Chemistry of anthracene-acetylene oligomers: Synthesis and enantiomeric resolution of a chiral 1,8-anthrylene-ethynylene cyclic tetramer

Article abstract of DOI:10.1002/chem.200501111

To construct a new type of chiral π-conjugated system, the title anthracene-acetylene oligomer containing two octyl groups at position 10 of 1,2-alternating anthracene groups was synthesized. Each anthracene unit was connected by Sonogashira coupling, and the tetrameric precursor was cyclized by a cross-coupling reaction to form the desired C₂-symmetric compound. Its enantiomers were resolved by chiral HPLC with a Chiralcel OD column, and the chiroptical properties were investigated by optical rotation ([α] _D²³ = -95 and +91) and circular dichroism (CD) measurements. The structural and spectroscopic features of this oligomer were discussed in terms of the molecular symmetry and the dynamic behavior of the macrocyclic framework.

Full text of DOI:10.1002/chem.200501111

DOI: 10.1002/chem.200501111
Chemistry of Anthracene–Acetylene Oligomers: Synthesis and Enantiomeric
Resolution of a Chiral 1,8-Anthrylene–Ethynylene Cyclic Tetramer**
Shinji Toyota,* Shinya Suzuki, and Michio Goichi[a]
Abstract: To construct a new type of
chiral p-conjugated system, the title an-
thracene–acetylene oligomer contain-
ing two octyl groups at position 10 of
1,2-alternating anthracene groups was
synthesized. Each anthracene unit was
connected by Sonogashira coupling,
and the tetrameric precursor was cy-
clized by a cross-coupling reaction to
form the desired C2-symmetric com-
pound. Its enantiomers were resolved
by chiral HPLC with a Chiralcel OD
column, and the chiroptical properties
were investigated by optical rotation
([a]2D3 =À95 and +91) and circular di-
chroism (CD) measurements. The
structural and spectroscopic features of
this oligomer were discussed in terms
of the molecular symmetry and the dy-
namic behavior of the macrocyclic
framework.
Keywords: arylene–ethynylenes
·
chiral resolution · cross-coupling ·
macrocycles · nanostructures
Introduction
Arylene-ethynylene oligomers are fascinating compounds,
and have gained much interest in the areas of structural and
functional organic chemistry.[1] The diversity of the molecu-
lar design, which is due to variations in the mode and con-
nection, the degree of oligomerization, the choice of arene
units, and the introduction of substituents has enabled re-
searchers to design a huge number of molecules containing
the desired molecular shape, mobility, or p-electronic prop-
erties. For example, shape-persistent macrocyclic com-
pounds,[2] graphyne derivatives,[3] and light emitting poly-
mers[4] have been extensively studied in the research field.
To create a new type of such oligomers, we utilized an-
thracene groups as arene units by taking advantage of their
unique shape and electronic properties.[5] Our initial efforts
were directed towards the 1,8-anthrylene oligomers, and the
framework of cyclic tetramer 1 was constructed by the Sono-
gashira coupling as
a three dimensional p-conjugated
system.[6] This compound features a diamond prism structure
of nearly D2 symmetry and conformational interconversion
between the two enantiomeric forms 1a and 1a’ via the
square form 1b (Scheme 1). We also synthesized cyclic tetra-
mer 2 containing butyl groups at position 10 of 1,3-alternat-
ing anthracene rings to improve solubility. In both com-
pounds 1 and 2, however, the isolation of optically active
forms is impossible because of the facile racemization by
the skeletal swing, as shown in Scheme 1. In contrast, the
framework itself becomes chiral upon the introduction of
alkyl groups at position 10 of the 1,2-alternating anthracene
rings. The skeletal swing does not affect the chirality of the
cyclic framework; rather, it leads to an interconversion be-
tween the two diamond forms, 3a and 3c, in which the two
substituted anthracene planes form obtuse and acute angles,
respectively. Therefore, enantiomers of such a compound
are, in principle, separable regardless of the rates of the
skeletal swing (these enantiomers can be designated as M or
P based on the helicity of the two substituted anthracene
[a] Prof. S. Toyota, S. Suzuki, M. Goichi
Department of Chemistry
Faculty of Science
Okayama University of Science
1-1 Ridaicho, Okayama, 700-0005 (Japan)
Fax: ( +81)86-256-9457
E-mail: stoyo@chem.ous.ac.jp
[**] Chemistry of Anthracene–Acetylene Oligomers, Part 3; for Parts 1
and 2 see: S. Toyota, M. Goichi, M. Kotani, Angew. Chem. 2004, 116,
2298–2301; Angew. Chem. Int. Ed. 2004, 43, 2248–2251 and S. Toyota,
M. Goichi, M. Kotani, M. Takezaki, Bull. Chem. Soc. Jpn. 2005, 78,
2214–2227, respectively.
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FULL PAPER
yield from 6 to the tetrameric precursor is satisfactory (35%
yield in five steps). Additionally, this stepwise route is also
applicable to the synthesis of cyclic tetramers with four dif-
ferently substituted anthracene groups, starting from 1,8-
diiodo- and 1,8-diethynylanthracene derivatives.
Compound 3 was obtained as a yellowish green solid that
melted at 2218C. A molecular ion peak was observed at
1024.5 (C80H64) by MALDI-TOF mass spectroscopy. This
compound was soluble in conventional organic solvents, and
the solutions were observed to glow a bright green color
under room light. Whereas significant decomposition occur-
red in dichloromethane solution, the decomposition became
slow in chloroform or aromatic solvents. As this compound
was sensitive to conventional silica gel, we used an NH-type
silica gel for the chromatographic separation. It was not
until we overcame these technical problems that we were
able to obtain the desired compound on a preparative scale.
1
NMRspectra : The signal modes of H and 13C NMR spectra
of 3 are consistent with those for a structure of C2 symmetry
in which the rotational axis passes through the midpoints of
two acetylene moieties connecting the same types of anthra-
cene rings; namely, the two octyl groups are magnetically
equivalent and the alkynic carbons give four peaks. The aro-
matic proton signals were observed as three singlets and
complicated multiplets (exactly four sets of ABC systems),
among which two singlets due to the 9-H atoms were shifted
downfield to d=10.5 ppm because of the anisotropic effect
of alkynic and aromatic moieties.
Scheme 1. Stereochemical and symmetric analyses of 1,8-anthrylene-ethy-
nylene cyclic tetramers 1–3 in equilibrium between the two diamond
forms via the square form. Molecular models are viewed along the acety-
lenic axes, where anthracene groups with and without 10-substituents are
indicated in red and blue, respectively. The diastereomeric relationship is
differentiated by a, b, or c, and the enantiomeric relationship is differen-
tiated by prime.
1
The H NMR spectra of 3 were recorded at low tempera-
ture in [D8]toluene (Figure 1). The multiplet signals in the
aromatic region became broad at À308C, and the singlets
also broadened at lower temperatures. The signal exchanges
were not completely frozen at À1008C, the lowest limit of
the measurement, thus producing very complicated signals
with the appearance of four peaks at d=5.5–6.2 ppm and at
least five peaks at d=10.2–11.0 ppm. This dynamic behavior
is explained by the skeletal swing illustrated in Scheme 1. If
the skeletal swing takes place very slowly on the NMR spec-
troscopic timescale, this compound should exist as a mixture
of two diastereomeric diamond forms (Scheme 1). The sig-
nals around d=6.0 ppm suggest that some of the aromatic
protons (2,3- or 6,7-H) are fixed in the shielding region of
the facing anthracene ring in the diamond structure.
Even though the exchange is not sufficiently slow at the
lowest temperature, the observed signals look more compli-
cated than those expected for the two diastereomeric forms,
each of which should give two singlets around d=10.5 ppm.
This means that another dynamic process, the rotation of
the octyl groups, is involved under the given conditions. We
observed that the rotation of the 10-butyl groups relative to
the attaching anthracene groups was restricted at low tem-
perature in 2 (barrier ca. 35 kJmolÀ1).[6b] Because the octyl
group is also a primary alkyl group, compound 3 should ex-
hibit similar dynamic behavior at comparable barriers. The
restricted rotation of the two octyl groups affords three dia-
stereomeric conformers for each diamond form; this is be-
rings, if necessary). We synthesized compound 3 with two
octyl groups at position 10 as a chiral derivative of the p-
conjugated macrocyclic compounds.[7] We herein report the
enantiomeric resolution of this hydrocarbon by chiral HPLC
and the spectroscopic features of the chiral cyclic tetramer
and its related oligomers.
Results and Discussion
Synthesis: Compound 3 was synthesized by the Sonogashira
coupling/desilylation strategy (Scheme 2).[8] Key compound
6 was prepared from 4,5-diiodo-9-anthrone 4[9] in two steps.
The cross-coupling between 6 and 7[6b] afforded dimer 8 in
82% yield. The trimethylsilyl group in 8 was selectively re-
moved by treatment with KF in ethanol, and terminal
alkyne 9 was again coupled with 6 to give trimer 10. This
product was desilylated with tetrabutylammonium fluoride
(TBAF)[10] and coupled with an excess of 1,8-diiodoanthra-
cene 12. Thus prepared, acyclic tetramer 13 was desilylated
with TBAF and the formed terminal alkyne was treated
with reagents for the Sonogashira coupling without isolation.
The chromatographic purification of the crude products af-
forded the desired cyclic product 3 in 31% yield. Although
this synthetic route, which involves the stepwise extension
of each anthracene unit, requires long steps, the overall
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S. Toyota et al.
Scheme 2. Synthesis of 3.
Table 1. UV/Vis and fluorescence data for cyclic tetramer 3 and the re-
lated acyclic oligomers in cyclohexane.
Absorption
Emission[d]
l [nm]
lmax [nm][b]
e[c]
Ff[e] Stokes shift [nm]
14[a] 351, 369, 390, 412 20900 416, 441, 469 0.53
4
8
10
13
3
373, 393, 405, 415 23500 445, 474
0.56
0.35
0.02
0.29
30
12
6
421, 443
31000 455, 477
31400 455, 480
35000 467, 492
401, 422, 449
419, 446
21
[a] 14: 1,8-bis[(triisopropylsilyl)ethynyl]anthracene see reference [6b].
[b] Wavelengths of maximum absorption in the p-band region. [c] Molar
extinction coefficient of the absorption at the longest wavelength. [d] Ex-
cited at 393 nm. [e] Fluorescence quantum yield determined relative to
9,10-diphenylanthracene.
Figure 1. Variable temperature (VT) 1H NMR spectra of 3 (solvent=
[D8]toluene). Signals labeled with * are due to the solvent.
approximately 30 nm to an even longer wavelength.[12] There
is no significant bathochromic effect for tetramers 13 and 3
compared with trimer 10. This trend indicates that trimer
and higher oligomers tend to take folded conformations
about the acetylenic axes to avoid further extension of the p
conjugation.
cause primary alkyl groups prefer to take bisected confor-
mations relative to the anthracene plane either inside or
outside the diamond.[11]
The emission band is shifted to a longer wavelength in the
order of 8, 10, and 3 from 445 to 467 nm with large values
of fluorescence quantum yields (Ff). In contrast, acyclic
tetramer 13 produces a weak and broad emission band at
480 nm. This quenching is attributed to the presence of an
iodine atom on the anthracene chromophore. The Stokes
Electronic spectra: The UV/Vis and fluorescence data of 3
and some acyclic oligomers are compiled in Table 1. The ab-
sorption at the longest wavelength was observed at approxi-
mately 415 nm for 1,8-bis[(triisopropylsilyl)ethynyl]anthra-
cene (14) and dimer 8, and that of trimer 10 was shifted by
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Anthracene–Acetylene Oligomers
FULL PAPER
shift of 3 is 21 nm, which is larger than that of the acyclic
analogue 13. There is no clear relationship between the
Stokes shift and the chain length.
small peaks and troughs in the other regions. The entire
band shape of the (+)-form is nearly a mirror image of that
of the (À)-form. The structured bands in the longer wave-
length region are correlated to the p band absorptions in the
UV spectrum. These chiroptical properties are conclusive
evidence of the enantiomeric resolution. Unfortunately, the
quantity of the resolved samples was too small to allow de-
termination of the absolute stereochemistry by experiment.
The theoretical approach seems to be very difficult at pres-
ent as one molecule consists of many atoms (144 atoms).
Further studies are needed to solve these problems.
Enantiomeric resolution: We attempted the enantiomeric
resolution of 3 by using several types of chiral HPLC col-
umns (see Experimental Section) under various conditions.
Among them, only the Daicel Chiralcel OD column permit-
ted partial separation, even though the solubility of the
sample in the eluent was very low. The chromatogram that
was taken under the optimized conditions is shown in
Figure 2 in which the retention times of the two enantiomers
are 34.1 and 38.5 min (a=1.16, Rs =0.56). While the easily
eluted isomer was rendered practically enantiopure by a
Conclusion
The chiral 1,8-anthrylene-ethynylene cyclic tetramer con-
taining two octyl groups was conveniently synthesized by
the Sonogashira reaction. This compound is stereochemical-
ly interesting because the molecular chirality is attributed to
the stereogenic axes along the acetylenic moieties rather
than the center. Although the resolution of chiral hydrocar-
bons without significant functional groups is generally diffi-
cult, the resolution of this macrocyclic compound was ach-
ieved with an appropriate type of chiral column. The suc-
cessful resolution opens a new aspect in the chemistry of an-
thracene–acetylene oligomers, and helps us deepen our un-
derstanding of the chiroptical properties of such a chiral
macrocyclic scaffold.
Figure 2. Chromatogram of chiral HPLC with a Chiralcel OD column
(eluent=hexane/2-propanol 100:1).
single separation, the less easily eluted isomer was further
chromatographed to give a sample of approximately 95% ee
(ee=enantiomeric excess). This procedure was repeated sev-
eral times to supply milligram order samples of both enan-
tiomers.
The specific rotations of the first and second eluted iso-
mers were determined as [a]2D3 =À95 and +91, respectively,
in cyclohexane. The CD spectra of these enantiomers are
shown in Figure 3. The (À)-form has an intense trough at
276 nm and complicated bands at 400–480 nm in addition to
Experimental Section
General: Melting points are uncorrected. Elemental analyses were per-
formed with a Perkin–Elmer 2400 series analyzer. NMR spectra were
measured on a Varian Gemini-300 (1H: 300 MHz, 13C: 75 MHz) or a
JEOL Lambda-500 (1H: 500 MHz, 13C: 125 MHz) spectrometer. HRMS
(FAB) were measured on a JEOL MStation-700 spectrometer. MALDI-
TOF mass spectra were measured on a Voyager-Biocad spectrometer.
UV/Vis spectra were measured on a Hitachi U-3000 spectrometer with a
10 mm cell. Optical rotations were measured on a JASCO DIP-370 polar-
imeter by using a 10 mm1”100 mm cell. CD spectra were measured on
a JASCO J-820 spectropolarimeter by using a 1 mm cell. Column chro-
matography was carried out with Merck Silica Gel 60 (70–230 mesh) or
Fuji Silysia Chromatorex-NH (100–200 mesh).
1,8-Diiodo-10-octylanthracene (5): A solution of octylmagnesium bro-
mide in diethyl ether (50 mL) was prepared from magnesium (1.39 g,
57.0 mmol) and 1-bromooctane (10.2 mL, 58.9 mmol) in an ordinary
manner. After this solution had been diluted with diethyl ether (150 mL),
4,5-diiodo-9-anthrone (4)[9] (8.48 g, 19.0 mmol) was added and the mix-
ture was stirred at room temperature for 20 h under Ar. The reaction
mixture was then quenched with aqueous NH4Cl (40 mL) and extracted
with diethyl ether. Finally, the organic solution was dried over MgSO4
and evaporated. The crude product was purified by chromatography on
silica gel (hexane). Recrystallization of the first fraction (Rf =0.55,
hexane) gave the desired compound as a yellow solid (5.36 g, 52%). The
second fraction afforded 1,8-diiodoanthracene as a byproduct (2.04 g,
25%), and the starting material (1.21 g, 14%) was recovered as the least
1
easily eluted fraction. M.p. 85.5–86.58C; H NMR (300 MHz, CDCl3): d=
0.89 (m, 3H), 1.28–1.37 (m, 8H), 1.55 (m, 2H), 1.76 (m, 2H), 3.55 (t, J=
8.2 Hz, 2H), 7.21 (dd, J=7.2, 8.8 Hz, 2H), 8.16 (d, J=7.2 Hz, 2H), 8.23
(d, J=8.8 Hz, 2H), 8.95 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=
14.11, 22.65, 28.47, 29.29, 29.48, 30.25, 31.58, 31.87, 101.53, 125.36, 126.61,
Figure 3. CD spectra of enantiomers of chiral cyclic tetramer 3 (solvent=
cyclohexane).
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S. Toyota et al.
130.14, 132.87, 136.34, 137.45, 137.56 ppm; HRMS (FAB): m/z: calcd for
C22H24I2: 541.9968; found: 541.9999 [M]+; elemental analysis calcd (%)
for C22H24I2 (542.23): C 48.73, H 4.46; found: C 48.39, H 4.38.
(hexane/dichloromethane) gave the pure material as a yellowish green
solid (1.02 g, 79%). M.p. 205–2078C; 1H NMR (500 MHz, CDCl3): d=
À0.14 (s, 9H), 0.76 (m, 21H), 0.90–0.92 (m, 6H), 1.31–1.48 (m, 16H),
1.54 (t, J=8.3 Hz, 2H), 1.62 (m, 2H), 1.70 (m, 2H), 1.87 (m, 2H), 3.41 (t,
J=8.3 Hz, 2H), 3.67 (t, J=8.3 Hz, 2H), 6.42 (dd, J=2.2, 8.9 Hz, 1H),
6.80 (dd, J=1.6, 8.6 Hz, 1H), 7.26–7.32 (m, 3H), 7.48 (d, J=6.7 Hz, 1H),
7.51–7.56 (m, 2H), 7.61–7.66 (m, 3H), 7.73 (d, J=8.9 Hz, 1H), 7.78 (d,
J=8.9 Hz, 1H), 7.88 (d, J=6.7 Hz, 1H), 7.91 (d, J=6.7 Hz, 1H), 8.02 (d,
J=8.9 Hz, 1H), 8.13 (s, 1H), 8.32–8.35 (m, 2H), 9.28 (s, 1H), 9.32 (s,
1H), 10.00 ppm (s, 1H); 13C NMR (125 MHz, CDCl3) d=À0.38, 11.23,
14.14, 14.16, 18.43, 22.70, 28.29, 29.37, 29.40, 29.59, 29.62, 30.35, 31.51,
31.75, 31.93, 92. 66, 92.73, 92.97, 93.69, 96.43, 99.59, 103.47, 104.91,
121.05, 121.58, 121.81, 122.11, 122.62, 122.90, 122.92, 123.79, 123.89,
124.34, 124.37, 124.64, 124.67, 124.95, 124.98, 125.17, 125.26, 126.99,
128.13, 128.54, 128.64, 128.77, 129.51, 129.53, 129.80, 129.96, 130.33,
130.66, 130.84, 130.87, 130.89, 131.04, 131.16, 131.50, 131.83, 135.74,
136.50 ppm (five aromatic signals missing); UV/Vis (cyclohexane): lmax
(e)=254 (214000), 421 (30800), 443 nm (31000 molÀ1 LcmÀ1); fluores-
cence (cyclohexane): lem =455, 477 nm (lex =393 nm, Ff =0.35); HRMS
(FAB): m/z: calcd for C78H86Si2: 1078.6268; found: 1078.6304 [M]+; ele-
mental analysis calcd (%) for C78H86Si2 (1079.69): C 86.77, H 8.03; found:
C 86.38, H 7.99.
1-Iodo-10-octyl-8-[(trimethylsilyl)ethynyl]anthracene (6): A solution of 5
(3.60 g, 6.64 mmol) in a mixture of isopropylamine (14 mL) and THF
(84 mL) was degassed by bubbling Ar for 20 min. TMSA (0.91 mL,
6.5 mmol), [Pd(PPh3)4] (149 mg, 0.129 mmol), and CuI (24.6 mg,
0.129 mmol) were added to the solution, and the resulting mixture was
refluxed for 17 h under Ar. After the solvent had been evaporated, the
residue was chromatographed on silica gel (hexane). The desired com-
pound was obtained as yellow oil (1.68 g, 49%) with recovery of the
starting material (1.15 g, 32%). 1H NMR (500 MHz, CDCl3): d=0.43 (s,
9H), 0.86 (m, 3H), 1.28 (m, 8H), 1.46 (m, 2H), 1.65 (m, 2H), 3.39 (t, J=
8.0 Hz, 2H), 7.07 (dd, J=1.3, 8.6 Hz, 1H), 7.36 (dd, J=1.6, 8.9 Hz, 1H),
7.69 (d, J=7.0 Hz, 1H), 8.05 (d, J=7.1 Hz, 1H), 8.09–8.12 (m, 2H),
9.12 ppm (s, 1H); 13C NMR (125 Hz, CDCl3): d=0.34, 14.13, 22.65, 28.25,
29.29, 29.46, 30.21, 31.53, 31.86, 100.60, 101.74, 103.19, 121.90, 125.07,
125.31, 125.40, 126.11, 129.26, 129.57, 129.73, 130.26, 132.05, 132.07,
136.93, 137.13 ppm; HRMS (FAB): m/z: calcd for C22H33ISi: 512.1396;
found: 512.1376 [M]+.
Dimer 8: [Pd(PPh3)4] (67.6 mg, 58.5 mmol) and CuI (11.1 mg, 58.5 mmol)
were added to a degassed solution of 6 (1.00 g, 1.95 mmol) and 7[6b]
(1.12 g, 2.93 mmol) in a mixture of triethylamine (50 mL) and THF
(50 mL). After the solution had been refluxed for 26 h under Ar, the sol-
vent was removed by evaporation. The crude product was purified by
chromatography on silica gel (hexane/dichloromethane 15:1). The desired
compound was obtained as yellowish green oil (1.23 g, 82%). 1H NMR
(500 MHz, CDCl3): d=À0.34 (s, 9H), 0.70 (m, 21H), 0.92 (m, 3H), 1.25–
1.41 (m, 8H), 1.59 (m, 2H), 1.82 (m, 2H), 3.62 (t, J=8.0 Hz, 2H), 7.40–
7.45 (m, 2H), 7.49–7.56 (m, 2H), 7.70 (d, J=6.7 Hz, 1H), 7.74 (d, J=
6.7 Hz, 1H), 7.91 (d, J=6.7 Hz, 1H), 7.95 (d, J=7.0 Hz, 1H), 8.00 (d, J=
8.6 Hz, 1H), 8.05 (d, J=8.6 Hz, 1H), 8.27 (d, J=8.9 Hz, 1H), 8.33 (d, J=
9.1 Hz, 1H), 8.47 (s, 1H), 9.57 (s, 1H), 9.59 ppm (s, 1H); 13C NMR
(125 MHz, CDCl3): d=À0.76, 11.01, 14.14, 18.33, 22.69, 28.30, 29.36,
29.59, 30.30, 31.69, 31.92, 92.21, 92.59, 96.74, 100.11, 103.03, 104.75,
121.83, 122.25, 122.53, 123.31, 124.35, 124.80, 124.91, 124.96, 125.07,
125.40, 125.46, 127.44, 128.82, 129.02, 129.27, 129.39, 130.57, 130.81,
131.42, 131.47, 131.53, 131.56, 131.68, 131.71, 136.58 ppm (three aromatic
signals missing); UV/Vis (cyclohexane): lmax (e)=266 (217000), 373
(12400), 393 (20100), 405 (22700), 415 nm (23500 molÀ1 LcmÀ1); fluores-
cence (cyclohexane): lem =445, 474 nm (lex =393 nm, Ff =0.56); HRMS
(FAB): m/z: calcd for C54H62Si2: 766.4390; found: 766.4409 [M]+.
Desilylated trimer 11: A solution of TBAF (0.50 mL, 0.50 mmol) in THF
(1.0 molLÀ1) was added to a solution of 10 (865 mg, 0.801 mmol) in
chloroform (120 mL). The solution was stirred for 5 h at room tempera-
ture, and was then quenched with water. The organic layer was separat-
ed, dried over MgSO4, and evaporated. The crude product was purified
by chromatography on silica gel (hexane/dichloromethane 5:1) to give
the pure compound as a yellowish green solid (757 mg, 94%). M.p. 165–
1678C; 1H NMR (500 MHz, CDCl3): d=0.75 (m, 21H), 0.89–0.92 (m,
6H), 1.31–1.45 (m, 16H), 1.54 (m, 2H), 1.63 (m, 2H), 1.71 (m, 2H), 1.87
(m, 2H), 3.00 (s, 1H), 3.36 (t, J=8.2 Hz, 2H), 3.65 (t, J=8.3 Hz, 2H),
6.58 (dd, J=2.2, 8.9 Hz, 1H), 6.80 (t, J=7.7 Hz, 1H), 7.14 (d, J=6.7 Hz,
1H), 7.16–7.22 (m, 2H), 7.48 (d, J=7.3 Hz, 2H), 7.52–7.57 (m, 3H), 7.61
(d, J=6.7 Hz, 1H), 7.72 (d, J=8.6 Hz, 1H), 7.76 (d, J=9.2 Hz, 1H),
7.89–7.91 (m, 2H), 7.93 (d, J=9.2 Hz, 1H), 7.99 (s, 1H), 8.31–8.35 (m,
2H), 9.33 (s, 1H), 9.34 (s, 1H), 10.09 ppm (s, 1H); 13C NMR (CDCl3) d=
11.27, 14.15, 14.16, 18.45, 22.71, 28.24, 28.41, 29.39, 29.59, 29.61, 30.39,
30.41, 31.50, 31.76, 31.94, 81.95, 82.58, 92.93, 93.13, 93.43, 93.58, 96.25,
105.02, 121.05, 121.23, 121.72, 121.83, 122.72, 122.99, 123.12, 123.78,
124.08, 124.17, 124.28, 124.30, 124.42, 124.50, 125.01, 125.11, 125.16,
125.18, 125.22, 126.90, 128.07, 128.60, 128.62, 129.34, 129.47, 129.50,
129.83, 129.91, 130.10, 130.57, 130.61, 130.82, 130.85, 130.87, 131.00,
131.08, 131.51, 131.63, 131.77, 135.50, 136.53 ppm (one aromatic signal
missing); UV/Vis (cyclohexane): lmax (e)=252 (215000), 419 (32200),
445 nm (38600 molÀ1 LcmÀ1); HRMS (FAB): m/z: calcd for C75H78Si:
1006.5873; found: 1006.5897 [M]+.
Desilylated dimer 9: A solution of 8 (1.22 g, 1.59 mmol) and KF (462 mg,
7.95 mmol) in ethanol (160 mL) was refluxed for 3 h. After this time, the
solvent was mostly removed by evaporation, and the resulting residue
was extracted with dichloromethane. The crude product was purified by
chromatography on silica gel (hexane/dichloromethane 7:1). The desired
compound was obtained as yellowish green oil (1.02 g, 92%). 1H NMR
(500 MHz, CDCl3): d=0.78 (m, 21H), 0.89 (t, J=6.8 Hz, 3H), 1.29–1.31
(m, 6H), 1.40 (m, 2H), 1.57 (m, 2H), 1.81 (m, 2H), 2.92 (s, 1H), 3.59 (t,
J=8.2 Hz, 2H), 7.39–7.44 (m, 2H), 7.49 (dd, J=1.5, 8.3 Hz, 1H), 7.53
(dd, J=2.2, 8.9 Hz, 1H), 7.69 (d, J=6.4 Hz, 1H), 7.76 (d, J=6.7 Hz, 1H),
7.91 (d, J=6.7 Hz, 1H), 7.96 (d, J=8.9 Hz, 1H), 7.98–8.02 (m, 2H), 8.26
(d, J=9.2 Hz, 1H), 8.30 (d, J=9.2 Hz, 1H), 8.34 (s, 1H), 9.66 (s, 1H),
9.70 ppm (s, 1H); 13C NMR (125 MHz, CDCl3): d=11.21, 14.13, 18.40,
22.68, 28.29, 29.35, 29.56, 30.33, 31.71, 31.91, 81.73, 82.64, 93.04, 93.23,
96.70, 104.89, 121.40, 121.81, 121.93, 122.57, 123.24, 124.41, 124.74, 124.96,
125.03, 125.09, 125.39, 125.66, 127.51, 128.84, 129.04, 129.20, 129.38,
129.94, 130.68, 131.29, 131.41, 131.47, 131.48, 131.50, 131.60, 131.73,
131.89, 136.68 ppm; UV/Vis (cyclohexane): lmax (e)=263 (205000), 390
(17600), 410 (23600), 420 nm (22900 molÀ1 LcmÀ1); HRMS (FAB): m/z:
calcd for C51H54Si: 694.3995; found: 694.4020 [M]+.
Tetramer 13: [Pd(PPh3)4] (64 mg, 56 mmol) and CuI (11 mg, 56 mmol)
were added to a degassed solution of 11 (600 mg, 0.56 mmol) and 1,8-
diiodoanthracene 12 (717 mg, 1.67 mmol) in a mixture of triethylamine
(24 mL) and THF (24 mL). After the solution had been refluxed for 41 h
under Ar, the solvent was removed by evaporation. The crude product
was purified by chromatography on silica gel (hexane/dichloromethane
5:1) to give the pure material as a yellowish green solid (460 mg, 63%),
along with some recovered 12 (131 mg). M.p. 208–2108C; 1H NMR
(500 MHz, CDCl3): d=0.60 (m, 21H), 0.89–0.95 (m, 6H), 1.35–1.52 (m,
16H), 1.61–1.64 (m, 4H), 1.76–1.79 (m, 4H), 3.38–3.41 (m, 4H), 6.58 (t,
J=8.3 Hz, 1H), 6.63 (t, J=8.2 Hz, 1H), 6.72 (t, J=8.5 Hz, 1H), 6.86 (t,
J=8.6 Hz, 1H), 6.94 (t, J=8.0 Hz, 1H), 7.14 (d, J=6.7 Hz, 1H), 7.18–
7.24 (m, 2H), 7.27–7.37 (m, 4H), 7.42 (d, J=6.4 Hz, 1H), 7.55 (d, J=
6.4 Hz, 1H), 7.60 (d, J=6.4 Hz, 1H), 7.68–7.70 (m, 2H), 7.74–7.79 (m,
3H), 7.81 (s, 1H), 7.86 (s, 1H), 7.92–7.98 (m, 4H), 9.00 (s, 1H), 9.10 (s,
1H), 9.70 (s, 1H), 9.72 ppm (s, 1H); 13C NMR (125 MHz, CDCl3): d=
11.24, 14.17, 14.18, 18.32, 22.74, 28.30, 28.40, 29.44, 29.66, 29.68, 30.50,
30.53, 31.50, 31.53, 31.97, 92.76, 92.88, 93.11, 93.37, 93.68, 93.77, 96.11,
100.87, 105.06, 120.87, 120.95, 120.97, 121.02, 121.90, 122.11, 122.35,
122.78, 122.93, 123.50, 123.55, 123.66, 123.94, 124.01, 124.21, 124.38,
124.41, 124.57, 124.94, 125.63, 126.60, 126.66, 126.70, 126.75, 127.09,
127.44, 128.46, 128.68, 128.75, 128.78, 128.85, 129.02, 129.23, 129.38,
Trimer 10: [Pd(PPh3)4] (50 mg, 43 mmol) and CuI (8.2 mg, 43 mmol) were
added to a degassed solution of 9 (831 mg, 1.20 mmol) and 6 (738 mg,
1.44 mmol) in a mixture of triethylamine (30 mL) and THF (30 mL).
After the solution had been refluxed for 43 h under Ar, the solvent was
removed by evaporation. The crude product was purified by chromatog-
raphy on silica gel (hexane/dichloromethane 7:1). Recrystallization
2486
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 2482 – 2487

Anthracene–Acetylene Oligomers
FULL PAPER
129.69, 130.18, 130.48, 130.51, 130.58, 130.66, 130.73, 130.74, 130.75,
130.91, 131.15, 131.21, 131.23, 131.34, 131.83, 135.02, 135.07, 136.65,
136.73, 137.70 ppm; UV/Vis (cyclohexane): lmax (e)=248 (304000), 401
(30400), 422 (33700), 449 nm (31400 molÀ1 LcmÀ1); fluorescence (cyclo-
hexane): lem =455, 480 nm (lex =393 nm, Ff =0.02); HRMS (MALDI-
TOF): m/z: calcd for C89H85ISi: 1308.39; found: 1308.55 [M]+.
[D8]toluene. The sample temperatures were read from a thermocouple
equipped with the instrument after calibration by using the chemical shift
differences of the methanol signals.
Cyclic tetramer 3:
A solution of TBAF (80 mL, 80 mmol) in THF
(1.0 molLÀ1) was added to a solution of 13 (100 mg, 76.4 mmol; Rf =0.54,
hexane/CHCl3 2:1) in THF (10 mL) under Ar. After this solution had
been stirred for 10 min at room temperature, the TLC spot due to 13 dis-
appeared. Triethylamine (38 mL), THF (28 mL), [Pd(PPh3)4] (27 mg,
23 mmol), and CuI (4.3 mg, 23 mmol) were added to the solution of the
desilylated compound (Rf =0.44, hexane/CHCl3 2:1). The resulting mix-
ture was then stirred for 8 h at room temperature. After this time, the
solvent was evaporated, and the residue was subjected to chromatogra-
phy on NH-type silica gel (hexane/CHCl3 5:1). Recrystallization (hexane/
CHCl3) afforded the cyclic tetramer as a yellowish green solid (24.5 mg,
31%, Rf =0.48 with hexane/CHCl3 2:1). M.p. 221–2238C; 1H NMR
(500 MHz, [D6]benzene: d=0.97–0.98 (m, 6H), 1.29–1.45 (m, 16H), 1.55–
1.59 (m, 4H), 1.77–1.83 (m, 4H), 3.37–3.41 (m, 4H), 6.59–6.71 (m, 8H),
7.30–7.37 (m, 8H), 7.46–7.49 (m, 4H), 7.83–7.86 (m, 4H), 7.93 (s, 2H),
10.44 (s, 2H), 10.46 ppm (s, 2H); 13C NMR (125 MHz, CDCl3): d=14.19,
22.75, 28.51, 29.47, 29.68, 30.54, 31.58, 31.97, 93.07, 93.17, 93.47, 93.58,
121.26, 121.34, 121.99, 122.09, 123.47, 124.25, 124.28, 124.37, 124.56,
124.62, 126.89, 128.07, 128.18, 128.83, 128.85, 129.46, 129.52, 129.71,
129.73, 130.75, 130.80, 130.98, 135.68 ppm (five aromatic signals missing);
UV/Vis (cyclohexane): lmax (e)=261 (196000), 419 (35000), 446 nm
(35000 molÀ1 LcmÀ1); fluorescence (cyclohexane): lem =467, 492 nm
Acknowledgements
This work was partly supported by the High-Tech Research Center Proj-
ect for Private Universities: matching fund subsidy from MEXT (Minis-
try of Education, Culture, Sports, Science, and Technology, Japan), 2001–
2005, and by a grant from the Sumitomo Foundation.
[1] a) Advances in Polymer Science, Vol. 117: Poly(arylene ethynylene)s
(Ed.: C. Weder), Springer, Heidelberg, 2005; b) Acetylene Chemistry
(Eds.: F. Diederich, P. J. Stang, R. R. Tykwinski), Wiley-VCH, Wein-
heim, 2005; c) Modern Arene Chemistry (Ed.: D. Astruc), Wiley-
VCH, Weinheim, 2002.
[2] a) S. Hçger, Chem. Eur. J. 2004, 10, 1320–1329; b) A. S. Shetty, J.
Zhang, J. S. Moore, J. Am. Chem. Soc. 1996, 118, 1019–1029; c) T.
Kawase, K. Tanaka, N. Shiono, Y. Seirai, M. Oda, Angew. Chem.
2004, 116, 1754–1756; Angew. Chem. Int. Ed. 2004, 43, 1722–1724;
d) D. Zhao, J. S. Moore, Chem. Commun. 2003, 807–818.
[3] J. A. Marsden, G. J. Palmer, M. M. Haley, Eur. J. Org. Chem. 2003,
2355–2369.
[4] a) C. A. Breen, S. Rifai, V. Bulovic, T. M. Swager, Nano Lett. 2005,
5, 1597–1601; b) C. A. Breen, T. Deng, T. Breiner, E. L. Thomas,
T. M. Swager, J. Am. Chem. Soc. 2003, 125, 9942–9943.
[5] For recent examples of anthrylene-ethynylene oligomers see: a) T.
Kaneko, T. Makino, H. Miyaji, A. Onuma, M. Teraguchi, T. Aoki,
Polyhedron 2003, 22, 1845–1850; b) T. Kaneko, T. Makino, H.
Miyaji, A. Onuma, M. Teraguchi, T. Aoki, J. Am. Chem. Soc. 2003,
125, 3554–3557.
[6] a) S. Toyota, M. Goichi, M. Kotani, Angew. Chem. 2004, 116, 2298–
2301; Angew. Chem. Int. Ed. 2004, 43, 2248–2251; b) S. Toyota, M.
Goichi, M. Kotani, M. Takezaki, Bull. Chem. Soc. Jpn. 2005, 78,
2214–2227.
(lex =393 nm, Ff =0.29); HRMS (MALDI-TOF): m/z: calcd for C80H64
:
1024.50; found: 1024.47 [M]+; elemental analysis calcd (%) for C80H64
(1025.36): C 93.71, H 6.29; found: C 93.33, H 6.18.
Enantiomeric resolution of 3: Chiral HPLC was carried out with a HI-
TACHI L-6250 pump by using Daicel Chiralcel OD, Chiralpak AD, and
Chiralpak IA columns (semi-preparative size: 10 mm1”250 mm). The
resolution was successful with the OD column under the following condi-
tions: eluent, hexane/2-propanol 100:1; flow rate, 2.0 mLminÀ1; and ap-
proximately 0.2 mg of racemic sample in 1.0 mL of the eluent. The enan-
tiomers were eluted at the retention times of 34.1 and 38.5 min with par-
tial separation. For preparative purposes, a racemic sample (0.8 mg in
2.0 mL of eluent) was injected for each batch, and a total of 21 mg of
sample was subjected to separation. The easily eluted part was collected
(before the valley of the two peaks, ca. 6 mg), which was practically enan-
tiopure as checked by HPLC analysis. The second fraction (after the
valley, ca. 14 mg) was separated again by chromatography to give an
almost enantiopure sample (ca. 4 mg) of the less easily eluted isomer.
Further purification was far from practical as the sample gradually de-
composed in the eluent system.
[7] For selected examples of chiral p-conjugated hydrocarbons in enan-
tiopure forms see: a) A. Rajca, H. Wang, P. Bolshov, S. Rajca, Tetra-
hedron 2001, 57, 3725–3735; b) A. Rajca, A. Safronov, S. Rajca, J.
Wongsriratanakul, J. Am. Chem. Soc. 2000, 122, 3351–3357; c) G.
Wittig, K. D. Rꢁmpler, Justus Liebigs Ann. Chem. 1971, 751, 1–16.
[8] K. Sonogashira in Handbook of Organopalladium Chemistry for Or-
ganic Synthesis, Vol. 1 (Eds.: E. -i. Negishi, Wiley, New York, 2002,
pp. 493–529, and references therein.
First fraction (À)-form: M.p. 114–1168C; >98% ee; [a]2D3 =À95 (c=0.075
in cyclohexane); CD (1.9”10À4 molLÀ1 in cyclohexane): l (De)=255 (+
7.9), 276 (À18.8), 318 (À0.1), 326 (À4.2), 344 (À0.5), 411 (À1.4), 427 (+
1.1), 436 (À3.6), 446 (+4.7), 459 nm (À1.3 molÀ1 LcmÀ1); HRMS
(MALDI-TOF): m/z: calcd for C80H64: 1024.50; found: 1024.40 [M]+.
[9] a) J. M. Lovell, J. A. Joule, Synth. Commun. 1997, 27, 1209–1215;
b) M. Goichi, K. Segawa, S. Suzuki, S. Toyota, Synthesis 2005, 2116–
2118.
[10] The desilylation of the TMS group with KF proceeded very slowly
for 10 as a result of steric hindrance and therefore, TBAF was used
in this step. The desilylation of the triisopropylsilyl (TIPS) group
was not observed when the reaction was carried out in chloroform.
In contrast, the desilylation of the TMS and TIPS groups took place
rapidly for 13 in THF.
[11] E. L. Eliel, S. H. Wilen, L. M. Mander, Stereochemistry of Organic
Compounds, Wiley, New York, 1994, Chapter 10.2.
[12] The bathochromic shift could be attributed to the through-space in-
teractions between the chromophores. Further studies will reveal
this point.
Second fraction (+)-form: M.p. 114–1178C; 95% ee; [a]2D3 =+91 (c=0.03
in cyclohexane); CD (1.4”10À4 molLÀ1 in cyclohexane): l (De)=255
(À8.8), 276 (+18.0), 318 (+0.6), 327 (+2.9), 344 (+1.5), 410 (+0.8), 427
(À0.9), 437 (+1.6), 447 (À2.4), 458 nm (+0.9 molÀ1 LcmÀ1); HRMS
(MALDI-TOF): m/z: calcd for C80H64: 1024.50; found: 1024.52 [M]+.
Fluorescence measurements: Fluorescence spectra were measured on a
JASCO FP-6500 spectrofluorometer with a 10 mm cell at room tempera-
ture. The sample was dissolved in cyclohexane (1.0”10À5–1.0”
10À6 molLÀ1), which was degassed with Ar immediately before the mea-
surement. The spectra were measured upon excitation at 393 nm. The
fluorescence quantum yields were determined with a 9,10-diphenylan-
thracene sample as standard by the standard method.[13]
[13] B. Valeur, Molecular Fluorescence, Wiley-VCH, Weinheim, 2002,
Chapter 3.2.
Variable temperature (VT) 1H NMRspectroscopic measurements : VT
Received: September 8, 2005
Published online: January 3, 2006
1H NMR spectra were measured on a JEOL GSX-400 at 400 MHz in
Chem. Eur. J. 2006, 12, 2482 – 2487
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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