Syntheses, structures, and properties of quinone-bridged calix[6]arenes

Article abstract of DOI:10.1246/bcsj.78.169

The quinone-bridged calix[6]arenes 1 and 2, carrying a 1,4-benzoquinone moiety in the cavity of a calixarene macrocycle, were synthesized from the corresponding p-methoxyphenol derivatives. X-ray crystallography revealed the structures of 1 and 2, in whic

Full text of DOI:10.1246/bcsj.78.169

ꢀ 2005 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 78, 169–179 (2005)
169
Syntheses, Structures, and Properties of Quinone-Bridged Calix[6]arenes
y
ꢀ
ꢀ
Shigehisa Akine, Kei Goto, and Takayuki Kawashima
Department of Chemistry, Graduate School of Science, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033
Received August 24, 2004; E-mail: goto@chem.s.u-tokyo.ac.jp
The quinone-bridged calix[6]arenes 1 and 2, carrying a 1,4-benzoquinone moiety in the cavity of a calixarene mac-
rocycle, were synthesized from the corresponding p-methoxyphenol derivatives. X-ray crystallography revealed the
structures of 1 and 2, in which the quinone moiety is located inside the cone-shaped calix[6]arene framework and sur-
rounded by the lower-rim substituents. Their 1H NMR spectra showed upfield shifts of the protons on the bridging unit in
comparison with reference compounds without the calixarene framework, in accordance with their crystal structures.
The cyclic voltammograms of 1 and 2 showed two waves, the second ones being considerably broadened. Their reduc-
tion potentials were found to be negatively shifted in comparison with those of the reference compounds. These shifts
were explained in terms of the nonbonded interaction between the ether oxygen atoms of the calixarene moiety and the
quinone moiety, as well as the sterically restricted access of the counter cation to the semiquinone anion radical. Reac-
tions of 1 with hydroxylamine and phenylhydrazine afforded the corresponding hydroquinone along with the quinone
monoimine derivatives, indicating that electron transfer from the amines proceeds quickly, although the negatively shift-
ed reduction potentials of 1 are apparently unfavorable for the electron transfer process.
Macrocyclic molecules constitute a major class of complex-
ing agents for metal ions and small organic molecules, and
their inner phase provides a unique microenvironment to the
included guest species.1–4 Recently, redox reactions of chemi-
cal species captured in the cavity of macrocyclic host mole-
cules such as cyclophanes, calixarenes, and carcerands have
been attracting increasing attention.5–10 In these complexes
based on noncovalent interaction, however, only the averaged
properties of the complexed and dissociated guest species are
observable. Furthermore, the geometry of the guest molecule
in the cavity of the macrocycle is often ambiguous. If the guest
molecule is covalently anchored in the cavity with well-de-
fined geometry, one can expect that the effects of the surround-
ing macrocycle on the properties of the intracavity species may
be elucidated much more definitely.
Chart 1.
We have been investigating the synthesis and applications of
calix[6]arenes bridged by a functionalized m-xylene-ꢀ,ꢀ0-diyl
unit.11–18 Stabilization of highly reactive species such as a sul-
fenic acid19,20 and selenenic acids21,22 has been achieved and
their reactivities were investigated. This framework has also
Results and Discussion
Synthesis. We previously reported that capping the lower
rim of the m-xylene-ꢀ,ꢀ0-diyl-bridged calix[6]arenes with ar-
ylmethyl groups can freeze the conformation of the calixarene
macrocycle.13,14 For construction of a rigid framework, we in-
troduced benzyl groups into the lower rim of the calixarene
moiety of 1. Synthesis of 1 was effected by the route shown
in Scheme 1, where a p-methoxyphenol unit was used as a pre-
cursor to the quinone moiety. Bridged compound 5 was pre-
pared by the reaction of p-t-butylcalix[6]arene (3)33 with tri-
bromide 434 in 73% yield by using the previously reported
method.17 Benzylation of the four hydroxy groups of 5 in
the presence of cesium carbonate afforded almost exclusively
the cone isomer 6 of the tetrasubstituted product in 93% yield.
The spectral features of 6 are essentially the same as those of
other bridged calix[6]arenes fixed in a cone conformation that
we have reported so far.13–16,21,22 The bromine atom of 6 was
been utilized for concave reagents by Luning et al.23–27 The
¨
large cavity of this framework is also expected to serve as a re-
action field for redox-active species covalently anchored in it.
Although a large number of macrocyclic quinones such as calix-
quinones have been reported so far,28–31 there has been no ex-
ample of a compound bearing a quinone moiety covalently fixed
in the cavity. In this paper, we describe the synthesis and struc-
tures of the quinone-bridged calix[6]arenes 1 and 2. The rela-
tionships between the electrochemical properties and the struc-
tural features of 1 and 2 as well as their chemical reactivities are
also delineated. Parts of this work have been communicated.32
y Present address: Department of Chemistry, University of
Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571
Published on the web January 13, 2005; DOI 10.1246/bcsj.78.169

170 Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
Quinone-Bridged Calix[6]arenes
Scheme 1. Synthesis of the quinone-bridged calix[6]arene 1. Reagents and conditions: (a) KOH, THF/DMF (10:1), rt; (b) PhCH2Br,
Cs2CO3, DMF, 70 ꢂC; (c) (i) t-BuLi, THF, ꢁ78 ꢂC, (ii) B(OMe)3, (iii) H2O2, aq. NaOH; (d) FeCl3, AcOH, C6H6/CH3CN (1:2), rt.
replaced by a hydroxy group via lithiation followed by reac-
tion with trimethyl borate and subsequent treatment with an al-
kaline solution of hydrogen peroxide. p-Methoxyphenols are
known to be oxidized to the corresponding quinones under
mild conditions.35 Oxidation of 7 with iron(III) chloride af-
forded the target compound 1 as pale yellow crystals. Com-
pound 1 was also found to adopt a cone conformation like
the intermediates 6 and 7, indicating that no conformational
change occurred during the chemical modification of the
bridging unit.
In order to investigate the effects of the lower-rim aromatic
rings on the properties of the quinone moiety of 1, the tetra-
ethylated derivative 2 was also prepared according to a similar
synthetic procedure (Scheme 2). Recently, we reported that the
conformational mobility of the m-xylene-ꢀ,ꢀ0-diyl-bridged
calix[6]arene can be modulated by the lower-rim capping
groups.36 In contrast with the tetrabenzylated compounds, the
Scheme 2. Synthesis of the quinone-bridged calix[6]arene 2.
Reagents and conditions: (a) EtI, Cs2CO3, DMF, 70 ꢂC;
(b) (i) t-BuLi, THF, ꢁ78 ꢂC, (ii) B(OMe)3, (iii) H2O2,
aq. NaOH; (c) FeCl3, AcOH, C6H6/CH3CN (1:2), rt.
corresponding tetraethylated compounds were found to exist
as equilibrium mixtures of the conformational isomers in solu-
tion, although they can be observed independently on the
NMR time-scale. We also reported that the ratios of the con-
formational isomers depend on the functionality on the bridg-
The reference compounds 10 and 11 without the calixarene
framework were also prepared. 2,6-Bis(phenoxymethyl)-1,4-
benzoquinone (10) was synthesized from the corresponding
p-bromoanisole derivative 12 in two steps (Scheme 3). 2,6-Di-
methyl-1,4-benzoquinone (11) was prepared according to the
literature.37
Spectroscopic Properties. In the infrared spectra of both 1
and 2, the C=O absorption was observed at 1653 cmꢁ1. This
value is almost the same as those of the reference compounds
10 (1657 cmꢁ1) and 11 (1653 cmꢁ1) without the calixarene
framework. On the other hand, in the 1H and 13C NMR spectra,
large upfield shifts for H2, C1, and C3 were observed for both
1 and 2 in comparison with the phenoxymethyl derivative 10
1
ing unit.36 In the H NMR spectra (CDCl3) of the ethyl deriv-
atives 2, 8, and 9, which are expected to exist as equilibrium
mixtures of the conformational isomers, only the cone isomers
were observed. These results indicate that the cone isomers of
2, 8, and 9 are thermodynamically much more stable than other
isomers. In the cone isomers of 8 and 9, the methoxy group in
the folded shape shows a good fit to the cavity of the cone-
shaped calix[6]arene framework, as described previously.36
In the case of quinone 2, the preference for the cone isomer
can be reasonably explained in terms of the interaction be-
tween ether oxygen atoms and olefinic carbon atoms of the
quinone moiety, as supported by its crystal structure.

S. Akine et al.
Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
171
Fig. 1. Electronic absorption spectra of 1, 2, 10, and 11
(5 ꢃ 10ꢁ4 M) in chloroform.
Scheme 3. Synthesis of the reference compounds. Reagents
and conditions: (a) PhOH, K2CO3, DMF, rt; (b) (i) t-BuLi,
THF, ꢁ78 ꢂC, (ii) B(OMe)3, (iii) H2O2, aq. NaOH; (c)
FeCl3, AcOH, C6H6/CH3CN (1:2), rt.
Table 1. 1H and 13C NMR Chemical Shifts (ꢁ)aÞ of Qui-
nones 1, 2, 10, and 11aÞ
Compound H1 H2 C1
C2
C3
C4
C5
1
2
10
11
6.36 2.47 182.99 143.58 127.44 187.28 67.38
6.62 2.34 183.16 144.78 126.80 189.06 67.45
6.96 4.96 186.29 144.03 132.09 186.86 63.11
6.56 2.06 187.59 145.76 133.26 188.16 15.93
a) Measured in CDCl3. Atom labeling is shown in Scheme 4.
Scheme 4. Atom labeling for Table 1.
(Table 1). These results indicate that the quinone moiety of 1
and 2 is magnetically shielded by the surrounding aromatic
rings of the calixarene framework. The upfield shift of H1,
which was observed only for the benzyl derivative 1, is prob-
ably due to the shielding effect of the four benzyl groups at the
lower rim.
The electronic absorption spectra of the quinone-bridged
calix[6]arenes 1 and 2 are shown in Fig. 1. The broad absorp-
tion feature of the benzyl derivative 1 was observed as a
shoulder at around 340 nm. However, it was difficult to deter-
mine the exact wavelength of maximum absorption and the ab-
sorption coefficient of the quinone moiety of 1 due to the
strong absorption of the ten benzene rings of the bridged
calix[6]arene framework. On the other hand, the ethyl deriva-
tive 2 showed an absorption peak at 334 nm. The molar extinc-
tion coefficients of 1 and 2 are larger than those of the refer-
ence compounds 10 and 11. This is probably due to weak
charge transfer from the electron-rich aromatic rings of the
calixarene framework to the quinone moiety.38,39
Fig. 2. X-ray structures of the quinone-bridged calix[6]-
arenes (a) 1 and (b) 2. (c) ORTEP drawing of reference
compound 10. Solvent molecules and hydrogen atoms
are omitted for clarity.
Crystal Structures. The crystal structures of the quinone-
bridged calix[6]arenes 1 and 2 were determined by X-ray crys-
tallography (Fig. 2). The quinone moiety of 1 and 2 is accom-

172 Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
Quinone-Bridged Calix[6]arenes
ꢀ
Table 2. Selected Bond Lengths (A) of Quinones 1, 2, and
10
1
2
10
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C6–C1
C1–O1
C4–O2
1.492(4)
1.327(4)
1.475(4)
1.486(4)
1.330(4)
1.481(4)
1.227(3)
1.227(4)
1.430(12)
1.377(15)
1.501(14)
1.465(11)
1.350(15)
1.458(15)
1.269(13)
1.252(12)
1.497(3)
1.335(3)
1.479(3)
1.481(3)
1.335(3)
1.494(3)
1.223(3)
1.223(3)
Scheme 5. Schematic drawing of the interaction between
quinone and calix[6]arene moieties. Compound 1: x ¼
Fig. 3. Cyclic voltammograms of 1, 2, and 10 (5 ꢃ 10ꢁ4
M) in dichloromethane containing 0.1 M tetrabutylammo-
nium perchlorate on a glassy carbon electrode. Reference
ꢀ
3:172ð3Þ, y ¼ 3:219ð3Þ A; compound 2: x ¼ 3:092ð10Þ,
ꢀ
y ¼ 3:224ð10Þ A.
electrode, Ag/Agþ, scan rate, 100 mV sꢁ1
.
modated inside the cone-shaped calixarene framework and is
surrounded by the lower rim substituents. It was found that
there is a strong resemblance between the conformations of
1 and 2 in the crystalline state. In both cases, the two carbonyl
groups of the quinone moiety are not particularly close to ei-
ther the six aromatic rings of the calixarene macrocycle or to
the benzyl and ethyl groups at the lower rim. The structural pa-
rameters of the quinone moieties of 1 and 2 are almost the
same as those of the reference compound 10 (Table 2), and
no unusual geometrical features were observed. However, sig-
nificant nonbonded contacts were observed between the olefin-
ic carbon atoms of the quinone moiety and the oxygen atoms
of the calixarene lower-rim in 1 and 2 (Scheme 5). Similar
contacts were reported for the [2.2]- and [3.3]cyclophanes con-
taining both 1,4-benzoquinone and hydroquinone moieties,
which were reported to show strong charge-transfer bands in
the electronic spectra.38,39
Electrochemistry. The cyclic voltammograms of quinones
1, 2, and 10 are shown in Fig. 3. Two waves were observed for
both of the quinone-bridged calix[6]arenes 1 and 2. These two
waves can be attributed to the formation of a monoanion radi-
cal and a dianion of the quinone moiety, which is similar to
other benzoquinone derivatives, including 10 and 11.40 The
second waves of 1 and 2 were found to be considerably broad-
ened. This can be explained either by a slower rate of electron
transfer through the calixarene macrocycle or by conforma-
tional changes during the redox processes.
ꢄ
Table 3. Reduction Potentials (V) of Quinones 1, 2, 10, and
11aÞ
1
2
10
11
E1 (0/ꢁ1)
ꢁ1:25
ꢁ1:27
ꢁ0:71
ꢁ1:37
ꢁ0:91
ꢁ1:44
E2 (ꢁ1/ꢁ2)
ꢁ1:6 (br)
ꢁ1:6 (br)
a) Measured in 5 ꢃ 10ꢁ4 M dichloromethane solution con-
taining 0.1 M tetrabutylammonium perchlorate on a glassy
carbon electrode. Reference electrode, Ag/Agþ, scan rate,
100 mV sꢁ1
.
ꢄ
that 1 and 2 are more difficult to reduce. A similar negative
shift was reported for the oxidation potential of ferrocene in-
corporated in a water-soluble calix[6]arene.5,6
There are several conceivable reasons for the observed neg-
ative shifts of the reduction potentials of 1 and 2. Since the po-
tential of the phenoxymethyl-substituted quinone 10 is more
positive than that of the methyl derivative 11, the two CH2OAr
substituents at the 2,6-positions of the quinone moiety of 1 do
not seem to be responsible for the observed negative shift.
Electrons are known to be particles for which tunneling is very
important. It is unlikely, therefore, that the steric hindrance
around the quinone moiety of 1 and 2 caused by the calixarene
framework restricts the access of electrons to the central qui-
none moiety. In fact, sterically hindered quinones such as
2,5- and 2,6-di-t-butyl-1,4-benzoquinone are reported to have
reduction potentials not so different from those of the corre-
sponding dimethyl derivatives.35
The reduction/oxidation potentials of 1, 2, 10, and 11 are
summarized in Table 3. The first reduction potentials of 1
and 2 (indicated as E1) are shifted to a more negative region
than those of the reference compounds 10 and 11, indicating
The calixarene frameworks of compounds 1 and 2 are con-

S. Akine et al.
Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
173
sidered to affect the redox properties of their quinone moieties
in the following two ways. One is the effect of the counter cat-
ion in electrochemical measurements. Usually, ionic species
generated in the redox processes of cyclic voltammetry are sta-
bilized by forming a tightly bound ion pair in organic solvents.
The calixarene frameworks of 1 and 2, however, interfere with
the access of the counter cations to the semiquinone anion
moiety, causing destabilization of the reduced form of the qui-
none and resulting in negatively shifted potentials. The other
factor is the through-space interaction between the quinone
moiety and the calixarene framework. X-ray crystallographic
analysis of 1 and 2 indicates the interaction between the olefin-
ic carbon atoms of the quinone moiety and the ether oxygen
atoms of the lower rim. Such nonbonded interactions are con-
sidered to raise the LUMO of the quinone, which result in the
more negative reduction potentials of 1 and 2. A similar obser-
vation was described in the literature, where the reduction po-
tentials of some cyclic monoquinones bearing ether oxygens
are more negative than their carbon analogues.41
The second waves (indicated as E2) of 1 and 2 were also ob-
served at more negative regions than those for 10 and 11, sim-
ilar to the first reduction potentials (E1). However, these shifts
of E2 are smaller than those of E1. This can be explained by
the change of the electron density of the bridging unit. After
the one-electron reduction, the increased electron density of
the bridging unit causes a conformational change in such a
way that it minimizes the electronic repulsion between the
ether oxygen and the semiquinone anion radical. As a result,
smaller shifts are expected for the second reduction potentials
because the effect of the ether oxygen becomes weaker in the
semiquinone anion radical intermediate.
Chemical Reduction. Reduction of 1 with borane/THF
afforded the hydroquinone derivative 14 in 43% yield; it could
be oxidized to 1 again with iron(III) chloride (Scheme 6). It is
noteworthy that the reversible chemical redox reactions of the
quinone-bridged calix[6]arene 1 are possible, in spite of the in-
complete reversibility of its cyclic voltammogram.
Fig. 4. (a) X-ray structure of hydroquinone 14. (b) Plot
showing the formation of a dimeric form. Hydrogen
atoms, disordered atoms, and a chloroform molecule are
omitted for clarity.
The structure of the hydroquinone derivative 14 was estab-
lished by X-ray crystallographic analysis, which shows its di-
meric structure with a cyclic hydrogen bonding network in-
cluding three molecules of methanol (Fig. 4). In the crystal
structure of 14, there is no nonbonded contact between the
ether oxygen and the bridging unit, such as was observed in
quinones 1 and 2. It was also revealed that the conformation
of the central bridging unit of 14 is different from those of 1
and 2 (Scheme 7). There is intramolecular hydrogen bonding
Scheme 7. Schematic drawings of the conformations of the
bridging units of (a) 1 and (b) 14.
between the central hydroxy group (O7–H) and the ether oxy-
gen atom of the bridging unit (O2) with an O2 O7 distance of
ꢄꢄꢄ
ꢀ
2.621(4) A, which stabilizes the unsymmetrical conformation
schematically depicted in Scheme 7(b). The bridging unit of
14 hangs down below the cavity of calix[6]arene in compari-
son with those of 1 and 2 bearing the symmetrical conforma-
tion shown in Scheme 7(a).
This structural change was also observed in solution. In the
1H NMR spectra of 1, the signal of the methylene protons con-
nected to the quinone moiety appeared at ꢁ 2.47, whereas those
of the corresponding methylene protons of 14 were observed at
ꢁ 4.14 (Fig. 5). These results clearly indicate that the shielding
effect of the surrounding calix[6]arene moiety of 14 on the
methylene protons is very small. This is probably because
Scheme 6. Chemical redox reactions of the quinone-bridged
calix[6]arene 1.

174 Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
Quinone-Bridged Calix[6]arenes
Fig. 5. 1H NMR spectra of (a) quinone 1 and (b) hydroquinone 14 in CDCl3.
the bridging unit of hydroquinone 14 lies much lower than that
of quinone 1, as shown in Scheme 7, which is consistent with
the conformations of 1 and 14 in the crystalline state. In addi-
tion, a downfield shift of the 1H NMR signal (ꢁ 5.25) of the hy-
droxy group directing towards the cavity of 14 was observed,
while the signal of the outer one was observed at ꢁ 3.48. This
also supports the presence of an intramolecular hydrogen bond
between the inner hydroxy group and the ether oxygen atom.
Reaction with Hydroxylamine or Phenylhydrazine. The
reactivities of the quinone-bridged calix[6]arenes are expected
to be different from those of the parent quinones because their
reduction potentials are negatively shifted. The reaction of the
quinone-bridged calix[6]arene 1 with an excess amount of hy-
droxylamine afforded a crude mixture containing the quinone
monooxime derivative 15 as a major product (Scheme 8),
none 14 was predominantly formed in this reaction. Com-
pound 14 is considered to be formed by reduction involving
an electron transfer from the amine. However, the process is
not considered to be favorable in view of the negatively shifted
reduction potentials of 1, which imply reduced ability as an
electron acceptor. The formation of 14 can be explained in
terms of the steric hindrance around the quinone moiety of
1. It is obvious that the addition of nucleophiles to the carbonyl
group in the cavity is severely hampered by the calix[6]arene
framework. Moreover, the four lower-rim benzyl groups of 1
hinder the access of amines to the carbonyl group on the low-
er-rim side, which results in the suppression of the addition re-
action also on this side. Thus the electron transfer from the
amine proceeds faster than the addition reaction, although
the negatively shifted reduction potentials are apparently un-
favorable for this process. This is one of the reactions that
reflect the structural features of the quinone-bridged calix[6]-
arene 1.
1
which was confirmed by its H NMR spectrum (Fig. 6). This
mixture was found to contain no quinone dioxime,42 indicating
that the reaction toward the intracavity carbonyl group of 1
was hampered by the calix[6]arene macrocycle. Interestingly,
chromatographic separation of this mixture on silica gel gave
the p-nitrosophenol derivative 16 (68%) and hydroquinone
14 (26%); no quinone monooxime 15 was observed. These
results indicate that quinone monooxime 15 readily isomerizes
on silica gel to afford p-nitrosophenol 16, even though the
inner carbonyl group of 15 is surrounded by the calix[6]arene
macrocycle.
Conclusion
The quinone-bridged calix[6]arenes 1 and 2 containing a
1,4-benzoquinone moiety in the cavity were synthesized. X-
ray crystallographic analysis of 1 and 2 revealed that the qui-
none moiety is located inside the cone-shaped calix[6]arene
framework and is surrounded by the lower-rim substituents.
Their structures can be viewed as an image of a 1,4-benzoqui-
none included in the cavity of calix[6]arene and covalently
anchored through the CH2O linkages. The spectroscopic prop-
erties of the quinone-bridged calix[6]arenes were investigated,
showing that the quinone moiety is located in a magnetically
shielded region. The reduction potentials of 1 and 2 were
found to be negatively shifted from those of the reference com-
pounds without the calix[6]arene framework. These shifts can
Similarly, the reaction of quinone 1 with an excess of phen-
ylhydrazine gave a crude mixture containing the phenylazo-
phenol derivative 18 and hydroquinone 14 (Scheme 8). It is
considered that addition of the hydrazine to one of the carbon-
yl groups of the quinone moiety led to the formation of the hy-
drazone derivative 17, which underwent isomerization to 18
under the reaction conditions. It should be noted that hydroqui-

S. Akine et al.
Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
175
Scheme 8. Reaction of quinone-bridged calix[6]arene 1 with hydroxylamine or phenylhydrazine.
Experimental
Melting points were determined on a Yanaco micro melting
point apparatus. All melting points were uncorrected. THF was
purified by distillation from sodium diphenylketyl under argon at-
mosphere before use. Benzene was distilled from lithium tetrahy-
dridoaluminate. DMF and acetonitrile (special grade) were pur-
chased from Wako Pure Chemical Industries Ltd. and used with-
out purification. Tetrabutylammonium perchlorate was supplied
from Tomiyama Chemicals as lithium battery grade. Dichloro-
methane for electrochemical measurements was purchased from
Kanto Chemicals as an HPLC grade and used without purification.
Column chromatography and preparative TLC were carried out
with Wakogel C-200 and Merck Kieselgel 60PF254 Art. 7747,
1
respectively. H NMR and 13C NMR spectra were recorded on a
Bruker DRX-500, a JEOL JNM-A500, and a JEOL EX-AL270
spectrometers. Assignments of NMR signals were based on 2D-
COSY, HMQC, and HMBC spectra. IR spectra were recorded
on a JASCO FT/IR-300E spectrometer. Elemental analyses were
performed by the Microanalytical Laboratory of the Department
of Chemistry, Faculty of Science, the University of Tokyo.
Materials. p-t-Butylcalix[6]arene (3),33 5-bromo-1,3-bis(bro-
momethyl)-2-methoxybenzene (4),34 and 2,6-dimethyl-1,4-benzo-
quinone (11)37 were prepared by the procedures described in the
literature.
37,40-[5-Bromo-2-methoxy-1,3-phenylenebis(methyleneoxy)]-
5,11,17,23,29,35-hexa-t-butylcalix[6]arene-38,39,41,42-tetrol (5).
To a suspension of potassium hydroxide (85%, 830 mg, 12.6
mmol) and p-t-butylcalix[6]arene (3) (900 mg, 0.92 mmol) in
THF (350 mL) and DMF (35 mL), which was stirred at room tem-
perature for 1 h, was added tribromide 4 (328 mg, 0.88 mmol) and
this mixture was stirred at room temperature for 24 h. After re-
moval of the solvent, the residue was treated with aq. NH4Cl, ex-
Fig. 6. Part of the 1H NMR spectra of (a) monooxime 15
and (b) nitrosophenol 16 in CDCl3.
be explained in terms of the nonbonded interaction between
the calixarene moiety and the quinone moiety, as well as the
restricted interaction between the anion radical and the counter
cation. Reactions of the quinone-bridged calix[6]arene 1 with
hydroxylamine and phenylhydrazine afforded the correspond-
ing hydroquinone in addition to the quinone monoimine deriv-
atives, indicating that electron transfer from the amine pro-
ceeds quickly despite the negatively-shifted reduction poten-
tials of 1.

176 Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
Quinone-Bridged Calix[6]arenes
tracted with chloroform, dried over MgSO4, and evaporated to
dryness. The residue was recrystallized from chloroform/meth-
anol to afford bridgedꢂcompound 5 (802 mg, 73%) as colorless
2H), 4.64 (d, J ¼ 11:8 Hz, 4H), 6.55 (s, 2H), 6.70 (d, J ¼ 1:9
Hz, 4H), 7.09–7.20 (m, 20H), 7.23 (d, J ¼ 1:9 Hz, 4H), 7.28 (s,
4H); 13C NMR (125 MHz, CDCl3) ꢁ 26.55 (CH2), 31.00 (CH2),
31.54 (CH3), 31.71 (CH3), 34.07 (C), 34.22 (C), 60.37 (CH3),
68.94 (CH2), 74.95 (CH2), 113.86 (CH), 123.99 (CH), 125.33
(CH), 127.11 (CH), 127.37 (CH), 128.09 (CH), 128.14 (CH),
132.34 (C), 132.76 (C), 133.13 (C), 133.75 (C), 138.01 (C),
144.94 (C), 145.10 (C), 149.96 (C), 150.03 (C), 152.39 (C),
153.01 (C). Found: C, 83.21; H, 7.93%. Calcd for C103H116O8:
C, 83.47; H, 7.93%.
37,40-[5-Bromo-2-methoxy-1,3-phenylenebis(methyleneoxy)]-
5,11,17,23,29,35-hexa-t-butyl-38,39,41,42-tetraethoxycalix[6]-
arene (8). Compound 8 was prepared in 72% yield from tetrol 5
(475 mg, 0.40 mmol) in a manner similar to that of 6. 8: colorless
crystals, mp > 300 ꢂC; 1H NMR (500 MHz, CDCl3) ꢁ 0.90 (s,
3H), 0.98 (s, 36H), 1.24 (t, J ¼ 6:9 Hz, 12H), 1.45 (s, 18H),
3.21 (d, J ¼ 14:3 Hz, 2H), 3.39 (d, J ¼ 15:0 Hz, 4H), 3.64–3.74
(m, 8H), 4.15 (s, 4H), 4.42 (d, J ¼ 14:3 Hz, 2H), 4.49 (d, J ¼
15:0 Hz, 4H), 6.70 (d, J ¼ 1:7 Hz, 4H), 7.08 (d, J ¼ 1:7 Hz,
4H), 7.33 (s, 4H), 7.38 (s, 2H); 13C NMR (125 MHz, CDCl3) ꢁ
15.51 (CH3), 27.19 (CH2), 30.73 (CH2), 31.47 (CH3), 31.71
(CH3), 34.00 (C), 34.24 (C), 60.31 (CH3), 68.45 (CH2), 68.66
(CH2), 114.28 (C), 123.81 (CH), 125.17 (CH), 128.11 (CH),
128.65 (CH), 132.27 (C), 133.19 (C), 133.67 (C), 134.76 (C),
144.60 (C), 145.12 (C), 152.39 (C), 152.76 (C), 155.83 (C).
Found: C, 76.20; H, 8.19; Br, 6.16%. Calcd for
1
ꢂ
crystals: mp 222–224 C; H NMR (270 MHz, CDCl3, ꢁ50 C)
ꢁ 1.20 (s, 18H), 1.23 (s, 18H), 1.29 (s, 18H), 3.22 (d, J ¼ 13:8
Hz, 1H), 3.32 (d, J ¼ 13:3 Hz, 1H), 3.52 (d, J ¼ 13:2 Hz, 2H),
3.63 (d, J ¼ 12:8 Hz, 2H), 4.02 (s, 3H), 4.04 (d, J ¼ 13:8 Hz,
1H), 4.06 (d, J ¼ 13:2 Hz, 1H), 4.22 (d, J ¼ 13:3 Hz, 2H), 4.59
(d, J ¼ 10:4 Hz, 2H), 4.61 (d, J ¼ 12:8 Hz, 2H), 5.81 (d, J ¼
10:4 Hz, 2H), 7.04 (brd, 2H), 7.09 (brd, 2H), 7.13 (brd, 2H),
7.15 (brd ꢃ 2, 4H), 7.20 (brd, 2H), 7.53 (s, 2H), 8.93 (s, 2H),
9.00 (s, 2H); 13C NMR (68 MHz, CDCl3, ꢁ50 ꢂC) ꢁ 31.15
(CH3), 31.49 (CH3 ꢃ 2), 32.69 (CH2), 32.75 (CH2), 32.98
(CH2), 33.15 (CH2), 33.71 (C), 33.84 (C), 34.17 (C), 60.12
(CH3), 74.70 (CH2), 116.23 (C), 125.12 (CH), 125.27 (CH),
125.62 (CH), 125.74 (CH ꢃ 2), 126.26 (CH), 126.53 (C),
126.67 (C), 126.98 (C), 127.39 (C), 131.80 (C), 132.67 (C),
132.71 (C), 134.59 (CH), 141.75 (C), 142.07 (C), 147.38 (C),
149.53 (C), 149.71 (C), 150.03 (C), 158.l9 (C). Found: C,
74.93; H, 7.77; Br, 7.26%. Calcd for C75H91BrO7: C, 74.92; H,
7.80; Br, 6.65%.
38,39,41,42-Tetrabenzyloxy-37,40-[5-bromo-2-methoxy-1,3-
phenylenebis(methyleneoxy)]-5,11,17,23,29,35-hexa-t-butyl-
calix[6]arene (6). To a suspension of tetrol 5 (475 mg, 0.40
mmol) and cesium carbonate (1.57 g, 4.8 mmol) in DMF (40
mL) was added benzyl bromide (290 mL, 2.4 mmol) and the reac-
tion mixture was stirred at 70 ꢂC for 1 d. After the addition of aq.
NH4Cl, the mixture was extracted with chloroform, dried over
MgSO4, and the solvent was evaporated to dryness. The crude
product was purified by recrystallization (chloroform/methanol)
to give 6 (576 mg, 93%) as colorless crystals: mp 291–300 ꢂC
(dec); 1H NMR (500 MHz, CDCl3) ꢁ 0.95 (s, 3H), 1.00 (s,
36H), 1.43 (s, 18H), 3.12 (d, J ¼ 14:5 Hz, 2H), 3.25 (d, J ¼
15:3 Hz, 4H), 4.10 (s, 4H), 4.47 (d, J ¼ 15:3 Hz, 4H), 4.50 (d, J ¼
14:5 Hz, 2H), 4.64 (d, J ¼ 12:1 Hz, 4H), 4.67 (d, J ¼ 12:1 Hz,
4H), 7.01 (d, J ¼ 1:5 Hz, 4H), 7.08–7.19 (m, 24H), 7.26 (s,
4H), 7.40 (s, 2H); 13C NMR (125 MHz, CDCl3) ꢁ 26.78 (CH2),
30.84 (CH2), 31.49 (CH3), 31.69 (CH3), 34.04 (C), 34.22 (C),
60.54 (CH3), 68.55 (CH2), 74.84 (CH2), 115.07 (C), 123.88
(CH), 125.22 (CH), 127.11 (CH ꢃ 2), 127.93 (CH), 128.13
(CH), 128.87 (CH), 132.19 (C), 133.39 (C), 133.70 (C), 134.45
(C), 137.78 (C), 144.85 (C), 145.25 (CH), 152.26 (C), 152.77
(C), 155.67 (C). Found: C, 79.15; H, 7.40; Br, 5.31%. Calcd for
C83H107BrO7 0.5H2O: C, 76.35; H, 8.34; Br, 6.12%.
ꢄ
3,5-{(5,11,17,23,29,35-Hexa-t-butyl-38,39,41,42-tetraethoxy-
calix[6]arene-37,40-diyl)bis(oxymethylene)}-4-methoxyphenol
(9). Compound 9 was prepared in 76% yield from bromide 8
(323 mg, 0.25 mmol) in a manner similar to that of 7. 9: colorless
ꢂ
1
crystals, mp 248–252 C; H NMR (500 MHz, CDCl3) ꢁ 0.80 (s,
3H), 0.98 (s, 36H), 1.24 (t, J ¼ 7:0 Hz, 12H), 1.45 (s, 18H), 3.23
(d, J ¼ 14:0 Hz, 2H), 3.40 (d, J ¼ 15:3 Hz, 4H), 3.60 (dq,
J ¼ 9:4, 7.0 Hz, 4H), 3.71 (dq, J ¼ 9:4, 7.0 Hz, 4H), 4.19 (s,
4H), 4.43 (d, J ¼ 14:0 Hz, 2H), 4.51 (d, J ¼ 15:3 Hz, 4H), 4.88
(br, 1H), 6.68 (d, J ¼ 1:8 Hz, 4H), 6.75 (s, 2H), 7.12 (d, J ¼
1:8 Hz, 4H), 7.32 (s, 4H); 13C NMR (125 MHz, CDCl3) ꢁ 15.53
(CH3), 27.05 (CH2), 30.79 (CH2), 31.48 (CH3), 31.71 (CH3),
33.97 (C), 34.19 (C), 60.04 (CH3), 68.62 (CH2), 68.74 (CH2),
112.81 (CH), 123.77 (CH), 125.21 (CH), 128.21 (CH), 132.34
(C), 132.92 (C), 133.18 (C), 133.64 (C), 144.53 (C), 144.81 (C),
149.87 (C), 150.20 (C), 152.34 (C), 152.75 (C). Found: C,
C
103H115BrO7 H2O: C, 79.15; H, 7.54; Br, 5.11%.
4-Methoxy-3,5-{(38,39,41,42-tetrabenzyloxy-5,11,17,23,29,
79.31; H, 8.62%. Calcd for C83H108O8 H2O: C, 79.64; H, 8.86%.
ꢄ
ꢄ
2,6-{(38,39,41,42-Tetrabenzyloxy-5,11,17,23,29,35-hexa-t-
butylcalix[6]arene-37,40-diyl)bis(oxymethylene)}-1,4-benzo-
quinone (1). To a solution of 7 (100 mg, 0.68 mmol) in benzene
(5 mL) was added dropwise a solution of iron(III) chloride (250
mg, 1.5 mmol) in acetic acid (0.5 mL) and acetonitrile (10 mL).
After 10 min, yellow precipitates were collected and dried to af-
ford 1 (73.6 mg, 74%) as pale yellow crystals: mp 187–198 ꢂC
(dec); 1H NMR (500 MHz, CDCl3) ꢁ 1.00 (s, 36H), 1.46 (s,
18H), 2.47 (s, 4H), 3.23 (d, J ¼ 16:5 Hz, 2H), 3.31 (d, J ¼ 14:7
Hz, 4H), 4.48 (d, J ¼ 14:7 Hz, 4H), 4.50 (d, J ¼ 16:5 Hz, 2H),
4.63 (d, J ¼ 11:4 Hz, 4H), 4.68 (d, J ¼ 11:4 Hz, 4H), 6.36 (s,
2H), 6.86 (s, 4H), 7.02 (s, 4H), 7.17–7.25 (m, 20H), 7.38 (s,
4H); 13C NMR (125 MHz, CDCl3) ꢁ 26.78 (CH2), 29.80 (CH2),
31.41 (CH3), 31.75 (CH3), 34.19 (C), 34.39 (C), 67.38 (CH2),
75.35 (CH2), 125.19 (CH), 125.43 (CH), 127.44 (CH), 127.72
(CH), 127.76 (CH), 127.79 (CH), 128.38 (CH), 130.99 (C),
133.90 (C), 134.45 (C), 137.31 (C), 143.58 (C), 145.41 (C),
146.16 (C), 152.71 (C), 153.54 (C), 182.99 (C), 187.28 (C); IR
35-hexa-t-butylcalix[6]arene-37,40-diyl)bis(oxymethylene)}-
phenol (7). To a solution of bromide 6 (228 mg, 0.15 mmol) in
THF (25 mL) was added t-butyllithium (1.68 M in pentane, 280
mL, 0.47 mmol) and the mixture was stirred for 20 min at ꢁ78
ꢂC. After the addition of trimethyl borate (100 mL, 0.9 mmol),
ꢂ
the mixture was stirred for 1 h at ꢁ78 C and then at room tem-
perature for 14 h. To the solution was added a solution of NaOH
(600 mg) and 30% hydrogen peroxide (3 mL) in water (10 mL)
and the mixture was stirred for 5 h at room temperature. After
the addition of water and aq. NH4Cl, the mixture was extracted
by chloroform, dried over MgSO4, and evaporated to dryness.
The residue was subjected to preparative TLC (silica gel, chloro-
form/hexane, 2:1) to give phenol 7 (138 mg, 63%) as colorless
crystals: mp 222–225 ꢂC; 1H NMR (500 MHz, CDCl3) ꢁ 0.82
(s, 3H), 1.01 (s, 36H), 1.43 (s, 18H), 3.25 (d, J ¼ 14:4 Hz, 2H),
3.34 (d, J ¼ 15:2 Hz, 4H), 3.38 (s, 1H), 4.15 (s, 4H), 4.53 (d, J ¼
15:2 Hz, 4H), 4.60 (d, J ¼ 11:8 Hz, 4H), 4.60 (d, J ¼ 14:4 Hz,

S. Akine et al.
Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
177
(KBr) ꢂ 1653 cmꢁ1 (C=O). HRMS (FAB+) m=z found
1465.8427, calcd for C102H113O8, 1465.8435 ½M þ Hꢅþ. Found:
(t, J ¼ 7:4 Hz, 4H); 13C NMR (125 MHz, CDCl3) ꢁ 63.11
(CH2), 114.71 (CH), 121.81 (CH), 129.71 (CH), 132.09 (CH),
144.03 (C), 157.74 (C), 186.29 (C), 186.86 (C); IR (KBr) ꢂ
1657 cmꢁ1 (C=O); UV (CHCl3) ꢃmax (") 309.5 nm (5:6 ꢃ
102). Found: C, 74.72; H, 5.11%. Calcd for C20H16O4: C, 74.99;
H, 5.03%.
C, 82.92; H, 7.71%. Calcd for C102H112O8 0.5H2O: C, 83.06;
H, 7.71%.
ꢄ
2,6-{(5,11,17,23,29,35-Hexa-t-butyl-38,39,41,42-tetraethoxy-
calix[6]arene-37,40-diyl)bis(oxymethylene)}-1,4-benzoquinone
(2). Compound 2 was prepared in 85% yield from 9 (20 mg,
0.017 mmol) in a manner similar to that of 1. 2: pale yellow crys-
tals, mp 224 ꢂC (dec); 1H NMR (500 MHz, CDCl3) ꢁ 0.98 (s,
36H), 1.32 (t, J ¼ 6:9 Hz, 12H), 1.47 (s, 18H), 2.34 (s, 4H),
3.32 (d, J ¼ 16:6 Hz, 2H), 3.39 (d, J ¼ 14:8 Hz, 4H), 3.79 (dq,
J ¼ 9:8, 6.9 Hz, 4H), 3.82 (dq, J ¼ 9:8, 6.9 Hz, 4H), 4.34 (d, J ¼
16:6 Hz, 2H), 4.47 (d, J ¼ 14:8 Hz, 4H), 6.62 (s, 2H), 6.87 (s,
4H), 6.96 (s, 4H), 7.42 (s, 4H); 13C NMR (125 MHz, CDCl3) ꢁ
15.68 (CH3), 26.92 (CH2), 29.61 (CH2), 31.37 (CH3), 31.76
(CH3), 34.14 (C), 34.42 (C), 67.45 (CH2), 69.27 (CH2), 125.12
(CH), 125.45 (CH), 126.80 (CH), 127.76 (CH), 130.93 (C),
133.92 (C), 134.72 (C), 144.78 (C), 145.15 (C), 146.26 (C),
153.12 (C), 153.48 (C), 183.16 (C), 189.06 (C); IR (KBr) ꢂ
1653 cmꢁ1 (C=O). Found: C, 79.70; H, 8.42%. Calcd for
Reduction of Quinone 1. To a solution of freshly prepared
quinone 1 (25.8 mg, 0.018 mmol) in THF (4 mL) was added a so-
lution of borane/THF (1.0 M, 60 mL) and the mixture was stirred
at room temperature for 2 d. After the addition of water, the mix-
ture was extracted with chloroform, dried over MgSO4, and
evaporated to dryness. The residue was purified by preparative
TLC (silica gel, chloroform/hexane, 1:1) to afford hydroquinone
14 (11.2 mg, 43%) as well as starting material 1 (5.6 mg, 21%).
14: colorless crystals, mp 242–246 ꢂC; 1H NMR (500 MHz,
CDCl3) ꢁ 0.99 (s, 36H), 1.42 (s, 18H), 3.26 (d, J ¼ 14:3 Hz,
2H), 3.37 (d, J ¼ 15:3 Hz, 4H), 3.48 (br, 1H), 4.14 (s, 4H),
4.45 (d, J ¼ 15:3 Hz, 4H), 4.54 (d, J ¼ 14:3 Hz, 2H), 4.57 (d, J ¼
11:9 Hz, 4H), 4.63 (d, J ¼ 11:9 Hz, 4H), 5.25 (s, 1H), 6.34 (s,
2H), 6.75 (d, J ¼ 1:8 Hz, 4H), 7.05–7.08 (m, 12H), 7.11–7.16
(m, 12H), 7.29 (s, 4H); 13C NMR (500 MHz, CDCl3) ꢁ 27.75
(CH2), 30.72 (CH2), 31.41 (CH3), 31.64 (CH3), 34.10 (C), 34.28
(C), 70.71 (CH2), 74.77 (CH2), 111.87 (CH), 123.94 (C), 124.14
(CH), 125.28 (CH), 127.04 (CH), 127.26 (CH), 127.85 (CH),
128.04 (CH), 132.10 (C), 133.08 (C), 133.63 (C), 137.94 (C),
145.26 (C), 146.06 (C), 146.27 (C), 146.83 (C), 152.03 (C),
152.52 (C). Found: C, 82.69; H, 7.79%. Calcd for
C82H104O8 H2O: C, 79.70; H, 8.65%.
ꢄ
5-Bromo-2-methoxy-1,3-bis(phenoxymethyl)benzene (12).
A suspension of tribromide 4 (358 mg, 1.0 mmol), phenol (243
mg, 2.6 mmol), and potassium carbonate (691 mg, 5 mmol) in
DMF (80 mL) was stirred for 24 h at room temperature. After
the addition of water and aq. NH4Cl, the mixture was extracted
with chloroform, dried over MgSO4, and evaporated to dryness.
The residue was purified by chromatography (silica gel, chloro-
form/hexane, 1:2) to give 12 (359 mg, 90%) as colorless oil:
1H NMR (500 MHz, CDCl3) ꢁ 3.84 (s, 3H), 5.08 (s, 4H), 7.00–
7.03 (m, 6H), 7.36 (t, J ¼ 7:9 Hz, 4H), 7.72 (s, 2H); 13C NMR
(125 MHz, CDCl3) ꢁ 62.68 (CH3), 64.28 (CH2), 114.70 (CH),
117.41 (C), 121.21 (CH), 129.52 (CH), 132.36 (CH), 132.55
(C), 155.20 (C), 158.54 (C).
C
102H114O8 H2O: C, 82.44; H, 7.87%.
ꢄ
Reaction of 1 with Hydroxylamine. To a solution of freshly
prepared quinone 1 (15 mg, 0.01 mmol) in pyridine-d5 (0.6 mL)
was added hydroxylamine hydrochloride (7.2 mg, 0.10 mmol)
ꢂ
and the mixture was heated at 60 C for 4 h. After the addition
of aqueous methanol, the precipitates were collected to give a
crude product of quinone monooxime 15. The precipitates were
subjected to preparative TLC (silica gel, chloroform/hexane
2:1) to give p-nitrosophenol 16 (9.3 mg, 68%) and hydroquinone
14 (3.9 mg, 26%). 16: pale green crystals, mp 237–241 ꢂC;
1H NMR (500 MHz, CDCl3) ꢁ 0.95 (s, 36H), 1.46 (s, 18H),
3.24 (d, J ¼ 14:5 Hz, 2H), 3.39 (d, J ¼ 15:4 Hz, 4H), 4.13 (brs,
4H), 4.49 (d, J ¼ 15:4 Hz, 4H), 4.53 (d, J ¼ 11:5 Hz, 4H), 4.54
(d, J ¼ 14:5 Hz, 2H), 4.58 (d, J ¼ 11:5 Hz, 4H), 6.44 (s, 1H),
6.78 (d, J ¼ 2:1 Hz, 4H), 6.95–6.97 (m, 14H), 7.02 (d, J ¼ 2:1
Hz, 4H), 7.02–7.06 (m, 8H), 7.34 (s, 4H). Found: C, 81.56; H,
4-Methoxy-3,5-bis(phenoxymethyl)phenol (13). To a solu-
tion of bromide 12 (360 mg, 0.90 mmol) in THF (20 mL) was add-
ed t-butyllithium (1.58 M, 1.7 mL, 2.7 mmol) and the mixture was
stirred for 20 min at ꢁ78 ꢂC. After the addition of trimethyl borate
(600 mL, 5.4 mmol), the mixture was stirred for 1 h at ꢁ78 ꢂC and
then at room temperature for 14 h. To the solution was added a
solution of NaOH (3.6 g) and 30% hydrogen peroxide (9 mL) in
water (30 mL) and the mixture was stirred for 8 h at room temper-
ature. After the addition of water and aq. NH4Cl, the mixture was
extracted by chloroform, dried over MgSO4, and evaporated to
dryness. The residue was chromatographed on silica gel (chloro-
form) to afford phenol 13 (198 mg, 65%) as colorless crystals:
mp 107–110 ꢂC; 1H NMR (500 MHz, CDCl3) ꢁ 3.77 (s, 3H),
5.05 (s, 4H), 5.50 (brs, 1H), 6.90 (s, 2H), 6.94–6.98 (m, 6H),
7.26–7.30 (m, 4H); 13C NMR (125 MHz, CDCl3) ꢁ 62.81
(CH3), 64.78 (CH2), 114.79 (CH), 116.08 (CH), 121.09 (CH),
129.52 (CH), 131.44 (C), 149.58 (C), 152.18 (C), 158.51 (C).
7.57; N, 1.15%. Calcd for C102H113NO8 H2O: C, 81.73; H,
7.73; N, 0.93%.
ꢄ
Reaction of 1 with Phenylhydrazine. To a solution of freshly
prepared quinone 1 (15 mg, 0.01 mmol) in benzene-d6 (0.6 mL)
was added phenylhydrazine (10 mL) and acetic acid (10 mL). After
ꢂ
heating at 60 C for 2 h, the mixture was evaporated and the res-
idue was subjected to preparative TLC (silica gel, chloroform/
hexane, 2:1) to give phenylazophenol 18 (2.1 mg, 12%) and hy-
droquinone 14 (7.0 mg, 45%). 18: yellow solids; 1H NMR (500
MHz, CDCl3) ꢁ 1.00 (s, 36H), 1.44 (s, 18H), 3.26 (d, J ¼ 14:7
Hz, 2H), 3.35 (d, J ¼ 15:4 Hz, 4H), 4.21 (brs, 4H), 4.49 (d, J ¼
15:4 Hz, 4H), 4.54 (d, J ¼ 14:7 Hz, 2H), 4.57 (d, J ¼ 12:2 Hz,
4H), 4.64 (d, J ¼ 12:2 Hz, 4H), 6.03 (s, 1H), 6.77 (d, J ¼ 1:8
Hz, 4H), 6.95–7.04 (m, 20H), 7.16 (d, J ¼ 1:8 Hz, 4H), 7.31 (s,
4H), 7.46 (t, J ¼ 7:7 Hz, 1H), 7.56 (t, J ¼ 7:7 Hz, 2H), 7.62
(brs, 2H), 7.91 (d, J ¼ 7:7 Hz, 2H).
Found: C, 73.94; H, 6.13%. Calcd for C21H20O4 0.25H2O: C,
73.99; H, 6.06%.
ꢄ
2,6-Bis(phenoxymethyl)-1,4-benzoquinone (10). To a solu-
tion of 13 (17 mg, 0.05 mmol) in benzene (5 mL) was added drop-
wise a solution of iron(III) chloride (250 mg, 1.5 mmol) and acetic
acid (0.5 mL) in acetonitrile (10 mL). After 10 min, the solvent
was removed and chromatographic separation on silica gel (ben-
zene) afforded yellow solids, which were recrystallized from ace-
tone/hexane to give 10 (14.6 mg, 92%) as yellow crystals: mp
140–142 ꢂC; 1H NMR (500 MHz, CDCl3) ꢁ 4.95 (s, 4H), 6.96
(s, 2H), 6.97 (d, J ¼ 7:4 Hz, 4H), 7.01 (t, J ¼ 7:4 Hz, 2H), 7.32
Electrochemical Measurements: A glassy carbon rod (out-
side diameter 3 mm, Tokai Carbon GC-20) was embedded in Pyr-
ex glass, and a cross-section was used as a working electrode. Cy-

178 Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
Quinone-Bridged Calix[6]arenes
Table 4. Crystallographic Data for 1 0.5C6H6, 2 THF, 10, and 14 1.5MeOH CHCl3
ꢄ
ꢄ
ꢄ
ꢄ
1 0.5C6H6
ꢄ
2 THF
ꢄ
10
14 1.5MeOH CHCl3
ꢄ
ꢄ
Formula
C105H115O8
120
C86H112O9
120
C20H16O4
120
C104:5H121Cl3O9:5
150
Temperature/K
Crystal system
Space group
monoclinic
C2=c
monoclinic
P21=c
monoclinic
P21=n
monoclinic
C2=c
ꢀ
a/A
47.782(2)
11.969(1)
30.850(1)
99.895(1)
17381(2)
8
23.250(2)
12.036(1)
27.297(1)
102.811(1)
7448.6(8)
4
7.030(3)
17.042(4)
13.050(4)
95.219(17)
1557.0(9)
4
51.115(3)
20.274(1)
18.132(1)
95.732(3)
18696(2)
8
ꢀ
b/A
ꢀ
c/A
ꢄ/deg
ꢀ 3
V/A
Z
Dcalcd/g cmꢁ3
Reflections collected
Unique reflections
Rint
1.150
47445
16036
0.050
1.150
19867
9765
0.065
1.367
4017
2243
0.030
1.162
53963
16045
0.047
F000
ꢅMoKꢀ/mmꢁ1
Limiting indices
6472
0.071
0 < h < 57
0 < k < 14
ꢁ37 < l < 36
0/1036
2800
0.073
0 < h < 27
0 < k < 14
ꢁ32 < l < 31
12/906
672
0.095
0 < h < 8
0 < k < 20
ꢁ15 < l < 15
0/281
7000
0.155
0 < h < 62
0 < k < 24
ꢁ21 < l < 21
6/1153
Restraints/parameters
Goodness of fit (F2)
R indices (I > 2ꢆðIÞ)
1.057
1.018
1.068
1.041
R1 ¼ 0:0713
wR2 ¼ 0:1823
R1 ¼ 0:0869
wR2 ¼ 0:1951
R1 ¼ 0:1088
R1 ¼ 0:631
wR2 ¼ 0:1602
R1 ¼ 0:0757
wR2 ¼ 0:1769
R1 ¼ 0:0868
wR2 ¼ 0:2175
R1 ¼ 0:1272
wR2 ¼ 0:2464
wR2 ¼ 0:2098
R1 ¼ 0:2900
wR2 ¼ 0:2506
R indices (all data)
clic voltammetry was carried out in a standard one-compartment
cell under an argon atmosphere equipped with a platinum-wire
counter electrode and a Ag/Agþ reference electrode (10 mM
AgClO4 in 0.1 M (n-Bu)4NClO4–MeCN, Eꢂ0 (ferrocene/ferroce-
nium in 0.1 M (n-Bu)4NClO4/CH2Cl2) = 0.214 V vs Ag/Agþ)
with a BAS CV-50W voltammetric analyzer. All runs were per-
formed in 0.5 mM solutions in dry dichloromethane in the pres-
ence of 0.1 M (n-Bu)4NClO4 under argon.
(K.G.) and 15105001 (T.K.)) and for The 21st Century COE
Program for Frontiers in Fundamental Chemistry (T.K.) from
the Ministry of Education, Culture, Sports, Science and Tech-
nology, and by the Sumitomo Foundation (K.G.). We also
thank Tosoh Finechem Corporation for the generous gifts of
alkyllithiums.
References
X-ray Crystallographic Study: Single crystals of 1 0.5C6H6,
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collected on a MAC Science DIP-2030 imaging plate area detec-
ꢄ
ꢄ
ꢄ
ꢄ
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