Tribenzotriquinacenes bearing six-fold benzofuran extensions: Electron-rich C3v-symmetrical hosts for C60

Article abstract of DOI:10.1021/jo2000918

New tribenzotriquinacene (TBTQ) hosts bearing six-fold peripheral benzofuran functionalization have been synthesized. The three polycondensed arene wings were shown to operate optically independently and to generate deeply bowl-shaped C_3v-symme

Full text of DOI:10.1021/jo2000918

ARTICLE
pubs.acs.org/joc
Tribenzotriquinacenes Bearing Six-Fold Benzofuran Extensions:
Electron-Rich C3v-Symmetrical Hosts for C60
Tao Wang,† Zi-Yang Li,† An-Le Xie,† Xiao-Jun Yao,† Xiao-Ping Cao,*,† and Dietmar Kuck*,‡
†State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University,
Lanzhou 730000, People’s Republic of China
‡Department of Chemistry, Bielefeld University, Universit€atsstrasse 25, 33615 Bielefeld, Germany
S Supporting Information
b
ABSTRACT: New tribenzotriquinacene (TBTQ) hosts bear-
ing six-fold peripheral benzofuran functionalization have been
synthesized. The three polycondensed arene wings were shown
to operate optically independently and to generate deeply bowl-
shaped C3v-symmetrical frameworks that act as relatively weak
hosts toward C60, as revealed by 1H NMR spectroscopy.
’ INTRODUCTION
the deep-cavity framework of the TBTQ core within the tristhian-
threne 2 and novel TBTQ-based “sockets”, such as 3, with respect to
their supramolecular interaction with fullerenes.35,36 In the present
report, we describe the synthesis of another set of rigid molecular
building blocks based on the TBTQ structural motif. In the title
compounds 12 and 13 (see below), six benzofuran groupings were
either attached or annelated, respectively, to the outer periphery of
the TBTQ skeleton. These strongly extended polycyclic TBTQ
structures turned out to act as suitable supramolecular hosts for C60
fullerene in solution. Because of the unique orthogonal orientation of
the three electronically independent indane wings of the TBTQ
core,26,27,37 the optical properties of the three-fold chromophores 12
and 13, as well as of their synthetic precursor, the TBTQ-based
hexatolane 10, were compared to those of the corresponding
monomeric units, for example, the bisbenzofurans 16 and 17 and
the ditolan 15.
The design and synthesis of preorganized bowl-shaped macro-
cyclic hosts which can have applications in supramolecular and
material chemistry has been of considerable interest in recent years.
In particular, calix[n]arenes,1ꢀ8 resorcarenes,9ꢀ14 cyclodextrins,15
cyclotriveratrylenes,16ꢀ18 corannulenes,19ꢀ21 and similar macro-
cyclic frameworks have been studied,22 all providing efficient
shape complementarity to spherical, mostly C60 fullerene, guests.
From all of these investigations, it has become evident that a
diversity of structures may be capable of associating with C60 at
different abilities and in various organic solvents, such as benzene,
toluene, or carbon disulfide. The solubilities of C60 in these
solvents are sufficiently high to enable the reliable determination
of the binding constants of such hostꢀguest complexes by
spectroscopic titration experiments. UVꢀvis spectroscopy and
1H NMR (complexation-induced chemical shift, “CIS”)23 mea-
surements have commonly been used to confirm the binding
constants. In some cases, C60 was found to cocrystallize with a
suitable guest in the solid state. Progress of the studies of C60
complexes in hostꢀguest chemistry, separation science, and
molecular electronics24,25 has prompted synthetic chemists to
construct well-designed host molecules possessing sizable bowl-,
belt-, or cage-shaped cavities.
The molecular framework of the tribenzotriquinacenes (TBTQs)
forms a unique conformationally rigid, C3v-symmetrical, bowl-shaped
structural motif consisting of three mutually fused indane units.
Unidirectional and strictly parallel columnar stacking was found for
single crystals of both 1a and 1b (Figure 1).26ꢀ28 The concave
molecular surface was found to exert a strongly negative electrostatic
potential.29,30 Various multiple functionalizations and sketetal exten-
sions have already been reported by us and others.26ꢀ28,31ꢀ38
Various applications have recently been suggested for the use of
’ RESULTS AND DISCUSSION
Our endeavors on the new benzofurano-annelated tribenzo-
triquinacenes has been based on the hexabromo derivative 926,33
and the protected ethynylphenol building block 8. The latter
compound was prepared in four steps with 44% overall yield
from commercially available 4-tert-butylphenol according to the
literature39ꢀ41 (Scheme 1). Six-fold Sonogashira coupling of 9
with the terminal alkyne 8 (g25 equiv) gave the TBTQ-based
hexatolane 10 in 82% yield, in analogy to previous results
1
(Scheme 2).12 The H NMR spectrum of 10 exhibited four
distinct resonances in the arene region, and the 13C NMR
spectrum showed exactly nine signals, which nicely reflect the
Received: January 13, 2011
Published: March 23, 2011
r
2011 American Chemical Society
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Figure 1. Parent tribenzotriquinacenes 1 and the TBTQ derivatives 2 and 3 studied with respect to their association with fullerenes in the liquid and/or
solid state.
Scheme 1. Synthesis of the Arylacetylene Building Block 8
molecular C3v-symmetry of this compound. Its structure was
further determined by X-ray single-crystal analysis (Figure 2a).
As expected, the TBTQ framework of 10 was found to have the
regular C3v-symmetry, but the two tolane units within each wing
adopt different angles about their acetylene axes. As a conse-
quence, the t-butyl and acetoxy groups pending at the respective
aryl groups are oriented in alternate directions, one to the
concave and the other to the convex side of the TBTQ frame-
work, giving rise to C3 molecular symmetry overall. Surprisingly,
two molecules of 10 form a large cavity through a strong face-to-
face interaction by hydrogen bonding and πꢀπ stacking
(Figure 2b). In fact, the whole crystal structure of 10 shows very
regular molecular stacking (Figure 2c), a frequently recurring
feature of multiply functionalized TBTQ derivatives.
Benzofurans are important building blocks in organic chem-
istry and in the life sciences because of their presence in many
natural products and their interesting chemical and physiological
properties.42ꢀ47 They have been the subject of extensive studies,
and numerous synthetic methods in benzofuran chemistry have
been developed.48ꢀ56 Benzofurans can be synthesized via reac-
tion of 2-halophenols with copper(I) acetylides57ꢀ59 and via
palladium-catalyzed heteroannulation of 2-halophenols with term-
inal or internal alkynes.60ꢀ64 As compared to monobenzofurans,
reports on the synthesis of dibenzofurans or higher congeners are
very limited. Aiming at the synthesis of the TBTQ-based trisben-
zofuran 13, we studied several strategies to generate six benzo-
furanyl residues in a single step by starting either from the
precursor 10 or from its deprotected analogue 11. In particular,
hexaphenol 11 was subjected to metal (PdII, AuI, ZnII) catalysis
by use of various bases, but different bases were also applied for
the direct conversion of the hexaester 10 by concomitant
saponification and cyclization. The best results were obtained
with the sodium-hydroxide-promoted reaction of the latter
compound in methanol under reflux, which afforded the desired
six-fold benzofuranyl-substituted tribenzotriquinacene 12 in 46%
yield. By contrast, hexaphenol 11 upon treatment with palla-
dium(II) acetate and cesium carbonate in dimethylacet-
1
amide at 80 °C gave this product in 26% yield only. H and
13C NMR spectroscopy unequivocally confirmed the constitu-
tion of 12. Subsequent oxidation using ferric chloride (4 equiv
per CꢀC bond) in nitromethane at 0 °C produced the target
compound 13 in 85% yield. Remarkably, use of an excess of
FeCl3 gave rise to decomposition. The 1H NMR spectrum of 13
reveals a downfield shift of all of the arene resonances due to the
much better conjugated arene units. The pronounced vaulting of
the convexꢀconcave molecular structures of the new TBTQ
derivatives and of the benzofuran derivatives 12 and 13, in
particular, is illustrated in Figure 4 (see below).
In order to shed some light on the interaction of the three
conjugated aromatic flaps attached to the TBTQ cores of 10ꢀ13
with their three mutually orthogonal arene units, the “mono-
mers” 15ꢀ17 were synthesized for comparison (Scheme 3). The
most efficient procedures that had led us to the TBTQ derivative
13 were successfully applied here, as well. Thus, Sonogashira
coupling of dibromoxylene 14 with an excess of alkyne 8 gave the
simple ditolane 15 in 87% yield. In further analogy, treatment of
the latter compound with sodium hydroxide (6 equiv) in
methanol afforded the di(benzofuranyl)xylene 16 and, finally,
cyclodehydrogenation of 16 using ferric chloride (8 equiv)
furnished the monomer 17 in 88% yield.
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Scheme 2. Synthesis of the Six-fold Benzofurano-Annelated Trinaphthotriquinacene 13 via the TBTQ-Based Hexatolanes 10 and
11 and Hexa(benzofuranyl)tribenzotriquinacene 12
Compounds 10ꢀ13 and 15ꢀ17 represent new extended
π-electron systems. Therefore, intramolecular interaction of two
or more well-defined chromophores in these compounds opens a
further manifold with respect to possible exciton effects65ꢀ69 as
well as energy70 and electron transfer71 processes that can take
place between the chromophores. TBTQ derivatives bearing up
to six mutually fused indane units27,72,73 within their particularly
rigid polycyclic molecular frameworks offer such suitable core
scaffolds owing to their “Cartesian” geometry.26ꢀ28 To assess the
exciton interaction of three monomeric chromophores 15ꢀ17
when attached to the TBTQ scaffold, the relevant compounds
were characterized by UVꢀvis and fluorescence spectroscopy.
The band positions of the UVꢀvis and fluorescence spectra were
found to be almost the same for the tris-chromophores 10, 12,
and 13 and the respective monomers 15, 16, and 17, with the
exception that the maximum absorption of the most highly
annelated system, 13, is red-shifted by ca. 7 nm with respect to
that of 17 (Table 1). The data suggest that operating three
monomers 15ꢀ17 at the TBTQ core does not bring about
significant changes of the optical properties, which proves that
the three chromophores assembled at the TBTQ core are
electronically independent. This finding is in accordance with
our early studies of the centropolyindane family28 and, in
particular, with the report of Langhals et al. in 2008.37 The
quantum yields of the tris-chromophores 10, 12, and 13 de-
graded markedly with respect to corresponding monomers
15ꢀ17. This can be traced to the reduced efficiency of πꢀπ
stacking due to the strongly bent TBTQ framework as compared
to the planar chromophores 15ꢀ17.
The new tris-chromophores 12 and 13 with their characteristic
C3v-symmetrical, deep-bowl topography represent analogues of the
TBTQ-based hosts 2and 3, which were shown to associate with C60
in solution and in the solid state.35,36 Therefore, 1H NMR titration
experiments of compounds 12 and 13 with C60 were carried out in
toluene-d8. Figure 3 shows the changes of the chemical shifts of 12
and 13 observed as a function of the molar ratio with C60 added. It is
evident that, in the case of the fully condensed compound 13, the
protons Hb at the periphery of the TBTQ core are increasingly
shielded by the guest molecule, whereas the benzofuran protons Hc
and Hd and the methyl protons Ha at the bridgeheads of the TBTQ
core are increasingly deshielded. The changes by deshielding are
somewhat smaller than that of the shielding effect. These observa-
tions are consistent with the formation of a complex in which the
C60 guest is deeply embedded into the cavity of 13. The Benesiꢀ
Hildebrand treatment for the calculation of Kassoc determined
for 298 K in toluene-d8 for the complex C60⊂12 gave a value of
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titration experiments with the hexatolan precursor 10 and C60 gave
no CIS changes at all. Therefore, we assume that steric hindance of
the acetyl and tert-butyl groups prevents access to the cavity of the
host in this case. The finding that host 13 forms a weaker complex
with C60 and that its protons Hb are strongly shielded, rather than
deshielded, by the guest molecule may indicate that the C60 is
positioned less deeply within the cavity of the host. This may be due
to a stronger interaction with the rigid and planar difurano[2,3:a,c]-
naphthalene unit of 13. Such extensive “face-to-face” πꢀπ stacking
is supported by the shortest distance of 3.18 Å of the C60 molecule
to the naphthalene plane of 13, as suggested by force-field (MMþ)
modeling.74 Since suitable crystals for X-ray crystal structure analysis
could not be obtained, molecular mechanics calculation using
MMþ force field was performed for the complexes of C60 with
the hosts 10, 12, and 13. The distances from the centroids of the C60
guest to the apexes (C-12d) of the TBTQ hosts in 10⊂C60,
12⊂C60, and 13⊂C60 were calculated to be markedly different,
13.11, 8.82, and 9.15 Å, respectively (Figure 4). These results are in
1
accordance with the H NMR titration experiments and thus
supportive of the hypothesis that the depth of the nesting of C60
into the concave surface of a TBTQ host molecule is an important
predictive criterion, as postulated previously.36 It appears that the
more flexible benzofuranyl-substituted tribenzotriquinacene 12
offers a tighter host—probably owing to an induced fitting of the
six electron-rich pendants—as compared to the much more rigid
annelated TBTQ analogue on 13.
’ CONCLUSION
We have developed a new and efficient extension of the bowl-
shaped tribenzotriquinacene framework by introducing either six
peripheral benzofuranyl residues or six annelated benzofurano
groups in a C3v-symmetrical orientation. Electron spectroscopy
confirms that the three mutually orthogonal chromophores are
electronically independent. These novel TBTQ-based trisbenzofur-
ans provide strongly extended molecular cavities that are suitable—
albeit relatively weak—hosts for C60, forming 1:1 complexes. We
expect that the great chemical versatility of tribenzotriquinacene
chemistry will increase the interest to study and apply TBTQ-based
hosts in supramolecular chemistry.
’ EXPERIMENTAL SECTION
General. All reactions that required anhydrous conditions were carried
out by standard procedures under argon. Commercially available reagents
were used as received. The solvents were dried by distillation over the
appropriate drying reagents. Petroleum ether used had a bp range of
60ꢀ90 °C. Reactions were monitored by TLC. Column chromatography
was generally performed through silica gel (200ꢀ300 mesh). IR spectra
were reported in wavenumbers (cmꢀ1). Melting points are uncorrected. 1H
NMR and 13C NMR spectra were recorded on a 400 or 600 MHz
spectrometer, as were the DEPT 135 experiments. Chemical shifts (δ)
are reported in parts per million relative to TMS (δ 0.00) for the 1H NMR
and to chloroform (δ 77.0) for the 13C NMR measurements. EI mass
spectra were recorded on a double focusing sector-field instrument; MALDI
spectra were measured on a ToF instrument and ESI spectra were obtained
with an ion trap mass spectrometer equipped with a standard nanoESI source.
Accurate mass measurements were obtained on an FT-ICR mass spectro-
meter (ESI, MALDI) or on the double focusing sector-field instrument (EI).
4-tert-Butyl-2-iodophenol (5). A solution of 4-tert-butylphenol
(4) (1.00 g, 6.67 mmol), potassium iodide (1.11 g, 6.69 mmol), and sulfuric
acid (0.56 mL, 10 mmol) in methanol (100 mL) was stirred at 0 °C while
hydrogen peroxide (30%) (1.38 mL, 13 mmol) was added dropwise.
Figure 2. X-ray crystallographic structures of 10: (a) molecular struc-
ture, (b) pairwise face-to-face aggregation, (c) crystal structure with a
top view onto the face-to-face dimers (see also Supporting Information).
544 ( 121 Mꢀ1, whereas the treatment for C60⊂13 gave a value of
321 ( 47 Mꢀ1. The calculations were based upon the chemical shift
changes observed for protons Hc of hosts 12 and 13. Job plots
confirmed the 1:1 stoichiometry of the complexation in both cases.
In the case of host 12, almost all of the protons, and Ha and Hb in
particular, were found to be increasingly deshielded upon com-
1
plexation with increasing amounts of C60. By contrast, H NMR
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Scheme 3. Synthesis of the “Monomeric” Chromophores 15ꢀ17
Table 1. Electron Spectroscopic Properties of the Simple
Chromophores 10, 12, and 13 and the Respective TBTQ-
Based Tris-Chromophores 15, 16, and 17
4-tert-Butyl-2-(2-trimethylsilylethynyl)phenyl acetate (7).
A solution of ester 6 (800 mg, 2.52 mmol), ethynyltrimethylsilane
(0.50 mL, 3.54 mmol), PdCl2(PPh3)2 (172 mg, 0.25 mmol), and cuprous
iodide (25 mg, 0.13 mmol) in dry triethylamine (15 mL) was stirred under
argon at ambient temperature for 48 h. The reaction was quenched with
water, the resulting mixture was extracted with dichloromethane, and the
combined extracts were washed with brine, dried over sodium sulfate,
filtered, and concentrated under reduced pressure. Flash chromatography
of the residue over silica gel (petroleum ether/AcOEt, 30:1) afforded the
product 7 (624 mg, 86%) as a colorless solid: mp 80ꢀ82 °C; IR (neat)
2958, 2161, 1766, 1493, 1368, 1250, 1206, 1187, 901, 845 cmꢀ1; 1H NMR
(400 MHz, CDCl3) δ 0.25 (s, 9H, 3 ꢁ CH3), 1.30 (s, 9H, 3 ꢁ CH3), 2.32
(s, 3H, CH3), 6.99 (d, 3J = 8.8 Hz, 1H), 7.35 (dd, 3J = 8.8 Hz, 4J = 2.4 Hz,
1H), 7.50 (d, 4J = 2.4 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 0.1 (p),
20.8 (p), 31.2 (p), 34.5 (q), 98.8 (q), 100.2 (q), 116.4 (q), 121.5 (t), 127.0
(t), 130.2 (t), 148.7 (q), 149.7 (q), 168.9 (q); MS (EI, 70 eV) m/z 288 (3,
compounds
10
15
12
16
13
17
λabsa (nm)
λexa (nm)
λemb (nm)
Φc (%)
252
280
374
252
280
374
251
245
378
251
245
376
309
275
399
289
275
392
15.7
29.4
14.1
70.7
33.2
44.0
a Only the largest absorption maxima are listed. b Wavelength of emis-
c
sion maximum when exicited at the absorption maximum. Quantum
yields obtained by using quinine sulfate (10 μM) as a standard.
Stirring was continued for 2 h at ambient temperature. Then the solvent was
removed under reduced pressure. The residue was diluted with concen-
trated sodium bisulfite (100 mL) and extracted with dichloromethane (3 ꢁ
100 mL). The combined organic layers were washed with brine, dried over
sodium sulfate, filtered, and concentrated under reduced pressure. Flash
chromatography of the residue over silica gel (petroleum ether/EtOAc,
100:1) afforded 5 (1.10 g, 60%) as an oil: IR (neat) 3487, 2960, 2866, 1494,
1465, 1398, 1364, 1264, 1179, 1032, 877, 819 cmꢀ1; 1H NMR (400 MHz,
CDCl3) δ 1.27 (s, 9H, 3 ꢁ CH3), 5.15 (s, 1H, OH), 6.91 (d, 3J = 8.8 Hz,
M
þ•), 246 (33, [M ꢀ CH2CO]þ•), 231 (100, [M ꢀ CH2CO ꢀ CH3]þ);
accurate mass (ESI-MS) m/z [M þ H]þ, calcd for C17H25O2Si 289.1618,
found 289.1616.
4-tert-Butyl-2-ethynylphenyl acetate (8). A solution of com-
pound 7 (600 mg, 2.08 mmol) and acetic acid (1 mL) in tetrahydrofuran
(40 mL) was stirred while tetrabutylammonium fluoride (1.02 g, 3.24
mmol) was added. Stirring was continued for 4 h at ambient tempera-
ture, and then the solvent was removed under reduced pressure. The
mixture was quenched by addition of aqueous hydrogen chloride
(25 mL, 1.2 M), and the product was extracted with dichloromethane
(3 ꢁ 30 mL). The combined organic layers were washed with brine,
dried over sodium sulfate, filtered, and concentrated under reduced
pressure. Flash chromatography of the residue over silica gel (petroleum
ether/CH2Cl2, 5:1) afforded the arylacetylene 8 (404 mg, 90%) as a
colorless solid: mp 61ꢀ62 °C; IR (neat) 3284, 2964, 1763, 1493, 1368,
1206, 1183, 1123, 1011, 893, 842 cmꢀ1; 1H NMR (400 MHz, CDCl3) δ
1.31 (s, 9H, 3 ꢁ CH3), 2.33 (s, 3H, CH3), 3.21 (s, 1H), 7.01 (d, 3J = 8.8
Hz, 1H), 7.39 (dd, 3J = 8.8 Hz, 4J = 2.4 Hz, 1H), 7.54 (d, 4J = 2.4 Hz, 1H);
13C NMR (100 MHz, CDCl3) δ 20.9 (p), 31.2 (p), 34.5 (q), 79.2 (t),
81.2 (q), 115.4 (q), 121.7 (t), 127.3 (t), 130.6 (t), 148.8 (q), 149.8 (q),
169.1 (q); MS (EI, 70 eV) m/z216 (4, Mþ•), 174 (41, [M ꢀ CH2CO]þ•),
159 (100, [M ꢀ CH2CO ꢀ CH3]þ); accurate mass (ESI-MS) m/z [M þ
NH4]þ, calcd for C14H20NO2 234.1489, found 234.1484.
1H), 7.26 (dd, 3J = 8.8 Hz, 4J = 2.4 Hz, 1H), 7.62 (d, 4J = 2.4 Hz, 1H); 13
C
NMR (100 MHz, CDCl3) δ 31.4 (p), 34.0 (q), 85.6 (q), 114.5 (t), 127.3
(t), 134.9 (t), 145.6 (q), 152.5 (q); MS (EI, 70 eV) m/z276 (34, Mþ•), 261
(100, [M ꢀ CH3]þ).
4-tert-Butyl-2-iodophenyl acetate (6). A solution of iodophe-
nol 5 (500 mg, 1.81 mmol) in pyridine (50 mL) was stirred while acetic
anhydride (0.3 mL, 2.33 mmol) was added dropwise. Stirring was
continued for 3 h atambient temperature, thenthe mixture wasneutralized
by the addition of aqueous hydrogen chloride (10 mL, 1 M). The resulting
mixture was extracted with dichloromethane (3 ꢁ 50 mL), dried over
sodium sulfate, filtered, and concentrated under reduced pressure. Flash
chromatography of the residue over silica gel (petroleum ether/EtOAc,
100:1) afforded 6 (547 mg, 95%) as oil: IR (neat) 2962, 1770, 1486, 1368,
1194, 1037, 909, 834 cmꢀ1; 1H NMR (400 MHz, CDCl3) δ 1.30 (s, 9H,
3ꢁ CH3), 2.36 (s, 3H, CH3), 7.01(d,3J= 8.4 Hz, 1H), 7.37 (dd, 3J=8.4Hz,
4J = 2.4 Hz, 1H), 7.80 (d, 4J = 2.4 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
21.2 (p), 31.3 (p), 34.4 (q), 90.2 (q), 122.2 (t), 126.6 (t), 136.4 (t), 148.8
(q), 150.9 (q), 168.8 (q); MS (EI, 70 eV) m/z 318 (18, Mþ•), 276 (57,
[M ꢀ CH2CO]þ•), 261 (100, [M ꢀ CH2CO ꢀ CH3]þ), 43 (36);
accurate mass (ESI-MS) m/z [M þ NH4]þ, calcd for C12H19NO2I
336.0455, found 336.0449.
2,3,6,7,10,11-Hexakis(5-tert-butyl-2-acetoxylphenylethynyl)-
4b,8b,12b,12d-tetramethyl-4b,8b,12b,12d-tetrahydrodibenzo-
[2,3:4,5]pentaleno[1,6-ab]indene (10). A solution of hexabromotri-
benzotriquinacene 926,33 (113 mg, 0.14 mmol), 4-tert-butyl-2-ethynylphenyl
acetate 8 (720 mg, 3.36 mmol), PdCl2(PPh3)2 (10 mg, 14 μmol), cuprous
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Figure 3. Plot of the chemical shift changes (Δδ) versus the molar ratios for (left) [C60]/[12], protons HaꢀHe, and (right) [C60]/[13], protons
HaꢀHd, in toluene-d8. For proton assignment, see Scheme 2.
Figure 4. Side views of the optimized structures of the 1:1 complexes (a) C60⊂10, (b) C60⊂12, and (c) C60⊂ 13 (calculated by molecular mechanics
method using MMþ force field).
iodide (5 mg, 26 μmol), and triphenylphosphine (7 mg, 27 μmol) in
anhydrous triethylamine (15 mL) was heated to reflux under argon for 48 h.
The reaction was quenched by addition of water, and the mixture was
extracted with dichloromethane, washed with brine, dried over sodium
sulfate, filtered, and concentrated under reduced pressure. Flash chromatog-
raphy of the residue over silica gel (petroleum ether/CH2Cl2/AcOEt,
30:15:1) afforded the product 10 (185 mg, 82%) as a colorless solid: mp
269ꢀ271 °C; IR (neat) 3407, 2959, 2926, 2865, 1765, 1495, 1462, 1367,
1195, 1122, 1011, 897, 835 cmꢀ1; 1H NMR (400 MHz, CDCl3) δ 1.30 (s,
54H, 18 ꢁ CH3), 1.57 (s, 3H, CH3), 1.71 (s, 9H, 3 ꢁ CH3), 2.19 (s, 18H, 6
ꢁ CH3), 7.01 (d, 3J = 8.8 Hz, 6H), 7.37 (dd, 3J = 8.8 Hz, 4J = 2.4 Hz, 6H),
7.55 (s, 6H), 7.67 (d, 4J= 2.4 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ14.2
(p), 20.8 (p), 25.6 (p), 31.3 (p), 34.5 (q), 62.6 (q), 70.8 (q), 88.9 (q), 92.2
(q), 116.5 (q), 121.7 (t), 125.4 (q), 126.7 (t), 126.9 (t), 130.2 (t), 148.6 (q),
148.8 (q), 149.5 (q), 169.2 (q); ESI(þ)-MS(CH2Cl2/MeOH) m/z1644.7
(100, [M þ Na]þ), ESI(þ)-CID/MSof [Mþ Na]þ m/z1601.7 (100, [M
þ Na ꢀ CH2CO]þ), 1559.6 (17, [M þ Na ꢀ 2CH2CO]þ); accurate mass
[ESI(þ)-MS] m/z [M þ Na]þ, calcd for C110H108O12Na 1643.7733,
found 1643.7705.
2,3,6,7,10,11-Hexakis(5-tert-butyl-2-hydroxyphenylethynyl)-
4b,8b,12b,12d-tetramethyl-4b,8b,12b,12d-tetrahydrodibenzo-
[2,3:4,5]pentaleno[1,6-ab]indene (11). Hexaacetate 10 (20 mg, 12
μmol) was dissolved in a mixture of methanol and tetrahydrofuran (1:1,
6 mL), and the solution was stirred at 0 °C while a portion of solid sodium
hydroxide (5 mg, 125 μmol) was added. The resulting solution was stirred at
room temperature overnight. Then the mixture was neutralized with aqueous
hydrogen chloride, extracted with ethyl ether, washed with brine, dried over
magnesium sulfate, filtered, and concentrated under reduced pressure. Flash
chromatography of the residue over silica gel (petroleum ether/CH2Cl2/
MeOH, 30:20:1) afforded compound 11 (12 mg, 72%) as a colorless solid:
mp 159ꢀ161 °C; IR (neat) 3477, 3405, 2960, 2929, 2868, 1710, 1496, 1463,
1365, 1258, 1239, 1182, 891, 823 cmꢀ1; 1H NMR (600 MHz, CDCl3) δ
1.29 (s, 54H, 18 ꢁ CH3), 1.48 (s, 3H, CH3), 1.73 (s, 9H, 3 ꢁ CH3), 6.06 (s,
6H, OH), 6.88 (d, 3J = 9.0 Hz, 6H), 7.29 (dd, 3J = 9.0 Hz, 4J = 2.4 Hz, 6H),
7.51 (d, 4J= 2.4 Hz, 6H), 7.65 (s, 6H); 13C NMR (125 MHz, CDCl3) δ14.2
(p), 25.7 (p), 31.4 (p), 34.1 (q), 62.8 (q), 70.8 (q), 88.6 (q), 94.6 (q), 108.3
(q), 114.5 (t), 125.0 (q), 126.5 (t), 128.2 (t), 128.5 (t), 143.2 (q), 148.7 (q),
154.7 (q); MALDI(þ)-MS (DCTB) m/z 1368.7 (100, Mþ•); accurate
mass (MALDI-MS, DCTB) m/z Mþ•, calcd for C98H96O6 1368.7201,
found 1368.7205.
2,3,6,7,10,11-Hexakis(5-tert-butylbenzofuran-2-yl)-4b,8b,12b,
12d-tetramethyl-4b,8b,12b,12d-tetrahydrodibenzo[2,3:4,5]pen-
taleno[1,6-ab]indene (12). Procedure A. A solution of compound 10
(30 mg, 18 μmol) and powdered sodium hydroxide (23 mg, 0.57 mmol) in
methanol (15 mL) was stirred under argon for 12 h. The solvent was
evaporated, and the residue was carefully neutralized with dilute hydrochloric
acid and then poured onto ethyl acetate. The separated layers were washed with
brine, dried over magnesium sulfate, filtered, and concentrated under reduced
pressure. Flash chromatography of the residue over silica gel (petroleum ether/
AcOEt, 30:1) afforded the product 12 (11 mg, 46%).
Procedure B. A solution of hexaphenol 11 (15 mg, 11 μmol) in
dimethylacetamide (2.0 mL) was stirred while palladium(II) acetate
(1 mg, 4 μmol) and cesium carbonate (43 mg, 0.13 mmol) were added
under normal atmosphere. The reaction mixture was stirred for 8 h at
80 °C. The solvent was evaporated, and the residual mixture was
carefully neutralized with dilute hydrochloric acid and then poured onto
ethyl acetate. The separated layers were washed with brine, dried over
MgSO4, filtered, and concentrated under reduced pressure. Flash
chromatography of the residue over silica gel (petroleum ether/AcOEt,
30:1) afforded the product 12 (4 mg, 26%) as a colorless solid; mp
230ꢀ232 °C; IR (neat) 2960, 2926, 2860, 1741, 1465, 1263, 1085, 1028,
1
878, 804 cmꢀ1; H NMR (400 MHz, CDCl3) δ 1.36 (s, 54H, 18 ꢁ
CH3), 1.56 (s, 3H, CH3), 1.86 (s, 9H, 3 ꢁ CH3), 6.49 (s, 6H), 7.35
3
4
3
(dd, J = 8.8 Hz, J = 2.0 Hz, 6H), 7.42 (d, J = 8.8 Hz, 6H), 7.50
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The Journal of Organic Chemistry
ARTICLE
(d, 4J = 2.0 Hz, 6H), 7.85 (s, 6H); 13C NMR (100 MHz, CDCl3) δ 14.1
(p), 25.8 (p), 31.8 (p), 34.7 (q), 62.9 (q), 71.2 (q), 105.4 (t), 110.7 (t),
117.3 (t), 122.2 (t), 124.6 (t), 128.8 (q), 129.8 (q), 145.7 (q), 149.2 (q),
152.9 (q), 155.1 (q); MALDI(þ)-MS (DCTB) m/z 1368.4 (100, Mþ•);
accurate mass [MALDI(þ)-MS, DCTB] m/z Mþ•, calcd for C98H96O6
1368.7201, found 1368.7197.
accurate mass (EI-MS) m/z Mþ•, calcd for C32H32O2 448.2402, found
448.2398.
’ ASSOCIATED CONTENT
S
Supporting Information. Optical properties of com-
b
Hexakis(benzofurano)trinaphthotriquinacene 13. A solu-
tion of compound 12 (14 mg, 10 μmol) in dichloromethane (10 mL)
was stirred under argon at 0 °C, while a solution of ferric chloride
(39 mg, 0.24 mmol) in dry nitromethane (2 mL) was added dropwise.
Stirring was continued at 0 °C for 0.5 h, then the solvent was removed
under reduced pressure. The residue was diluted with water (15 mL) and
extracted with dichloromethane (3 ꢁ 20 mL). The combined organic
layers were washed with brine, dried over sodium sulfate, filtered, and
concentrated under reduced pressure. Flash chromatography of the
residue over silica gel (petroleum ether/CH2Cl2 = 10:1) afforded 13 as
amorphous colorless solid: mp >360 °C; IR (neat) 3421, 2958, 2924,
pounds 10ꢀ13 and 15ꢀ17, crystal packing of 10 and its X-ray
crystallographic file, complexation measurements of compounds
12 and 13 with C60, 1H NMR, 13C NMR, and DEPT 135 spectra
of compounds 5ꢀ8, 10ꢀ13, and 15ꢀ17. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: caoxplzu@163.com (X.-P.C.), dietmar.kuck@uni-
bielefeld.de (D.K.).
1
2855, 1651, 1461, 1385, 1261, 1110, 1025, 806 cmꢀ1; H NMR (400
MHz, CDCl3) δ 1.55 (s, 54H, 18 ꢁ CH3), 1.68 (s, 3H, CH3), 2.20 (s,
9H, 3 ꢁ CH3), 7.63 (dd, 3J = 8.8 Hz, 4J = 1.6 Hz, 6H), 7.85 (d, 3J = 8.8
Hz, 6H), 8.57 (s, 6H), 8.88 (s, 6H); 13C NMR (100 MHz, CDCl3) δ
16.7 (p), 27.8 (p), 32.0 (p), 35.0 (q), 63.2 (q), 71.1 (q), 111.4 (t), 113.6
(q), 116.0 (t), 118.7 (t), 121.1 (q), 123.9 (t), 124.7 (q), 145.8 (q), 149.3
(q), 149.4 (q), 154.3 (q); MALDI(þ)-MS (DCTB) m/z 1362.7 (100,
’ ACKNOWLEDGMENT
The authors are grateful to the National Basic Research Program
(973 Program) of China (Grant No. 2010CB833203), the National
Natural Science Foundation of China (Grant Nos. 20972060 and
21061160494), Specialized Research Fund for the Doctoral Pro-
gram of Higher Education (20090211110007), and the 111 Project
for continuing financial support. We gratefully acknowledge Yong-
Liang Shao of Lanzhou University for X-ray crystallographic
analyses. We also thank Dr. Matthias Letzel, Bielefeld University,
for accurate mass measurements.
M
þ•); accurate mass [MALDI(þ)-MS], DCTB) m/z Mþ•, calcd for
C98H90O6 1362.6732, found 1362.6738.
1,2-Di(5-tert-butyl-2-acetoxylphenylethynyl)-4,5-dimethyl-
benzene(15). Inanalogytothe synthesisofcompound10, thiscoupling
reaction was carried out by starting from dibromoxylene 14. Two hundred
milligrams (0.76 mmol) of 14 gave 15 (354 mg, 87%) as an oil: IR (neat)
2961, 2869, 1767, 1499, 1366, 1193, 1123, 1010, 894, 837 cmꢀ1; 1H NMR
(400 MHz, CDCl3) δ 1.29 (s, 18H, 6 ꢁ CH3), 2.24 (s, 6H, 2 ꢁ CH3),
2.28 (s, 6H, 2 ꢁ CH3), 7.03 (d, 3J = 8.8 Hz, 2H), 7.32 (s, 2H), 7.36 (dd,
3J = 8.8 Hz, 4J = 2.4 Hz, 2H), 7.64 (d, 4J = 2.4 Hz, 2H); 13C NMR (100
MHz, CDCl3) δ 19.6 (p), 20.8 (p), 31.2 (p), 34.5 (q), 87.9 (q), 92.4 (q),
116.8 (q), 121.6 (t), 122.7 (q), 126.6 (t), 130.3 (t), 133.0 (t), 137.3 (q),
148.7 (q), 149.2 (q), 169.2 (q); MS (EI, 70 eV) m/z 534 (8, Mþ•), 492
(18, [M ꢀ CH2CO]þ•), 450 (34, [M ꢀ 2 CH2CO]þ•), 43 (100);
accurate mass (ESI-MS) m/z [M þ NH4]þ, calcd for C36H42NO4
552.3108, found 552.3112.
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