Synthesis of new tetrathiafulvalene modules for acetylenic scaffolding

Article abstract of DOI:10.1055/s-2003-40841

Benzene-extended derivatives of tetrathiafulvalene (TTF) containing silyl-protected acetylene groups at the exo-cyclic fulvene carbons were prepared by a double Wittig olefination of a diacetylenic derivative of terephthalaldehyde. Acetylenic coupling rea

Full text of DOI:10.1055/s-2003-40841

LETTER
1423
Synthesis of New Tetrathiafulvalene Modules for Acetylenic Scaffolding
New
T
etrathiafulvalen
o
e
Modules
f
o
g
r
A
cetylenic
e
Scaffoldin
n
g
s Brøndsted Nielsen*
Department of Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
Fax +45 66158780; E-mail: mbn@chem.sdu.dk
Received 5 May 2003
MeO2C
Abstract: Benzene-extended derivatives of tetrathiafulvalene
S
S
S
S
S
S
(TTF) containing silyl-protected acetylene groups at the exo-cyclic
fulvene carbons were prepared by a double Wittig olefination of a
diacetylenic derivative of terephthalaldehyde. Acetylenic coupling
reactions at the lateral acetylene appendages with phenylacetylene
and 4-iodonitrobenzene afforded large p-conjugated chromophores.
CO2Me
MeO2C
S
S
TTF
CO2Me
1
Figure 1 Structures of TTF and 1.
Key words: alkynes, arenes, conjugation, cross-coupling, Wittig
reactions
phthalaldehyde (2) was treated with lithium triisopropyl-
silylacetylide generated in situ. The resulting diol 3 was
subsequently oxidized by PCC to the diketone 4. This
compound was then reacted with the ylide of 510 (2.2
equivalents), generated by treating 5 with n-butyllithium.
The outcome of this double Wittig reaction was the new
TTF derivative 6.11 Although this compound experiences
good solubility in common organic solvents such as THF
and CH2Cl2, it was decided to enhance the solubility fur-
ther in order for it to be incorporated into larger soluble
scaffolds. Transesterification under basic conditions was
accomplished by reacting 6 with 1-decanol and potassium
carbonate, affording the decyl ester 7. Both TTFs 6 and 7
are very stable compounds that were subjected to normal
chromatographic work-up and stored at room tempera-
ture. Removal of the silyl protecting groups was carried
out by the action of a fluoride source such as tetrabutylam-
monium fluoride (2 equivalents). This deprotection step
was very fast, and the mixture was worked up after 15 min
of stirring at room temperature. After chromatographic
purification, TTF 8 containing two terminal acetylene
units was obtained. This desilylated compound was very
unstable and decomposed (turning dark) after prolonged
standing at room temperature. Nevertheless, it was com-
pletely characterized by mass spectrometry (High-res
Tetrathiafulvalene (TTF) is a reversible, two-electron do-
nor that has been widely exploited in both materials and
supramolecular chemistry.1 Many structural variations of
the parent TTF system have been carried out during the
last 30 years, mainly with the aim of developing low-tem-
perature organic superconductors.2 Yet, owing to the three
reversible redox states of TTF, the possibility for employ-
ing TTF in molecular sensors, switches, and devices has
also attracted an enormous focus recently.1a,3 Synthetic
protocols are today available for stepwise functionaliza-
tion of the TTF core, which has allowed its ready incorpo-
ration into macrocyclic and oligomeric structures.4
Efficient procedures for incorporating p-conjugated spac-
ers between the two dithiole rings offer access to so-called
extended TTFs that in many cases exhibit enhanced p-do-
nor properties and a stabilization of the dication state.5
Very recently, the versatility and high functional group
tolerance of acetylenic couplings6 stimulated synthesis of
acetylenic derivatives of either TTF itself or of the 1,4-
dithiafulvene half-unit.7 Indeed, some of these com-
pounds were successfully employed as precursors for
TTF-polymers and alkyne-extended TTFs. This approach
is now continued by the development of a synthetic proto-
col for obtaining acetylenic derivatives of the benzene-ex-
tended TTF 1,8 that is, derivatives containing acetylenic
appendages at the exo-cyclic fulvene carbons. These new
modules for acetylenic scaffolding were subjected to dif-
ferent cross-coupling conditions, which allowed construc-
tion of new large p-conjugated chromophores.
1
FT-MALDI-MS) and H- and 13C NMR spectroscopies.
The terminal acetylene protons were found resonating as
a singlet at dH 3.76 ppm. The presence of CCH groups was
furthermore confirmed by IR spectroscopy that revealed
the C–H stretching band at 3307 cm–1. Moreover, the CC
stretching band was shifted from 2126 cm–1 in 6 to 2085
cm–1 in 8.
Extended TTFs are conveniently prepared by a double
Wittig olefination reaction between a dialdehyde and a
phosphorus ylide.8,9 In order to follow this strategy, the
acetylenic functions were first attached to the benzene
spacer before forming the TTF skeleton. The synthetic
procedure is outlined in Scheme 1. In the first step, tere-
The possibility for performing acetylenic coupling reac-
tions with 8 was exploited next. Thus, it was treated with
an excess of phenylacetylene under oxidative Hay
conditions12 (Scheme 2), i.e. employing the CuCl,
N,N,N¢,N¢-tetramethylethylenediamine (TMEDA) cata-
lyst system in the presence of oxygen (from the air).
This reaction afforded in good yield the extended TTF 9
in which each dithiole ring is in linear conjugation to a
Synlett 2003, No. 10, Print: 05 08 2003.
Art Id.1437-2096,E;2003,0,10,1423,1426,ftx,en;G09903ST.pdf.
© Georg Thieme Verlag Stuttgart · New York

1424
M. B. Nielsen
LETTER
Si(i-Pr)3
HO
O
Si(i-Pr)3
PCC
n-BuLi, THF
CH2Cl2
77%
OH
O
2
3
55%
(i-Pr)3Si
MeO2C
MeO2C
Si(i-Pr)3
S
H
O
PBu3
S
BF4
5
O
n-BuLi, THF
4
(i-Pr)3Si
66%
CO2R
S
CO2R
Si(i-Pr)3
H
S
RO2C
RO2C
S
n-Bu4NF
S
S
THF
76%
S
S
RO2C
S
CO2R
CO2R
(i-Pr)3Si
H
RO2C
6: R = Me
7: R = C10H21
8: R = C10H21
C10H21OH
K2CO3, THF
55%
Scheme 1 Synthesis of benzene-extended TTF with lateral alkyne appendages.
phenyl ring via a buta-1,3-diynediyl spacer.11 This com- In conclusion, a synthetic protocol has been developed for
pound seemed very stable and suffered from no apparent obtaining benzene-extended TTFs that – via alkyne ap-
decomposition under chromatographic work-up on nor- pendages – act as new modules for acetylenic scaffolding.
mal silica gel. In order to explore further the synthetic ver-
satility of 8, it was subjected to a Pd-catalyzed cross-
Acknowledgment
coupling reaction with 4-iodonitrobenzene under Sono-
gashira conditions13 (Scheme 2). This reaction gave in a
The Danish Technical Research Council (STVF) is gratefully ack-
nowledged for financial support (Research project # 26-01-0033).
modest yield of 29% the desired TTF 10, containing two
Laboratory technician Lone Marquard Jensen is thanked for the
electron-withdrawing 4-nitrophenyl groups.11 Yet, since
preparation of starting materials.
two cross-couplings are carried out in this step, the yield
corresponds to an efficiency of 54% for each coupling re-
action. The separation of 10 from by-products, not yet References
identified, of similar polarity was very tedious and re-
quired repeated chromatographic purification. [2+2]Cy-
(1) (a) Nielsen, M. B.; Lomholt, C.; Becher, J. Chem. Soc. Rev.
2000, 29, 153. (b) Bryce, M. R. J. Mater. Chem. 2000, 10,
cloadditions with subsequent ring-openings have earlier
been observed between the central TTF double bond and
electron-deficient acetylenes14 and may possibly account
for the by-products. Owing to the large donor-acceptor
substituted p-system, compound 10 might be a good can-
didate for NLO applications.7f It is a very strong chro-
mophore exhibiting a charge-transfer transition at lmax
426 nm (e 38500 M–1cm–1). This longest wavelength ab-
sorption maximum is bathochromically shifted by +32 nm
and +29 nm relative to the maxima of 7 and 9, respectively
(7: lmax 394 nm, e 32900 M–1cm–1; 9: lmax 397 nm, e
43600 M–1cm–1). The CC stretching band of 10 was ob-
served at 2183 cm–1.
589. (c) Segura, J. L.; Martín, N. Angew. Chem. Int. Ed.
2001, 40, 1372.
(2) Williams, J. M.; Ferraro, J. R.; Thorn, R. J.; Carlson, K. D.;
Geiser, U.; Wang, H. H.; Kini, A. M.; Whangbo, M.-H.
Organic Superconductors(Including Fullerenes): Synthesis,
Structure, Properties, and Theory; Prentice Hall:
Englewood Cliffs, New Jersey, 1992.
(3) Luo, Y.; Collier, C. P.; Jeppesen, J. O.; Nielsen, K. A.;
Delonno, E.; Ho, G.; Perkins, J.; Tseng, H.-R.; Yamamoto,
T.; Stoddart, J. F.; Heath, J. R. ChemPhysChem 2002, 3, 519.
(4) Nielsen, M. B.; Becher, J. Liebigs Ann. Rec. 1997, 2177.
(5) Roncali, J. J. Mater. Chem. 1997, 7, 2307.
Synlett 2003, No. 10, 1423–1426 © Thieme Stuttgart · New York

LETTER
New Tetrathiafulvalene Modules for Acetylenic Scaffolding
1425
CO2C10H21
C10H21O2C
S
S
CuCl, TMEDA
CH2Cl2, air
S
S
CO2C10H21
60%
C10H21O2C
9
8
NO2
CO2C10H21
S
C10H21O2C
I
NO2
S
[PdCl2(PPh3)2], CuI
(i-Pr)2NH, THF
S
S
CO2C10H21
29%
C10H21O2C
10
O2N
Scheme 2 Functionalization at the lateral positions. TMEDA = N,N,N¢,N¢-tetramethylethylenediamine.
(6) (a) Siemsen, P.; Livingston, R. C.; Diederich, F. Angew.
Chem. Int. Ed. 2000, 39, 2632. (b) Nielsen, M. B.;
Diederich, F. Synlett 2002, 544.
Et2O (300 mL) was added, the organic phase was separated,
dried (MgSO4), and concentrated in vacuo. Column
chromatography (SiO2, CH2Cl2) afforded 6 (0.652 g, 66%)
as an orange solid. Mp 155–156 °C. 1H NMR (300 MHz,
CDCl3): d = 1.14 (s, 42 H), 3.84 (s, 6 H), 3.89 (s, 6 H), 7.55
(s, 4 H). 13C NMR (75 MHz, CDCl3): d = 11.3, 18.7, 53.3,
53.5, 101.6, 104.8, 107.7, 126.5, 129.6, 133.0, 135.4, 141.2,
159.4, 160.2. MALDI-TOF-MS [matrix: 2,5-
(7) (a) Otsubo, T.; Kochi, Y.; Bitoh, A.; Ogura, F. Chem. Lett.
1994, 2047. (b) Yamamoto, T.; Shimizu, T. J. Mater. Chem.
1997, 7, 1967. (c) Yamamoto, T.; Shimizu, T. J. Mater.
Chem. 1997, 7, 1967. (d) Solooki, D.; Parker, T. C.; Khan,
S. I.; Rubin, Y. Tetrahedron Lett. 1998, 39, 1327.
(e) Nielsen, M. B.; Moonen, N. N. P.; Boudon, C.;
Gisselbrecht, J.-P.; Seiler, P.; Gross, M.; Diederich, F.
Chem. Commun. 2001, 1848. (f) Nielsen, M. B.; Utesch, N.
F.; Moonen, N. N. P.; Boudon, C.; Gisselbrecht, J.-P.;
Concilio, S.; Piotto, S. P.; Seiler, P.; Günter, P.; Gross, M.;
Diederich, F. Chem.–Eur. J. 2002, 8, 3601.
dihydroxybenzoic acid (DHB)]: m/z = 898 (M+). Elemental
analysis: Calcd for C44H58O8S4Si2 (899.35): C, 58.76; H,
6.50; S, 14.26; Found: C, 58.94; H, 6.38; S, 14.38.
Compound 9: To a solution of 8 (126 mg, 0.12 mmol) in
CH2Cl2 (10 mL) was added phenylacetylene (1 mL) and
thereafter Hay catalyst (1 mL) [Hay catalyst: CuCl (0.13 g,
1.3 mmol) and TMEDA (0.16 g, 1.4 mmol) in CH2Cl2 (4.5
mL)]. The mixture was stirred for 20 min and then
(8) Salle, M.; Belyasmine, A.; Gorgues, A.; Jubault, M.; Soyer,
N. Tetrahedron Lett. 1991, 32, 2897.
(9) Some examples: (a) Adger, B. J.; Barrett, C.; Brennan, J.;
McGuigan, P.; McKervey, M. A.; Tarbit, B. J. Chem. Soc.,
Chem. Commun. 1993, 1220. (b) Märkl, G.; Pöll, A.;
Aschenbrenner, N. G.; Schmaus, C.; Troll, T.; Kreitmeier,
P.; Nöth, H.; Schmidt, M. Helv. Chim. Acta 1996, 79, 1497.
(10) Sato, M.; Gonella, N. C.; Cava, M. P. J. Org. Chem. 1979,
44, 930.
concentrated in vacuo without heating. Column
chromatography (SiO2, CH2Cl2/cyclohexane, 1:1)afforded9
(89 mg, 60%) as an orange oily solid. 1H NMR (300 MHz,
CDCl3): d = 0.88 (t, 6.6 Hz, 12 H), 1.27 (br s, 56 H), 1.66–
1.74 (m, 8 H), 4.22 (t, 7.0 Hz, 4 H), 4.27 (t, 6.5 Hz, 4 H),
7.34-7.36 (m, 6 H), 7.53 (dd, 2.1/7.2 Hz, 4 H), 7.56 (s, 4 H).
13C NMR (75 MHz, CDCl3): d = 14.1, 22.7, 25.7, 25.8, 28.3,
29.1, 29.2, 29.3, 29.5 (× 2), 31.9, 67.0, 67.2, 73.8, 79.9, 83.6,
86.2, 105.4, 121.8, 126.9, 128.4, 129.2, 130.4, 132.3, 132.7,
135.4, 145.5, 158.9, 159.5. MALDI-TOF-MS (DHB): m/z =
1291 (M+). HR-FT-MALDI-MS (DHB): Calcd for
(11) All new compounds were fully characterized by 1H- and 13
NMR spectroscopy, elemental analysis and/or HR-MS.
Selected experimental procedures: Compound 6: To a
C
solution of the phosphonium salt 5 (1.23 g, 2.42 mmol) in
dry THF (40 mL) at –78 ºC was slowly added n-BuLi (1.6 M
in hexane, 1.5 mL, 2.4 mmol), resulting in a red solution.
Then 4 (0.543 g, 1.10 mmol) in dry THF (15 mL) was slowly
added. The resulting orange solution was stirred at –78 ºC
for 2 h, whereupon sat aq NH4Cl (200 mL) was added. Then
C78H98O8S4 (M+): 1290.6145; Found: 1290.6161.
Compound 10: 8 (209 mg, 0.19 mmol) and 4-iodonitro-
benzene (490 mg, 1.97 mmol) were dissolved in dry THF
(10 mL), and the mixture was thoroughly Ar-degassed. Then
[PdCl2(PPh3)2] (10 mg, 0.014 mmol) and diisopropylamine
Synlett 2003, No. 10, 1423–1426 © Thieme Stuttgart · New York

1426
M. B. Nielsen
LETTER
(1.5 mL) were added under Ar-degassing. Finally, CuI (3
mg, 0.016 mmol) was added, and the mixture was stirred for
3 h. Then Et2O (300 mL) was added, and the organic phase
was washed with H2O (250 mL) and saturated aqueous
NH4Cl (250 mL), dried (MgSO4), and concentrated in vacuo.
Column chromatography (SiO2, CH2Cl2/cyclohexane, 2:1)
afforded 10 (74 mg, 29%) as an orange oily solid. 1H NMR
(300 MHz, CDCl3): d = 0.88 (m, 12 H), 1.27 (br s, 56 H),
1.70–1.76 (m, 8 H), 4.24 (t, 6.8 Hz, 4 H), 4.29 (t, 6.5 Hz, 4
H), 7.62 (s, 4 H), 7.63 (d, 8.8 Hz, 4 H), 8.21 (d, 8.8 Hz, 4 H).
13C NMR (75 MHz, CDCl3): d = 14.1, 22.7, 25.7, 25.8, 28.3,
29.2 (× 2), 29.3, 29.5 (× 3), 31.9, 67.1, 67.3, 93.4, 97.3,
105.8, 123.7, 126.9, 129.8, 130.6, 131.6, 132.7, 135.5,
144.3, 146.9, 158.9, 159.5. HR-FT-MALDI-MS (DHB):
Calcd for C74H96N2O12S4: 1332.5846 (M+); Found:
1332.5833. Elemental analysis: Calcd for C74H96N2O12S4
(1333.82): C, 66.64; H, 7.25; N, 2.10; S, 9.61; Found: C,
66.84; H, 7.33; N, 2.15; S 9.55.
(12) Hay, A. S. J. Org. Chem. 1962, 27, 3320.
(13) Sonogashira, K. In Metal-catalyzed Cross-coupling
Reactions; Diederich, F.; Stang, P. J., Eds.; Wiley-VCH:
Weinheim, 1998, 203–229.
(14) (a) Hopf, H.; Kreutzer, M.; Jones, P. G. Angew. Chem., Int.
Ed. Engl. 1991, 30, 1127. (b) Schermann, G.; Vostrowsky,
O.; Hirsch, A. Eur. J. Org. Chem. 1999, 2491.
Synlett 2003, No. 10, 1423–1426 © Thieme Stuttgart · New York