Synthesis and Properties of α,α -Bis(heteroazulen-3-yl)-1,4-benzoquinonemethides

Article abstract of DOI:10.1246/bcsj.76.2035

The synthesis and properties of a novel type of α,α -bis(heteroazulen-3-yl)-1,4-benzoquinonemethides 11a-f are studied. The synthetic method was based on a TFA-catalyzed electrophilic aromatic substitution on the heteroazulenes with 4-hydroxybenzaldehyde to afford the corresponding methane derivatives, followed by oxidative hydrogen abstraction with DDQ, and subsequent exchange of the counter-anion by using aq. HBF ₄ or aq. HBF₆ and neutralization. The polarization of 11a-f was evaluated by their ¹³C NMR and UV-vis spectral data. The thermodynamic stability of the conjugated acid of 11a-f was evaluated to be in the order 11a < 11b < 11c and in the order 11d < 11e < 11f based on their pK_a values (<0-5.4) obtained spectrophotometrically. The substituent effect of t-Bu was discussed based on the UV-vis spectra and pK _a values. In CV measurements, the reduction waves of quinonemethides 11a-f were reversible, suggesting a stabilizing effect of heteroazulenes toward the radical and anion species. Moreover, quinonemethides 11a-f showed two oxidation waves, and that the first oxidation potentials (EI_ox) of 11a-c, which have two t-Bu groups, are reversible.

Full text of DOI:10.1246/bcsj.76.2035

Ó 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 2035–2043 (2003) 2035
Synthesis and Properties of ꢀ,ꢀ-Bis(heteroazulen-3-yl)-
1,4-benzoquinonemethides
ꢀ
Shin-ichi Naya, Tetsuhiro Watano, and Makoto Nitta
Department of Chemistry, School of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555
Received April 24, 2003; E-mail: nitta@waseda.jp
The synthesis and properties of a novel type of ꢀ,ꢀ-bis(heteroazulen-3-yl)-1,4-benzoquinonemethides 11a–f are
studied. The synthetic method was based on a TFA-catalyzed electrophilic aromatic substitution on the heteroazulenes
with 4-hydroxybenzaldehyde to afford the corresponding methane derivatives, followed by oxidative hydrogen abstrac-
tion with DDQ, and subsequent exchange of the counter-anion by using aq. HBF4 or aq. HPF6 and neutralization. The
polarization of 11a–f was evaluated by their 13C NMR and UV–vis spectral data. The thermodynamic stability of the
conjugated acid of 11a–f was evaluated to be in the order 11a < 11b < 11c and in the order 11d < 11e < 11f based on
their pKa values (<0–5.4) obtained spectrophotometrically. The substituent effect of t-Bu was discussed based on the
UV–vis spectra and pKa values. In CV measurements, the reduction waves of quinonemethides 11a–f were reversible,
suggesting a stabilizing effect of heteroazulenes toward the radical and anion species. Moreover, quinonemethides 11a–f
showed two oxidation waves, and that the first oxidation potentials (E1ox) of 11a–c, which have two t-Bu groups, are
reversible.
Conjugated ꢁ-electron chromophores containing a donor
and an acceptor group have attracted current interest in terms
of optoelectronic materials,1 such as nonlinear optics2 and
near-infrared dyes.3 Among numerous classes of these chro-
mophores, compounds containing a quinonoid unit as a spacer
are especially promising,4 because such conjugated systems
have generally been recognized to possess marked push–pull
electronic effects, which induce large dipole moments, leading
to a high nonlinear response5 and ready intramolecular charge-
transfer transitions, leading to deep coloration.6 In this regard,
the parent compound, ꢀ,ꢀ-diphenyl-1,4-benzoquinoneme-
thide, has been known for many years;7 numerous substituted
compounds have been described in the literature.8 In this con-
text, the synthesis and properties of compounds 1a,b have
been investigated.9 Moreover, benzoquinonoid compounds
have hitherto played a most important role in the development
of organic redox chemistry due to their multistage redox
properties.10 Recently, Ito, Asao, and co-workers have report-
ed the synthesis and properties of ꢀ,ꢀ-bis(azulen-1-yl)-1,4-
benzoquinonemethides 2a,b and their derivatives.11 These
quinonemethides 2a,b are highly polarized by the extreme
electron-donating properties of the azulenyl group, and the
highly polarized properties of 2a,b are reflected in the high
pKa values of their conjugated acid. In addition, the solvato-
chromic effect and redox properties of 2a,b were also
reported. On the other hand, we studied the synthesis and
properties of heteroazulene analogues of the triphenylmethyl
Fig. 1.
cation, i.e., the tris(2-oxo-2H-cyclohepta[b]furan-3-yl)methyl
cation and pyrrole analogues,12 as well as the bis(2-oxo-2H-cy-
clohepta[b]furan-3-yl)phenylmethyl cations 3a–e and pyrrole
analogues 4a–e13 (Fig. 1).
In these reports, we clarified the stabilizing ability of hetero-
azulenes 5a–c (Scheme 1) toward methyl cations and the re-
markable substituent effect of cations 3a–e and 4a–e. In this
context, we also reported on the synthesis and properties of
heteroazulene-substituted benzene-1,3-bismethylium deriva-
tives14 and benzene-1,3,5-trismethylium derivatives.15 In the
studies, two or three methylium units of dications or trications
were twisted against the central phenyl group, respectively,
and no conjugation among the methylium units is suggested.
In order to evaluate the electronic effect of heteroazulenes,
Published on the web October 15, 2003; DOI 10.1246/bcsj.76.2035

2036 Bull. Chem. Soc. Jpn., 76, No. 10 (2003)
Bis(heteroazulen-3-yl)benzoquinonemethide
Scheꢁme 1. Reagents and conditions:ffi, CHCl3–TFA (5:1), reflux, 8 h;ffl, DDQ, CH2Cl2, rt, 1 h; ƒ, 60% HPF6 or 42% HBF4, Ac2O,
0 C, 1 h; Ð, aq. NaHCO3;ð, K2CO3.
we also studied the synthesis and properties of (heteroazulen-
3-yl)tropylium ions16 and bis(heteroazulen-3-yl)methyl cat-
ions,17 which are expected to have a smaller steric effect. In
these studies, we clarified that the heteroazulenes 5a–c can
be demonstrated to stabilize not only cations, but also radical
species and anions based on their pKR+ values and reduction
potentials.13,16 From this viewpoint, we investigated the syn-
thesis and properties of ꢀ,ꢀ-bis(heteroazulen-3-yl)-1,4-benzo-
quinonemethides 11a–f, which are expected to have a highly
polarized structure and multistage redox properties. To gain
insight into the polarized structure of 11a–f, the chemical
shifts of quinone carbonyl carbon and solvatochromic effects
as well as the pKa values of the conjugate acids of 11a–f were
studied. Based on a measurement of a CV, the redox property
of the quinonemethides 11a–f was also clarified. We report
herein on the results in detail.
acid-catalyzed condensation of 4-hydroxybenzaldehyde with
heteroazulene at room temperature ꢁproceeded slowly; thus,
the reactions were carried out at 80 C. The reactions of 3,5-
di-t-butyl-4-hydroxybenzaldehyde 6 or 4-hydroxybenzalde-
hyde 7 with two molar equivalent amounts of 2H-cyclohep-
ta[b]furan-2-one 5a,18 1,2-dihydro-N-phenylcyclohepta[b]pyr-
rol-2-one 5b,19 and 1,2-dihydro-N-methylcyclohepta[b]pyr-
rol-2-one 5c20 in CHCl3–TFA (5/1) at 80 C for 8 h afforded
ꢁ
(3,5-di-t-butyl-4-hydroxyphenyl)bis(heteroazulen-3-yl)meth-
ane derivatives 8a–c or bis(heteroazulen-3-yl)(4-hydroxyphen-
yl)methane derivatives 8d–f in good yields, respectively
(Scheme 1, Table 1, Runs 1–4, 6, and 8). Compound 8a
was obtained in modest yield and the starting material 5a
was recovered in 55% yield. Compounds 8a–f were powdery,
orange or yellow crystals, the structures of which were as-
1
signed based on their IR, H and 13C NMR spectral data, as
well as the mass spectral data and elemental analyses. The ox-
idative hydrogen abstraction of 8a–c with 1.2 molar equivalent
amounts of DDQ in CH2Cl2 at rt gave 9a–c, followed by the
addition of an aq. 42% HBFꢂ4 solution (Table 1, Condition
Results and Discussion
Synthesis. The preparation of ꢀ,ꢀ-bis(heteroazulen-3-yl)-
1,4-benzoquinonemethides was easily accomplished by the
TFA-catalyzed electrophilic substitution of heteroazulenes
with 4-hydroxybenzaldehyde and subsequent oxidation. The
A) afforded salts 10a–c BF
in the yields (also listed in
Á
4
ꢂ
Table 1 (Runs 1–3)). Since the cations 10a–c BF were un-
4
Á

S. Naya et al.
Bull. Chem. Soc. Jpn., 76, No. 10 (2003) 2037
ꢂ
Table 1. Results for the Preparation of Methane Derivatives 8a–f, Cations 10a–c BF ꢂ, 12d–f BF ꢂ, and 10d–f PF and
Quinone Methides 11a–f
Á
Á
Á
4
4
6
Hetero-
azulene
Substitution
Hydride abstraction
Neutralization
Aldehyde
Run
5
6 or 7
Product
Yield/%
Conditions Product
Yield/%
Product
Yield/%
ꢂ
1
2
3
4
5
6
7
8
9
5a
5b
5c
5a
6
6
6
7
8a
8b
8c
8d
45
86A
89
A
10a BF
Á
100
98
90
100
100
100
93
100
100
11a
11b
11c
11d
11d
11e
11e
11f
11f
92
93
100
71
100
44
100
71
4
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
10b BF
Á
4
A
A
B
A
B
A
B
10c BF
Á
4
100
12d BF
Á
4
10d PF
Á
6
5b
5c
7
7
8e
8f
92
83
12e BF
Á
4
10e PF
Á
6
12f BF
Á
4
10f PF
Á
100
6
a) Conditions A: 1) 8a–f and DDQ in CH2Cl2, 2) 42% HBF4 and Ac2O. Conditions B: 1) 8d–f and DDQ in CH2Cl2, 2) 6 0%
HPF6.
stable (vide infra), further pꢂurification was not carried out.
observed at 1058–1084 ꢂcmꢂ1, and the characteristic bands
840–845 cmꢂ1 in the IR spectra. These features also support
ꢂ
Neutralization of 10a–c BF with a saturated aq. NaHCO3
Á
for the counter ion PF6 of 10d–f PF were observed at
Á
the cationic nature of 10a–c, 12d–f, and 10d–f.
4
6
solution afforded quinonemethides 11a–c in good yields
(Table 1, Runs 1–3). On the other hand, a similaꢂr treatment
of 8d–f afforded acetylated compounds 12d–f BF (Table 1,
ꢂ
The structures of quinonemethides 11a–f were assigned
based on their spectral data and elemental analyses. The qui-
nonemethides 11a–f were easily crystallized to give complexes
containing H2O or the solvent molecule in the crystal lattice;
this feature is similar to the cases of heteroazulene-substituted
methyl cations and Crystal Violet [tris(4-dimethylaminophen-
yl)methyl chloride], which forms two crystal structures con-
taining H2O as the monohydrate and the nonahydrate.21 In
Á
K2CO3 for 16h afforded quinonemethides 11d–f in poor
4
Runs 4, 6, and 8). The treatment of cations 12d–f BF with
Á
4
yields. Thus, 60% aq. HPF6 ꢂwas used for exchange of the
counter ion to give 10d–f PF (Table 1, Condition B). Neu-
6
Á
ꢂ
tralization of 10d–f PF with a 4% aq. NaOH solution af-
6
Á
forded quinonemethides 11d–f in good yields (Table 1, Runs
5, 7, and 9). This feature suggests that the t-Bu groups have
a large steric hindrance to prevent acetylation.
1
the H NMR spectra at room temperature, proton signals on
Properties. The deprotonation reaction of the cations 10a–
proceeded gradually under re-
the seven-membered ring of 11a–f appear as broad signals.
However, these signals become sharp at elevated temperature
(50–70 ꢁC). Thus, a rapid conformational change of the hetero-
azulene moieties in these quinonemethides occurs at those
temperatures on the NMR time scale. The 13C NMR spectra
of 11a–f were recorded and the chemical shifts of the quinone
carbonyl carbon were assigned by using the C–H COSY spec-
tra (HMBC). The chemical shifts of the quinone carbonyl car-
bon of 11a–f as well as those of the reference compounds 2a,b
are summarized in Table 2. These values of 11a–f are similar
to those of 2a,b and 1a,b (1a: ꢂC 186.2, 1b: ꢂC 185.9). These
values become higher in the order 11a < 11b < 11c and 11d <
ꢂ
c BF ꢂ, and 10d–f PF
crystallization. The deacetylation reaction of the cations
Á
12d–f BF also proceeded gradually under recrystallization.
Á
4
6
ꢂ
Á
4
Thus, satisfactory analytical data of these cations were not
obtained. However, the structures of 10a–c BF ꢂ, 12d–
Á
4
f BF ꢂ, and 10d–f PF were assigned based on their speꢂc-
ꢂ
Á
Á
4
6
tral data. Mass spectra of the salts 10a–c BF ꢂ, 12d–f BF
,
Á
Á
and 10d–f PF ꢂ, ionized by FAB, exhibit the correct Mþ4 ꢂ
4
Á
PF6 or Mþ ꢂ 6BF4 ion peaks, indicative of the cationic struc-
ture of these compounds. The characteristic bands ꢂfor the
ꢂ
ꢂ
counter ion BF4 of 10a–c BF
Á
and 12d–f BF
Á
were
4
4
Table 2. 13C NMR Spectral Data, the Longest Wavelength Absorption Maxima of UV–Vis Spectra, and pKa Values of
11a–f and Reference Compound 2a,b
ꢃ
max/nm (log "/dm3 molꢂ1 cmꢂ1
)
13C NMR/ꢂa)
CH3CN
CH3CN + TFAb)
CH2Cl2
MeOH
Áꢃc)
pKa
d)
Compd
11a
11b
11c
11d
11e
11f
187.0
186.3
185.9
187.4
186.3
185.2
185.6—
186.6
453 (4.41)
486 (4.49)
486 (4.46)
467 (4.50)
508 (4.36)
512 (4.42)
620 (4.75)
654 (4.73)
650 (4.73)
618 (4.78)
651 (4.59)
646 (4.65)
452 (4.51)
480 (4.46)
481 (4.47)
471 (4.53)
508 (4.39)
511 (4.34)
521 (4.45)
522 (4.43)
454 (4.42)
478 (4.42)
481 (4.49)
483 (4.32)
543 (4.38)
548 (4.33)
þ2
ꢂ2
<0
1.6
1.9
4.2
5.3
5.4
3.4
6.5
0
þ12
þ35
þ37
þ14
þ27
2ae)
2be)
—
507 (4.42)
—
—
549 (4.55)
a) Chemical shift of 4-position. b) Generation of cations 10a–f. c) Difference in wavelength between the values in
CH2Cl2 and in MeOH. d) The pKa values of the conjugate acids of 11a–f were determined spectrophotometrically
in a buffered solution prepared in 50% aqueous CH3CN. e) Ref. 11.

2038 Bull. Chem. Soc. Jpn., 76, No. 10 (2003)
Bis(heteroazulen-3-yl)benzoquinonemethide
11e < 11f and two quinonemethides having the same hetero-
azulene show similar values, respectively. Thus, the contribu-
tion of the charge-separated ionic forms 11a–f-B (Scheme 1)
becomes larger in this order; however, these low chemical
shifts suggest that the contribution of the charge-separated ion-
ic forms 11a–f-B is not very large in the ground state.
The UV–vis spectra of quinonemethides 11a–f in acetoni-
trile are shown in Figs. 2 and 3. The longest wavelength ab-
sorption maxima of 11a–f are also summarized in Table 2.
The spectra of 11a–c are similar, and the longest wavelength
absorption maximum of 11a shows a blue-shift by 33 nm,
compared with those of 11b and 11c in a CH3CN solution.
The spectra of 11d–f are also similar, and the longest wave-
length absorption maximum of 11d shows a blue-shift by
41 and 45 nm compared with those of 11e and 11f,
respectively. In addition, the longest wavelength absorption
maxima of t-Bu-substituted 11a–c show a blue-shift compared
with those of unsubstituted 11d–f, respectively. By additing a
drop of TFA, compounds 11a–f were completely protonated to
give cations 10a–f. Moreover, these cations 10a–f regenerated
quinonemethides 11a–f quantitatively upon the addition of a
drop of Et3N. Thus, the protonation–deprotonation cycle is
completely reversible. The longest wavelength absorption
maxima of 10a–f are also summarized in Table 2. Pairs of qui-
nonemethides having the same heteroazulene-unit show simi-
lar values, respectively, suggesting no substituent effect of
the t-Bu group. Moreover, the values of 10a,d are similar
to those of 3b–e (621 nm) and the values of 10b,e are similar
to those of 4b–e (652 nm). This feature seems to be reasonable
based on our previous study considering the longest wave-
length absorption maxima of 3a–e and 4a–e as well as the cal-
culation of the stable conformations of 3a–e and 4a–e. Re-
garding the charge-separated ionic forms 11a–f-B, the phenox-
ide-moiety has a larger electron-donating ability than the het-
eroazulene-moiety. Thus, the phenoxide-moiety has a more
planar conformation and the heteroazulene-moiety is twisted
against the cationic plane. On the contrary, the heteroazu-
lene-moiety has a larger electron-donating ability than the hy-
droxyphenyl-moiety in cations 10a–f. Since the heteroazu-
lene-moiety has a more planar conformation and the hydroxy-
phenyl-moiety is twisted against the cationic plane, conjuga-
tion between the hydroxyphenyl-moiety and the methylium
carbon becomes smaller. Thus, the substituent effect of the
t-Bu group on the hydroxyphenyl-moiety becomes less impor-
tant.
It is well known that highly polarized compounds, such as
quinonemethides, show large solvatochromic effects.4 The
large solvatochromic effects of 2a,b were also reported.11
Thus, the UV–vis spectra of 11a–f were measured in CH2Cl2
and in MeOH. The longest wavelength absorption maxima of
11a–f in CH2Cl2 and in MeOH as well as the difference in
these wavelengths (Áꢃ) are summarized in Table 2. Com-
pounds 11d–f show large solvatochromic effects, although t-
Bu-substituted compounds 11a–c show weak or no solvato-
chromic effects due to the steric effect of the t-Bu group,
which hinders the solvation of protic solvents as well as
protonation. The negative solvatochromic effects of 11d–f
can be rationalized by stabilization of their excited states by
hydrogen bonding of the quinonemethides with protic
solvents.22 Thus, the contribution of the charge-separated ion-
ic forms 11a–f-B seems to be larger in their excited states
compared with their ground state. The solvatochromic effects
are larger in the order 11d < 11e < 11f, which are rationalized
by the electron-donating ability of the heteroazulenes 5a–c (5a
< 5b < 5c).12–17
Fig. 2. UV–vis spectra of 11a–c in CH3CN and in CH3CN
and TFA.
The pKa values of the conjugate acids of 11a–f provide a
criterion of stability of the protonated forms of 11a–f. The
pKa values of the conjugated acids of 11a–f (10a–f) were de-
termined spectrophotometrically in buffer solutions prepared
in 50% aqueous CH3CN, and are summarized in Table 2.
Compound 11a in all buffer solutions was not protonated com-
pletely, and the pKa value of 11a was estimated to be <0. The
relatively low pKa values for conjugate acids of 11a–c, as
Fig. 3. UV–vis spectra of 11d–f in CH3CN and in CH3CN
and TFA.

S. Naya et al.
Bull. Chem. Soc. Jpn., 76, No. 10 (2003) 2039
Table 3. Redox Potentials of 11a–f and Reference Compounds 2a,b, and Reduction of 11a–f with Zn Powder
Redox potentialsa)
Reduction with Zn powder
Compd
E1red
E2red
E3red
E1ox
E2ox
Product
Yield/%
11a
11b
11c
11d
11e
11f
ꢂ1:24
ꢂ1:40
ꢂ1:42
ꢂ1:07
ꢂ1:22
ꢂ1:26
(ꢂ1:55)
ꢂ1:38
ꢂ1:56
ꢂ1:77
ꢂ1:83
ꢂ1:44
ꢂ1:63
ꢂ1:65
—
—
—
—
ꢂ1:66
—
—
—
—
þ0:74
þ0:55
(þ1:09)
(þ0:95)
(þ0:92)
(þ1:47)
(þ1:11)
(þ1:06)
(þ0:95)
—
8a
8b
8c
8d
8e
8f
100
98
93
100
100
94
þ0:51
(þ0:78)
(þ0:59)
(þ0:55)
þ0:47
2ab)
2bb)
(ꢂ1:75)
(þ0:45)
a) V vs Ag/AgNO3; mean value of the cathodic and anodic peaks. Irreversible processes are shown in
parentheses. b) Ref. 11.
compared with those of 11d–f, indicate the steric effects of the
t-Bu group, which hinder the protonation of the quinoneme-
thides 11a–c. The pKa values of the conjugated acids of
11a–c are larger in the order 11a < 11b < 11c, while the
pKa values of the conjugated acids of 11d–f are larger in the
order 11d < 11e < 11f. This feature is rationalized by the
electon-donating ability of heteroazulenes 5a–c (5a < 5b <
5c).12–17
The reduction and oxidation potentials of quinonemethides
11a–f determined by cyclic voltammentry (CV) in CH3CN
are summarized in Table 3 along with those of reference com-
pounds 2a,b.11 The reduction waves of 11a–f are reversible
under the conditions of the CV measurements, and quinoneme-
thides 11a–c and 11e,f showed two reversible waves. The
quinonemethide 11d showed three reversible waves. The
two waves (E1red and E2red) are explained by the formation
of stable radical anions 13a–f and dianions 14a–f, rescpective-
ly (Scheme 2). The additional wave (E3red) of 11d is ration-
alized by reduction of the heteroazulene-moiety of 14d. These
characteristics are due to the heteroazulenes which stabilize
the radical species and anion species.13 On the other hand,
two oxidation waves were recorded in the measurements of
quinonemethides 11a–f, as summarized in Table 3. The first
oxidation waves (E1ox) of 11a–c are reversible, while the sec-
ond oxidation waves (E2ox) of 11a–c and the two oxidation
waves of 11d–f are irreversible. The two waves can also be
explained by the formation of radical cations 15a–f and dicat-
ions 16a–f, respectively (Scheme 2). The reversible oxidation
waves (E1ox) of 11a–c suggest stabilization of the phenoxyl
radicals by the steric hindrance of the t-Bu group. On the con-
trary, after the first cycle of CV measurements of 11d–f, other
reduction waves were recorded at ꢂ0:32 V, ꢂ0:57 V, and
ꢂ0:61 V, respectively. These waves are suggested to be the
reduction waves of 10d–f, which are generated by the hydro-
gen abstraction of phenoxyl radicals 15d–f. On the other hand,
we recently reported that the one-electron reduction of the
bis(2-oxo-2H-cyclohepta[b]furan-3-yl)methyl cation by using
Zn powder afforded a radical species, which rapidly dimerizes
to give 1,1,2,2-tetrakis(2-oxo-2H-cyclohepta[b]furan-3-yl)-
ethane.17 Thus, the reaction of 11a–f with Zn powder was car-
ried out (Scheme 3). The quinonemethides 11a–f were pro-
tonated in HCl/AcOH to give cations 10a–f, which were re-
Scheme 2.
duced to afford the methane derivative 8a–f in good yield
(Table 3). This feature shows that the quinonemethides
11a–f have good redox properties.
In summary, a convenient preparation of fairly stable ꢀ,ꢀ-
bis(heteroazulen-3-yl)-1,4-benzoquinonemethides 11a–f was
accomplished. The properties of 11a–f were clarified by mea-

2040 Bull. Chem. Soc. Jpn., 76, No. 10 (2003)
Bis(heteroazulen-3-yl)benzoquinonemethide
int.) m=z 508 (Mþ, 26), 51 (100%). Anal. Calcd for C33H32O5: C,
77.55; H, 6.31%. Found: C, 77.93; H, 6.34%.
3,5-Di-t-butyl-4-hydroxyphenyl-bis(1,2-dihydro-2-oxo-N-
phenylcyclohepta[b]pyrrol-3-yl)methane (8b): Orange powder;
mp 272–273 ꢁC (from CH2Cl2/EtOH); 1H NMR (500 MHz,
CDCl3) ꢂ 1.40 (18H, s, Bu), 5.20 (1H, s, OH), 6.20 (1H, s,
CH), 6.70 (2H, d, J ¼ 8:9 Hz, H-8), 6.75 (2H, dd, J ¼ 10:6, 8.5
Hz, H-6), 6.82 (2H, dd, J ¼ 10:6, 8.9 Hz, H-7), 6.88 (2H, dd,
J ¼ 11:5, 8.5 Hz, H-5), 7.13 (2H, s, Ph-2,6), 7.30 (4H, d,
J ¼ 8:1 Hz, NPh-2,6), 7.41 (2H, t, J ¼ 7:7 Hz, NPh-4), 7.50
(4H, dd, J ¼ 8:1, 7.7 Hz, NPh-3,5), 7.80 (2H, d, J ¼ 11:5 Hz,
H-4); 13C NMR (125.7 MHz, CDCl3) ꢂ 30.4, 34.4, 35.9, 112.6,
114.3, 124.8, 128.4, 128.8, 129.3, 129.4, 129.5, 129.6, 130.1,
130.3, 134.7, 135.6, 141.2, 145.5, 152.1, 168.9; IR (KBr) ꢄ
1679 cmꢂ1; MS (rel, int.) m=z 659 (Mþ, 46), 658 (100%). Anal.
Scheme 3. Reagents and conditions:ffi, Zn, 3% HCl, AcOH,
reflux, 8 h.
Calcd for C45H42N2O3 1/3H2O: C, 81.18; H, 6.43; N, 4.09%.
Found: C, 81.30; H, 6.47; N, 4.21%.
ꢃ
suring the 13C NMR and UV–vis spectra and the solvatochro-
mic effects as well as the pKa values of their conjugate acids.
The contribution of the polarized structure of quinonemethides
11a–f was clarified to be small in the ground state, but larger in
the excited state. Owing to the stabilizing ability of heteroazu-
lenes toward the radical and anion species, quinonemethides
11a–f show two or three reversible reduction waves in the
CV measurements. Moreover, the quinonemethides 11a–f
showed two oxidation waves, and the first oxidation potentials
(E1ox) of 11a–c, which have t-Bu substituents, were reversible.
Further studies concerning the synthesis and properties of het-
eroazulene-substituted quinonemethide analogues are under-
way.
3,5-Di-t-butyl-4-hydroxyphenyl-bis(1,2-dihydro-N-methyl-
2-oxocyclohepta[b]pyrrol-3-yl)methane (8c): Yellow powder;
mp 242–243 ꢁC (from CH2Cl2/EtOH); 1H NMR (500 MHz,
CDCl3) ꢂ 1.31 (18H, s, Bu), 3.50 (6H, s, NMe), 5.05 (1H, s,
OH), 6.05 (1H, s, CH), 6.80 (2H, dd, J ¼ 11:0, 9.9 Hz, H-6),
6.81 (2H, d, J ¼ 9:8 Hz, H-8), 6.90 (2H, dd, J ¼ 11:0, 9.8 Hz,
H-7), 6.96 (2H, dd, J ¼ 11:3, 9.9 Hz, H-5), 6.99 (2H, s, Ph-2,
6), 7.74 (2H, d, J ¼ 11:3 Hz, H-4); 13C NMR (125.7 MHz,
CDCl3) ꢂ 26.4, 30.3, 34.3, 35.8, 110.8, 115.0, 124.7, 128.7,
128.9, 129.6, 129.7, 129.9, 135.6, 140.7, 144.8, 152.0, 168.8; IR
(KBr) ꢄ 1669 cmꢂ1; MS (rel, int.) m=z 534 (Mþ, 23), 57
(100%). Anal. Calcd for C35H38N2O3 1/2H2O: C, 77.14; H,
7.20; N, 5.11%. Found: C, 77.32; H, 7.23; N, 5.15%.
ꢃ
4-Hydroxyphenyl-bis(2-oxo-2H-cyclohepta[b]furan-3-yl)-
methane (8d): Yellow powder; mp 250–252 ꢁC (from CH2Cl2/
EtOH); 1H NMR (500 MHz, CDCl3) ꢂ 5.40 (1H, s, CH), 6.71 (2H,
d, J ¼ 8:7 Hz, Ph-3,5), 6.91 (2H, dd, J ¼ 9:6, 8.1 Hz, H-6), 6.98
(2H, d, J ¼ 8:7 Hz, Ph-2,6), 7.02–7.15 (6H, m, H-5,7,8), 7.19 (2H,
d, J ¼ 11:5 Hz, H-4), 9.37 (1H, s, OH); 13C NMR (125.7 MHz,
CDCl3) ꢂ 26.9, 31.3, 35.2, 112.3, 114.9, 115.8, 128.2, 129.1,
130.8, 131.3, 140.7, 144.8, 156.1, 168.1; IR (KBr) ꢄ 1653, 1221
cmꢂ1; MS (ESI) m=z 395 (Mþ, 100%). Anal. Calcd for
Experimental
IR spectra were recorded on a HORIBA FT-710 spectrometer.
Mass spectra and high-resolution mass spectra were run on JMS-
AUTOMASS 150 and JMS-SX102A spectrometers. Unless other-
wise specified, 1H NMR spectra and 13C NMR spectra were re-
corded on JNM-lambda 500 spectrometers, and the chemical
shifts are given relative to internal SiMe4 standard: J-values are
given in Hz. Mps were recorded on a Yamato MP-21 apparatus
and were uncorrected.
The heteroazulenes, 2H-cyclohep-
C25H16O5 1/2H2O: C, 73.78; H, 3.88%. Found: C, 74.07; H,
4.23%.
ꢃ
ta[b]furan-2-one 5a,18 1,2-dihydro-N-phenylcyclohepta[b]pyrrol-
2-one 5b,19 and 1,2-dihydro-N-methylcyclohepta[b]pyrrol-2-one
5c20 were prepared as described previously.
Bis(1,2-dihydro-2-oxo-N-phenylcyclohepta[b]pyrrol-3-yl)(4-
hydroxyphenyl)methane (8e): Yellow powder; mp 216–218 ꢁC
(from CH2Cl2/EtOH); 1H NMR (500 MHz, CDCl3) ꢂ 5.98 (1H, s,
OH), 6.19 (1H, s, CH), 6.72–6.78 (6H, m, H-6,7,8), 6.85 (2H, d,
J ¼ 8:3 Hz, Ph-3,5), 6.90 (2H, dd, J ¼ 11:1, 8.3 Hz, H-5), 7.18
(2H, d, J ¼ 8:3 Hz, Ph-2,6), 7.35 (4H, d, J ¼ 8:2 Hz, NPh-2,
6), 7.43 (2H, t, J ¼ 8:3 Hz, NPh-4), 7.50 (4H, dd, J ¼ 8:3, 8.2
Hz, NPh-3,5), 7.86(2H, d, J ¼ 8:3 Hz, H-4); 13C NMR (125.7
MHz, CDCl3) ꢂ 35.9, 113.8, 114.4, 116.1, 129.1, 129.4, 129.9,
130.0, 130.1, 130.2, 131.0, 131.5, 131.8, 135.1, 142.1, 146.0,
155.1, 169.5; IR (KBr) ꢄ 1684 cmꢂ1; MS (ESI) m=z 545 (Mþ,
General Synthetic Procedure for Heteroazulene-Substituted
Methane Derivatives 8a–f. A solution of heteroazulene 5a–c (2
mmol) and 3,5-di-t-butyl-4-hydroxybenzaldehyde 6 (234 mg, 1
mmol) [or 4-hydroxybenzaldehyde 7 (122 mg, 1 mmol)] in a mix-
ture of CHCl3 (10 cm3) and trifluoroacetic acid (2 cm3) was stir-
ꢁ
red at 80 C for 6h. After the reaction was completed, the mix-
ture was poured into an aqueous NaHCO3 solution. The mixture
was extracted with CH2Cl2, and the extract was dried over
Na2SO4 and concentrated in vacuo. The resulting residue was pu-
rified by recrystallization to give products 8a–c [or products 8d–f]
(Table 1, Runs 1–4, 6, and 8).
3,5-Di-t-butyl-4-hydroxyphenyl-bis(2-oxo-2H-cyclohepta[b]-
furan-3-yl)methane (8a): Orange powder; mp 237–238 ꢁC (from
CH2Cl2/EtOH); 1H NMR (500 MHz, CDCl3) ꢂ 1.35 (18H, s, Bu),
5.10 (1H, s, OH), 5.65 (1H, s, CH), 6.76 (2H, dd, J ¼ 8:7, 8.3 Hz,
H-6), 6.88–6.95 (6H, m, H-5,7,8), 7.01 (2H, s, Ph-2,6), 7.38 (2H,
d, J ¼ 12:0 Hz, H-4); 13C NMR (125.7 MHz, CDCl3) ꢂ 30.3, 34.4,
35.2, 109.8, 113.7, 124.3, 126.9, 128.4, 130.8, 131.9, 134.1, 136.2,
148.3, 152.6, 157.7, 169.5; IR (KBr) ꢄ 1635, 1236 cmꢂ1; MS (rel,
100%). Anal. Calcd for C37H26N2O3 3/2H2O: C, 77.28; H,
5.41; N, 4.50%. Found: C, 77.47; H, 5.10; N, 4.88%.
ꢃ
Bis(1,2-dihydro-N-methyl-2-oxocyclohepta[b]pyrrol-3-yl)(4-
hydroxyphenyl)methane (8f): Yellow powder; mp 272–273 ꢁC
(from CH2Cl2/EtOH); 1H NMR (500 MHz, CDCl3) ꢂ 3.25 (6H, s,
NMe), 5.80 (1H, s, CH), 6.64 (2H, d, J ¼ 8:2 Hz, Ph-2,6), 6.84–
6.90 (4H, m, Ph-3,5, H-8), 6.94 (2H, dd, J ¼ 9:6, 8.2 Hz, H-6),
7.05–7.15 (4H, m, H-5,7), 7.62 (2H, d, J ¼ 10:9 Hz, H-4), 9.25
(1H, s, OH); 13C NMR (125.7 MHz, CDCl3) ꢂ 26.1, 30.6, 34.4,
110.1, 111.6, 114.1, 115.0, 127.5, 128.4, 130.1, 130.6, 140.0,

S. Naya et al.
Bull. Chem. Soc. Jpn., 76, No. 10 (2003) 2041
144.1, 155.4, 167.4; IR (KBr) ꢄ 1653 cmꢂ1; MS (ESI) m=z 421
J ¼ 10:9 Hz, Ph-3,5), 6.85–8.00 (22H, m); IR (KBr) ꢄ 1630,
1083 cmꢂ1; MS (FAB) m=z 587 (Mþ ꢂ BF4); HRMS Calcd for
C39H27BF4N2O4: 587.1964 (M ꢂ BF4). Found: 587.1965 (Mþ
ꢂ BF4).
(Mþ, 100%). Anal. Calcd for C27H22N2O3 1/2H2O: C, 75.09;
H, 5.20; N, 6.16%. Found: C, 75.16; H, 5.37; N, 6.49%.
ꢃ
À
Preparation of Methylium Tetrafluoroborates 10a–c BF
.
Á
4
To a stirred solution of 8a–c (0.25 mmol) in CH2Cl2 (10 cm3) was
added DDQ (70 mg, 0.30 mmol), and the mixture was stirred at rt
for 1 h. After evaporation of the CH2Cl2, the residue was dis-
4-Acetoxyphenyl-bis(1,2-dihydro-N-methyl-2-oxocyclohep-
ta[b]pyrrol-3-yl)methyl tetrafluoroborate (12f BF À): Dark
Á
4
green powder; mp 175–180 ꢁC (from CH3CN/Et2O, decomp.);
1H NMR (400 MHz, CD3CN) ꢂ 2.30 (3H, s, OAc), 3.57 (6H, s,
NMe), 6.48 (2H, d, J ¼ 10:7 Hz, Ph-3,5), 6.80–8.20 (12H, m);
IR (KBr) ꢄ 1600, 1083 cmꢂ1; MS (FAB) m=z 463 (Mþ ꢂ BF4);
HRMS Calcd for C29H23BF4N2O4: 463.1697 (M ꢂ BF4). Found:
463.1690 (Mþ ꢂ BF4).
solved in Ac2O (5 cm3) and 42% HBF4 (1 cm3) at 0 C and the
ꢁ
mixture was stirred for 1 h. To the mixture was added Et2O
(100 cm3) and the precipitates were collected by filtration to give
ꢂ
10a–c BF (Table 1, Runs 1–3).
Á
4
3,5-Di-t-butyl-4-hydroxyphenyl-bis(2-oxo-2H-cyclohep-
ta[b]furan-3-yl)methyl tetrafluoroborate (10a BF À): Dark
General Synthetic Procedure for Methylium Hexafluoro-
Á
4
À
brown powder; mp 230–232 ꢁC (from CH3CN/Et2O, decomp.);
1H NMR (400 MHz, CD3CN) ꢂ 1.40 (18H, s, Bu), 7.53 (2H, s,
Ph-2,6), 7.60–8.20 (11H, m, OH, H-4,5,6,7,8); IR (KBr) ꢄ 1628,
1084 cmꢂ1; MS (FAB) m=z 507 (Mþ ꢂ BF4); HRMS Calcd for
phosphates 10d–f PF
.
To a stirred solution of 8d–f (0.25
Á
6
mol) in CH2Cl2 (10 cm3) was added DDQ (70 mg, 0.3 mmol)
and the mixture was stirred at rt for 1 h until the reaction
completed. To the reaction mixture was added a 60% aqueous
HPF6 (1 cm3) solution, and the resulting mixture was filtered.
The filtrate was extracted with CH2Cl2, and the extract was dried
over Na2SO4 and concentrated in vacuo. The resulting residue
was dissolved in CH2Cl2 and ether was added to the solution.
The precipitates were colleꢂcted by filtration, washed with ether
C33H31BF4O5: 507.2187 (M ꢂ BF4). Found: 507.2191 (Mþ
BF4).
3,5-Di-t-butyl-4-hydroxyphenyl-bis(1,2-dihydro-2-oxo-N-
ꢂ
phenylcyclohepta[b]pyrrol-3-yl)methyl
tetrafluoroborate
(10b BF À):
Dark brown powder; mp 260–263 ꢁC (from
Á
4
CH3CN/Et2O, decomp.); 1H NMR (400 MHz, CD3CN) ꢂ 1.48
(18H, s, Bu), 6.63 (1H, bs, OH), 7.45 (2H, bs, Ph-2,6), 7.58–
7.90 (20H, m, NPh-2,3,4,5,6, H-4,5,6,7,8); IR (KBr) ꢄ 1636,
1083 cmꢂ1; MS (FAB) m=z 657 (Mþ ꢂ BF4); HRMS Calcd for
C45H41BF4N2O3: 657.3113 (M ꢂ BF4). Found: 657.3114 (Mþ
ꢂ BF4).
to give the salts 10d–f PF (Table 1, Runs 5, 7, and 9).
Á
6
4-Hydroxyphenyl-bis(2-oxo-2H-cyclohepta[b]furan-3-yl)-
methyl hexafluorophosphate (10d PF À): Dark brown powder;
Á
6
mp 170–172 ꢁC (from CH3CN/Et2O, decomp.); 1H NMR (400
MHz, CD3CN) ꢂ 5.35 (1H, s, OH), 6.98 (2H, d, J ¼ 9:8 Hz,
Ph-3,5), 7.65 (2H, d, J ¼ 9:8 Hz, Ph-2,6), 7.76 (2H, m), 7.90–
3,5-Di-t-butyl-4-hydroxyphenyl-bis(1,2-dihydro-N-methyl-
8.01 (4H, m), 8.15–8.27 (4H, m); IR (KBr) ꢄ 1737, 840 cmꢂ1
;
2-oxocyclohepta[b]pyrrol-3-yl)methyl
tetrafluoroborate
MS (FAB) m=z 395 (Mþ ꢂ PF6); HRMS Calcd for C25H15F6O5P:
(10c BF À):
Dark brown powder; mp 250–255 ꢁC (from
395.0949 (M ꢂ PF6). Found: 395.0943 (Mþ ꢂ PF6).
Á
4
CH3CN/Et2O, decomp.); 1H NMR (400 MHz, CD3CN) ꢂ 1.30
(18H, s, Bu), 3.57 (6H, s, NMe), 5.50 (1H, s, OH), 7.38 (2H, s,
Ph-2,6), 7.52–7.65 (6H, m), 7.86 (2H, m), 8.00 (2H, m); 13C NMR
(125.7 MHz, CH3CN) ꢂ 27.9, 30.4, 35.4, 115.3, 123.2, 128.5,
132.5, 134.6, 137.8, 139.8, 140.0, 142.0, 149.8, 153.5, 162.4,
163.1, 165.6; IR (KBr) ꢄ 1636, 1083 cmꢂ1; MS (FAB) m=z 533
(Mþ ꢂ BF4); HRMS Calcd for C35H37BF4 N2O3: 533.2840 (M
ꢂ BF4). Found: 533.2848 (Mþ ꢂ BF4). Anal. Calcd for
Bis(1,2-dihydro-2-oxo-N-phenylcyclohepta[b]pyrrol-3-yl)(4-
hydroxyphenyl)methyl hexafluorophosphate (10e PF À):
Á
6
Dark brown powder; mp 180–185 ꢁC (from CH3CN/Et2O, de-
comp.); 1H NMR (400 MHz, CD3CN) ꢂ 5.35 (1H, s, OH), 6.98
(2H, d, J ¼ 9:3 Hz, Ph-3,5), 7.45 (4H, d, J ¼ 9:3 Hz, NPh-2,
6), 7.59–7.95 (18H, m, Ph-2,6, NPh-3,4,5, H-4,5,6,7,8); IR
(KBr) ꢄ 1675, 845 cmꢂ1; MS (FAB) m=z 545 (Mþ ꢂ PF6); HRMS
Calcd for C37H25F6N2O3P: 545.1873 (M ꢂ PF6). Found:
545.1868 (Mþ ꢂ PF6).
C35H37BF4N2O3 1/3BF4: C, 64.63; H, 5.70; N, 4.17%. Found:
ꢃ
C, 64.70; H, 5.79; N, 4.31%.
Bis(1,2-dihydro-N-methyl-2-oxocyclohepta[b]pyrrol-3-yl)(4-
hydroxyphenyl)methyl hexafluorophosphate (10f PF À): Dark
À
Preparation of Methylium Tetrafluoroborates 12d–f BF
.
Á
Á
4
6
To a stirred solution of 8d–f (0.25 mmol) in CH2Cl2 (10 cm3)
was added DDQ (70 mg, 0.30 mmol), and the mixture was stirred
at rt for 1 h. After evaporation of the CH2Cl2, the residue was dis-
brown powder; mp 155–157 ꢁC (from CH3CN/Et2O, decomp.);
1H NMR (400 MHz, CD3CN) ꢂ 3.55 (6H, s, NMe), 5.10 (1H, s,
OH), 6.88 (2H, d, J ¼ 10:5 Hz, Ph-3,5), 7.45 (2H, d, J ¼ 10:5
Hz, Ph-2,6), 7.60–7.75 (6H, m, H-6,7,8), 7.92 (2H, d, J ¼ 11:6
Hz, H-4), 8.09 (2H, dd, J ¼ 11:6, 10.5 Hz, H-5); IR (KBr) ꢄ
1634, 845 cmꢂ1; MS (FAB) m=z 421 (Mþ ꢂ PF6); HRMS Calcd
for C27H21F6N2O3P: 421.1576(M ꢂ PF6). Found: 421.1571
(Mþ ꢂ PF6).
solved in Ac2O (5 cm3) and 42% HBF4 (1 cm3) at 0 C and the
ꢁ
mixture was stirred for 1 h. To the mixture was added Et2O
(100 cm3) and the precipitates were collected by filtration to give
ꢂ
12d–f BF (Table 1, Runs 4, 6, and 8).
Á
4
4-Acetoxyphenyl-bis(2-oxo-2H-cyclohepta[b]furan-3-yl)-
methyl tetrafluoroborate (12d BF À): Dark green powder; mp
Preparation of ꢀ,ꢀ-Bis(heteroazulen-3-yl)-1,4-benzoqui-
ꢂ
nonemethides 11a–c from 10a–c BF À. The cation 10a–c BF
4
Á
4
ꢁ
1
150–155 C (from CH3CN/Et2O, decomp.); H NMR (400 MHz,
CD3CN) ꢂ 2.30 (3H, s, OAc), 7.35 (2H, d, J ¼ 10:4 Hz, Ph-3,5),
7.68–7.83 (4H, m), 7.91–8.13 (4H, m), 8.25–8.40 (4H, m); IR
(KBr) ꢄ 1752, 1083 cmꢂ1; MS (FAB) m=z 437 (Mþ ꢂ BF4);
HRMS Calcd for C27H17BF4O6: 437.1036(M ꢂ BF4). Found:
Á
Á
4
(0.25 mmol) was dissolved in aqueous NaHCO3 solution and ex-
tracted with CH2Cl2. The extract was dried over Na2SO4 and con-
centrated in vacuo to give the products 11a–c (Table 1, Runs 1–3).
3,5-Di-t-butyl-ꢀ,ꢀ-bis(2-oxo-2H-cyclohepta[b]furan-3-yl)-
1,4-benzoquinonemethides (11a): Dark green powder; mp 228–
230 ꢁC (from CH2Cl2/AcOEt); 1H NMR (500 MHz, DMSO-d6,
80 ꢁC) ꢂ 1.18 (18H, s, Bu), 7.01 (2H, s, Ph-2,6), 7.19 (2H, d, J ¼
11:2 Hz, H-4), 7.16–7.20 (2H, m, H-6), 7.37–7.43 (6H, m, H-
5,7,8); 13C NMR (125.7 MHz, DMSO-d6) ꢂ 30.3, 31.6, 35.9,
55.7, 60.6, 118.1, 128.8, 130.7, 134.3, 136.3, 138.9, 147.3,
437.1028 (Mþ ꢂ BF4). Anal. Calcd for C27H17BF4O6 H2O: C,
ꢃ
59.94; H, 3.48%. Found: C, 59.81; H, 3.53%.
4-Acetoxyphenyl-bis(1,2-dihydro-2-oxo-N-phenylcyclohep-
ta[b]pyrrol-3-yl)methyl tetrafluoroborate (12e BF À): Dark
Á
4
green powder; mp 190–195 ꢁC (from CH3CN/Et2O, decomp.);
1H NMR (400 MHz, CD3CN) ꢂ 2.25 (3H, s, OAc), 6.47 (2H, d,

2042 Bull. Chem. Soc. Jpn., 76, No. 10 (2003)
Bis(heteroazulen-3-yl)benzoquinonemethide
150.6, 158.5, 171.2, 187.0; IR (KBr) ꢄ 1652 cmꢂ1; MS (rel, int.)
yl)-1,4-benzoquinonemethides (11f): Dark green powder; mp
220–223 ꢁC (from CH2Cl2/AcOEt, decomp.); 1H NMR (500
MHz, DMSO-d6, 50 ꢁC) ꢂ 3.50 (6H, s, NMe), 6.23 (2H, d,
J ¼ 9:6 Hz, Ph-3,5), 7.16(2H, dd, J ¼ 9:0, 8.7 Hz, H-6), 7.25
(2H, d, J ¼ 9:6, Ph-2,6), 7.28 (2H, dd, J ¼ 10:8, 8.7 Hz, H-5),
7.31 (2H, d, J ¼ 10:8 Hz, H-4), 7.46(2H, d, J ¼ 9:5 Hz, H-8),
7.49 (2H, dd, J ¼ 9:5, 9.0 Hz, H-7); 13C NMR (125.7 MHz,
DMSO-d6) ꢂ 26.6, 60.0, 111.4, 115.4, 125.8, 127.5, 128.5,
130.9, 134.2, 134.4, 138.0, 144.3, 146.1, 165.4, 185.2; IR (KBr)
ꢄ 1663 cmꢂ1; MS (ESI) m=z 421 (Mþ + H, 100%). Anal. Calcd
m=z 657 (Mþ, 18), 84 (100%). Anal. Calcd for C33H30O5 3/2-
H2O: C, 74.49; H, 6.55%. Found: C, 74.28; H, 6.23%.
ꢃ
3,5-Di-t-butyl-ꢀ,ꢀ-bis(1,2-dihydro-2-oxo-N-phenylcyclohep-
ta[b]pyrrol-3-yl)-1,4-benzoquinonemethides (11b): Dark green
powder; mp 279–280 ꢁC (from CH2Cl2/AcOEt); 1H NMR (500
MHz, DMSO-d6, 80 ꢁC) ꢂ 1.30 (18H, s, Bu), 6.94 (2H, d,
J ¼ 9:5 Hz, H-8), 7.07 (2H, dd, J ¼ 10:5, 9.5 Hz, H-6), 7.18
(2H, s, Ph-2,6), 7.27 (4H, dd, J ¼ 10:5, 9.5 Hz, H-5,7), 7.36
(2H, d, J ¼ 10:5 Hz, H-4), 7.36(4H, d, J ¼ 7:4 Hz, NPh-2,6),
7.53 (2H, t, J ¼ 7:2 Hz, NPh-4), 7.60 (4H, dd, J ¼ 7:4, 7.2 Hz,
NPh-3,5); 13C NMR (125.7 MHz, DMSO-d6) ꢂ 29.7, 33.1, 35.1,
112.1, 114.7, 128.0, 128.7, 129.0, 129.7, 130.4, 130.8, 131.0,
133.9, 134.5, 137.7, 143.7, 146.0, 146.3, 166.1, 186.3; IR (KBr)
ꢄ 1680 cmꢂ1; MS (ESI) m=z 657 (Mþ + H, 100%). Anal. Calcd
for C27H20N2O3 1/2CH2Cl2: C, 71.41; H, 4.79; N, 6.03%. Found:
C, 71.35; H, 4.57; N, 6.05%.
ꢃ
Preparation of ꢀ,ꢀ-Bis(heteroazulen-3-yl)-1,4-benzoqui-
ꢂ
nonemethides 11d–f from 10d–f PF À. The cation 10d–f PF
Á
Á
6
6
(0.25 mmol) was dissolved in a 4% aqueous NaOH solution and
extracted with CH2Cl2. The extract was dried over Na2SO4 and
concentrated in vacuo to give the products 11d–f (Table 1, Runs
5, 7, and 9).
for C45H40N2O3 1/5CH2Cl2: C, 80.79; H, 6.02; N, 4.00%.
Found: C, 80.57; H, 6.04; N, 4.16%.
ꢃ
3,5-Di-t-butyl-ꢀ,ꢀ-bis(1,2-dihydro-N-methyl-2-oxocyclohep-
ta[b]pyrrol-3-yl)-1,4-benzoquinonemethides (11c): Dark green
powder; mp 235–236 ꢁC (from CH2Cl2/AcOEt); 1H NMR (500
MHz, DMSO-d6, 80 ꢁC) ꢂ 1.14 (18H, s, Bu), 3.48 (6H, s,
NMe), 7.03 (2H, s, Ph-2,6), 7.08 (2H, dd, J ¼ 10:2, 8.7 Hz, H-
6), 7.20 (2H, dd, J ¼ 10:7, 8.7 Hz, H-5), 7.25 (2H, d, J ¼ 10:7
Hz, H-4), 7.34 (2H, d, J ¼ 8:5 Hz, H-8), 7.39 (2H, dd,
J ¼ 10:2, 8.5 Hz, H-7): 13C NMR (125.7 MHz, DMSO-d6) ꢂ
26.4, 29.4, 34.8, 112.2, 113.9, 127.3, 129.9, 130.7, 131.9, 133.1,
133.2, 143.1, 145.5, 145.6, 165.9, 177.9, 185.9; IR (KBr) ꢄ
1662 cmꢂ1; MS (ESI) m=z 421 (Mþ, 100%). Anal. Calcd for
Determination of pKa Value of Conjugate Acids of Quinone-
methides 11a–f. Buffer solutions of slightly different acidities
were prepared by mixing aqueous solutions of potassium hydro-
gen phthalate (0.1 M) and HCl (0.1 M) (for pH 0.0–4.0), potassi-
um hydrogen phthalate (0.1 M) and NaOH (0.1 M) (for pH 4.1–
5.9), KH2PO4 (0.1 M) and NaOH (0.1 M) (for pH 6.0–8.0) in var-
ious portions. For preparing of sample solutions, 1 cm3 portions
of the stock solution, prepared by dissolving 3–5 mg of quinone-
methides 11a–f in MeCN (20 cm3), were diluted to 10 cm3 with
the buffer solution (8 cm3) and MeCN (1 cm3). The UV–vis spec-
trum was recorded for each quinonemethide 11a–f in 50 different
buffer solutions. Immediately after recording the spectrum, the
pH of each solution was determined on a pH meter calibrated with
standard buffers. The observed absorbance at the specific absorp-
tion wavelengths of each quinonemethide 11a–f (453 nm for 11a;
489 nm for 11b; 487 nm for 11c; 467 nm for 11d; 509 nm for 11e;
507 nm for 11f) was plotted against the pH to give a classical ti-
tration curve, whose midpoint was taken as the pKa value.
Cyclic Voltammetry of Quinonemethides 11a–f. The reduc-
tion potentials of 11a–f were determined by means of a CV-27
voltammetry controller (BAS Co). A three-electrode cell was
used, consisting of Pt working and counter electrodes and a refer-
ence Ag/AgNO3 electrode. Nitrogen was bubbled through an
C35H36N2O3 H2O: C, 76.21; H, 6.74; N, 5.09%. Found: C,
76.34; H, 6.96; N, 5.09%.
ꢃ
Preparation of ꢀ,ꢀ-Bis(heteroazulen-3-yl)-1,4-benzoqui-
nonemethides 11d–f from 12d–f BF À. To a solution of 12d–
Á
4
ꢂ
f BF (0.25 mmol) in CH2Cl2 (1 cm3) was added K2CO3 (138
Á
4
mg, 1 mmol), and the mixture was stirred at rt for 48 h. After
the reaction was completed, the mixture was extracted with
CH2Cl2. The extract was dried over Na2SO4 and concentrated
in vacuo to give 11d–f (Table 1, Runs 4, 6, and 8).
ꢀ,ꢀ-Bis(2-oxo-2H-cyclohepta[b]furan-3-yl)-1,4-benzoqui-
nonemethides (11d): Dark green powder; mp 260–263 ꢁC (from
CH2Cl2/AcOEt, decomp.); 1H NMR (500 MHz, DMSO-d6, 50
ꢁC) ꢂ 6.25 (2H, d, J ¼ 10:0 Hz, Ph-3,5), 7.20–7.26(2H, m, H-
6), 7.27 (2H, d, J ¼ 11:3 Hz, H-4), 7.32 (2H, d, J ¼ 10:0 Hz,
Ph-2,6), 7.40–7.51 (6H, m, H-5,7,8); 13C NMR (125.7 MHz,
DMSO-d6) ꢂ 118.8, 128.0, 128.8, 134.8, 136.7, 138.1, 138.2,
139.6, 151.6, 151.7, 158.8, 166.8, 166.9, 187.4; IR (KBr) ꢄ
1617 cmꢂ1; MS (ESI) m=z 395 (Mþ + H, 100%). Anal. Calcd
acetonitrile solution (4 cm3) of each compound (0.5 mmol dmꢂ3
)
and Bu4NClO4 (0.1 mol dmꢂ3) to deaerate it. The measurements
were made at a scan rate of 0.1 V sꢂ1 and the voltammograms
were recorded on a WX-1000-UM-019 (Graphtec Co) X–Y
recorder. Immediately after the measurements, ferrocene (0.1
mmol) (E1=2 ¼ þ0:083) was added as the internal standard, and
the observed peak potentials were corrected with reference to this
standard. The compounds exhibited oxidation–reduction waves,
which are summarized in Table 3.
for C25H14O5 CH2Cl2: C, 66.05; H, 3.05%. Found: C, 66.00; H,
3.28%.
ꢃ
ꢀ,ꢀ-Bis(1,2-dihydro-2-oxo-N-phenylcyclohepta[b]pyrrol-3-
yl)-1,4-benzoquinonemethides (11e): Dark green powder; mp
272–275 ꢁC (from CH2Cl2/AcOEt, decomp.); (500 MHz,
Reduction of 11a–f with Zn Powder. To a solution of 11a–f
(0.1 mmol) in AcOH (1 cm3) and 3% HCl (0.1 cm3) was added
powdery Zn (65 mg, 1.0 mmol), and the mixture was stirred at
80 ꢁC for 8 h. After filtration, the filtrate was concentrated in
vacuo. The mixture was poured into an aqueous NaHCO3 solu-
tion; this new mixture was extracted with CH2Cl2. The extract
was dried over Na2SO4 and concentrated in vacuo to give prod-
ucts 8a–f (Table 3).
ꢁ
DMSO-d6, 50 C) ꢂ 6.27 (2H, d, J ¼ 9:9 Hz, Ph-3,5), 7.03 (2H,
d, J ¼ 9:3 Hz, H-8), 7.17 (2H, dd, J ¼ 10:1, 9.3 Hz, H-7),
7.34–7.46 (12H, m, H-4,5,6, Ph-2,6, NPh-2,6), 7.55 (2H, t,
J ¼ 7:5 Hz, NPh-4), 7.62 (4H, dd, J ¼ 7:8, 7.5 Hz, NPh-3,5);
13C NMR (125.7 MHz, DMSO-d6) ꢂ 31.0, 54.8, 59.7, 115.6,
126.4, 127.8, 128.5, 129.2, 129.5, 131.3, 133.8, 134.4, 134.8,
138.2, 144.4, 146.2, 165.4, 186.2; IR (KBr) ꢄ 1688 cmꢂ1; MS
(ESI) m=z 545 (Mþ
+
C37H24N2O3 2H2O: C, 76.56; H, 4.94; N, 4.59%. Found: C,
H, 100%).
Anal. Calcd for
Financial support from a Waseda University Grant for Spe-
cial Research Project and 21COE ‘‘Practical Nano-chemistry’’
from MEXT is gratefully acknowledged. We thank the Mate-
ꢃ
76.54; H, 4.86; N, 4.82%.
ꢀ,ꢀ-Bis(1,2-dihydro-N-methyl-2-oxocyclohepta[b]pyrrol-3-

S. Naya et al.
Bull. Chem. Soc. Jpn., 76, No. 10 (2003) 2043
10 J. Q. Chambers, ‘‘The Chemistry of the Quinonoid Com-
pounds,’’ ed by S. Patai, Wiley (1974), Chapter 14, p. 737.
11 S. Ito, S. Kikuchi, H. Kobayashi, N. Morita, and T. Asao, J.
Org. Chem., 62, 2423 (1997).
rials Characterization Central Laboratory, Waseda University,
for technical assistance with the spectral data and elemental
analyses.
12 S. Naya and M. Nitta, J. Chem. Soc., Perkin Trans. 1,
2000, 2777.
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