Synthesis and properties of p-benzoquinone-fused hexadehydro[18]annulenes

Article abstract of DOI:10.1016/j.tet.2004.02.041

A series of hexadehydro[18]annulenes fused with different numbers of p-benzoquinone, 4-6, were synthesized by stepwise transformation of the p-dimethoxybenzene moiety of the precursor dehydroannulene 3 fused with three 3,6-dimethoxy-4,5-dimethylbenzene un

Full text of DOI:10.1016/j.tet.2004.02.041

Tetrahedron 60 (2004) 3375–3382
Synthesis and properties of p-benzoquinone-fused
hexadehydro[18]annulenes
*
Tohru Nishinaga, Yasuo Miyata, Nobutake Nodera and Koichi Komatsu
Institute for Chemical Research, Kyoto University, Gokasho Uji, Kyoto 611-0011, Japan
Received 28 January 2004; revised 20 February 2004; accepted 23 February 2004
Abstract—A series of hexadehydro[18]annulenes fused with different numbers of p-benzoquinone, 4-6, were synthesized by stepwise
transformation of the p-dimethoxybenzene moiety of the precursor dehydroannulene 3 fused with three 3,6-dimethoxy-4,5-dimethylbenzene
units at 1,2-positions into p-benzoquinone using ceric ammonium nitrate. The UV–vis spectra of compounds 4 and 5, which have both
electron-donating p-dimethoxybenzene unit(s) and electron-accepting p-benzoquinone unit(s) in the p-systems, showed the maximum
absorption bands bathochromically shifted in comparison with 3 having only p-dimethoxybenzene units and 6 having only p-benzoquinone
units. However, the solvatochromism expected for 4 and 5 was found to be quite weak possibly because the HOMO and LUMO (B3LYP/
6-31G(d)) are not localized but rather delocalized over the whole p-systems.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
such an electron-accepting group to the highly conjugated
dehydroannulenes is of interest, since such compounds
would constitute a new type of push–pull p-systems when
electron-donating moieties are introduced on other site(s) of
the macrocyle. In 1993, Youngs and co-workers reported
the transformation of p-dimethoxybenezene units fused to
tridehydro[12]annulene into p-benzoquinone using ceric
ammonium nitrate (CAN), and they found that only one of
three p-dimethoxybenezene units in the precursor tri-
dehydro[12]annulene 1 can be transformed into p-benzo-
quinone to give p-conjugated system 2.9 However, although
the synthesis and NMR, IR, and MS spectral data of 2 were
reported, no discussion has been made as to the structural
and electronic properties of 2 and/or related compounds. In
the present paper, we report the synthesis of hexa-
dehydro[18]annulene fused with 3,6-dimethoxy-4,5-
dimethylbenzene units at 1,2-positions 3 and its stepwise
transformation into p-benzoquinone-fused dehydro-
annulenes 4-6. Also their electronic properties investigated
by means of 1H NMR, electronic spectra, and cyclic
voltammetry will be described together with the results of
theoretical calculations.
There is considerable interest in macrocyclic dehydro-
annulenes1 from various viewpoints. For example, the
cyclic p-systems containing triple bonds have been shown
to be useful precursors for a variety of carbon rich polymeric
compounds.1a,2 Possible application of the macrocycles
toward photonic devices has also been studied owing to the
unique optical properties of p-conjugated systems.3,4 In
addition, fundamental physical properties such as tropicity
of the macrocyclic rings5 have also been the subject of
continued discussion in the dehydroannulene chemistry. In
the previous studies, we synthesized a series of dehydro-
annulenes fused with electron-donating systems such as
bicyclo[2.2.2]octene6 and 1,4-dimethoxynaphthalene (at
2,3-positions),7 as well as electron-withdrawing system
such as tetrafluorobenzene.8 The electronic effects of these
subunits have been shown to significantly affect the
properties of the macrocycles as exemplified by the
formation of stable complex with Ag(I) ion at the central
cavity of tetradehydro[16]annulene when fused with the
electron-donating bicyclo[2.2.2]octene systems6b and by
reduction of the solid-state reactivity of highly strained
tetradehydro[12]annulene when fused with electron-with-
drawing perfluorobenzene.8
2. Results and discussion
As a good p-electron acceptor, p-benzoquinone is known to
have characteristic electronic properties, and the fusion of
2.1. Synthesis of hexadehydro[18]annulenes 3-6
For the synthesis of dehydroannulene 3 fused with three 3,6-
dimethoxy-4,5-dimethylbenzene units at 1,2-positions,
which is the precursor of a series of p-benzoquinone-fused
dehydroannulene 4-6, the simple copper-mediated coupling
Keywords: Dehydroannulenes; Benzoquinones; Absorption spectra; Redox
potential; DFT calculation.
*
Corresponding author. Tel.: þ81-774-38-3172; fax: þ81-774-38-3178;
e-mail address: komatsu@scl.kyoto-u.ac.jp
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.02.041

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T. Nishinaga et al. / Tetrahedron 60 (2004) 3375–3382
of the corresponding 1,2-diethynylarene was employed. As
shown in Scheme 1, the Pd-catalyzed Sonogashira cross-
coupling reaction between 1,2-dibromo-3,6-dimethoxy-4,5-
dimethylbenzene (7)10 and trimethylsilylacetylene afforded
1,2-bis(trimethylsilylethynyl)-3,6-dimethoxy-4,5-dimethyl-
benzene (8) in 83% yield. After desilylation, the cyclization
reaction by the copper-mediated oxidative coupling under
Eglinton’s condition11 gave dehydro[18]annulene 3 as
yellow solid in 38% yield together with hardly soluble
byproducts, which are possibly the higher oligomers.
Transformation of the p-dimethoxybenzene unit(s) into
p-benzoquinone unit(s) was conducted by the use of CAN.
The reaction was found to proceed stepwise. Thus, when the
reaction of 3 was conducted with 15–20 equiv. of CAN in a
mixed solvent of CHCl3 and CH3CN (1:1 by volume) at
room temperature for 0.5–1 h, monoquinone 4 was obtained
as a main product in 48% yield, while bisquinone 5 was
obtained in 60% yield after stirring overnight. For the
synthesis of trisquinone 6, a larger amount, that is, 80 equiv.
of CAN was used to complete the reaction by stirring for
24 h at room temperature. For separation of the crude
products of annulenes 4-6, chromatography using either
silica gel or alumina was not suitable because of
decomposition of the annulenes, and the only applicable
method was reprecipitation using chloroform–hexane
resulting in rather modest isolated yield (19%) of 6. All of
4-6 were obtained as red powders.
Scheme 1.

T. Nishinaga et al. / Tetrahedron 60 (2004) 3375–3382
3377
Figure 1. (a) ORTEP drawing (50% probability) showing the X-ray structure of 3 and (b) its crystal packing in a space-filling diagram. The averaged bond
lengths (in A) and angles (in degree) in the [18]annulene core are given with esd’s calculated by the following equation; s(l)¼( (1/s2i ))21/2
P
˚
.
formation of the [18]annulene hexagon. In the packing
structure (Fig. 1(b)), the nearest intermolecular contact was
observed between a hydrogen atom of one of the methoxy
groups and an sp carbon (the distance between C(MeO) and
˚
C(sp), 3.26 A) rather than between the sp carbons of the
˚
central annulene rings (3.61 A). Thus, no p stacking
structure was observed. Rather, the CH/p interaction
between the methoxyl protons and the butadiyne p-system
in the central ring is likely to operate in the solid state.
The crystal structure with no p stacking mode of 3 suggests
less reactivity and enhanced thermal stability of the
hexadehydro[18]annulene p-system in 3 in the solid state.
In this respect, for example, unsubstituted hexa-
dehydro[18]annulene turns black at 75 8C and explodes at
85 8C,12 and the corresponding tribenzo-13 and tris(tetra-
fluorobenzo)-8 derivatives start to decompose at 210 and
193 8C, respectively. A series of other benzodehydro[18]-
annulenes with various substituents also undergo exo-
thermic polymerization at the temperature range of
164–240 8C.3 Among the benzodehydro[18]annulenes so
far reported, 3 was found to be most stable against heating:
it only turned black at 272 8C. On the other hand, the
thermal decomposition took place for 4-6 (4; 237 8C, 5;
220 8C, 6; 208 8C) at the similar decomposing temperatures
observed in the other benzodehydro[18]annulenes.
Figure 2. Structure of 9. The averaged bond lengths in the [18]annulene
P
core are given with esd’s calculated by the following equation; s(l)¼( (1/
s2i ))21/2
.
2.2. Structures and diatropicity of hexadehydro[18]-
annulenes 3-6
Among the newly synthesized four hexadehydro[18]-
annulenes 3-6, a single crystal suitable for X-ray structural
analysis was obtained only for 3, and the result is shown in
Figure 1. As expected from the structures reported for
analogous benzodehydro[18]annulenes,3 the central
18-membered ring in 3 is essentially planar and the bending
of butadiyne moiety is quite small since the averaged angle
of C(sp2)–C(sp2)–C(sp) (120.28) is nearly ideal for the
As concerns the bond-length alternation in the [18]annulene
a
Table 1. Calculated bond lengths (A) of the [18]annulene core and NICS(1) values (ppm) for 3-6
b
˚
Compound
Bond length
C(sp2)–C(sp)
NICS(1)
Benzene
C(sp2)–C(sp2)
C(sp)uC(sp)
C(sp)–C(sp)
[18]Annulene
Quinone
3
4
5
6
1.425
1.414
1.223
1.356
0.43
20.1
21.0
22.6
211.4
211.5
212.0
—
—
1.384, 1.426
1.387, 1.429
1.387
1.401, 1.411, 1.413
1.398, 1.398, 1.408
1.398
1.223, 1.224, 1.225
1.227, 1.227, 1.226
1.227
1.351, 1.355
1.346, 1.348
1.346
0.5
0.5
1.0
a
B3LYP/6-31G(d).
GIAO/HF/6-31þG(d)//B3LYP/6-31G(d).
b

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T. Nishinaga et al. / Tetrahedron 60 (2004) 3375–3382
core, which is one of the indicators for aromaticity, the
2
˚
averaged length (1.422(1) A) of C(sp )–C(sp) single bonds
˚
in 3 is slightly longer than that (1.408(2) A) in the
[18]annulene 9 fused with bicyclo[2.2.2]octene units6a
˚
(Fig. 2), while the C(sp)uC(sp) triple bond (1.192(1) A)
˚
in 3 is shorter than that (1.201(2) A) in 9. Thus, the bond
alternation in 3 is larger than that in 9 and, hence, the
aromaticity of 3 is considered to be lower than that of 9. The
presence of diamagnetic ring current in 9 has already been
proven based on an upfield shift of the bridgehead protons of
the bicyclic framework (d 3.41) in comparison with that (d
2.72) of 2,3-diethynylbicyclo[2.2.2]octene.6a Apparently,
the local ring current in the fused benzene rings of 3 reduces
the aromaticity of the central 18-membered ring.
From the same reason, the bond alternation in the
[18]annulene core of benzoquinone-fused systems 4-6 is
expected to become smaller with the increase in the number
of the quinone unit because the aromatic character of the
[18]annulene should be enhanced when the dimethoxy-
benzene units are transformed into non-aromatic benzo-
quinone units. This supposition is supported by the
comparison of the optimized structures for 3-6 at
the B3LYP/6-31G(d) level. As shown in Table 1, the
C(sp)uC(sp) triple bond becomes very slightly longer and
C(sp2)–C(sp) and C(sp)–C(sp) single bonds become
shorter as the number of the fused-quinone ring increases.
The aromaticity for the quinone-fused [18]annulene core is
also experimentally supported by the gradual downfield
shift of the 1H NMR signals for methoxy and methyl groups
in 3, 4, 5, and 6 as shown in Figure 3, reflecting the
increasing diamagnetic ring current in this order. In accord
with this, the NICS values14 (HF/6-31þG(d)//B3LYP/
˚
6-31G(d)) calculated for a dummy atom at 1 A above the
center of the ring (NICS(1)) in the central core of the
[18]annulenes indicate that the diamagnetic ring current
become larger, albeit in a minute degree, with increasing
number of the quinone units in 4-6, as shown in Table 1.
The successful transformation of all the three p-dimethoxy-
benzene units in 3 into p-benzoquinone units in 6, albeit in a
rather modest yield, may be attributed to the enhanced
aromaticity in the dehydro[18]annulene system. This result
is in contrast to the case of dehydro[12]annulene 1, in which
only one p-dimethoxybenzene unit could be transformed
into p-benzoquinone9 possibly due to the antiaromaticity
resulting in the dehydro[12]annulene system fused with
larger numbers of p-benzoquinone units.
2.3. Electronic properties of hexadehydro[18]annulenes
3-6
To compare the electronic properties of 3-6, UV–vis
spectral measurements and cyclic voltammetry (CV) were
carried out. As shown in Figure 4, the longest-wavelength
absorptions of 4 and 5 showed bathochromic shift in
comparison with 3 and 6, suggesting that the HOMO-
LUMO gaps of 4 and 5 are reduced due to the presence of
both electron-donating p-dimethoxybenzene unit(s) and
electron-withdrawing p-benzoquinone unit(s) in the same
p-conjugated system. On the other hand, the cyclic
voltammetry of 4-6 in benzonitrile showed multi-step
reversible reduction waves at 20.69 and 21.21 V vs Fc/
Figure 3. 1H NMR spectra of 3, 4, 5, and 6 in CDCl3.

T. Nishinaga et al. / Tetrahedron 60 (2004) 3375–3382
3379
Figure 4. UV–vis spectra of 3, 4, 5, and 6 in CHCl3.
Fcþ for 4, 20.60, 20.82, and 21.41 V for 5, and 20.58,
20.75, 20.97, and 21.50 V for 6. Each wave corresponded
to the transfer of one electron and no further reduction wave
was observed for these compounds in the potential range
lower than 22.0 V. In contrast, no redox wave was observed
in a range from þ1.2 to 22.2 V for 3. Thus, the LUMO
levels of 4-6 are shown to be significantly lowered as
compared with 3 due to the presence of p-benzoquinone
unit(s). The negative charge generated upon one-electron
reduction is considered not to localize on the p-benzo-
quinone moiety but to delocalize over the whole p-system
since the one-electron reduction was found to take place
stepwise reflecting the effective electronic interaction
between the multiple p-benzoquinone units in 5 and 6.
Thus, no more than three electrons are accommodated in 5
and no more than four electrons in 6 under the present
experimental conditions.
the number of quinone unit increases, which is consistent
with the gradual lowering of the first reduction potential
with increasing number of the quinone unit.
In many p-conjugated systems containing both donor- and
acceptor-substituents, the intramolecular charge-transfer
(CT) interaction, which is recognized as an important factor
for second-order nonlinear optical properties,15 has been
observed, and such interaction has been proven by
observation of the solvatochromism. In the case of 4 and
5, however, only a small extent of solvatochromism was
These experimental observations are in qualitative agree-
ment with the results of DFT calculations (B3LYP/
6-31G(d)). As shown in Table 2, the calculated HOMO-
LUMO gaps for 4 and 5 are smaller than those of 3 and 6,
causing the bathochromic shifts in 4 and 5 in comparison
with 3 and 6. Also the calculated LUMO level is lowered as
Table 2. The longest-wavelength UV–vis absorptions, first reduction
potentials, and Kohn-Sham (KS) HOMO and LUMO levels of 3-6
calculated at B3LYP/6-31G(d)
a
b
Compound
lmax
(nm)
E1/2
(V)
HOMO
(eV)
LUMO
(eV)
Dc
(eV)
d
3
4
5
6
387
529
562
481
—
25.31
25.53
25.82
26.41
21.90
23.31
23.68
23.93
3.41
2.22
2.14
2.48
20.69
20.60
20.58
a
Measured in CHCl3.
Measured in benzonitrile. Electrolyte; 0.1 M TBAP. V vs Fc/Fcþ.
b
c
d
D¼ELUMO2EHOMO
.
Figure 5. Solvent effects upon the longest-wavelength absorptions of (a) 4
and (b) 5.
No redox wave was observed at the range from þ1.2 to 22.2 V.

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T. Nishinaga et al. / Tetrahedron 60 (2004) 3375–3382
Figure 6. KS HOMOs and LUMOs of 4 and 5 calculated at the B3LYP/6-31G(d) level.
observed, although the examined solvents were quite
limited due to the solubility problem (Fig. 5). This result
may be rationalized as follows. According to ZINDO
calculations, the longest absorption for 4 and 5 can be
assigned to the HOMO!LUMO transition (4; 531 nm
(coefficient 0.66, oscillator strength 0.254), 5; 562 nm
(coefficient 0.61, oscillator strength 0.089)). The HOMO
and LUMO are not localized only on the electron donating
or accepting moieties, that is, p-dimethoxybenzene or
p-benzoquinone units, but rather delocalized extensively
over the whole p-system as shown in Figure 6. Therefore,
there would result only a small change in charge
distribution, or polarity, upon the HOMO!LUMO tran-
sition in the dehydro[18]annulene molecules of 4 and 5, and
hence the extent of solvatochromic shifts becomes small.
of intramolecular charge-transfer is very small, due to the
delocalization of both HOMO and LUMO over the whole
dehydro[18]annulene p-systems.
4. Experimental
4.1. General
Melting points were measured on a Yanaco MP-500D
apparatus and are uncorrected. Elemental analyses were
performed at the Microanalysis Division of Institute for
1
Chemical Research, Kyoto University. H and 13C NMR
spectra were recorded on a Varian Mercury-300 or a JEOL
JNM-GX 400 spectrometer. The chemical shifts of NMR
are expressed in ppm from TMS as determined with
1
reference to the internal CHCl3 and CDCl3 (d 7.26 in H
3. Conclusion
and d 77.0 in 13C NMR). UV–vis spectra were taken on a
SHIMADZU UV-2100PC spectrometer. Mass spectra were
taken on a JEOL JMS 700 spectrometer for EI method and
on a Finigan TSQ7000 for APCI method. Preparative gel
permeation chromatography (GPC) was performed with a
JAI LC-908 chromatograph equipped with JAIGEL 1H and
2H columns.
A series of hexadehydro[18]annulenes 4-6 fused with
one, two, and three p-benzoquinone unit(s) were
synthesized by the stepwise oxidation of p-dimethoxy-
benzene units of tris(3,6-dimethoxy-1,2-benzo)-
dehydro[18]annulene 3. In these annulenes, the
diatropicity of the central 18-membered ring was shown
to gradually increase with the increasing number of
p-benzoquinone unit(s) due to the enhanced double bond
character at the fused position(s). Although 4 and 5 have
both the p-electron donating and accepting groups and can
be regarded as novel push–pull type p-systems, the extent
Ether and THF were distilled from sodium benzophenone
ketyl. Methanol was distilled from sodium methoxide.
Piperidine, pyridine, chloroform, and acetonitrile were
distilled over CaH2. All other solvents and reagents were

T. Nishinaga et al. / Tetrahedron 60 (2004) 3375–3382
3381
used as purchased. Theoretical calculations were performed
using the Gaussian 98 program.16
4.1.3. Transformation of 3 to p-benzoquinone-fused
dehydro[18]annulenes 4-6. To a stirred solution of 3
(15 mg, 0.023 mmol) in a mixed solvent of CH3CN (6 mL)
and CHCl3 (6 mL) was added dropwise a solution of ceric
ammonium nitrate (CAN) (190 mg, 0.35 mmol) in distilled
water (0.8 mL) over 5 min. After 25 min of stirring, the
reaction was quenched by adding water (ca. 10 mL). The
aqueous layer was extracted with CHCl3. The combined
organic solution was dried over MgSO4 and evaporated to
give a crude mixture containing the mono-benzoquinone
derivative 4 as a major component. The mixture was
dissolved in CHCl3 (ca. 10 mL), and 10 mL of hexane was
slowly diffused into the solution to give pure 4 (7.0 mg,
0.011 mmol, 48%) as a red powder.
4.1.1. 1,2-Bis(trimethylsilylethynyl)-3,6-dimethoxy-4,5-
dimethylbenzene (8). To a degassed solution of 1,2-
dibromo-3,6-dimethoxy-4,5-dimethylbenzene (7)10 (671 mg,
2.07 mmol), Pd(PPh3)4 (106 mg, 0.092 mmol), and CuI
(37 mg, 0.19 mmol) in dry piperidine (70 mL) was added
trimethylsilylacetylene (1.0 mL, 0.70 g, 7.1 mmol), and the
reaction mixture was stirred at 100 8C for 13 h under an Ar
atmosphere in a sealed tube. After the reaction was
quenched with water, the mixture was extracted with
ether, and the ethereal solution washed with aqueous
NaCl, and dried over MgSO4. After the removal of the
solvent and the volatile under reduced pressure, the product
was purified by chromatography over silica gel (hexane–
EtOAc (20:1)) to give 8 (615 mg, 1.72 mmol, 83%) as a
Compound 4: mp .300 8C (the color turned to black at
1
237 8C); H NMR (300 MHz, CDCl3) d 3.98 (s, 6H), 3.97
(s, 6H), 2.31 (s, 6H), 2.30 (s, 6H), 2.13 (s, 6H); IR (KBr)
1
colorless solid: mp 112.7–113.0 8C; H NMR (300 MHz,
CDCl3) d 3.82 (s, 6H), 2.16 (s, 6H), 0.28 (s, 18H); 13C NMR
(75.5 MHz, CDCl3) d 155.8, 132.4, 117.7, 102.1, 99.5, 60.4,
12.8, 0.0. Anal. Calcd for C20H30O2Si2: C, 66.98; H, 8.43%.
Found: C, 66.70; H, 8.47%.
2192, 2172, and 2129 (CuC), 1656 (CvO) cm21
.
HRMS (FAB) calcd for C40H30O6 606.2042, found
606.2029. The poor solubility of 4 hampered the 13C
NMR measurement.
4.1.2. tris(3,6-Dimethoxy-4,5-dimethyl-1,2-benzo)hexa-
dehydro[18]annulene (3). A solution of KOH (ca. 0.5 g)
in distilled water (2 mL) was added in one portion to a
solution of 8 (1.39 g, 3.86 mmol) in a mixed solvent of
methanol (40 mL) and THF (9 mL). The reaction mixture
was vigorously stirred at room temperature for 15 min,
diluted quickly with water (10 mL), extracted with ether,
and the ethereal solution dried over MgSO4. The volatiles
were removed in vacuo and the crude product was separated
by flash chromatography over silica gel eluted with
hexane–AcOEt (20:1) to give crude 1,2-diethynyl-3,6-
dimethoxy-4,5-dimethylbenzene (0.791 g, 3,69 mmol,
In the same way, the reaction of 3 (11 mg, 0.017 mmol) with
CAN (200 mg, 0.36 mmol) was conducted by stirring at
room temperature overnight. The reaction mixture was
treated in exactly the same way as above. Reprecipitation
with CHCl3–hexane gave bis-benzoquinone derivative 5
(5.7 mg, 0.10 mmol, 60%) as a red powder.
Compound 5: mp .300 8C (the color turned to black at
220 8C); 1H NMR (300 MHz, CDCl3) d 4.04 (s, 6H), 2.38 (s,
6H), 2.17 (s, 12H); 13C NMR (75.5 MHz, CDCl3) d 181.9,
181.7, 157.6, 142.7, 142.5, 135.6, 133.1, 130.8, 116.3, 94.2,
92.5, 91.1, 85.4, 82.5, 81.9, 78.1, 62.0, 13.5, 13.1; IR (KBr)
2189 (CuC), 1650 and 1628 (CvO) cm21; MS (APCI) m/z
576 (Mþ).
1
95%) as a colorless solid; H NMR (300 MHz, CDCl3) d
3.82 (s, 6H), 3.50 (s, 2H), 2.19 (s, 6H); 13C NMR
(75.5 MHz, CDCl3) d 156.2, 133.1, 117.1, 84.4, 78.3,
60.8, 12.9. The crude diyne was used for the next step
without further purification.
In the same way, the reaction of 3 (25 mg, 0.039 mmol)
with CAN (1.86 g, 3.39 mmol) was conducted in a mixed
solvent of CH3CN (10 mL) and CHCl3 (10 mL) at room
temperature overnight. The post treatment as described
above and the similar reprecipitation afforded tris-benzo-
quinone derivative 6 (4 mg, 0.007 mmol, 19%) as a red
powder.
To a solution of Cu(OAc)2 (1.38 g, 7.59 mmol) in a mixed
solvent of pyridine (50 mL), methanol (50 mL), and ether
(10 mL) was added a solution of 1,2-diethynyl-3,6-
dimethoxy-4,5-dimethylbenzene (434 mg, 2.03 mmol) in a
mixed solvent of pyridine (20 mL) and methanol (20 mL)
over a period of 2 h. The mixture was stirred at 60 8C for
0.5 h and overnight at room temperature under air. The
reaction was quenched by 30% aqueous H2SO4, and the
aqueous layer was extracted with CHCl3. The combined
organic solution was washed with 50% aqueous H2SO4 and
with aqueous NaHCO3, and dried over MgSO4. The organic
solution was evaporated and the crude mixture was
separated by preparative GPC to give crude 3 (163 mg,
0.256 mmol, 38%). The crude product was recrystallized
from CHCl3 to give single crystals of 3 suitable for X-ray
analysis.
Compound 6: mp .300 8C (the color turned to black at
1
208 8C); H NMR (300 MHz, CDCl3) d 2.24(s); 13C NMR
(75.5 MHz, CDCl3) d 181.5, 143.2, 132.0, 92.5, 83.5, 13.2;
IR (KBr) 2178 and 2126 (CuC), 1655 (CvO) cm21; MS
(APCI) m/z 546 (Mþ).
4.2. Cyclic voltammetry
Cyclic voltammetry (CV) was performed on a BAS-50W
electrochemical analyzer. The CV cell consisted of a glassy
carbon working electrode, a Pt wire counter electrode, and a
Ag/AgNO3 reference electrode. The measurements were
carried out for 1.0 mM solutions of each sample with
tetrabutylammonium perchlorate as a supporting electrolyte
(0.1 M) in benzonitrile, and the values for oxidation
potentials were calibrated with ferrocene as an internal
standard.
Compound 3: mp .300 8C (the color turned to black at
272 8C); 1H NMR (300 MHz, CDCl3) d 3.94 (s, 18H), 2.23
(s, 18H); 13C NMR (75.5 MHz, CDCl3) d 156.8, 133.6,
117.2, 81.5, 77.7, 61.4, 13.1; IR (KBr) 2210 (CuC) cm21
.
HRMS (EI) calcd for C42H36O6 636.2512, found 636.2514.

3382
T. Nishinaga et al. / Tetrahedron 60 (2004) 3375–3382
Soc. 1997, 119, 2052. (b) Dosa, P. I.; Erben, C.; Iyer, V. S.;
4.3. X-ray structural determination
Vollhardt, K. P. C.; Wasser, I. M. J. Am. Chem. Soc. 1999,
121, 10430.
Crystal data for 3: (C42H36O6)·CHCl3, FW¼1392.79,
˚
3. Pak, J. J.; Weakley, T. J. R.; Haley, M. M. J. Am. Chem. Soc.
1999, 121, 8182.
triclinic; space group P-1; a¼11.755(5) A, b¼
˚
˚
17.474(7) A, c¼20.099(8) A, a¼66.685(9)8, b¼84.648
3
˚
4. Mitzel, F.; Boudon, C.; Gisselbrecht, J.-P.; Gross, M.;
Diederich, F. Chem. Commun. 2002, 2318.
(11)8, g¼78.572(9)8, V¼3716(3) A , Z¼4, Dcalc¼2.488
mg/m3. Intensity data were collected at 123 K on a Bruker
SMART APEX diffractometer with Mo Ka radiation
5. For recent example, see (a) Matzger, A. J.; Vollhardt, K. P. C.
Tetrahedron Lett. 1998, 39, 6791. (b) Wan, W. B.; Kimball,
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˚
(l¼0.71073 A) and graphite monochromater. Frames
corresponding to an arbitrary hemisphere of data were
collected using v scans of 0.38 counted for a total of 10 s per
frame. A total of 21075 reflections were measured and
14161 were independent. The structure was solved by direct
methods (SHELXTL) and refined by the full-matrix least-
squares on F 2 (SHELXL-93). The presence of a disordered
solvent molecule in the lattice was evident, and the
SQUEEZE17 data processed with the program implemented
in PLATON-9618 were used for the further refinement. All
non-hydrogen atoms were refined anisotropically and
hydrogen atoms were refined isotropically and the refine-
ment converged to R1¼0.0667, wR2¼0.1739 (I.2s(I)), and
GOF¼0.948. Crystallographic data (excluding structure
factors) for the structures in this paper have been deposited
with the Cambridge Crystallographic Data Centre as
supplementary publication numbers CCDC 229724. Copies
of the data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
þ44-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
´
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(C) 1968, 2414.
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Acknowledgements
This work was supported by the Grant-in-Aid for COE
Research on Elements Science (No. 12CE2005) from the
Ministry of Education, Culture, Sports, Science and
Technology, Japan. Computation time was provided by
the Supercomputer Laboratory, Institute for Chemical
Research, Kyoto University.
16. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.;
Montgomery, Jr., J. A.; Stratmann, R. E.; Burant, J. C.;
Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.;
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