Synthesis of hexa(furan-2-yl)benzenes and their π-extended derivatives

Article abstract of DOI:10.1021/jo302652r

The first synthesis of hexa(furan-2-yl)benzene derivatives is described. The RhCl₃/i-Pr₂NEt-catalyzed cyclotrimerization of di(furan-2-yl)acetylenes was an effective method for constructing hexa(furan-2-yl)benzene derivatives in good

Full text of DOI:10.1021/jo302652r

Note
pubs.acs.org/joc
Synthesis of Hexa(furan-2-yl)benzenes and Their π‑Extended
Derivatives
Koichi Mitsudo,*,† Jyunji Harada,† Yo Tanaka,† Hiroki Mandai,† Chie Nishioka,† Hideo Tanaka,†
Atsushi Wakamiya,‡ Yasujiro Murata,‡ and Seiji Suga*,†
†Division of Chemistry and Biotechnology, Graduate School of Natural Science and Technology, Okayama University, 3-1-1
Tsushima-naka, Kita-ku, Okayama 700-8530, Japan
‡Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
S
* Supporting Information
ABSTRACT: The first synthesis of hexa(furan-2-yl)benzene
derivatives is described. The RhCl3/i-Pr2NEt-catalyzed cyclo-
trimerization of di(furan-2-yl)acetylenes was an effective
method for constructing hexa(furan-2-yl)benzene derivatives
in good yields. Their π-extended derivatives were also
synthesized by Suzuki−Miyaura coupling between hexakis(5-
Bpinfuran-2-yl)benzene (Bpin = (pinacolato)boryl) and
several aryl iodides.
product, a benzothiophene derivative, as the major product, and
uran is an important skeleton that is commonly observed
Fin nature. Over the past decade, furan has also attracted hexa(thiophene-2-yl)benzene was obtained in only 5% yield.7a
1
To avoid this problem, several methods have been reported.
attention as a key building block for π-conjugated compounds
that have the potential for application in organic materials such
as semiconductors2 and photovoltaics.3 Therefore, a facile
access to a variety of π-conjugated furans is an important
research field in organic chemistry. In addition, two-dimen-
sional aromatic cores, such as starburst hexaarylbenzene
derivatives,4 have been synthesized, and their electrochemical
and optical properties have been intensively studied.5 In
Mullen reported that the Co-catalyzed cyclotrimerization of
̈
di(thiophene-2-yl)acetylene bearing a long alkyl chain at the α-
position of thiophenes proceeded to give hexa(thiophene-2-
yl)benzene in good yield.7b Lin and Tao reported a tandem
Kosugi−Migita−Stille coupling between tributyl(thiophene-2-
yl)stannane and hexabromobenzene.7c For the synthesis of
hexapyrrolylbenzene, Meijer reported an elimination−addition-
type reaction using 1-pyrrolylsodium and hexafluorobenzene.9c
Breslow reported another type of transformation of hexa-
(pyridin-4-yl)benzene, which was synthesized by the reductive
dimerization of a cyclopentene intermediate.8a
particular, Mullen and co-workers have reported several studies
̈
on this topic.6 However, there have been a few reports on the
synthesis of hexaheteroarylbenzenes. For instance, there have
been few reports on the preparation of hexathienylbenzene,7
hexapyridylbenzene,8 and hexapyrrolylbenzene9 derivatives and
no report on hexafurylbenzenes, although they should serve as
novel fascinating building blocks (Scheme 1). Additionally, to
the best of our knowledge, the crystal structures of these
heteroarylbenzenes have not yet been reported, except for that
of hexa(1-pyrrolyl)benzene,9c and there is no information
available on the conformations of other hexaheteroarylben-
zenes, which should be important from the perspective of
material science.
We recently reported an efficient method for the synthesis of
hexa(thienyl)benzene derivatives by RhCl3/i-Pr2NEt-catalyzed
cyclotrimerization of dithienylacetylenes and found that they
are potent candidates for capacitor materials.7d,e,11 In the
present study, we turned our attention to the synthesis of
hexa(furan-2-yl)benzenes, and we report here the first synthesis
and X-ray single-crystal analyses of hexa(furan-2-yl)benzene
derivatives.
We first carried out the synthesis of hexa(furan-2-yl)benzene
(2a) by cyclotrimerization of di(furan-2-yl)acetylene (1a)
(Table 1). Optimization of the catalyst revealed that the
combination of RhCl3·3H2O and i-Pr2NEt was essential for the
reaction. In the presence of a catalytic amount of RhCl3·3H2O
(8 mol %) and i-Pr2NEt (30 mol %), the cyclotrimerization of
While one of the most straightforward ways for constructing
hexaarylbenzenes is the transition-metal-catalyzed cyclotrimeri-
zation of diarylacetylenes,10 this method is usually not suitable
for use with hexaheteroarylbenzenes. The difficulty of the
synthesis of hexaheteroarylbenzenes is caused by the
competitive dimerization of the internal alkynes (Scheme 2).
Weber reported that the reaction of di(thiophene-2-yl)-
acetylene catalyzed by RuH2(CO)(PPh3)3 gave a dimerized
Received: December 19, 2012
Published: February 25, 2013
© 2013 American Chemical Society
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Note
Scheme 1. Hexaarylbenzenes and Hexaheteroarylbenzenes
Scheme 2. Competition between the Trimerization and
Dimerization of Diheteroarylacetylenes
Table 1. Rh-Catalyzed [2 + 2 + 2] Cyclization of
Difurylalkyne 1
a
b
entry
R (1)
2
yield (%)
1
2
3
H (1a)
2a
2b
2c
50
81
Me (1b)
Bpin (1c)
c
80 (55)
a
Reaction conditions: 1 (0.5 mmol), RhCl3·3H2O (8 mol %), i-Pr2NEt
b
c
(30 mol %), toluene (2 mL), reflux, 24 h. Isolated yield. Performed
with 2.5 mmol of 1c.
1a proceeded smoothly to give 2a in 50% yield (entry 1). In a
similar manner, the cyclotrimerization of bis(5-methylfuran-2-
yl)acetylene (1b) afforded hexakis(5-methylfuran-2-yl)benzene
(2b) in 81% yield (entry 2). Compound 2c bearing six
(pinacolato)boryl (Bpin) moieties could also be obtained in
80% yield from a di(furan-2-yl)acetylene bearing two Bpin
moieties (1c) (entry 3). Increasing the amount of 1c to 2.5
mmol, the yield of 2c decreased to 55%. The structures of 2a−c
were confirmed by X-ray single crystal analyses (Figure 1). To
the best of our knowledge, 2a−c are the first hexafurylbenzene
derivatives to be synthesized, and this is the first report on the
crystal structures of hexa(2-heteroaryl)benzenes.
NMR analyses of 2a−c exhibited that their six furan rings,
and the six substituents at the 5-position of the furan rings were
equivalent on the NMR time scale. In contrast, X-ray analyses
revealed that their crystal structures were different. For
instance, X-ray analysis of 2b revealed that it has a C2-
symmetric structure in the crystal, and there are two kinds of
nonequivalent furan rings. The two furan rings associated with
the p-position were nearly perpendicular to the benzene ring,
and the dihedral angles were 82°. The four other furan rings
leaned toward the benzene ring with a dihedral angle of 42°.
The optimized structures calculated by density functional
theory (DFT) at the B3LYP/6-31G(d) level were similar to the
X-ray structures (Figure 2). At the HOMO-level, π−π
conjugation was observed between the four leaning furan
rings and the benzene. These results suggest that the six furan
rings of 2 freely rotated in solution and were fixed in a
conjugated structure in crystal form.
To expand the synthetic utility of the reaction, we next
converted hexakis(5-Bpinfuran-2-yl)benzene (2c) to hexakis(5-
arylfuran-2-yl)benzenes by Suzuki−Miyaura coupling (Table
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Note
Table 2. Suzuki−Miyaura Coupling of 2c and Iodobenzene
a
(3a)
b
entry
Pd catalyst
base
solvent
yield (%)
c
1
2
3
4
5
6
7
8
Pd(PPh3)4
NaOAc
Na2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
DME
DME
DME
DME
nd
Pd(PPh3)4
nd
48
Pd(PPh3)4
d
Pd[P(t-Bu)3]2
Pd[P(t-Bu)3]2
Pd[P(t-Bu)3]2
Pd[P(t-Bu)3]2
Pd[P(t-Bu)3]2
50 (70)
DME/H2O (4/1)
DMF
38
56
26
6
toluene
1,4-dioxane
a
Reaction conditions: 2c (0.05 mmol), iodobenzene 3a (0.35 mmol),
Pd catalyst (10 mol %), base (0.6 mmol), solvent (0.5 mL), 100 °C, 24
b
c
d
h. Isolated yield. Not detected. Performed in 1.0 mL of solvent.
Figure 1. ORTEP drawings of 2a (left top), 2b (right top), and 2c
(bottom) (50% probability ellipsoids; hydrogen atoms omitted for
clarity).
entry 4). The concentration of the reaction mixture also highly
influenced the reaction. With 1.0 mL of DME, the yield of 4a
dramatically increased to 70%. Screening of the solvent was
examined next (entries 5−8). In the presence of water,
protonated byproducts were observed and the yield of 4a
decreased (entry 5). DMF was similarly an effective solvent,
and 4a was obtained in 56% yield (entry 6). In contrast, toluene
and 1,4-dioxane were ineffective solvents in the reaction
(entries 7 and 8).
Finally, under the optimized conditions, several aryl iodides
were applied to the sequential Suzuki−Miyaura coupling
(Table 3). With p-iodotoluene (3b) or p-iodoanisole (3c),
the corresponding coupling products 4b and 4c were obtained
in 60% and 76% yields, respectively (entries 2 and 3). We next
performed the coupling reaction using iodoarenes bearing
electron-withdrawing groups. With p-chloroiodobenzene (3d),
4d was obtained in 62% yield (entry 4). p-Fluoroiodobenzene
(3e) and p-trifluoromethyliodobenzene (3f) could also be
applied to the reaction, and the corresponding hexafurylben-
zene derivatives were both obtained in 60% yield (entries 5 and
6). We next sought to construct molecules with a further π-
extended system. With the use of p-cyanoiodobenzene (3g) or
1-iodonaphthalene (1-NpI, 3h), coupling adducts 4g and 4h
were obtained (92% and 88%, entries 7 and 8).
Figure 2. Kohn−Sham HOMO and LUMO of 2a (a) and 2b (b)
calculated at the B3LYP/6-31G(d) level of theory.
The crystal structures of 4a and 4f were confirmed by X-ray
crystallography (Figure 3). While the conformation of the furan
rings of these compounds was different from those of 2a−c, the
six furan rings of 4a−h were equivalent in NMR measurement,
the same as those of 2a−c. In particular, the packing structure
of 4f was quite different from those in the other compounds,
probably due to the intra- and intermolecular interactions
between trifluoromethyl groups. These results suggest that their
furan rings would rotate freely, and their structures in the solid
state highly depend on the substituents on the furan rings.
In conclusion, we have achieved the first synthesis of
hexa(furan-2-yl)benzene derivatives by the RhCl3/i-Pr2NEt-
2). In the presence of Pd(PPh3)4 (10 mol %) and base (0.6
mmol), 2c (0.05 mmol) was treated with iodobenzene 3a (0.35
mmol) in 0.5 mL of DME at 100 °C. When NaOAc or Na2CO3
was used as a base, the desired coupling product was not
obtained at all (entries 1 and 2). Screening of the base revealed
that Cs2CO3 was an effective base for the reaction, and
hexaphenyl-substituted hexa(furan-2-yl)benzene (4a) was
obtained in 48% yield (entry 3). In the next step, we evaluated
different Pd(0) complexes as catalysts and found that the use of
Pd[P(t-Bu)3]2 slightly increased the yield of 4a (50% yield,
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Note
2-iodofuran (5.82 g, 30.0 mmol) and distilled water (216 μL, 12.0
mmol). The reaction vessel was covered with aluminum foil and
stirred at room temperature for 22 h. The resulting mixture was
extracted with diethyl ether (3 × 30 mL). The organic phase was
washed with brine (200 mL), dried over MgSO4, filtered, and
concentrated under reduced pressure. The residue was purified by
column chromatography on silica gel (hexane/EtOAc 10:1) to afford
Table 3. Synthesis of Various Hexakis(5-arylfuran-2-
yl)benzenes
a
1
di(furan-2-yl)acetylene as a yellow oil (1.57 g, 9.95 mmol, 66%). H
NMR (400 MHz, CDCl3) δ 6.43 (dd, J = 3.4, 1.8 Hz, 2H), 6.71 (dd, J
= 3.4, 0.6 Hz, 2H), 7.44 (dd, J = 1.8, 0.6 Hz, 2H); 13C NMR (100
MHz, CDCl3) δ 83.2, 111.1, 116.5, 136.4, 144.2; IR (neat) 3145, 3131,
1494, 1462 cm−1. Anal. Calcd for C10H6O2: C, 75.94; H, 3.82. Found:
C, 76.04; H, 3.76.
Synthesis of Bis(5-methylfuran-2-yl)acetylene (1b). Similar
procedure to 1a: yellow oil (1.81 g, 9.74 mmol, 62%); 1H NMR (600
MHz, CDCl3) δ 2.32 (brs, 6H), 6.01 (dq, J = 3.2, 1.0 Hz, 2H), 6.58
(dd, J = 3.2, 0.4 Hz, 2H); 13C NMR (150 MHz, CDCl3) δ 13.9, 83.3,
107.3, 117.4, 134.8, 154.3; IR (KBr) 2922, 2181, 1557, 1198, 1021,
948, 785 cm−1. Anal. Calcd for C12H10O2: C, 77.40; H, 5.41. Found: C,
77.32; H, 5.69.
b
entry
Ar (3)
4
yield (%)
1
2
3
4
5
C6H5 (3a)
4a
4b
4c
4d
4e
4f
70
60
76
62
60
60
92
88
p-MeC6H4 (3b)
p-MeOC6H4 (3c)
p-ClC6H4 (3d)
p-FC6H4 (3e)
p-CF3C6H4 (3f)
p-CNC6H4 (3g)
1-Np (3h)
c
6
Synthesis of Bis[5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)furan-2-yl]acetylene (1c). To a solution of di(furan-2-
yl)acetylene (1.541 g, 9.75 mmol) in Et2O (100 mL) was added
dropwise a solution of n-BuLi (1.6 M in hexane, 13.8 mL, 22.0 mmol)
at −78 °C. The reaction mixture was then stirred at the same
temperature for 30 min and then stirred at 0 °C for 2.5 h. 2-
Isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (10.2 mL, 50.0
mmol) was added to the mixture at −78 °C. The resulting mixture
was allowed to warm to room temperature and stirred for 24 h. The
reaction was quenched with aq saturated NH4Cl (20 mL). The
aqueous phase was extracted with EtOAc (3 × 10 mL). The combined
organic phase was washed with brine (30 mL), dried over MgSO4,
filtered, and concentrated under reduced pressure. The residue was
purified by column chromatography on silica gel (EtOAc) and then
recrystallized from CH2Cl2/hexane to afford bis[5-(4,4,5,5-tetrameth-
yl-1,3,2-dioxaborolan-2-yl)furan-2-yl]acetylene (1c) as a yellow solid
7
8
4g
4h
a
Reaction conditions: 2c (0.05 mmol), iodoarene (0.35 mmol),
Pd[P(t-Bu)3]2 (10 mol %), Cs2CO3 (0.6 mmol), DME (1.0 mL), 100
b
c
°C, 24 h. Isolated yield. Performed in 0.5 mL of DME.
1
(2.83 g, 6.91 mmol, 71%): H NMR (400 MHz, CDCl3) δ 1.34 (s,
24H), 6.67 (d, J = 3.5 Hz, 2H), 7.04 (d, J = 3.5 Hz, 2H); 13C NMR
(150 MHz, CDCl3) δ 24.7, 84.3, 84.5, 116.6, 124.0, 140.5; IR (KBr)
3125, 2980, 2934, 2870, 1756 cm−1; mp 214.5−217.5 °C. Anal. Calcd
for C22H28B2O6: C, 64.44; H, 6.88. Found: C, 64.56; H, 6.84.
Figure 3. ORTEP drawings of 4a (left) and 4f (right) (50%
probability ellipsoids; hydrogen atoms omitted for clarity; trifluor-
omethyl groups of 4f disordered).
Hexa(furan-2-yl)benzene (2a). To a solution of RhCl3·3H2O
(10.4 mg, 0.04 mmol) and i-Pr2NEt (26.2 μL, 0.15 mmol) in toluene
(2.0 mL) was added di(furan-2-yl)acetylene (79.0 mg, 0.50 mmol),
and the mixture was stirred at 120 °C for 24 h. After being cooled to
room temperature, the reaction mixture was filtered and concentrated
under reduced pressure. The residue was purified by column
chromatography on silica gel (hexane/EtOAc 5:1) to afford hexa-
(furan-2-yl)benzene (2a) as a yellow solid (39.4 mg, 0.08 mmol, 50%):
1H NMR (400 MHz, CDCl3) δ 5.92 (dd, J = 3.3, 0.8 Hz, 6H), 6.20
catalyzed cyclotrimerization of di(furan-2-yl)acetylenes. A 6-
fold Bpin-substituted hexa(furan-2-yl)benzene could also be
prepared by this method, and a wide variety of π-extended
hexa(furan-2-yl)benzene derivatives were obtained by subse-
quent Suzuki−Miyaura coupling.
(dd, J = 3.3, 1.8 Hz, 6H), 7.23 (dd, J = 1.8, 0.8 Hz, 6H); 13C NMR
(150 MHz, CDCl3) δ 109.7, 110.6, 133.9, 141.9, 150.2; IR (KBr)
2363, 2341, 1507, 1002, 731 cm−1; mp >280 °C. Anal. Calcd for
C30H18O6: C, 75.94; H, 3.82. Found: C, 75.85; H, 3.79.
EXPERIMENTAL SECTION
■
General Methods. Nuclear magnetic resonance (NMR) spectra
were recorded on 600 or 400 MHz in CDCl3. Chemical shifts for H
1
NMR are expressed in parts per million (ppm) relative to residual
CHCl3 in CDCl3 (δ 7.26 ppm). Chemical shifts for 13C NMR are
expressed in ppm relative to CDCl3 (δ 77.0 ppm). All new compounds
were further characterized by elemental analyses or HRMS (DART),
and the mass analyzer type used for HRMS was orbitrap.
2-Iodofuran and 5-methyl-2-iodofuran were prepared according to
the literature.12 1,2-Dimethoxyethane (DME) was dried over MS 4A
prior to use. Toluene was distilled from CaH2. Dry dimethylforma-
mide (DMF) and dry 1,4-dioxane were purchased from commercial
suppliers. Unless otherwise noted, all materials were obtained from
commercial suppliers and used without further purification. All
reactions were performed under argon.
Hexakis(5-methylfuran-2-yl)benzene (2b). To a solution of
RhCl3·3H2O (10.6 mg, 0.04 mmol) and i-Pr2NEt (26.2 μL, 0.15
mmol) in toluene (2.0 mL) was added bis(5-methylfuran-2-yl)-
acetylene (93.6 mg, 0.50 mmol), and the mixture was stirred at 130 °C
for 24 h. After being cooled to room temperature, the reaction mixture
was filtered and concentrated under reduced pressure. The residue was
purified by column chromatography on silica gel (hexane/EtOAc =
5:1) to afford hexakis(5-methylfuran-2-yl)benzene (2b) as a yellow
solid (75.5 mg, 0.14 mmol, 81%): 1H NMR (600 MHz, CDCl3) δ 2.13
(d, J = 0.8 Hz, 18H), 5.78 (d, J = 3.0 Hz, 6H), 5.80 (dd, J = 0.8, 3.0
Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 13.4, 106.5, 110.2, 133.2,
149.2, 150.8; IR (KBr) 3440, 3103, 2947, 2919, 2882 cm−1; mp
149.8−152.5 °C. Anal. Calcd for C36H30O6: C, 77.40; H, 5.41. Found:
C, 77.36; H, 5.11.
Synthesis of Di(furan-2-yl)acetylene (1a). To a mixture of
Pd(PPh3)2Cl2 (633 mg, 0.902 mmol) and CuCl (298 mg, 3.01 mmol)
in DMF (60 mL) were added DBU (26.9 mL, 180 mmol) and
trimethylsilylacetylene (2.1 mL, 15 mmol). To the mixture were added
Synthesis of Hexakis[5-(4,4,5,5-tetramethyl-1,3,2-
dioxaboryl)furan-2-yl]benzene (2c). To a solution of RhCl3·3H2O
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Note
(10.4 mg, 0.04 mmol) and i-Pr2NEt (26.2 μL, 0.15 mmol) in toluene
(2.0 mL) was added bis[5-(4,4,5,5-tetramethyl-1,3,2-dioxaboryl)furan-
2-yl]acetylene (0.206 g, 0.50 mmol), and the mixture was stirred at
120 °C for 24 h. After being cooled to room temperature, the resulting
mixture was filtered through a Celite pad and concentrated under
reduced pressure. The residue was recrystallized from CH2Cl2/hexane
to afford hexakis[5-(4,4,5,5-tetramethyl-1,3,2-dioxaboryl)furan-2-yl]-
133.7, 150.4, 152.1; IR (KBr) 1617.0, 1323.9, 1172.5, 1122.4, 1073.2
cm−1; mp >280 °C; HRMS (DART) m/z calcd for C72H36O6F18 [M+]
1338.2219, found 1338.2198.
Hexakis[5-(4-cyanophenyl)furan-2-yl]benzene (4g): yellow
1
solid (50.0 mg, 0.046 mmol, 92%); H NMR (400 MHz, CDCl3) δ
6.22 (d, J = 3.5 Hz, 6H), 6.64 (d, J = 3.5 Hz, 6H), 7.42 (d, J = 8.5 Hz,
12H), 7.47 (d, J = 8.5 Hz, 12H); 13C NMR (150 MHz, CDCl3) δ
109.5, 110.6, 113.3, 118.6, 123.6, 132.5, 133.4, 133.7, 150.7, 151.7; mp
>280 °C; HRMS (DART) m/z calcd for C72H36O6N6 [M+]
1080.2691, found 1080.2712.
1
benzene (2c) as a colorless solid (164 mg, 0.133 mmol, 80%): H
NMR (300 MHz, CDCl3) δ 1.26 (s, 72H), 6.04 (d, J = 3.4 Hz, 6H),
6.80 (d, J = 3.4 Hz, 6H); 13C NMR (150 MHz, CDCl3) δ 24.7, 83.7,
111.5, 124.4, 133.1, 154.8; IR (KBr) 3426, 2979, 2933, 1589, 1542
cm−1; mp >280 °C; Anal. Calcd for C66H84B6O18: C, 64.44; H, 6.88.
Found: C, 64.64; H 6.83.
Typical Procedure of Suzuki−Miyaura Coupling between 2c
and Iodoarene (Table 3, Entry 1). To a solution of Pd[P(t-Bu)3]2
(2.9 mg, 0.006 mmol) and Cs2CO3 (198.7 mg, 0.60 mmol) in DME
(1.0 mL) were added hexakis[5-(4,4,5,5-tetramethyl-1,3,2-dioxaboryl)-
furan-2-yl]benzene (2c) (61.9 mg, 0.05 mmol) and iodobenzene (3a,
72.8 mg, 0.36 mmol). The mixture was stirred at 100 °C for 24 h. After
being cooled to room temperature, aq saturated NH4Cl was poured
into the mixture, and the aqueous phase was extracted with CHCl3 (3
× 10 mL). To the combined organic phase was added EtOH (10 mL),
and the mixture was concentrated under reduced pressure. The residue
was recrystallized from CHCl3/hexane to afford hexakis(5-phenyfuran-
2-yl)benzene (4a) as a yellow solid.
Hexakis[5-(naphthalen-1-yl)furan-2-yl]benzene (4h): yellow
1
solid (53.7 mg, 0.044 mmol, 88%); H NMR (400 MHz, CDCl3) δ
6.39 (d, J = 3.2 Hz, 6H), 6.68 (d, J = 3.2 Hz, 6H), 7.15−7.22 (m,
12H), 7.33 (t, J = 8.0 Hz, 6H), 7.45 (d, J = 6,4 Hz, 6H), 7.68 (d, J =
8.0 Hz, 6H), 7.77 (d, J = 8.0 Hz, 6H), 8.19 (t, J = 8.6 Hz, 6H); 13C
NMR (150 MHz, CDCl3) δ 110.7, 112.3, 125.2, 125.5, 125.6, 125.9,
126.4, 128.0, 128.1, 128.2, 129.8, 133.8, 134.1, 150.3, 152.9; IR (KBr)
3048.9, 1395.3, 788.7, 772.4 cm−1; mp 216.3−217.0 °C; HRMS
(DART) m/z calcd for C90H55O6 [M + H]+ 1231.3993, found
1231.3981.
ASSOCIATED CONTENT
* Supporting Information
■
S
Spectral data for all new compounds; X-ray data for 1c, 2a−c,
and 4a,f (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
Hexakis(5-phenylfuran-2-yl)benzene (4a): yellow solid (32.6
1
mg, 0.035 mmol, 70%); H NMR (400 MHz, CDCl3) δ 6.13 (d, J =
3.4 Hz, 6H), 6.46 (d, J = 3.4 Hz, 6H), 7.14−7.16 (m,18H), 7.44−7.47
(m,12H); 13C NMR (100 MHz, CDCl3) δ 106.5, 112.1, 123.7, 127.0,
128.4, 130.6, 133.8, 149.9, 153.3; IR (KBr) 3060.5, 1484.9, 1022.1,
757.9 cm−1; mp: 246.0−246.2 °C; HRMS (DART) m/z calcd for
C66H43O6 [M + H]+ 931.3054, found 931.3034.
AUTHOR INFORMATION
Corresponding Author
*E-mail: mitsudo@cc.okayama-u.ac.jp, suga@cc.okayama-u.ac.
■
jp.
Hexakis[5-(4-methyl-phenyl)furan-2-yl]benzene (4b): yellow
1
Notes
solid (30.0 mg, 0.030 mmol, 60%); H NMR (400 MHz, CDCl3) δ
2.29 (s, 18H), 6.09 (d, J = 3.4 Hz, 6H), 6.38 (d, J = 3.4 Hz, 6H), 6.96
(d, J = 8.0 Hz, 12H), 7.33 (d, J = 8.0 Hz, 12H); 13C NMR (100 MHz,
CDCl3) δ 21.2, 105.8, 111.9, 123.7, 128.1, 129.0, 133.7, 136.7, 149.7,
153.4; IR (KBr) 3120.3, 3025.8, 2917.8, 2859.0, 1496.5, 783.9 cm−1;
mp >280 °C; HRMS (DART) m/z calcd for C72H55O6 [M + H]+
1015.3993, found 1015.3969.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported in by a Grant-in-Aid for Scientific
Research on Innovative Areas “Organic Synthesis based on
Reaction Integration” (No. 2105) from MEXT, Japan, by a
Grant-in-Aid for Young Scientists (B) from JSPS, Japan, and by
the Collaborative Research Program of the Institute for
Chemical Research, Kyoto University (grant no. 2012-31).
We thank Prof. Jun-ichi Yoshida and Dr. Keiko Kuwata in
Kyoto University for HRMS measurements. We are also
grateful to the SC-NMR Laboratory of Okayama University for
the NMR measurements.
Hexakis[5-(4-methoxyphenyl)furan-2-yl]benzene (4c): yellow
1
solid (42.6 mg, 0.038 mmol, 76%); H NMR (400 MHz, CDCl3) δ
3.76 (s, 18H), 6.08 (d, J = 3.4 Hz, 6H), 6.32 (d, J = 3.4 Hz, 6H), 6.70
(d, J = 8.8 Hz, 12H), 7.39 (d, J = 8.8 Hz, 12H); 13C NMR (100 MHz,
CDCl3) δ 55.2, 105.0, 111.9, 113.8, 123.9, 125.2, 133.6, 149.5, 153.2,
158.7; IR (KBr) 3126.0, 3001.7, 2940.0, 2834.9, 1497.5, 1251.6 cm−1;
mp >280 °C; HRMS (DART) m/z calcd for C72H55O12 [M + H]+
1111.3688, found 1111.3664.
Hexakis[5-(4-chlorophenyl)furan-2-yl]benzene (4d): yellow
1
solid (35.3 mg, 0.031 mmol, 62%); H NMR (600 MHz, CDCl3) δ
REFERENCES
6.12 (d, J = 3.4 Hz, 6H), 6.44 (d, J = 3.4 Hz, 6H), 6.15 (d, J = 8.7 Hz,
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to the low solubility; IR (KBr) 3125.1, 1480.1, 1093.4, 787.8 cm−1; mp
>280 °C; HRMS (DART) m/z calcd for C66H37O6Cl6 [M + H]+
1135.0716, found 1135.0696.
■
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