Novel synthesis of protected thiol end-capped stilbenes and oligo(phenylenevinylene)s (OPVs)

Article abstract of DOI:10.1021/jo0263770

The first general procedures for preparation of thiol end-capped stilbenes and oligo(phenylenevinylene)s (OPVs) with tert-butyl- and acetyl-protected thiol termini have been developed. These reactions proceed via Br/Li exchange, McMurry, and Wittig-type reactions. The thiol functionality is protected against strong basic and acidic reaction conditions as a t-Bu sulfide. As a key point in the method, reprotection of the thiol group is accomplished by means of acetyl chloride and boron tribromide. The novel strategy forms the basis for stepwise introduction of 4-mercaptostyryl units in OPVs. The new mono-, di-, and trimercapto OPVs have potential applications as one, two, and three terminal molecular devices in gold nanoparticle clusters, self-assembled monolayers, and optoelectronic devices.

Full text of DOI:10.1021/jo0263770

Novel Syn th esis of P r otected Th iol En d -Ca p p ed Stilben es a n d
Oligo(p h en ylen evin ylen e)s (OP Vs)
Nicolai Stuhr-Hansen, J ørn B. Christensen, Niels Harrit, and Thomas Bjørnholm*
Nano-Science Center, Department of Chemistry, University of Copenhagen, Universitetsparken 5,
DK-2100 Copenhagen, Denmark
tb@nano.ku.dk
Received August 31, 2002
The first general procedures for preparation of thiol end-capped stilbenes and oligo(phenylene-
vinylene)s (OPVs) with tert-butyl- and acetyl-protected thiol termini have been developed. These
reactions proceed via Br/Li exchange, McMurry, and Wittig-type reactions. The thiol functionality
is protected against strong basic and acidic reaction conditions as a t-Bu sulfide. As a key point in
the method, reprotection of the thiol group is accomplished by means of acetyl chloride and boron
tribromide. The novel strategy forms the basis for stepwise introduction of 4-mercaptostyryl units
in OPVs. The new mono-, di-, and trimercapto OPVs have potential applications as one, two, and
three terminal molecular devices in gold nanoparticle clusters, self-assembled monolayers, and
optoelectronic devices.
In tr od u ction
Repeating phenylenevinylene units have not been
investigated in this respect until the recently reported
work by Dudek et al.,13 who prepared asymmetric OPVs
with ferrocene on one end and methyl thiol on the other
end, making them capable of self-assembly on gold
electrodes. However, common to the synthetic procedures
applied there and reported syntheses of other thiol-
terminated systems (such as oligo(1,4-phenylene ethyn-
ylene)s5,6,14-16 and oligo(2,5-thiophene ethynylene)s17) is
the introduction of the protected thiol groups at the very
end of the synthetic sequence.
The present work adopts a different approach. In this
case aryl thiol functionality is introduced as the t-Bu
sulfide at the beginning of the synthetic sequences and
maintained through the following steps owing to the
resistance of t-Bu-S-Ar to both strongly basic and acidic
conditions. In order for this principle to be useful, the
strong protection group must be converted into a more
reactive functionality, which is easily removable in situ
prior to, e.g., self-assembly experiments, while still
protecting the conjugated thiol against oxidation by air.
The Ac group meets these two demands. Thus, as a final
step the t-BuS group is converted into the AcS moiety
by means of AcCl/BBr3 following our recently described
method.18
Much current research is devoted to the study of charge
transport through organic materials.1 These efforts are
inspired by phenomena and applications such as elec-
troluminescence and light-emitting diodes (LEDs).2,3
Conductivity measurements on individual molecules
require an electronic coupling between the “molecular
wire” and the metal electrodes. This can be accomplished
through terminal thiol groups that have high affinity to
gold.4 Thus, dithiol functionalized oligo(phenylene-
ethynylenes)5-8 and terthiophene9 have been mounted as
wires between gold electrodes. Related investigations
have been performed on thiol-terminated oligo(phen-
yleneethynylenes)10 and oligothiophenes.11,12
(1) Mu¨llen, K.; Wegner, G. Electronic Materials: The Oligomer
Approach; Wiley-VCH: Weinheim, 1998.
(2) Burroughes, J . H.; Bradley, D. D. C.; Brown, A. R.; Marks, R.
N.; Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Nature
(London) 1990, 347, 539.
(3) Friend, R. H.; Greenham, N. C. In Handbook of Conducting
Polymers, 2nd ed.; Skotheim, T. A., Elsenbaumer, R. L., Reynolds, J .
R., Eds.; Marcel Dekker: New York, 1998; p 823.
(4) Yaliraki, S. N.; Kemp, M.; Ratner, M. A. J . Am. Chem. Soc. 1999,
121, 3428.
(5) Novak, J . P.; Brousseau, I. L. C.; Vance, F. W.; J ohnson, R. C.;
Lemon, B. I.; Hupp, J . T.; Feldheim, D. L. J . Am. Chem. Soc. 2000,
122, 12029.
With this protection strategy, we have applied several
classic synthetic methods as means for obtaining the OPV
(6) Tour, J . M.; J ones, I. L.; Pearson, D. L.; Lamba, J . J . S.; Burgin,
T. P.; Whitesides, G. M.; Allara, D. L.; Parikh, A. N.; Atre, S. V. J .
Am. Chem. Soc. 1995, 117, 9529.
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Lam, E.; Chong, Y.; Olsen, G. T.; Luo, J .; Gozin, M.; Kayyem, J . F. J .
Am. Chem. Soc. 1999, 121, 1059.
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Dirk, S. M.; Price, D. W.; Reed, M. A.; Zhou, C. W.; Chen, J .; Wang,
W.; Campbell, I. Chem.sEur. J . 2001, 7, 5118.
(12) Purcell, S. T.; Garcia, N.; Binh, V. T.; J ones, L., II; Tour, J . M.
J . Am. Chem. Soc. 1994, 116, 11985.
(13) Dudek, S. P.; Sikes, H. D.; Chidsey, C. E. D. J . Am. Chem. Soc.
2001, 123, 8033.
(14) Fan, F.-R. F.; Yang, Y.; Dirk, S. M.; Price, D. W.; Kosynkin, D.;
Tour, J . M.; Bard, A. J . J . Am. Chem. Soc. 2001, 123, 2454.
(15) J ones, L., II; Schumm, J . S.; Tour, J . M. J . Org. Chem. 1997,
62, 1388.
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10, 8.
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P.; Sita, L. R. J . Am. Chem. Soc. 1996, 118, 3319.
(11) Hicks, R. G.; Nodwell, M. B. J . Am. Chem. Soc. 2000, 122, 6746.
(16) Novak, J . P.; Feldheim, D. L. J . Am. Chem. Soc. 2000, 122, 3979.
(17) Pearson, D. L.; Tour, J . M. J . Org. Chem. 1997, 62, 1376.
(18) Stuhr-Hansen, N. Synth. Commun. 2002, in press.
10.1021/jo0263770 CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/09/2003
J . Org. Chem. 2003, 68, 1275-1282
1275

Stuhr-Hansen et al.
CHART 1
SCHEME 1
carbon structures. Among them, Wittig19-24 and Horner-
Wadsworth-Emmons (HWE)25-28 reactions are well de-
scribed as efficient routes to OPVs and substituted
stilbenes. Usually, various amounts of cis-stilbenes are
produced,29 but all-trans conversion can be accomplished
as part of the recrystallization procedure. Although t-Bu
sulfides proved to be perfectly resistant to the strong
basic reaction conditions involved in these standard
methods, the thioester group would have been cleaved.
The presence of free thiols also would not have been
possible, since they react with aldehydes leading to
polymeric material.30
Other methods that are used successfully in this work
include McMurry24 and Knoevenagel31,32 reaction proce-
dures. Again, thioesters would have been absolutely
intolerable, whereas these methods proved fully compat-
ible with t-Bu sulfide protection.
SCHEME 2
served as the essential precursor for a number of 4-mer-
capto end-capped OPVs. It was prepared from com-
mercially available 4-bromothiophenol (1), which was
reacted with 2-chloro-2-methylpropane in the presence
of a catalytic amount of aluminum chloride. The resulting
4-bromophenyl tert-butyl sulfide34 (2) was lithiated using
BuLi and subsequently treated with DMF to give 3 in
high yield.
Protected thiol end-capped stilbenes can be obtained
from aldehyde 3 by conventional Wittig reactions.35,36
Thus, addition of t-BuOK to a slurry of 3 and benzyl-
triphenylphosphonium bromide (Scheme 2) produced
trans-4-(tert-butylthio)stilbene (4), which was easily con-
verted into trans-(S-acetyl)-4-stilbenethiol (5) by means
of AcCl/BBr3 following the recently described procedure.18
In principle, an asymmetrical alkene can be prepared
by two routes following the so-called umpolung strategy
as illustrated in Scheme 3. Aldehyde 3 was reduced with
NaBH4 to afford 4-(tert-butylthio)benzyl alcohol (6) in
excellent yield. This was cleanly converted into 4-(tert-
butylthio)benzyl bromide (7) using PBr3. Importantly,
there was no acid-induced t-Bu/S bond cleavage observed
during the benzyl bromide synthesis. Compound 7 was
converted into two p-mercaptostyryl end-block synthetic
equivalents, that is, (i) 4-(tert-butylthio)benzyl cyanide
(8) by reaction with sodium cyanide, and (ii) diethyl
4-(tert-butylthio)benzylphosphonate (9) via an Arbuzov
reaction with triethyl phosphite (Scheme 3).
1-Pyrenecarboxaldehyde and 4-stilbenecarboxaldehyde
were used as model systems for generation of 4-(tert-
butylthio)styryl compounds by HWE reaction with 9 upon
t-BuOK treatment. The reaction was quenched with
water, and the raw product was isolated by filtration.
Following all-trans conversion (iodine in boiling toluene),
(E)-1-[4-(tert-butylthio)styryl]pyrene (10) and (E,E)-4-[4-
(tert-butylthio)styryl]stilbene (11), respectively, were ob-
tained.
The new compounds presented in this work are rep-
resented by the three general structures shown in Chart
1.
Resu lts a n d Discu ssion
ter t-Bu tylth io- a n d Acetylth io-Su bstitu ted Stil-
ben es. 4-(tert-Butylthio)benzaldehyde18,33 (3, Scheme 1)
(19) Campbell, T. W.; McDonald, R. N. J . Org. Chem. 1959, 24, 1246.
(20) Drehfahl, G.; Ku¨hmstedt, R.; Oswald, H.; Ho¨rhold, H.-H.
Makromol. Chem. 1970, 131, 89.
(21) Gill, R. E.; Meetsma, A.; Hadziioannou, G. Adv. Mater. (Wein-
heim, Ger.) 1996, 8, 212.
(22) Kossmehl, G.; Ha¨rtel, M.; Manecke, G. Makromol. Chem. 1970,
37.
(23) Rumi, M.; Ehrlich, J . E.; Heikal, A. A.; Perry, J . W.; Barlow,
S.; Hu, Z.; McCord-Maughon, D.; Parker, T. C.; Ro¨ckel, H.; Th-
ayumanavan, S.; Marder, S. R.; Beljonne, D.; Bre´das, J .-L. J . Am.
Chem. Soc. 2000, 122, 9500.
(24) Schenk, R.; Gregorius, H.; Meerholz, K.; Heinze, J .; Mu¨llen, K.
J . Am. Chem. Soc. 1991, 113, 2634.
(25) Cho, B. R.; Chajara, K.; Oh, H. J .; Son, K. H.; J eon, S.-J . Org.
Lett. 2002, 4, 1703.
(26) Diez-Barra, E.; Garcia-Martinez, J . C.; Rodriguez-Lopes, J .
Tetrahedron Lett. 1999, 40, 8181.
(27) Diez-Barra, E.; Garcia-Martinez, J . C.; Merino, S.; del Rey, R.;
Rodriguez-Lopez, J .; Sanchez-Verdu, P.; Tejeda, J . J . Org. Chem. 2001,
66, 5664.
(28) Segura, J . L.; Gomez, R.; Martin, N.; Guldi, D. M. Org. Lett.
2001, 3, 2645.
(29) Vedejs, E.; Fleck, T. J . J . Am. Chem. Soc. 1989, 111, 5861.
(30) Friedla¨nder, P.; Lenk, E. Chem. Ber. 1912, 45, 2083.
(31) Detert, H.; Sugiono, E. J . Phys. Org. Chem. 2000, 13, 587.
(32) Stalmach, U.; Detert, H. J . Prakt. Chem. 2000, 342, 10.
(33) Dickman, D. A.; Chemburkar, S.; Konopacki, D. B.; Elisseou,
E. M. Synthesis 1993, 573.
(34) Adams, R.; Ferretti, A. J . Am. Chem. Soc. 1959, 81, 4927.
(35) Ludley, F.; Breitmaier, E. Synthesis 1994, 949.
(36) Manecke, G.; Lu¨ttke, S. Chem. Ber. 1970, 103, 700.
1276 J . Org. Chem., Vol. 68, No. 4, 2003

Thiol End-Capped Stilbenes and OPVs
SCHEME 3
SCHEME 4
The reaction of 10 with AcCl/BBr3 did not afford 2-[4-
(acetylthio)styryl]pyrene, because monoacetylation of the
pyrene ring system occurred simultaneously, resulting
in isolation of 1-[4-(acetylthio)styryl]-3-acetylpyrene. Ob-
viously, the reactivity of the pyrene system illustrates a
limitation in the reprotection procedure. In contrast, none
of the OPVs obtained in this work were acetylated on
carbon by the Ac+ formed from the AcCl/BBr3 reagent
couple. Low solubility was another obstacle met in
reprotection reactions. For example, t-BuS-OPV 11 was
never completely converted according to TLC, even
though dilution and elongated reaction time gave higher
degrees of reactant consumption. However, (E,E)-4-[4-
(acetylthio)styryl]stilbene (12) was purified by means of
liquid chromatography.
(Z)-2,3-bis[4-(tert-butylthio)phenyl]acrylonitrile (13) was
isolated. Unfortunately, the corresponding bis-AcS com-
pound, 2,3-bis[4-acetylthio)phenyl]acrylonitrile, could not
be obtained in satisfactory purity. The cyano stilbene
tended to decompose during attempted reprotection with
AcCl/BBr3.
ter t-Bu tylth io- a n d Acetylth io-Su bstitu ted Lon g
Ch a in OP Vs. t-BuS end-capped 1,4-distyrylbenzene can
be obtained in a reaction between 3 and the difunctional
HWE reagent tetraethyl 1,4-xylylenediphosphonate (14)
when treated with t-BuOK in THF (Scheme 4). Pure
(E,E)-1,4-bis[4-(tert-butylthio)styryl]benzene (15) was iso-
lated in good yield after isomerization (iodine in toluene)
into the all-trans OPV isomer. During conversion of 15
into (E,E)-1,4-bis[4-(acetylthio)styryl]benzene (16) high
dilution and extended reaction times were required to
avoid precipitation of unreacted starting material.
Among other applications, OPVs with electron-donat-
ing end-groups and an electron-accepting middle section
are interesting for their nonlinear optical properties.37
To prepare such a model system with sulfide end groups,
a Knoevenagel reaction was carried out between 8 and 3
in the presence of t-BuOK (Scheme 3). After acidification,
Stepwise elongation of an OPV chain with one styryl
unit can be accomplished with the new reagent diethyl
4-(1,3-dioxolan-2-yl)benzylphosphonate (17) (Scheme 4).
Thus, alkene formation occurred smoothly by treatment
of aldehyde 3 with 17 and t-BuOK. This reaction is
generally applicable, efficient, and convenient, since the
phosphorus products formed are water-soluble in contrast
to earlier methods. Upon acetal cleavage with water/p-
(37) Albota, M.; Beljonne, D.; Bredas, J . L.; Ehrlich, J . E.; Fu, J . Y.;
Heikal, A. A.; Hess, S. E.; Kogej, T.; Levin, M. D.; Marder, S. R.;
McCord-Maughon, D.; Perry, J . W.; Rockel, H.; Rumi, M.; Subrama-
niam, G.; Webb, W. W.; Wu, X. L.; Xu, C. Science (Washington, D.C.)
1998, 281, 1653.
J . Org. Chem, Vol. 68, No. 4, 2003 1277

Stuhr-Hansen et al.
SCHEME 5
toluenesulfonic acid followed by reflux in toluene in the
presence of a catalytic amount of iodine, (E)-4-(tert-
butylthio)styrylbenzaldehyde (18) was isolated in high
yield. Importantly, the tert-butylthio group survived the
acidic acetal cleavage conditions, and the yield of purified
18 remained comparable to the raw yield of the acetal-
protected precursor.
ylbenzene (23), which was easily converted into the
corresponding bis-phosphonium salt [1,4-didodecyl-2,5-
bis(triphenylphosphoniomethyl)benzene] dibromide (24)
by reaction with triphenylphosphine. A classical Wittig
reaction between the bis-ylide of 24 and 18 gave the
soluble (E,E)-1,4-bis[4-{(E)-4-(tert-butylthio)styryl}styryl]-
2,5-didodecylbenzene (25) (Scheme 5). The high solubility
of 25 in organic solvents facilitated t-Bu/Ac exchange and
isolation of (E,E)-1,4-bis[4-{(E)-4-(acetylthio)styryl}styryl]-
2,5-didodecylbenzene (26).
ter t-Bu tylth io- a n d Acetylth io-Su bstitu ted 1,3,5-
Tr istyr ylben zen es. Three-terminal molecular systems
have potential applications as the central building block
in gold particle trimers.16 To obtain thiol end-capped
1,3,5-tristyrylbenzenes,26-28,41 3 was reacted with [1,3,5-
tris(triphenylphosphoniomethyl)benzene] tribromide42 (27)
(Scheme 6) upon treatment with t-BuOK forming (E,E,E)-
1,3,5-tris[(4-(tert-butylthio)styryl]benzene (28), which was
easily purified by simple means. Upon t-Bu/Ac exchange
using AcCl/BBr3, (E,E,E)-1,3,5-tris[(4-(acetylthio)styryl]-
benzene (29) was isolated in high purity. The 1,3,5-
substitution pattern made this molecular system much
more soluble than the linearly unsubstituted 1,4-OPVs.
Thus, further elongation was performed without encoun-
tering serious solubility problems. The 4-formylstilbenyl
elongated aldehyde 18 reacted with tris-ylide 27, and the
second-generation molecule (E,E,E)-1,3,5-tris[4-{(E)-4-
(tert-butylthio)styryl}styryl]benzene (30) was isolated,
being the first 1,3,5-tris(4-stilbenylvinyl)benzene re-
ported. However, it has not yet been possible to isolate
the corresponding tris-AcS compound (E,E,E)-1,3,5-tris-
[4-{(E)-4-(acetylthio)styryl}styryl]benzene.
Proceeding from compound 18, a McMurry18 coupling
was undertaken (Scheme 4). The reaction occurred
smoothly, but purification was hampered by the insolu-
bility generally met among long unbranched OPVs.38
However, Soxhlet extraction provided (E,E,E)-4,4′-bis[4-
(tert-butylthio)styryl]stilbene (19) in sufficient purity.
One additional styryl unit could be introduced in a typical
HWE-reaction between 18 and 14. Water quenching and
filtration provided the raw (cis/trans) product in good
yield. This was completely insoluble in common solvents
but (E,E)-1,4-bis[4-{(E)-4-(tert-butylthio)styryl}styryl]-
benzene (20) was obtained in 41% yield after Soxhlet
extraction (chlorobenzene/I2). Compounds 19 and 20
could not be converted into the corresponding bis-AcS
compounds because of solubility problems.
Alk yl-Su bstitu ted OP Vs. To obtain soluble OPV
dithiols, a synthetic procedure was developed for prepa-
ration of the alkyl-substituted OPV (E,E)-1,4-bis[4-{(E)-
4-(acetylthio)styryl}styryl]-2,5-didodecylbenzene (26)
(Scheme 5). 1,4-Dibromo-2,5-bis(methoxymethyl)ben-
zene39 (21) reacted with 4 equiv of t-BuLi in TMEDA/
THF during warm-up from dry ice to room temperature.
1,4-Bis(methoxymethyl)-2,5-dilithiobenzene was formed
as a white precipitate, which remained stable at room
temperature under argon for several hours. No sign of
polymerization was observed, nor during preparation and
handling of the unsubstituted 1,4-dilithiobenzene in
model experiments, in contrast to observations reported
in the literature.40 In a substitution reaction with 1-io-
dododecane, 1,4-bis(methoxymethyl)-2,5-didodecylben-
zene (22) was smoothly isolated. Since the reactivity of
dilithiobenzenes has only been sparsely investigated,40
this procedure for attachment of two alkyl chains to one
benzene ring is a new method of broad scope.
Ch a r a cter iza tion of OP Vs. All 1H NMR spectra
obtained (and displayed in Supporting Information) of
the final recrystallization products 4, 5, 10, 11, 15, 16,
18, 25, 26, 28, 29, and 30 are consistent with the all-
trans stereoisomers21 as the only species present. An
X-ray crystal structure43 obtained of 29 shows that all
four benzene rings are coplanar, while the acetyl groups
are twisted out of plane. Because of solubility problems,
1H NMR spectra could not be obtained from compounds
12, 19, and 20. However, by analogy, these oligomers are
believed to exist in all-trans configuration too.21 13C NMR
Treatment of 22 with BBr3 established the benzylic
bromide functions in 1,4-bis(bromomethyl)-2,5-didodec-
(38) van Hutten, P. F.; Wildeman, J .; Meetsma, A.; Hadziioannou,
G. J . Am. Chem. Soc. 1999, 121, 5910.
(39) Bedard, T. C.; Moore, J . S. J . Am. Chem. Soc. 1995, 117, 10662.
(40) Stephens, E. B.; Kinsey, K. E.; Davis, J . F.; Tour, J . M.
Macromolecules 1993, 26, 3519.
(41) Meier, H.; Zertani, R.; Noller, K.; Oelkrug, D.; Krabichler, G.
Chem. Ber. 1986, 119, 1716.
(42) Storck, W.; Manecke, G. Makromol. Chem. 1975, 176, 97.
(43) Larsen, K.; Magnussen, M.; Nielsen, S. F.; Soerensen, H. O.;
Stuhr-Hansen, N. Unpublished work.
1278 J . Org. Chem., Vol. 68, No. 4, 2003

Thiol End-Capped Stilbenes and OPVs
SCHEME 6
(4.60 g, 17 mmol) in a dropwise fashion during a 10 min period.
The reaction mixture was stirred at room temperature for 1 h
and then poured into ice (100 g). The layers were separated,
and the aqueous phase was further extracted with Et2O (2 ×
25 mL). The organic layer was washed with water (10 mL),
dried over anhydrous MgSO4, and filtered. Removal of solvent
in vacuo gave a white crystalline material, which upon
recrystallization from heptane afforded the benzyl bromide 7
(3.02 g, 78%) as white needles. Mp: 59-60 °C. Anal. Calcd
for C11H15BrS: C, 50.97; H, 5.83; S, 12.37. Found: C, 51.39;
spectra from all soluble compounds are reproduced in
Supporting Information. The individual absorptions are
not listed and assigned in the Experimental Section
because of the complexity of the spectra.
Many of the stilbenes and OPVs prepared in the course
of this work display intense fluorescence. Together with
absorption data, their maximum emission wavelengths
are reported in the Experimental Section.
1
H, 5.81; S, 12.40. H NMR (250 MHz, CDCl3): δ 1.29 (s, 9H),
Con clu sion s
4.49 (s, 2H), 7.35 (d, J ) 8.2 Hz, 2H), 7.50 (d, J ) 8.2 Hz, 2H).
GC-MS: EI (m/z, relative intensity) 260 (M+, 3), 204 (11), 179
(7), 123 (100).
Implementation of t-Bu as protecting group for the
thiol functionality allows synthetic procedures to be
carried out under extremely basic and acidic conditions.
In combination with classical methods such as Horner-
Wadsworth-Emmons reactions and McMurry couplings,
a range of new t-BuS-substituted stilbenes and OPVs
have been prepared. The combination of an umpolung
strategy and building-block principles allows for selection
of the best synthetic route to a specific OPV in consid-
eration of available starting materials.
Usually, the t-Bu group is converted into the versatile
AcS group by means of AcCl/BBr3. Introductions of long
alkyl substituents circumvent the solubility problems
usually encountered among long unbranched OPV chains
and render these new compounds promising candidates
for elements in future nanocircuits and supramolecular
systems. Investigations of their electrical and optical
properties are in progress.
4-(ter t-Bu tylth io)ben zyl Cya n id e (8). 4-(tert-Butylthio)-
benzyl bromide (7) (1.30 g, 5 mmol) was added to a slurry of
sodium cyanide (1.30 g, 5.5 mmol) in 1-methyl-2-pyrrolidinone
(10 mL). The reaction mixture was stirred at room temperature
for 12 h and then poured into sodium carbonate (10% aq, 50
mL) and extracted with Et2O (3 × 15 mL). The combined
etheral phases were washed with water and filtered through
basic alumina (10 g) by means of Et2O. Removal of solvent in
vacuo gave the benzyl cyanide as a crystalline material, which
upon recrystallization from heptane gave 8 (0.85 g, 83%) as
white needles. Mp: 68-69 °C. Anal. Calcd for C12H15NS: C,
70.20; H, 7.36; N, 6.82; S, 15.61. Found: C, 70.40; H, 7.52; N,
6.82; S, 15.62. 1H NMR (250 MHz, CDCl3): δ 1.26 (s, 9H), 3.74
(s, 2H), 7.28 (d, J ) 7.9 Hz, 2H), 7.52 (d, J ) 7.9 Hz, 2H).
GC-MS: EI (m/z, relative intensity) 205 (M+, 12), 190 (3), 149
(100).
Dieth yl 4-(ter t-Bu tylth io)ben zylp h osp h on a te (9). A
solution of 4-(tert-butylthio)benzyl bromide (7) (5.18 g, 20
mmol) and triethyl phosphite (4.15 g, 25 mmol) in dioxane (30
mL) was refluxed under nitrogen for 12 h. The solvent was
evaporated in vacuo, and bulb-to-bulb distillation (100 Pa, air
bath 130 °C) gave the 4-mercaptostyryl precursor 9 (5.38 g,
85%) as a colorless liquid. Anal. Calcd for C15H25O3PS: C,
Exp er im en ta l Section
4-(ter t-Bu tylth io)ben zyl a lcoh ol (6). To a mixture of
4-(tert-butylthio)benzaldehyde (3)18,33 (5.83 g, 30 mmol) and
EtOH (80 mL) cooled in an ice bath was added NaBH4 (1.25
g, 33 mmol) in small portions during a 10 min period. The
reaction mixture was stirred at room temperature for 1 h and
then poured into ice (150 g) containing hydrochloric acid (4
M, 50 mL), followed by extraction with petroleums ether (3 ×
40 mL). The organic layer was washed with water, dried over
anhydrous MgSO4, and filtered. Removal of solvent in vacuo
gave the benzyl alcohol 6 (5.41 g, 92%) as a colorless oil, which
crystallized into white crystals upon standing at room tem-
perature. Mp: 40-42 °C. Anal. Calcd for C11H16OS: C, 67.30;
H, 8.21. Found: C, 67.18; H, 8.32. 1H NMR (250 MHz,
CDCl3): δ 1.27 (s, 9H), 2.84 (br.s, 1H), 4.63 (s, 2H), 7.28 (d, J
) 6.4 Hz, 2H), 7.48 (d, J ) 6.4 Hz, 2H). GC-MS: EI (m/z,
relative intensity) 196 (M+, 15), 181 (3), 140 (100).
1
56.94; H, 7.96; S, 10.13. Found: C, 56.60; H, 7.96; S, 9.87. H
NMR (400 MHz, CDCl3): δ 1.16 (t, J ) 7.0 Hz, 6H), 1.20 (s,
9H), 3.09 (d, J ) 21.8 Hz, 2H), 3.90-3.98 (m, 4H), 7.21 (dd, J
) 2.4, 8.2 Hz, 2H), 7.40 (d, J ) 8.2 Hz, 2H). GC-MS: EI (m/z,
relative intensity) 316 (M+, 13), 260 (100), 232 (26).
(Z)-2,3-Bis[4-(ter t-bu tylth io)p h en yl]a cr ylon itr ile (13).
To a solution of 4-(tert-butylthio)benzaldehyde (3) (0.19 g, 1
mmol) and 4-(tert-butylthio)benzyl cyanide (8) (0.21 g, 1 mmol)
in THF (10 mL) cooled in an ice/ethanol bath was added
t-BuOK (0.12 g, 1.1 mmol) in small portions during a 10 min
period. Stirring at room temperature was maintained for 1 h.
The reaction mixture was diluted with hydrochloric acid (2 M,
25 mL), stirred for 10 min at room temperature, poured into
water, and extracted with CH2Cl2/pentane (1:2, 3 × 20 mL).
The organic layer was washed with water and filtered through
silica gel (60F, 10 g) by means of CH2Cl2. Removal of solvent
in vacuo gave a crystalline material, which was recrystallized
4-(ter t-Bu tylth io)ben zyl br om id e (7). To a mixture of
4-(tert-butylthio)benzyl alcohol (6) (2.94 g, 15 mmol) in Et2O
(30 mL) cooled in an ice bath was added phosphorus tribromide
J . Org. Chem, Vol. 68, No. 4, 2003 1279

Stuhr-Hansen et al.
from heptane affording the R-cyanostilbene 13 (0.22 g, 58%)
pooled extracts were washed with water (40 mL), dried with
magnesium sulfate, and concentrated. The residual material
was boiled for 12 h in a solution of iodine in toluene (0.1 mM,
5 mL). After evaporation of the solvent, recrystallization from
heptane gave the acetyl protected stilbenethiol 5 (0.31 g, 61%)
as white plates. Mp: 153-155 °C. Anal. Calcd for C16H14OS:
C, 75.56; H, 5.55; S, 12.60. Found: C, 75.36; H, 5.66; S, 12.33.
1H NMR (400 MHz, CDCl3): δ 2.43 (s, 3H), 7.10 (d, J ) 16.3
Hz, 1H), 7.16 (d, J ) 16.3 Hz, 1H), 7.28 (t, J ) 7.3 Hz, 1H),
7.37 (d, J ) 7.9 Hz, 2H), 7.40 (d, J ) 8.6 Hz, 2H), 7.51-7.55
(m, 4H). GC-MS: EI (m/z, relative intensity) 254 (M+, 23), 212
(100), 178 (44).
(E,E)-4-[4-(ter t-Bu tylth io)styr yl]stilben e (11). To a mix-
ture of diethyl 4-(tert-butylthio)benzylphosphonate (9) (0.95 g,
3 mmol) and trans-4-stilbenecarboxaldehyde (0.62 g, 3 mmol)
in THF (50 mL) cooled in an ice bath was added t-BuOK (0.37
g, 3.3 mmol) in small portions during a 10 min period. After
stirring at room temperature for 1 h the reaction mixture was
poured into water (200 mL). The product was filtered off,
washed with water, dried, and dissolved in a limiting amount
of boiling iodine solution in toluene (0.1 mM). Reflux was
maintained for 12 h. By slow cooling to room temperature the
pure all-trans vinylene crystallized, and filtration afforded 11
(0.64 g, 58%) as white needles. Mp: 267-269 °C. Anal. Calcd
for C26H26S: C, 84.28; H, 7.07; S, 8.65. Found: C, 84.02; H,
6.98; S, 8.52. MS: EI (m/z, relative intensity) 370 (M+, 48), 314
(100), 279 (7).
(E,E)-4-[4-(Acetylth io)styr yl]stilben e (12). To a slurry
of (E,E)-4-[4-(tert-butylthio)styryl]stilbene (11) (0.18 g, 0.5
mmol), AcCl (0.5 mL), CH2Cl2 (20 mL), and toluene (40 mL)
was added BBr3 (1.0 M solution in CH2Cl2, 0.55 mL, 0.55
mmol). After stirring for 12 h at room temperature under
nitrogen, the dark reaction mixture was poured into water (200
mL), and the crystalline precipitate was filtered off, washed
with water, and dried. The crystalline residue was boiled for
12 h in the minimum amount of a solution containing iodine
in toluene (0.1 mM). By slow cooling at room temperature the
protected vinylene thiol crystallized, and filtration gave 12
(0.08 g, 45%) as pale yellow plates. Mp: 268-270 °C (dec).
Anal. Calcd for C24H20OS: C, 80.86; H, 5.65; S, 8.99. Found:
C, 80.49; H, 5.58; S, 8.42. MS: EI (m/z, relative intensity) 356
(M+, 69), 314 (100), 279 (7).
as yellow crystals. Mp: 100-102 °C. Anal. Calcd for C23H27
-
NS2: C, 72.39; H, 7.13; N, 3.67; S, 16.80. Found: C, 72.00; H,
1
7.06; N, 3.77; S, 16.59. H NMR (250 MHz, CDCl3): δ 1.32 (s,
9H), 1.33 (s, 9H), 7.58 (s, 1H), 7.59 (d, J ) 8.8 Hz, 2H), 7.62
(d, J ) 8.3 Hz, 2H), 7.64 (d, J ) 8.8 Hz, 2H), 7.85 (d, J ) 8.3
Hz, 2H). MS (FAB+): (M+) 381.
Dieth yl 4-(1,3-Dioxola n -2-yl)ben zylp h osp h on a te (17).
A solution of 4-(1,3-dioxolan-2-yl)benzyl bromide35 (7.29 g, 30
mmol) and triethyl phosphite (20 mL) was heated at 120 °C
under nitrogen for 6 h. Excess phosphite was removed on a
rotary evaporator, and bulb-to-bulb distillation (10 Pa, air bath
120 °C) gave 17 (7.71 g, 86%) as a colorless liquid. Anal. Calcd
for C14H21PO5: C, 56.00; H, 7.05. Found: C, 55.62; H, 7.00.
1H NMR (250 MHz, CDCl3): δ 1.17 (t, J ) 7.1 Hz, 6H), 3.15
(d, J ) 21.8 Hz, 2H), 3.94-4.05 (m, 4H), 4.07-4.14 (m, 4H),
5.78 (s, 1H), 7.31 (dd, J ) 2.4, 8.2 Hz, 2H), 7.42 (d, J ) 8.2
Hz, 2H). GC-MS: EI (m/z, relative intensity) 299 (M+, 44), 271
(6), 255 (5), 228 (23), 91 (100).
tr a n s-4-(ter t-Bu tylth io)styr ylben za ld eh yd e (18). To a
mixture of diethyl 4-(1,3-dioxolan-2-yl)benzylphosphonate (17)
(6.01 g, 20 mmol) and 4-(tert-butylthio)benzaldehyde (3) (3.89
g, 20 mmol) in THF (50 mL) cooled in an ice bath was added
t-BuOK (2.47 g, 22 mmol) in small portions during a 10 min
period. The reaction mixture was stirred at room temperature
for 1 h and then poured into water (200 mL). A yellow
crystalline material was filtered off, refluxed in a water/
acetonitrile mixture (1:19, 200 mL) for 2 h in the presence of
p-toluenesulfonic acid monohydrate (1.9 g, 10 mmol), and then
poured into water (300 mL). After extraction with toluene (3
× 40 mL) the combined extracts were washed with water, dried
over anhydrous MgSO4, filtered, and evaporated. The residue
was boiled for 12 h in a solution of iodine in toluene (0.1 mM,
30 mL). Evaporation of the solvent followed by recrystallization
from heptane gave the stilbenecarboxaldehyde 18 (4.78 g, 81%)
as yellow crystals. Mp: 111-113 °C. Anal. Calcd for C19H20
-
OS: C, 76.99; H, 6.80; S, 10.82. Found: C, 76.69; H, 6.85; S,
10.74. 1H NMR (400 MHz, CDCl3): δ 1.31 (s, 9H), 7.16 (d, J )
16.3 Hz, 1H), 7.25 (d, J ) 16.3 Hz, 1H), 7.50 (d, J ) 8.3 Hz,
2H), 7.55 (d, J ) 8.3 Hz, 2H), 7.66 (d, J ) 8.4 Hz, 2H), 7.88 (d,
J ) 8.4 Hz, 2H), 10.00 (s, 1H). GC-MS: EI (m/z, relative
intensity) 296 (M+, 13), 281 (3), 240 (100).
(E)-1-[4-(ter t-Bu tylth io)styr yl]p yr en e (10). To a mixture
of diethyl 4-(tert-butylthio)benzylphosphonate (9) (0.95 g, 3
mmol) and 1-pyrenecarboxaldehyde (0.69 g, 3 mmol) in THF
(50 mL) cooled in an ice bath was added t-BuOK (0.37 g, 3.3
mmol) in small portions during a 10 min period. After stirring
at room temperature for 1 h the reaction mixture was poured
into water (200 mL). The product was filtered off, washed with
water, dried, and dissolved in a limiting amount of boiling
iodine solution in toluene (0.1 mM). Reflux was maintained
for 12 h. By slow cooling to room temperature the pure all-t
vinylene crystallized, and filtration afforded 10 (0.71 g, 60%)
as yellow microcrystals. Mp: 174-175 °C. Anal. Calcd for
tr a n s-4-(ter t-Bu tylth io)stilben e (4). To a mixture of
benzyltriphenylphosphonium bromide (1.94 g, 5 mmol) and
4-(tert-butylthio)benzaldehyde (3) (0.97 g, 5 mmol) in THF (30
mL) cooled in an ice bath was added t-BuOK (0.62 g, 5.5 mmol)
in small portions during a 10 min period. The reaction mixture
was stirred at room temperature for 1 h and then poured into
water (100 mL). The phases were separated, and the water
phase was further extracted with toluene (2 × 25 mL). The
pooled organic phases were washed with water, dried over
anhydrous MgSO4, filtered, and evaporated. The product was
separated by flash chromatography on silica gel 60F (30 g) by
means of CH2Cl2. After evaporation of solvent the white
crystalline product was dissolved in the minimum amount of
a boiling solution containing iodine in toluene (0.1 mM). Reflux
was maintained for 12 h. By slow cooling at room temperature
the pure trans-stilbene crystallized, and filtration afforded 4
(1.08 g, 80%) as white plates. Mp: 164-165 °C. Anal. Calcd
for C18H20S: C, 80.55; H, 7.51; S, 11.94. Found: C, 80.41; H,
7.55; S, 11.49. 1H NMR (400 MHz, CDCl3): δ 1.31 (s, 9H), 7.10
(d, J ) 16.3 Hz, 1H), 7.15 (d, J ) 16.3 Hz, 1H), 7.27 (t, J ) 7.3
Hz, 1H), 7.37 (t, J ) 7.6 Hz, 2H), 7.47 (d, J ) 8.4 Hz, 2H),
7.52-7.54 (m, 4H). GC-MS: EI (m/z, relative intensity) 268
(M+, 22), 212 (100), 208 (4), 178 (39).
C
28H24S: C, 85.67; H, 6.16; S, 8.17. Found: C, 85.40; H, 6.16;
S, 8.34. MS: EI (m/z, relative intensity) 392 (M+, 68), 336 (100),
ABS
302 (29), 291 (14). ꢀ (1,2-dichlorobenzene) ) 4.22 × 104 M-1
387
FLU
max
cm-1. λ (1,2-dichlorobenzene) ) 435 (1.00), 459 (0.83) nm.
(E,E)-1,4-Bis[4-(ter t-bu tylth io)styr yl]ben zen e (15). To
a solution of 4-(tert-butylthio)benzaldehyde (3) (7.77 g, 40
mmol) and tetraethyl 1,4-xylylenediphosphonate (14)44 (7.57
g, 20 mmol) in THF (200 mL) cooled in an ice bath was added
t-BuOK (4.94 g, 44 mmol) in small portions during a 10 min
period. The reaction mixture was further stirred at room
temperature for 6 h under nitrogen and then poured into water
(300 mL). A yellow material was filtered off, washed with
water, and dried. The product was dissolved in the minimum
amount of a boiling solution containing iodine in toluene (0.1
mM). Reflux was maintained for 12 h. By slow cooling at room
temperature the pure trans-stilbene crystallized, and filtration
4-(S-Acetyl)stilben eth iol (5). To a solution of trans-4-(tert-
butylthio)stilbene (4) (0.54 g, 2 mmol) and AcCl (1 mL) in CH2-
Cl2 (20 mL) was added BBr3 (1.0 M solution in CH2Cl2, 2.2
mL, 2.2 mmol). Stirring was maintained for 2 h at room
temperature. The dark reaction mixture was poured into ice
(100 g), the phases were separated, and the water phase was
further extracted with Et2O/heptane (1:2, 2 × 20 mL). The
(44) Schwo¨ppe, D.; Meier, H. J . Prakt. Chem. 2000, 342, 459.
1280 J . Org. Chem., Vol. 68, No. 4, 2003

Thiol End-Capped Stilbenes and OPVs
afforded 15 (6.67 g, 73%) as light-yellow crystals. Mp: 268-
270 °C. Anal. Calcd for C30H34S2: C, 78.55; H, 7.47; S, 13.98.
Found: C, 78.37; H, 7.46; S, 13.61. 1H NMR (400 MHz,
CDCl3): δ 1.18 (18H), 7.131 (s, 2H), 7.134 (s, 2H), 7.48 (d, J )
8.5 Hz, 4H), 7.52 (s, 4H), 7.53 (d, J ) 8.5 Hz, 4H). MS: EI
room temperature for 12 h under nitrogen, poured into water
(100 mL), and extracted with toluene (3 × 25 mL). The
combined organic phases were washed with water, dried over
anhydrous MgSO4, filtered, and evaporated. The product was
separated by flash chromatography on silica gel 60F (20 g) by
means of CH2Cl2/pentane (1:2). After evaporation of solvent
the white crystalline product was dissolved in the minimum
amount of a boiling solution containing iodine in toluene (0.1
mM). Reflux was maintained for 12 h. By slow cooling 28 (0.67
g, 52%) crystallized as white needles. Mp: 207-209 °C. Anal.
Calcd for C42H48S3: C, 77.73; H, 7.45. Found: C, 77.30; H, 7.45.
1H NMR (400 MHz, CDCl3): δ 1.32 (s, 27H), 7.19 (s, 6H (alkene
proton signals appearing at same chemical shift)), 7.51 (d, J
) 8.5 Hz, 6H), 7.55 (d, J ) 8.5 Hz, 6H), 7.57 (s, 3H). MS: EI
(m/z, relative intensity): 458 (M+, 62), 402 (18), 346 (100),
ABS
374
312 (6). ꢀ (1,2-dichlorobenzene) ) 7.02 × 104 M-1 cm-1
.
λFmLaUx (1,2-dichlorobenzene) ) 440 nm.
(E,E)-1,4-Bis[4-(a cetylth io)styr yl]ben zen e (16). To a
solution of 4,4′-bis[4-(tert-butylthio)styryl]benzene (15) (0.92
g, 2 mmol) in AcCl (1 mL), CH2Cl2 (20 mL), and toluene (40
mL) was dropwise added BBr3 (1.0 M solution in CH2Cl2, 4.4
mL, 4.4 mmol). Stirring was maintained for 12 h at room
temperature. The dark reaction mixture was poured into ice
(100 g). The phases were separated, and the water phase was
further extracted with toluene (1:2, 2 × 20 mL). The pooled
extracts were washed with water (40 mL), dried with magne-
sium sulfate, and concentrated. The residual material was
separated by flash chromatography on silica gel 60F (60 g) by
means of CH2Cl2. After evaporation of solvent the yellow
crystalline product was dissolved in the minimum amount of
a boiling solution containing iodine in toluene (0.1 mM). Reflux
was maintained for 12 h. By slow cooling and filtration 16 (0.42
g, 49%) was obtained as light yellow plates. Mp: >300 °C.
Anal. Calcd for C26H22O2S2: C, 72.53; H, 5.15. Found: C, 72.50;
(m/z, relative intensity) 648 (M+, 78), 592 (20), 536 (25),
ABS
330
480 (100). ꢀ (1,2-dichlorobenzene) ) 8.37 × 104 M-1 cm-1
.
λFmLaUx (1,2-dichlorobenzene) ) 404 (0.97), 421 (1.00) nm.
(E,E,E)-1,3,5-Tr is[(4-(a cetylth io)styr yl]ben zen e (29). To
a solution of 1,3,5-tris[(4-(tert-butylthio)styryl]benzene (28)
(0.32 g, 0.5 mmol) and AcCl (1 mL) in CH2Cl2 (20 mL) was
dropwise added BBr3 (1.0 M solution in CH2Cl2, 1.6 mL, 1.6
mmol). Stirring was continued for 2 h at room temperature.
The dark reaction mixture was poured into ice (100 g), the
phases were separated, and the water phase was further
extracted with toluene (1:2, 2 × 20 mL). The pooled extracts
were washed with water (40 mL), dried with magnesium
sulfate, and concentrated. The residual material was separated
by flash chromatography on silica gel 60F (20 g) by means of
CH2Cl2/pentane (1:1). After evaporation of solvent the yellow
crystalline product was dissolved in the minimum amount of
a boiling solution containing iodine in toluene (0.01 M). Reflux
was maintained for 12 h. Upon cooling and filtration 29 (0.23
g, 76%) was isolated as light yellow needles. Mp: 160-161
°C. Anal. Calcd for C36H30O3S3: C, 71.26; H, 4.98; S, 15.85.
Found: C, 71.18; H, 4.85; S, 15.57. 1H NMR (400 MHz,
CDCl3): δ 2.45 (s, 9H), 7.19 (s, 6H (alkene proton signals
appear at the same chemical shift)), 7.46 (d, J ) 8.4 Hz, 6H),
7.57 (s, 3H), 7.58 (d, J ) 8.4 Hz, 6H). MS: EI (m/z, relative
intensity) 606 (M+, 49), 564 (59), 522 (57), 480 (100). X-ray
crystals were prepared by slow crystallization from an unsat-
urated toluene solution.
1
H, 5.16. H NMR (400 MHz, CDCl3): δ 2.44 (s, 6H), 7.11 (d, J
) 16.3 Hz, 2H), 7.16 (d, J ) 16.3 Hz, 2H), 7.41 (d, J ) 8.2 Hz,
4H), 7.52 (s, 4H), 7.55 (d, J ) 8.2 Hz, 4H). MS: EI (m/z, relative
intensity) 430 (M+, 87), 388 (50), 346 (100).
(E,E,E)-4,4′-Bis[4-(ter t-bu tylth io)styr yl]stilben e (19). To
a suspension of low valent titanium45 prepared by very slow
addition of TiCl4 (0.92 mL, 8.4 mmol) to a slurry of zink dust
(1.10 g, 16.8 mmol) in THF (50 mL) at 0 °C under nitrogen
was added 4-(tert-butylthio)styrylbenzaldehyde (18) (2.08 g, 7
mmol). After heating at reflux under nitrogen for 6 h the
reaction mixture was diluted with water (200 mL) and
extracted with CH2Cl2/toluene (1:2, 4 × 100 mL). The combined
extracts were washed with water, dried over magnesium
sulfate, and filtered. Evaporation af solvent gave a yellow slimy
substance that was Soxhlet extracted with a boiling solution
of iodine in chlorobenzene (0.1 mM, 100 mL) for 12 h. Cooling
and filtration gave 19 (0.94 g, 48%) as a yellow microcrystalline
powder. Mp: >300 °C. Anal. Calcd for C38H40S2: C, 81.38; H,
7.19; S, 11.43. Found: C, 80.87; H, 7.09; S, 10.99. MS: EI
(E,E,E)-1,3,5-Tr is[4-{(E)-4-(ter t-bu tylth io)styr yl}styr yl]-
ben zen e (30). To a slurry of 4-(tert-butylthio)styrylbenzalde-
hyde (18) (0.27 g, 0.9 mmol) and [1,3,5-tris(triphenylphospho-
niomethyl)benzene] tribromide (27)42 (0.34 g, 0.3 mmol) in THF
(15 mL) cooled in an ice bath was added t-BuOK (0.11 g, 1
mmol) in small portions during a 10 min period. The reaction
mixture was stirred at room temperature for 12 h under
nitrogen, poured into water (100 mL), and extracted with
toluene (3 × 25 mL). The combined organic phases were
washed with water, dried over anhydrous MgSO4, filtered, and
evaporated. The product was separated by flash chromatog-
raphy on silica gel by means of CH2Cl2/pentane (1:2). After
evaporation of solvent the white crystalline product was
dissolved in the minimum amount of a boiling solution
containing iodine in toluene (0.1 mM). Reflux was maintained
for 12 h. By slow cooling 30 (0.12 g, 42%) precipitated as a
yellow powder. Anal. Calcd for C66H66S3: C, 82.97; H, 6.96.
(m/z, relative intensity) 560 (M+, 92), 504 (24), 448 (100).
FLU
ꢀA39B8S(1,2-dichlorobenzene)
(1,2-dichlorobenzene) ) 444 (1.00), 469 (0.90) nm.
)
9.2
×
104 M-1 cm-1
.
λ
-
max
(E ,E )-1,4-Bis[4-{(E )-4-(t er t -b u t ylt h io)st yr yl}st yr yl]-
ben zen e (20). To a solution of 4-(tert-butylthio)styrylbenzal-
dehyde (18) (2.97 g, 10 mmol) and tetraethyl 1,4-xylylene-
diphosphonate (14)44 (1.89 g, 5 mmol) in THF (100 mL) cooled
in an ice bath was added t-BuOK (1.23 g, 11 mmol) in small
portions during a 10 min period. The reaction mixture was
further stirred at room temperature for 6 h under nitrogen
and poured into water (300 mL). A yellow material was filtered
off, washed with water, and dried. Soxhlet extraction with a
boiling solution of iodine in chlorobenzene (0.1 mM) for 12 h,
cooling, and filtration gave 20 (1.36 g, 41%) as yellow crystals.
Mp: >300 °C. Anal. Calcd for C46H46S2: C, 83.34; H, 6.99; S,
9.67. Found: C, 82.97; H, 7.04; S, 9.58. MS: EI (m/z, rela-
1
Found: C, 83.04; H, 7.06. H NMR (400 MHz, CDCl3): δ 1.32
(s, 27H), 7.11 (d, J ) 20.7 Hz, 3H), 7.12 (d, J ) 19.0 Hz, 3H),
7.20 (d, J ) 20.7 Hz, 3H), 7.21 (d, J ) 19.0 Hz, 3H),
tive intensity) 662 (M+, 100), 606 (16), 560 (40), 550 (47).
7.46-7.57 (m, 27H). MS (FAB+): (M+) 956. ꢀ3A7B7S(1,2-di-
FLU
ꢀA40B9S(1,2-dichlorobenzene)
(1,2-dichlorobenzene) ) 459 (1.00), 485 (0.70) nm.
)
5.7
×
104 M-1 cm-1
.
λ
-
max
FLU
chlorobenzene) ) 1.72 × 105 M-1 cm-1. λ (1,2-dichloro-
max
(E,E,E)-1,3,5-Tr is[(4-(ter t-bu tylth io)styr yl]ben zen e (28).
To a slurry of 4-(tert-butylthio)benzaldehyde (3) (1.17 g, 6
mmol) and [1,3,5-tris(triphenylphosphoniomethyl)benzene] tri-
bromide42 (27) (2.29 g, 2 mmol) in THF (50 mL) cooled in an
ice bath was added t-BuOK (0.67 g, 6.6 mmol) in small portions
during a 10 min period. The reaction mixture was stirred at
benzene) ) 420 (1.00), 440 (0.97) nm.
1,4-Bis(m eth oxym eth yl)-2,5-d id od ecylben zen e (22). Di-
bromo-2,5-bis(methoxymethyl)benzene (21)39 (4.86 g, 15 mmol)
was added in one portion to a solution of t-BuLi (1.5 M in
hexane, 40 mL, 60 mmol) and TMEDA (10 mL) in THF (100
mL) cooled in a dry ice/acetone bath under Ar. The reaction
mixture was stirred at room temperature for 1 h. After few
minutes at room temperature the dilithiosalt began to form
as a white precipitate. The reaction mixture was cooled in a
(45) Elandaloussi, E. H.; Frere, P.; Richomme, P.; Orduna, J .; Garin,
J .; Roncali, J . J . Am. Chem. Soc. 1997, 119, 10774.
J . Org. Chem, Vol. 68, No. 4, 2003 1281

Stuhr-Hansen et al.
dry ice/acetone bath, while 1-iodododecane (9.78 g, 33 mmol)
was added rapidly. After 1 h of stirring at room temperature
for, water (350 mL) was added. The phases were separated,
and the aqueous phase was further extracted with pentane
(2 × 50 mL). The combined organic layers were washed with
saturated sodium chloride (10 mL), dried over anhydrous
MgSO4, and filtered. Removal of solvent in vacuo gave a white
crystalline material, which upon recrystallization from acetone
afforded the bis(methoxymethyl) compound 22 (4.70 g, 62%)
white crystals. Mp: 53-54 °C. Anal. Calcd for C34H62O2: C,
81.21; H, 12.43. Found: C, 80.92; H, 12.45. 1H NMR (400 MHz,
CDCl3): δ 0.86-0.90 (m, 6H), 1.26-1.37 (m, 36H), 1.54-1.59
(m, 4H), 2.57-2.61 (m, 4H), 3.38 (s, 6H), 4.44 (s, 4H), 7.14 (s,
2H). MS: EI (m/z, relative intensity) 503 (M+, 9), 471 (100),
439 (72).
1,4-Bis(br om om eth yl)-2,5-d id od ecylben zen e (23). To a
solution of 1,4-bis(methoxymethyl)-2,5-didodecylbenzene (22)
(4.02 g, 8 mmol) in CH2Cl2 (50 mL) was added BBr3 (1.0 M
solution in CH2Cl2, 18 mL, 18 mmol) in one portion. The
reaction mixture was stirred at room temperature for 2 h and
poured into water (200 mL). The phases were separated, and
the aqueous phase was further extracted with pentane (2 ×
50 mL). The combined organic layers were washed with
saturated sodium chloride (10 mL), dried over anhydrous
MgSO4, and filtered. Removal of solvent in vacuo gave a white
crystalline material. Recrystallization from acetonitrile gave
23 (1.31 g, 27%) as white plates. Mp: 96-97 °C. Anal. Calcd
for C32H56Br2: C, 63.99; H, 9.40. Found: C, 63.95; H, 9.48. 1H
NMR (250 MHz, CDCl3): δ 0.86-0.91 (m, 6H), 1.27-1.39 (m,
36H), 1.58-1.70 (m, 4H), 2.63-2.69 (m, 4H), 4.50 (s, 4H), 7.15
(s, 2H). MS: EI (m/z, relative intensity) 600 (M+, 9), 521 (44),
441 (12), 367 (17), 287 (19), 212 (100).
[1,4-Did od ecyl-2,5-b is(t r ip h en ylp h osp h on iom et h yl)-
b en zen e] Dib r om id e (24). A solution of 1,4-bis(bromo-
methyl)-2,5-didodecylbenzene (23) (1.20 g, 2 mmol) and triph-
enylphosphine (1.15 g, 4.4 mmol) in DMF (20 mL) was heated
at 130 °C for 12 h under nitrogen. Evaporation gave a white
crystalline residue, which was dissolved in boiling acetonitrile
(10 mL). Precipitation occurred slowly on addition of boiling
EtOAc (30 mL). Filtration and drying afforded the bis-ylide
synthetic equivalent 24 (1.85 g, 82%) as a white powder. Mp:
236-237 °C. Anal. Calcd for C68H86Br2P2: C, 72.59; H, 7.70.
Found: C, 72.12; H, 7.78. 1H NMR (400 MHz, CDCl3): δ 0.63-
0.67 (m, 6H), 0.81-0.89 (m, 12H), 0.97-1.00 (m, 4H), 1.09-
1.13 (m, 4H), 1.21-1.30 (m, 20H), 1.58-1.62 (m, 4H), 4.97 (d,
J ) 14.3 Hz, 4H), 6.69 (s, 2H), 7.60-7.72 (m, 18H), 7.88-7.92
(m, 12H). MS: electrospray (m/z, relative intensity) 1046
(M2+Br-, 68), 482 (M2+,100).
were washed with water, dried over anhydrous MgSO4,
filtered, and evaporated. The product was separated by flash
chromatography on silica gel 60F (30 g) by means of CH2-
Cl2.pentane (1:2). After evaporation of solvent the white
crystalline product was dissolved in the minimum amount of
a boiling solution containing iodine in toluene (0.1 mM). Reflux
was maintained for 12 h. After gentle removal af solvent in
vacuo the yellow residue was recrystallized from ethyl acetate
giving the soluble OPV 25 (0.32 g, 32%) as light-yellow highly
fluorescent microcrystals. Mp: 173-174 °C. Anal. Calcd for
C
70H94S2: C, 84.11; H, 9.48; S, 6.41. Found: C, 83.79; H, 9.48;
S, 6.58. 1H NMR (400 MHz, CDCl3): δ 0.86-0.89 (m, 6H),
1.27-1.28 (m, 32H), 1.32 (s, 18H), 1.37-1.43 (m, 4H), 1.60-
1.66 (m, 4H), 2.75-2.79 (m, 4H), 7.04 (d, J ) 16.1 Hz, 2H),
7.11 (d, J ) 16.3 Hz, 2H), 7.16 (d, J ) 16.3 Hz, 2H), 7.39 (d,
J ) 16.1 Hz, 2H), 7.45 (s, 2H), 7.48 (d, J ) 8.4 Hz, 4H), 7.52
(d, J ) 8.4 Hz, 4H), 7.53 (br-s, 8H (two aromatic proton signals
appearing at same chemical shift)). MS (FAB+): (M+
isobutylene) 942. ꢀ408
-
ABS(1,2-dichlorobenzene) ) 1.27 × 105 M-1
FLU
cm-1. λ (1,2-dichlorobenzene) ) 468 (1.00), 497 (0.67) nm.
max
(E,E)-1,4-Bis[4-{(E)-4-(a cetylth io)styr yl}styr yl]-2,5-d i-
d od ecylben zen e (26). To a solution of (E,E)-1,4-bis[4-{(E)-
4-(tert-butylthio)styryl}styryl]-2,5-didodecylbenzene (25) (0.20
g, 0.2 mmol) and AcCl (0.5 mL) in CH2Cl2 (10 mL) was added
BBr3 (1.0 M solution in CH2Cl2, 0.5 mL, 0.5 mmol). Stirring
was maintained for 2 h at room temperature. The dark
reaction mixture was poured into ice (100 g), the phases were
separated, and the water phase was further extracted with
Et2O/heptane (1:2, 2 × 15 mL). The pooled extracts were
washed with saturated sodium chloride (aq, 20 mL), dried with
magnesium sulfate, and concentrated. The product was sepa-
rated by flash chromatography on silica gel 60F (10 g) by
means of CH2Cl2. After evaporation of solvent the yellow oil
was dissolved in the minimum amount of a boiling solution
containing iodine in toluene (0.1 mM). The residual material
was boiled for 12 h in a solution of iodine in toluene (0.1 mM,
5 mL). After evaporation of the solvent, recrystallization from
acetonitrile gave the alkyl-substituted Ac-protected OPV 26
(0.09 g, 46%) as yellow crystalline material without a defined
melting point. The crystals soften gradually upon heating.
Anal. Calcd for C66H82O2S2: C, 81.60; H, 8.51; S, 6.60. Found:
C, 82.07; H, 8.59; S, 6.09. 1H NMR (400 MHz, CDCl3): δ 0.86-
0.88 (m, 6H), 1.26-1.43 (m, 36H), 1.64-1.68 (s, 4H), 2.44 (s,
6H), 2.75-2.77 (m, 4H), 7.04 (d, J ) 16 Hz, 2H), 7.11 (d, J )
16 Hz, 2H), 7.17 (d, J ) 16 Hz, 2H), 7.38 (d, J ) 12 Hz, 4H),
7.41 (s, 2H), 7.43 (d, J ) 12 Hz, 2H), 7.53 (br-s, 8H), 7.56 (d,
J ) 8 Hz, 4H).
(E,E)-1,4-Bis[4-{(E)-4-(ter t-bu tylth io)styr yl}styr yl]-2,5-
d id od ecylben zen e (25). To a mixture of [1,4-didodecyl-2,5-
bis(triphenylphosphoniomethyl)benzene] dibromide (24) (1.13
g, 1 mmol) and 4-(tert-butylthio)styrylbenzaldehyde (18) (0.59
g, 2 mmol) in THF (20 mL) cooled in an ice bath was added
t-BuOK (0.25 g, 2.2 mmol) in small portions during a 10 min
period. The reaction mixture was stirred at room temperature
for 1 h and poured into water (100 mL). The phases were
separated, and the water phase was further extracted with
CH2Cl2/pentane (1:2, 2 × 25 mL). The pooled organic phases
Ack n ow led gm en t. Financial support from the Eu-
ropean Union under the IST program “NANOMOL”
(contract IST-1999-12603) is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Copies of 13C and
1H NMR spectra. This material is available free of charge via
the Internet at http://pubs.acs.org.
J O0263770
1282 J . Org. Chem., Vol. 68, No. 4, 2003