); λmax(CHCl3) 308 nm; 1H NMR (CDCl3, TMS/
0.36 (s, 6H), 0.32 (s, 6H); 13C NMR (CDCl3, TMS/ppm): 142.6,
141.9, 140.4, 140.2, 138.8, 138.6, 137.7, 137.5, 136.9, 136.1,
135.3, 134.8, 130.2, 125.8, 124.9, 124.8, 124.4, 124.3, 116.4,
26.3, 26.2, 17.3, 16.9. Anal. Calcd for C32H40O2S5Si2: C, 57.10;
H, 5.99. Found: C, 56.98; H, 6.01.
5,5′′-Bis(d im e t h yl-t er t -b u t ylsilyl)-2,2′:5′,2′′-t e r t h io-
p h en e 1,1,1′′,1′′-Tetr a oxid e, 11, a n d 5-(Dim eth yl-ter t-
b u t ylsilyl)-5′-(t r ib u t ylst a n n yl)-2,2′-b it h iop h en e 1,1-Di-
oxid e, 13. To a 10 mL toluene solution containing 0.018 mmol
of Pd(AsPh3)4 prepared in situ4c were added 0.28 g (0.9 mmol)
of 3 and 0.597 g (0.9 mmol) of 2,5-bis(tributylstannyl)thiophene
10.19 After being heated at reflux for 1 h, the toluene was
evaporated and the residue was chromatographed on silica gel.
Petrolueum ether was used as the first eluent, and 0.087 g
(16%) of 13 as a yellow oil was recovered. Subsequent elution
with petroleum ether/CH2Cl2 5:1 gave 0.097 g (40%) of a
compound corresponding to tetradioxide 11.4a
3
3
ppm) 6.76 (d, J ) 4.8 Hz, 1H), 6.36 (doublet of triplets, J )
4
4.8 Hz, J ) 2.0 Hz, 1H), 2.50 (m, 2H), 1.65 (m, 2H), 1.30 (m,
6H), 0.90 (m, 3H); 13C NMR (CDCl3, TMS/ppm) 145.5, 127.5,
122.5, 119.2, 31.3, 28.6, 26.3, 25.3, 22.4, 13.9. Anal. Calcd
for C10H15BrO2S: C, 43.02; H, 5.42. Found: C, 42.96; H, 5.43.
5-(Dim eth yl-ter t-bu tylsilyl)-2,2′-bith iop h en e 1,1-Diox-
id e, 6. To a solution of 0.05 mmol of Pd(AsPh3)4 in 10 mL of
toluene prepared in situ4c was added 0.515 g (1.67 mmol) of 3
and 0.621 g (1.67 mmol) of 2-(tributylstannyl)thiophene at
room temperature. After being heated at reflux for 1 h, the
reaction mixture was hydrolyzed with a saturated solution of
NH4Cl, extracted with ethyl ether, dried over MgSO4, and
evaporated. The residue was crystallized from pentane to give
0.42 g (83% yield) of yellow crystals: mp 75-76 °C; MS m/e
13: MS m/e 602 (M•+); 1H NMR (CDCl3, TMS/ppm) 7.73 (d,
3
3
3J ) 3.3 Hz, 1H), 7.18 (d, J ) 3.3 Hz, 1H), 6.96 (d, J ) 4.3
3
Hz, 1H), 6.69 (d, J ) 4.3 Hz, 1H), 1.55 (m, 6H), 1.30 (m, 6H),
1.12 (t, 6H), 0.99 (s, 9H), 0.87 (t, 9H), 0.32 (s, 6H); 13C NMR
(CDCl3, TMS/ppm) 143.3, 141.8, 140.6, 139.1, 136.8, 134.8,
129.6, 116.6, 27.2, 27.0, 26.2, 17.2, 13.6, 11.0.
1
312 (M•+); λmax(CHCl3) 376 nm; H NMR (CDCl3, TMS/ppm)
5,5′′-Bis(n -h exyl)-2,2′:5′,2′′-ter th iop h en e 1,1,1′′,1′′-Tet-
r a oxid e, 12. To a 12 mL toluene solution containing 0.018
mmol of Pd(AsPh3)4 prepared in situ4c was added 0.30 g (0.45
mmol) of 2,5-bis(tributylstannyl)thiophene 10,19 and 0.25 g
(0.90 mmol) of 2-n-hexyl-5-bromothiophene 1,1-dioxide 4 was
then added. The mixture was refluxed for 5 h, treated with a
saturated solution of NH4Cl, and washed with water, and the
organic layer was separated, dried over MgSO4, and evapo-
rated. The crude product was chromatographed on silica gel
using petroleum ether/methylene chloride 80:20. A total of
3
7.65 (m, 1H), 7.44 (m, 1H), 7.13 (m, 1H), 6.97 (d, J ) 4.1 Hz,
3
1H), 6.63 (d, J ) 4.1 Hz, 1H), 0.99 (s, 9H), 0.35 (s, 6H); 13C
NMR (CDCl3, TMS/ppm) 142.8, 140.7, 138.7, 129.9, 129.0,
128.6, 128.5, 117.3, 26.4, 17.2. Anal. Calcd for C14H20O2S2Si:
C, 53.80; H, 6.45. Found: C, 53.73; H, 6.43.
5-(Dim eth yl-ter t-bu tylsilyl)-5′-br om o-2,2′-bith iop h en e
1,1-Dioxid e, 7. To a solution containing 0.312 g (1.0 mmol)
of 6 in 5 mL of DMF was added stepwise 0.178 g (1.0 mmol) of
N-bromosuccinimide at room temperature. After 2 days of

5504 J . Org. Chem., Vol. 63, No. 16, 1998
Barbarella et al.
96 mg (44% yield) of 12 as a deep orange polycrystalline
compound, mp 191-192 °C, was separated: MS m/e 480 (M•+);
the mixture stirred overnight. After usual workup, 3.70 g
(94%) of 19 as a yellow oil was isolated, which was used as
such: MS m/e 540 (M•+); 1H NMR (CDCl3, TMS/ppm) 7.26 (d,
λ
max(CHCl3) 442 nm; 1H NMR (CDCl3, TMS/ppm) 7.53 (s, 2H),
6.67 (d, 3J ) 4.8 Hz, 2H), 6.44 (doublet of triplets, 3J ) 4.8
Hz, 4J ) 1.8 Hz, 2H), 2.55 (t, 4H), 1.70 (m, 4H), 1.30 (m, 12H),
0.9 (m, 6H); 13C NMR (CDCl3, TMS/ppm) 144.8, 134.2, 131.5,
128.8, 122.3, 119.8, 31.3, 28.8, 26.6, 24.5, 22.5, 14.0. Anal.
Calcd for C24H32O4S3: C, 59.97; H, 6.71. Found: C, 59.88; H,
6.69.
3J ) 3.3 Hz, 1H), 7.11 (d, J ) 3.3 Hz, 1H), 7.02 (d, J ) 3.5
3
3
3
Hz, 1H), 6.72 (d, J ) 3.5 Hz, 1H), 2.82 (t, 2H), 1.7 (m, 8H),
1.4 (m, 10 H), 1.2 (m, 6H), 0.9 (m, 12H); 13C NMR (CDCl3, TMS/
ppm) 145.5, 143.8, 136.6, 136.3, 135.5, 125.2, 124.6, 123.5, 32.1,
30.6, 29.5, 29.3, 27.8, 23.1, 14.4, 13.9, 11.3.
5,5′′-Bis(d im e t h yl-t er t -b u t ylsilyl)-2,2′:5′,2′′-t e r t h io-
p h en e 1,1-Dioxid e, 20. To a 25 mL toluene solution
containing 0.018 mmol of Pd(AsPh3)4 prepared in situ4c were
added 0.68 g (1.2 mmol) of 18 and 0.37 g (1.2 mmol) of 3. The
mixture was refluxed for 2 h and then hydrolyzed with a
saturated solution of NH4Cl and extracted with CH2Cl2. After
usual workup, the residue was repeatedly washed with ethyl
ether, and 0.36 g (60% yield) of 204a was recovered.
5-(n -H exyl)-5′-(t r ib u t ylst a n n yl)-2,2′-b it h iop h en e 1,1-
Dioxid e, 14. To a solution of 0.84 g (0,003 mol) of 2-(n-hexyl)-
5-bromo-thiophene 1,1-dioxide 4 and 0.17 g (0.15 mmol) of
commercial Pd(PPh3)4 in 20 mL of toluene was added stepwise
2.00 g (0.003 mol) of 2,5-bis(tributylstannyl)thiophene 1019
dissolved in 8 mL of toluene over 1 h. The solution was
refluxed for 1 h. After usual workup, 0.87 g (51% yield) of a
yellow oil was obtained. The product was used as such: MS
m/e 572 (M•+); λmax(CHCl3) 360 nm; 1H NMR (CDCl3, TMS/
5,5′′-Bis-(n -h exyl)-2,2′:5′,2′′-t er t h iop h en e 1,1-Dioxid e,
21. To a 15 mL toluene solution containing 0.011 mmol of
Pd(AsPh3)4 prepared in situ4c were added 0.4 g (0.74 mmol) of
19 and 0.2 g (0.74 mmol) of 4. After being refluxed for 2 h,
the reaction mixture was filtered through aluminum oxide.
After usual workup, 0.17 g (52% yield) of an orange red,
polycrystalline compound, mp 105-106 °C, was obtained: MS
m/e 448 (M•+); λmax(CHCl3) 430 nm; 1H NMR (CDCl3, TMS/
3
3
ppm) 7.67 (d, J ) 3.5 Hz, 1H), 7.15 (d, J ) 3.5 Hz, 1H), 6.59
3
3
4
(d, J ) 4.8 Hz, 1H), 6.41 (doublet of triplets, J ) 4.8 Hz, J
) 1.0 Hz, 1H), 2.52 (t, 2H), 1.6 (m, 8H), 1.3 (18H), 0.85 (m,
12H).
5,5′′′′-Bis(dim eth yl-ter t-bu tylsilyl)-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-
qu in qu eth iop h en e 1,1,1′′,1′′,1′′′′,1′′′′-Hexa oxid e, 16. To a
10 mL toluene solution containing 0.003 mmol of Pd(AsPh3)4
prepared in situ4c were added 15.1 mg (0.055 mmol) of 151a
and 67 mg (0.11 mmol) of 13. After being refluxed for 4 h,
the reaction mixture was filtered through silica gel. A first
fraction was collected using petroleum ether as the eluent. A
second fraction was obtained using petroleum ether/CH2Cl2
1:1 as the eluent. After evaporation of the solvent and washing
with ethyl ether, the second fraction afforded 16 mg (40% yield)
of 16 as a brown solid, mp > 340 °C (upper limit of our
apparatus). The solid did not show any sign of decomposition
at 340 °C and was not soluble in most organic solvents: MS
m/e 736 (M•+); λmax(CHCl3) 542 nm; 1H NMR (CDCl3, TMS/
3
3
ppm) 7.46 (d, J ) 3.9 Hz, 1H), 7.07 (d, J ) 3.9 Hz, 1H), 7.03
3
3
3
(d, J ) 3.6 Hz, 1H), 6.69 (d, J ) 3.6 Hz, 1H), 6.53 (d, J )
4.9 Hz, 1H), 6.42 (doublet of triplets, 3J ) 4.9 Hz, 5J ) 1.0 Hz,
1H), 2.77 (t, 2H), 2.52 (t, 2H), 1.65 (m, 4H), 1.3 (m, 12H), 0.9
(m, 6H); 13C NMR (CDCl3, TMS/ppm) 147.2, 143.4, 140.4,
136.4, 133.7, 128.9, 127.8, 125.1, 124.7, 123.9, 122.7, 116.7,
31.5, 31.4, 30.2, 28.8, 28.7, 26.7, 24.4, 22.5, 22.4, 14.0. Anal.
Calcd for C24H32O2S3: C, 64.24; H, 7.19. Found: C, 64.39; H,
7.21.
5,5′′′-Bis[(d im eth yl-ter t-bu tylsilyl)]-2,2′:5′,2′′:5′′,2′′′-qu a -
ter th iop h en e 1,1,1′′′,1′′′-Tetr a oxid e, 24. To a 6 mL toluene
solution containing 0.01 mmol of Pd(AsPh3)4 prepared in situ4c
were added 0.24 g (0.32 mmol) of 5,5′-bis(tributylstannyl)-2,2′-
bithiophene 2219 and 0.19 g (0.64 mmol) of 3. After being
refluxed for 6 h, the reaction mixture was hydrolyzed with a
saturated solution of NH4Cl and extracted with CH2Cl2. The
organic phase was dried over MgSO4, concentrated, and
filtered through silica gel. After evaporation of the solvent,
the residue was washed with ethyl ether, and 0.118 g (59%
yield) of 244a was obtained.
3
ppm) 7.64 (s, 4H), 7.00(d, J ) 4.6 Hz, 2H), 6.87 (s, 2H), 6.71
(d, 3J ) 4.6 Hz, 2H), 1.00 (s, 18H), 0.34 (s, 12H). Anal. Calcd
for C32H40O6S5Si2: C, 52.14; H, 5.47. Found: C, 52.21; H, 5.46.
5,5′′′′-Bis(n -h exyl)-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-q u in q u et h io-
p h en e 1,1,1′′,1′′,1′′′′,1′′′′-Hexa oxid e, 17. To a 15 mL toluene
solution containing 0.007 mmol of Pd(AsPh3)4 prepared in situ4c
were added 514 mg (0.90 mmol) of 14 and 166 mg (0,45 mmol)
of 2,5-diiodiothiophene 1,1-dioxide.1d After being refluxed for
4 h, the solution was stirred overnight at room temperature.
After usual workup, the crude product was repeatedly washed
with freshly distilled pentane. Then the product was purified
by filtering on silica gel with CH2Cl2/CH3COCH3 1:1 as the
eluent and subsequent Soxlet extraction with toluene.
5,5′′′′-[Bis(dim eth yl-ter t-bu tylsilyl)]-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-
qu in qu eth iop h en e 1,1,1′′′′,1′′′′-Tetr a oxid e, 25. To an 8 mL
toluene solution containing 0.016 mmol of Pd(AsPh3)4 prepared
in situ4c were added 0.31 g (1.0 mmol) of 3 and 0.41 g (0.50
mmol) of 5,5′′-bis(tributylstannyl)-2,2′:5′,2′′-terthiophene 23.19
After being refluxed for 6 h, the reaction mixture was
hydrolyzed with a saturated solution of NH4Cl and extracted
with CH2Cl2. The organic phase was dried over MgSO4,
concentrated, and filtered through silica gel. After evaporation
of the solvent, the residue was washed with ethyl ether, and
0.186 g (53% yield) of 25 as a red polycrystalline solid, mp
199-200 °C, was obtained. The product was insoluble in most
A total of 21 mg (7% yield) of a brown powder, mp > 340 °C
(upper limit of our apparatus), was obtained. The solid did
not show any sign of decomposition at 340 °C and was not
soluble in most organic solvents: MS m/e 676 (M•+); λmax
-
(CHCl3) 526 nm. Anal. Calcd for C32H36O6S5: C, 56.78; H,
5.36. Found: C, 56.92; H, 5.38.
5-(d im et h yl-ter t-b u t ylsilyl)-5′-(t r ib u t ylst a n n yl)-2,2′-
bith iop h en e, 18. To a solution of 6 mL of THF containing
0.56 g (2.0 mmol) of 5-(dimethyl-tert-butylsilyl)-2,2′-bithiophene4a
was added 0.8 mL (2.0 mmol) of a 2.5 M solution of BuLi in
hexane. After 1 h, 0.65 g (2.0 mmol) of Bu3SnCl was added
and the mixture stirred overnight at room temperature. After
addition of a saturated solution of NH4Cl and extraction with
ethyl ether, the organic phase was dried over MgSO4 and
evaporated. A total of 0.90 g (78% yield) of 18 as a dark green
1
organic solvents: MS m/e 704 (M•+); λmax(CHCl3) 520 nm; H
3
3
NMR (CDCl3, TMS/ppm) 7.56 (d, J ) 3.9 Hz, 2H), 7.22 (d, J
3
) 3.9 Hz, 2H), 7.17 (s, 2H), 6.98 (d, J ) 4.6 Hz, 2H), 6.59 (d,
3J ) 4.6 Hz, 2H), 1.01 (s, 18H), 0.35 (s, 12H). Anal. Calcd for
C
32H40O4S5Si2: C, 54.51; H, 5.72. Found: C, 54.47; H, 5.73.
5,5′′′-Bis(n -h e xyl)-2,2′:5′,2′′:5′′,2′′′-q u a t e r t h iop h e n e
1,1,1′′′,1′′′-Tetr a oxid e, 26. To an 11 mL toluene solution
containing 0.016 mmol of Pd(AsPh3)4 prepared in situ4c was
added 270 mg (0.50 mmol) of 5,5′-bis(tributylstannyl)-2,2′-
bithiophene 19, and 300 mg (1.00 mmol) of 2-(n-hexyl)-5-
bromothiophene 2 in 11 mL of toluene was then added
dropwise. The mixture was refluxed for 5 h, treated with a
saturated solution of NH4Cl, and washed with water, and the
organic layer was separated, dried over MgSO4, and evapo-
rated. The crude product was chromatographed on silica gel
using pentane/ethyl acetate 90:10. A total of 150 mg (53%
yield) of an orange polycrystalline compound, mp 233 °C, was
1
oil was obtained: MS m/e 570 (M•+); H NMR (CDCl3, TMS/
3
3
ppm) 7.31 (d, J ) 3.4 Hz, 2H), 7.25 (d, J ) 3.5 Hz, 2H), 7.13
3
3
(d, J ) 3.5 Hz, 2H), 7.06 (d, J ) 3.4 Hz, 2H), 1.55 (m, 6H),
1.34 (m, 6H), 1.10 (t, 6H), 0.92 (s, 9H), 0.87 (t, 9H), 0.30 (s,
6H); 13C NMR (CDCl3, TMS/ppm) 142.9, 142.8, 136.6, 136.2,
136.1, 135.8, 125.0, 124.5, 29.0, 27.2, 26.3, 16.9, 13.7, 10.9.
5-(n -Hexyl)-5′-(tr ibu tylsta n n yl)-2,2′-bith iop h en e, 19. A
1.82 g (7.28 mmol) portion of 2-(n-hexyl)-2,2′-bithiophene 39
was dissolved in 40 mL of anhydrous ethyl ether, and 3.20
mL (8.00 mmol) of BuLi 2.5 M in hexane was added dropwise.
After 30 min, 2.16 mL (8.00 mmol) of Bu3SnCl was added and
1
recovered: MS m/e 562 (M•+); λmax(CHCl3) 480 nm; H NMR
3
3
(CDCl3, TMS/ppm) 7.49 (d, J ) 4.0 Hz, 2H), 7.20 (d, J ) 4.0

Oligothiophene S,S-Dioxides
J . Org. Chem., Vol. 63, No. 16, 1998 5505
3
3
Hz, 2H), 6.60 (d, J ) 4.7 Hz, 2H), 6.45 (doublet of triplets, J
) 4.7 Hz, 4J ) 1.8 Hz, 2H), 2.56 (t, 4H), 1.70 (m, 4H), 1.30 (m,
12H), 0.9 (m, 6H); 13C NMR (CDCl3, TMS/ppm) 144.1, 138.3,
135.9, 129.7, 128.9, 125.9, 122.5, 118.1, 31.4, 28.8, 26.7, 24.5,
22.5, 14.0. Anal. Calcd for C28H34O4S4: C, 59.75; H, 6.09.
Found: C, 59.83; H, 7.00.
gel using pentane/ethyl acetate 90:10. A total of 110 mg (50%
yield) of an orange powder, mp 172 °C, were recovered: MS
m/e 530 (M•+); λmax(CHCl3) 448 nm; 1H NMR (CDCl3, TMS/
3
3
ppm) 7.48 (d, J ) 4.0 Hz, 1H), 7.13 (d, J ) 4.0 Hz, 1H), 7.10
3
3
3
(d, J ) 3.8 Hz, 1H), 7.00 (d, J ) 4.0 Hz, 2 H), 6.69 (d, J )
3.8 Hz, 1H), 6.55 (d, 3J ) 4.9 Hz, 1H), 6.43 (doublet of triplets,
4
5-(n -Hexyl)-5′′-(tr ibu tylsta n n yl)-2,2′:5′,2′′-ter th iop h en e,
27. A solution containing 4.0 g (0.024 mol) of commercial 2,2′-
bithiophene and 4.5 mL (0.03 mol) of TMEDA in 80 mL of THF
was cooled to -70 °C, and 9.6 mL (0.024 mol) of BuLi 2.5 M
in hexane was added. After being stirred for a few minutes,
the solution was allowed to reach room temperature and then
stirred for 3 h. Then the solution was again cooled to -70 °C,
and 8.12 mL (0.03 mol) of Bu3SnCl was added dropwise. The
solution was allowed to reach rt and stirred overnight. After
usual workup, the yellow oil obtained was distilled (170 °C, 3
× 10-3 mmHg), and 8.74 g (80% yield) of a white oil identified
as 5-(tributylstannyl)-2,2′-bithiophene (compound 41 of Scheme
3J ) 4.9 Hz, J ) 1.8 Hz, 1H), 2.78 (t, 2H), 2.52 (t, 2H), 1.65
(m, 4H), 1.30 (m, 12H), 0.9 (m, 6H); 13C NMR (CDCl3, TMS/
ppm) 146.3, 143.6, 139.5, 138.4, 136.1, 134.1, 133.8, 128.8,
128.2, 125.8, 124.9, 124.3, 123.8, 123.6, 122.5, 117.0, 31.6, 31.4,
30.2, 28.8, 28.7, 26.8, 24.5, 22.6, 22.5, 14.1, 14.0. Anal. Calcd
for C28H34O2S4: C, 63.35; H, 6.46. Found: C, 63.17; H, 6.47.
5,5′′′′-Bis(dim eth yl-ter t-bu tylsilyl)-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-
qu in qu eth iop h en e 1′′,1′′-Dioxid e, 30. To a 5 mL toluene
solution of Pd(AsPh3)4 (0.01 mmol) prepared in situ4c were
added 0.05 g (0.18 mmol) of 2,5-dibromothiophene 1,1-dioxide
151d and 0.2 g (0.36 mmol) of 5-(dimethyl-tert-butylsilyl)-5′-
(tributylstannyl)-2,2′-bithiophene 18. After being refluxed for
4 h, the reaction mixture was filtered through silica gel using
petroleum ether for the first fraction and petroleum ether/
methylene chloride for the second one. After evaporation of
the solvent from the second fraction, the residue was washed
with ethyl ether, and 63 mg (52% yield) of a brown solid, mp
233-234 °C, was obtained: MS m/e 672 (M•+); λmax(CHCl3) 512
nm; 1H NMR (CDCl3, TMS/ppm) 7.54 (d, 3J ) 3.7 Hz, 2H),
3) was recovered: 1H NMR (acetone-d6, TMS/ppm) 7.39 (q, J
3
) 5.0, 4J ) 1.1 Hz, 1H), 7.36 (d, 3J ) 3.3 Hz, 1H),7.24 (q, 3J )
3
3
3
3.6, J ) 3.3 Hz, 1H), 7.15 (d, J ) 3.3 Hz, 1H), 7.06 (q, J )
3.6, 3J ) 3.3 Hz, 1H), 1.60 (m, 6H), 1.30 (m, 6H), 1.15 (m, 6H),
0.90 (t, 9H); 13C NMR (CDCl3, TMS/ppm) 137.5, 129.0, 126.1,
125.9, 125.8, 125.4, 124.9, 124.6, 29.9, 28.0, 13.6, 11.1.
To a solution of 1.00 g (2.22 mmol) of 41 in 8 mL of toluene
was added dropwise 1.08 g (4.39 mmol) of 2 dissolved in 10
mL toluene. After the mixture was stirred for a few minutes,
0.20 g (0.17 mmol) of commercial Pd(PPh3)4 was added and
the mixture refluxed overnight. After usual workup, 0.44 g
(60%) of a yellow powder identified as 5-(n-hexyl)-2,2′:5′,2′′-
terthiophene (compound 42 of Scheme 3), mp 48 °C, was
obtained: 1H NMR (CDCl3, TMS/ppm) 7.21 (doublet of dou-
blets, 3J ) 4.9 Hz, 4J ) 1.1 Hz, 1H), 7.13 (doublet of doublets,
3
3
3
7.30 (d, J ) 3.5 Hz, 2H), 7.21 (d, J ) 3.7 Hz, 2H), 7.16 (d, J
) 3.5 Hz, 2 H), 6.72 (s, 2H), 0.95 (s, 18H), 0.34 (s, 12H); 13C
NMR (CDCl3, TMS/ppm) 141.3, 140.3, 139.2, 136.1, 135.8,
129.0, 128.6, 126.1, 125.1, 117.9, 26.3, 16.9. Anal. Calcd for
C
32H40O2S5Si2: C, 57.10; H, 5.99. Found: C, 57.22; H, 6.00.
2-(Dim et h yl-ter t-b u t ylsilyl)-5-(t r ib u t ylst a n n yl)t h io-
p h en e, 31. To 30 mL of an ethyl ether solution of 5.07 g
(0.0256 mol) of 2-(dimethyl-tert-butylsilyl)thiophene4a was
added 10.3 mL (0.0257 mol) of BuLi 2.5 M in hexane at -10
°C. After the mixture was stirred for 1 h, an ethyl ether
solution of 6.39 mL (0.0256 mol) of Bu3SnCl was added to the
solution at room temperature and the mixture stirred over-
night. After usual workup, the crude product was distilled
(185 °C, 0.1 mmHg), and 10.60 g (85% yield) of 31 as a white
3J ) 3.6 Hz, J ) 1.1 Hz, 1H), 7.02 (d, J ) 3.5 Hz, 1H), 7.00
(doublet of doublets, J ) 3.6 Hz, J ) 4.9 Hz, 1H), 7.00 (d, J
) 3.5 Hz, 1H), 6.98 (d, J ) 3.5 Hz, 1H), 6.64 (d, J ) 5.0 Hz,
1H), 2.78 (t, 2H), 1.66 (t, 2H), 1.3 (m, 6H), 0.9 (t, 3H); 13C NMR
(CDCl3, TMS/ppm) 145.6, 137.3, 136.8, 135.5, 134.4, 127.8,
124.8, 124.3, 123.5, 123.4, 31.5, 30.2, 28.7, 22.5, 14.1.
4
3
3
3
3
3
3
1
To a solution of 1.00 g (0.003 mol) of 42 in 5 mL of THF and
containing 0.54 mL (0.0036 mol) of TMEDA was added 1.2 mL
(0.003 mol) of BuLi 2.5 M in hexane and 1.0 mL (0.0036 mol)
of Bu3SnCl at -10 °C. The temperature was then allowed to
rise to ambient and the mixture stirred overnight. After
solvent evaporation, the mixture was chromatographed on
aluminum oxide using petroleum ether 30-40 °C as the eluent.
A total of 0.51 g (27% yield) of 27 as a yellow oil was obtained.
oil was recovered: MS m/e 488 (M•+); H NMR (CDCl3, TMS/
3
3
ppm) 7.42 (d, J ) 3.6 Hz, 1H), 7.30 (d, J ) 3.6 Hz, 1H), 1.58
(m, 6H), 1.36 (m, 6H), 1.12 (t, 6H), 0.98 (s, 9H), 0.30 (s, 6H);
13C NMR (CDCl3, TMS/ppm) 142.8, 142.3, 136.0, 135.8, 29.0,
27.3, 26.5, 17.0, 13.7, 10.9, -4.6.
2,2′:5′,2′′-Ter th iop h en e 1′,1′-Dioxid e, 32. To a 12 mL
toluene solution containing 0.024 mmol of Pd(AsPh3)4 prepared
in situ4c was added 0.20 g (0.73 mmol) of 2,5-dibromothiophene
1,1-dioxide 15,1d 0.54 g (1.50 mmol) of 2-(tributylstannyl)-
thiophene 5 was added dropwise, and the mixture was stirred
overnight. The solvent was evaporated, and the crude product
was chromatographed on silica gel using petroleum ether/ethyl
alcohol 80:20. A total of 0.13 g (65% yield) of orange-red poly-
crystalline powder, 155 °C, was recovered: MS m/e 280 (M•+);
The product was used as such: MS m/e 622 (M•+); H NMR
1
3
3
(C6D6, TMS/ppm) 7.30 (d, J ) 3.3 Hz, 1H), 7.08 (d, J ) 3.3
3
3
Hz, 1H), 6.96 (d, J ) 3.7 Hz, 1H), 6.92 (d, J ) 3.6 Hz, 1 H),
3
3
6.88 (d, J ) 3.7 Hz, 1H), 6.47 (d, J ) 3.6 Hz, 1 H), 2.55 (t,
2H), 1.6 (m, 8H), 1.3 (m, 8 H), 1.2 (m, 10H), 0.9 (m, 12H); 13
C
NMR (C6D6, TMS/ppm) 145.5, 143.4, 137.1, 136.7, 136.5, 136.4,
135.3, 125.4, 125.2, 124.6, 124.1, 123.8, 31.9, 30.4, 29.4, 29.0,
27.6, 22.9, 14.2, 13.8, 11.2.
λ
max(CHCl3) 428 nm; 1H NMR (CDCl3, TMS/ppm) 7.65 (doublet
of doublets, 3J ) 4.0 Hz, 4J ) 1.2 Hz, 2H), 7.44 (doublet of
3
4
3
5,5′′′-Bis(d im et h yl-ter t-b u t ylsilyl)-2,2′:5′,2′′:5′′,2′′′-q u a -
ter th iop h en e 1,1-Dioxid e, 28. To an 8 mL toluene solution
containing 0.017 mmol of Pd(AsPh3)4 prepared in situ4c were
added 0.37 g (0.569 mmol) of 8 and 0.176 g (0.569 mmol) of 3.
After being refluxed for 6 h, the reaction mixture was
hydrolyzed with a saturated solution of NH4Cl and extracted
with CH2Cl2. The organic phase was dried over MgSO4,
concentrated, and filtered through silica gel.
After evaporation of the solvent, the residue was washed
with ethyl ether, and 0.163 g (49% yield) of 281a was recovered.
5,5′′′-Bis(n -h exyl)-2,2′:5′,2′′:5′′,2′′′-qu a ter th iop h en e 1,1-
Dioxid e, 29. To a 9 mL toluene solution containing 0.012
mmol of Pd(AsPh3)4 prepared in situ4c was added 260 mg (0.
42 mmol) of 5-(n-hexyl)-5′′-(tributylstannyl)-2,2′:5′,2′′-ter-
thiophene 27, and 120 mg (0.42 mmol) of 2-(n-hexyl)-5-
bromothiophene 1,1-dioxide 4 in 9 mL of toluene was added
dropwise. The mixture was refluxed overnight, treated with
a saturated solution of NH4Cl, and washed with water, and
the organic layer was separated, dried over MgSO4, and
evaporated. The crude product was chromatographed on silica
doublets, J ) 5.0 Hz, J ) 1.2 Hz, 2H), 7.15 (q, J ) 4.0 Hz,
3J ) 5.0 Hz, 2H), 6.78 (s, 2H); 13C NMR (CDCl3, TMS/ppm)
136.2, 129.8, 128.7, 128.2, 128.0, 118.6. Anal. Calcd for
C
12H8O2S3: C, 51.40; H, 2.88. Found: C, 51.21; H, 2.87.
5,5′′-Bis(d im e t h yl-t er t -b u t ylsilyl)-2,2′:5′,2′′-t e r t h io-
p h en e 1′,1′-Dioxid e, 33. A 0.01 mmol (12 mg) portion of
Pd2dba3 and 0.05 mmol (15 mg) of AsPh3 were dissolved in 10
mL of THF, and the solution was stirred for 30 min. Then a
solution containing 0.33 g (1.2 mmol) of 2,5-dibromothiophene
1,1-dioxide 151d and 1.16 g (2.4 mmol) of 2-dimethyl(tert-
butylsilyl)-5-(tributylstannyl)thiophene 31 was added drop-
wise, and the mixture was stirred for 6 h. The solvent was
evaporated, and the crude product was chromatographed on
silica gel using petroleum ether/ethyl alcohol 80:20. From
chromatography, two fractions were isolated. The first (105
mg, 17% yield) was a brown polycrystalline product, mp 199-
203 °C, identified as trimer 33. The second (160 mg, 34% yield)
was a yellow orange powder, mp 102-103 °C, identified as
5-(dimethyl-tert-butylsilyl)-5′-bromo-2,2′-bithiophene 1′,1′-
dioxide 33′.

5506 J . Org. Chem., Vol. 63, No. 16, 1998
Barbarella et al.
1
33: MS m/e 508 (M•+); λmax(CHCl3) 440 nm; 1H NMR (CDCl3,
TMS/ppm) 7.69 (d, 3J ) 3.5 Hz, 2H), 7.25 (d, 3J ) 3.5 Hz, 2H),
6.79 (s, 2H), 0.93 (s, 18H), 0.31 (s, 12H); 13C NMR (CDCl3,
TMS/ppm) 142.1, 136.5, 135.9, 134.4, 128.6, 118.7, 26.2, 16.9.
Anal. Calcd for C24H36O2S3Si2: C, 56.64; H, 7.13. Found: C,
56.76; H, 7.10.
MS m/e 250 (M•+); H NMR (CDCl3, TMS/ppm) 7.2 (m, 2H),
7.1 (m, 2H), 6.7 (m, 1H), 2.85 (t, 2H), 1.75 (m, 2H), 1.41 (m,
6H), 1.0 (t, 3H); 13C NMR (CDCl3, TMS/ppm) 145.2, 137.9,
134.7, 127.6, 124.6, 123.6, 123.3, 122.9, 31.5, 30.1, 28.7, 22.5,
14.1. Anal. Calcd for C14H18S2: C, 67.15; H, 7.25. Found: C,
67.38; H, 7.23.
33′: MS m/e 390 (M•+); λmax(CHCl3) 394 nm; 1H NMR
5,5′′′-Bis(n -h exyl)-2,2′:5′,2′′:5′′,2′′′-qu a ter th iop h en e, 40.
A 0.37 g (0.0015 mol) portion of 39 dissolved in 10 mL of
anhydrous THF was added dropwise to a solution of 0.68 mL
(0.0017 mol) of BuLi 2.5 M in hexane. The mixture was stirred
for 1 h at room temperature, then 1.0 g (0.003 mol) of Fe(acac)3
was added stepwise and the mixture stirred overnight. Sub-
sequently, 20 mL of distilled water was added followed by 100
mL of HCl 3 M. After usual workup, the crude product was
chromatographed on silica gel using hexane/ethyl acetate 70:
30. A total of 0.22 g (60% yield) of 40 as an orange polycrys-
3
3
(CDCl3, TMS/ppm) 7.67 (d, J ) 3.5 Hz, 1H), 7.23 (d, J ) 3.5
3
3
Hz, 1H), 6.91 (d, J ) 5.0 Hz, 1H), 6.68 (d, J ) 5.0 Hz, 1H),
0.92 (s, 9H), 0.31 (s, 6H); 13C NMR (CDCl3, TMS/ppm) 143.0,
137.4, 136.5, 134.2, 129.7, 128.4, 118.6, 117.6, 26.2, 16.9. Anal.
Calcd for C14H19BrO2S2Si: C, 42.96; H, 4.89. Found: C, 42.74;
H, 4.91.
5,5′′-Bis(n -h exyl)-2,2′:5′,2′′-ter th iop h en e, 35. To a solu-
tion containing 0.5 g (0.002 mol) of 2,2′:5′,2′′-terthiophene 34
dissolved in 30 mL of anhydrous THF was added dropwise 1.72
mL (0.0043 mol) of BuLi 2.5 M in hexane. The solution was
stirred for about 1 h, and then 0.74 g (0.0045 mol) of n-hexyl
bromide was added dropwise and the solution stirred at room
temperature overnight. After the usual workup, 0.50 g (60%
yield) of yellow crystals, mp 79 °C, was obtained: MS m/e 416
talline compound, mp 166 °C, was obtained: MS m/e 498 (M•+);
1
λ
max(CHCl3) 400 nm; H NMR (CDCl3, TMS/ppm) 7.03 (d, 3J
3
3
) 4.0 Hz, 2H), 6.99 (d, J ) 4.0 Hz, 2H), 6.98 (d, J ) 3.5 Hz,
3
4
2H), 6.68 (doublet of triplets, J ) 3.5 Hz, J ) 0.8 Hz, 2H),
2.78 (t, 4H), 1.65 (m, 4H), 1.28 (m, 12H), 0.88 (m, 6H); 13C
NMR (CDCl3, TMS/ppm) 145.7, 136.8, 135.4, 134.5, 124.9,
124.1, 123.6, 123.4, 31.6, 30.3, 28.8, 22.6, 14.1. Anal. Calcd
for C28H34S4: C, 67.42; H, 6.87. Found: C, 67.61; H, 6.89.
1
(M•+); λmax(CHCl3) 380 nm; H NMR (CDCl3, TMS/ppm) 6.97
3
3
(s, 2H), 6.96 (d, J ) 3.5 Hz, 2H), 6.67 (doublet of triplets, J
4
) 3.5 Hz, J ) 1.0 Hz, 2H), 2.75 (t, 4H), 1.65 (t, 4H), 1.3 (m,
12H), 0.85 (t, 6H); 13C NMR (CDCl3, TMS/ppm) 146.0, 136.8,
135.3, 125.4, 124.1, 123.8, 32.2, 30.8, 29.4, 23.2, 14.7. Anal.
Calcd for C24H32S3: C, 69.18; H, 7.74. Found: C, 69.23; H, 7.75.
5,5′-Bis(n -h exyl)-2,2′-bith iop h en e, 37. To a solution
containing 2.00 g (0.012 mol) of 2-n-hexylthiophene 36 dis-
solved in 75 mL of anhydrous THF was added 6.4 mL (0.016
mol) of 2.5 M BuLi in hexane dropwise at -60 °C. The solution
was stirred for about 2 h while the temperature was allowed
to increase to 0 °C. The temperature was again decreased to
-60 °C, and 8.5 g (0.024 mol) of solid Fe(acac)3 was added
stepwise. The solution was stirred at -60 °C for 2 h, and then
the temperature was allowed to increase to room temperature
overnight. The reaction mixture was first washed with a 5%
HCl solution and then with a solution of 10% KOH and finally
with distilled water. The organic phase was separated, dried
with MgSO4, and evaporated. A red oil was obtained that was
redissolved in hot methanol. A total of 1.4 g (70% yield) of 37
2,5-Bis(n -h exyl)th iop h en e, 43. To a solution containing
1.0 g (0.006 mol) of 2-n-hexylthiophene 36 dissolved in 40 mL
of anhydrous THF was added dropwise 3.2 mL (0.008 mol) of
2.5 M BuLi in hexane at -10 °C. The solution was stirred for
about 2 h while the temperature was allowed to increase to 0
°C. Then the temperature was decreased again to -10 °C,
and 1 mL (0.006 mol) of n-hexyl bromide dissolved in 5 mL of
THF was added dropwise. After 1 night at room temperature,
50 mL of distilled water was added, and the organic phase
was separated, dried over Na2SO4, and evaporated. A yellow
oil was obtained that was chromatographed on silica gel using
petroleum ether as the eluent. A total of 1.21 g (80% yield) of
43 as a white oil was obtained: MS m/e 252 (M•+); λmax(CHCl3)
254 nm; 1H NMR (CDCl3, TMS/ppm) 6.56 (s, 2H), 2.75 (t, 4H),
1.65 (m, 4H), 1.32 (m, 12H), 0.89 (t, 6H); 13C NMR (CDCl3,
TMS/ppm) 143.3, 123.3, 31.7, 31.6, 30.2, 28.9, 22.6, 14.1. Anal.
Calcd for C16H28S: C, 76.12; H, 11.18. Found: C, 76.22; H,
11.16.
as white crystals, mp 34 °C, was separated: MS m/e 334 (M•+);
1
λ
max(CHCl3) 338 nm; H NMR (CDCl3, TMS/ppm) 6.89 (d, 3J
3
4
) 3.5 Hz, 2H), 6.64 (doublet of triplets, J ) 3.5 Hz, J ) 0.8
Hz, 2H), 2.75 (triplets of doublets, J ) 0.8 Hz, 4H), 1.65 (m,
2,5-Bis(n -h exyl)th iop h en e 1,1-Dioxid e, 44. A 0.5 g
(0.002 mol) portion of 43 was dissolved in 3 mL of methylene
chloride, and 1.23 g (0.005 mol) of solid m-MCPA 70% was
added stepwise. The mixture was stirred for 2 days and
filtered and washed first with 10% NaHCO3 and then with
distilled water, and the organic layer was separated, dried with
Na2SO4, and evaporated. The white oil obtained in this way
was chromatographed on silica gel using pentane/ethyl acetate
90:10. A total of 0.4 g (70% yield) of 44 as a white crystalline
4
4H), 1.32 (m, 12H), 0.90 (m, 6H); 13C NMR (CDCl3, TMS/ppm)
144.8, 135.4, 124.6, 122.7, 31.6, 30.2, 28.8, 22.6, 14.1. Anal.
Calcd for C20H30S2: C, 71.80; H, 9.04. Found: C, 71.87; H, 9.03.
5,5′-Bis(n -h exyl)-2,2′-bith iop h en e 1,1-Dioxid e, 38. A 0.5
g (1.50 mmol) portion of 37 was dissolved in 5 mL of freshly
distilled methylene chloride, and 0.93 g (3.74 mmol) of solid
m-CPBA 70% was added stepwise. The solution was stirred
for 3 h, filtered, and washed first with a 10% solution of
NaHCO3 and then with distilled water, the organic layer was
separated, dried with Na2SO4, and evaporated, and the crude
product was chromatographed on silica gel using pentane/ethyl
acetate 93:7. A total of 55 mg (10% yield) of 38 as a pale yellow
solid, mp 45 °C, was obtained: MS m/e 366 (M•+); λmax(CHCl3)
402 nm; 1H NMR (CDCl3, TMS/ppm) 7.39 (d, 3J ) 3.7 Hz, 1H),
6.77 (d, 3J ) 3.7 Hz, 1H), 6.47 (d, 3J ) 4.9 Hz, 1H), 6.40
material, mp 41 °C, was obtained: MS m/e 284 (M•+); λmax
-
(CHCl3) 298 nm; 1H NMR (CDCl3, TMS/ppm) 6.25 (s, 2H), 2.46
(t, 4H), 1.62 (m, 4H), 1.30 (m, 12H), 0.89 (t, 6H); 13C NMR
(CDCl3, TMS/ppm) 144.0, 121.6, 31.4, 28.7, 26.5, 24.3, 22.5,
14.0. Anal. Calcd for C16H28O2S: C, 67.56; H, 9.92. Found:
C, 67.63; H, 9.91.
Ack n ow led gm en t. This research was supported by
the NATO Guest Fellowship Program 199.
3
4
(doublet of triplets, J ) 4.9 Hz, J ) 1.9 Hz, 1H),2.80 (t, 2H),
4
2.50 (triplet of doublets, J ) 1.9 Hz, 2H), 1.65 (m, 4H), 1.35
(m, 12H), 0.90 (m, 6H); 13C NMR (CDCl3, TMS/ppm) 149.4,
143.0, 136.7, 128.0, 127.4, 125.7, 122.6, 116.2, 31.4, 31.3, 30.2,
28.7, 28.6, 26.7, 24.3, 22.8, 14.0. Anal. Calcd for C20H30O2S2:
C, 65.53; H, 8.25. Found: C, 65.69; H, 8.24.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement, final fractional coordinates and
equivalent isotropic thermal parameters, anisotropic displace-
ment parameters, bond distances and angles, torsion angles,
selected least-squares planes, and shortest nonbonded dis-
tances. Fully optimized geometries and energies of 2,2′-
bithiophene and of the corresponding mono- and bis-S,S-
dioxides (8 pages). This material is contained in libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
5-(n -Hexyl)-2,2′-bith iop h en e, 39. A 2.11 g (12.5 mmol)
portion of 2,2′-bithiophene was dissolved in 25 mL of anhy-
drous THF, and the mixture was cooled to -50 °C. A 5 mL
(12.5 mmol) portion of BuLi 2.5 M in hexane was added
dropwise followed by 1.76 mL (12.5 mmol) of n-hexyl bromide.
The mixture was then stirred for 30 min at room temperature.
After the usual workup, the crude product was chromato-
graphed on silica gel RP 18 using CH3OH/CH2Cl2 9:1. A total
of 1.96 g (63% yield) of 39 as a yellow-green oil was recovered:
J O980507G