Synthesis, Stabilities, and Redox Behavior of Di(1-azulenyl) (6-azulenyl) methylium Hexafluorophosphates. Generation of a Donor-Acceptor-Substituted Neutral Radical by Azulenes

Article abstract of DOI:10.1021/jo035053o

Several di(1-azulenyl)(6-azulenyl)methanes and 1,3-bis[(1-azulenyl)(6-azulenyl)methyl]azulenes were prepared by the condensation reaction of azulenes with diethyl 6-formylazulene-1, 3-dicarboxylate under acidic conditions. The products were converted into di(1-azulenyl)(6-azulenyl)-methylium hexafluorophosphates and azulene-1,3-diylbis[(1-azulenyl)(6-azulenyl)methylium] bis- (hexafluorophosphate)s via hydride abstraction reaction with DDQ following the exchange of counterions. These mono- and dications exhibited high stability with large pK_R⁺ values (5.6- 10.1), despite the capto-dative substitution of azulenes. The electrochemical reduction of the monocations upon cyclic voltammetry (CV) exhibited a reversible two-step, one-electron reduction wave with a small difference between the first reduction potential (E₁^red) and the second one (E₂ ^red), which exhibited the generation of highly amphoteric neutral radicals in solution. The electrochemical reduction of dications showed voltammograms, which were characterized by subsequent two single-electron waves and a two-electron transfer upon CV attributable to the formation of a radical cation, a diradical (or twitter ionic structure), and a dianionic species, respectively. Formation of a persistent neutral radical from a monocation was revealed by ESR and UV-vis spectroscopies and theoretical calculations. The ESR spectra of the neutral radical gave two hyperfine coupling constants: a _H = 0.083 (6H) and 0.166 mT (9H) (g = 2.0024), indicating that an unpaired electron delocalizes over all three of the azulene rings. The stable monoanion, which shows the localization of the charge on the 6-azulenyl substituent, was also successfully generated from the di(1-azulenyl)(6-azulenyl)-methane derivative.

Full text of DOI:10.1021/jo035053o

Syn th esis, Sta bilities, a n d Red ox Beh a vior of
Di(1-a zu len yl)(6-a zu len yl)m eth yliu m Hexa flu or op h osp h a tes.
Gen er a tion of a Don or -Accep tor -Su bstitu ted Neu tr a l Ra d ica l by
Azu len es
Shunji Ito,*,† Takahiro Kubo,† Noboru Morita,† Tadaaki Ikoma,‡ Shozo Tero-Kubota,‡ and
Akio Tajiri§
Department of Chemistry, Graduate School of Science, Tohoku University,
Sendai 980-8578, J apan, Institute of Multidisciplinary Research for
Advanced Materials, Tohoku University, Sendai 980-8577, J apan, and
Department of Materials Science, Faculty of Science and Technology,
Hirosaki University, Hirosaki 036-8561, J apan
ito@funorg.chem.tohoku.ac.jp
Received J uly 22, 2003
Several di(1-azulenyl)(6-azulenyl)methanes and 1,3-bis[(1-azulenyl)(6-azulenyl)methyl]azulenes
were prepared by the condensation reaction of azulenes with diethyl 6-formylazulene-1,3-
dicarboxylate under acidic conditions. The products were converted into di(1-azulenyl)(6-azulenyl)-
methylium hexafluorophosphates and azulene-1,3-diylbis[(1-azulenyl)(6-azulenyl)methylium] bis-
(hexafluorophosphate)s via hydride abstraction reaction with DDQ following the exchange of
counterions. These mono- and dications exhibited high stability with large pKR+ values (5.6-10.1),
despite the capto-dative substitution of azulenes. The electrochemical reduction of the monocations
upon cyclic voltammetry (CV) exhibited a reversible two-step, one-electron reduction wave with a
small difference between the first reduction potential (E1red) and the second one (E2red), which
exhibited the generation of highly amphoteric neutral radicals in solution. The electrochemical
reduction of dications showed voltammograms, which were characterized by subsequent two single-
electron waves and a two-electron transfer upon CV attributable to the formation of a radical cation,
a diradical (or twitter ionic structure), and a dianionic species, respectively. Formation of a persistent
neutral radical from a monocation was revealed by ESR and UV-vis spectroscopies and theoretical
calculations. The ESR spectra of the neutral radical gave two hyperfine coupling constants: aH
)
0.083 (6H) and 0.166 mT (9H) (g ) 2.0024), indicating that an unpaired electron delocalizes over
all three of the azulene rings. The stable monoanion, which shows the localization of the charge on
the 6-azulenyl substituent, was also successfully generated from the di(1-azulenyl)(6-azulenyl)-
methane derivative.
In tr od u ction
to the stabilization of the ionic state, the simultaneous
substitution with a donor and an acceptor positions of
azulenes might stabilize neutral radicals by the capto-
dative substitution effect,4 although the effect admits of
argument.5 Donor- and acceptor-substituted neutral radi-
cals, e.g., 2-cyano-10-methyl-5-phenazinyl, have been
examined as the conducting materials composed of one
Recently, much attention has been focused on multi-
stage redox systems because of their special properties
such as conductivity and organic ferromagnetism.1 Sta-
bilization of the radical state produced by the redox cycle
is fairly important in the construction of materials with
potentially useful electronic properties, because the
molecules for the application require excellent redox-
stability.2 Azulene (C10H8) has attracted the interest of
many research groups due to its unusual properties as
well as its beautiful blue color.3 Especially, the azulene
system has a tendency to stabilize cations, as well as
anions, owing to its remarkable polarizability. In addition
(2) (a) Hu¨nig, S.; Kemmer, M.; Wenner, H.; Perepichka, I. F.;
Ba¨uerle, P.; Emge, A.; Gescheid, G. Chem. Eur. J . 1999, 5, 1969-1973.
(b) Hu¨nig, S.; Kemmer, M.; Wenner, H.; Barbosa, F.; Gescheidt, G.;
Perepichka, I. F.; Ba¨uerle, P.; Emge, A.; Peters, K. Chem. Eur. J . 2000,
6, 2618-2632. (c) Hu¨nig, S.; Perepichka, I. F.; Kemmer, M.; Wenner,
H.; Ba¨uerle, P.; Emge, A. Tetrahedron 2000, 56, 4203-4211. (d) Hu¨nig,
S.; Langels, A.; Schmittel, M.; Wenner, H.; Perepichka, I. F.; Peters,
K. Eur. J . Org. Chem. 2001, 1393-1399.
(3) (a) Zeller, K.-P. Azulene. In Houben-Weyl; Methoden der Orga-
nischen. Chemie, 4th ed.; Georg Thieme: Stuttgart, Germany, 1985;
Vol. V, Part 2c, pp 127-418. (b) Lemal, D. M.; Goldman, G. D. J . J .
Chem. Edu. 1988, 65, 923-925.
(4) (a) Stella, L.; J anousek, Z.; Mere´nyi, R.; Viehe, H. G. Angew.
Chem., Int. Ed. Engl. 1978, 17, 691-692. (b) Viehe, H. G.; Mere´nyi,
R.; Stella, L.; J anousek, Z. Angew. Chem., Int. Ed. Engl. 1979, 18, 917-
932. (c) Viehe, H. G.; J anousek, Z.; Mere´nyi, R. Acc. Chem. Res. 1985,
18, 148-154.
* Address correspondence to this author. Phone: +81-22-217-7714.
Fax: +81-22-217-7714.
† Graduate School of Science, Tohoku University.
‡ Institute of Multidisciplinary Research for Advanced Materials,
Tohoku University.
§ Hirosaki University.
(1) Deuchert, K.; Hu¨nig, S. Angew. Chem., Int. Ed. Engl. 1978, 17,
875-886.
10.1021/jo035053o CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/19/2003
J . Org. Chem. 2003, 68, 9753-9762
9753

Ito et al.
CHART 1
CHART 3
CHART 2
kind of molecule.6 Phenalenyl radicals having donor and
acceptor substituents have been produced as highly
amphoteric hydrocarbons.7 Preparation of the azulene
derivatives incorporating the capto-dative substituent
effect would also provide an opportunity to construct a
reversible redox system with high redox-stability. In
addition to the redox-stability, the azulene derivatives
should exhibit strong absorption in the visible region in
both cationic and anionic states.8-10 The molecules might
be applied to the preparation of novel polyelectrochromic
materials with high redox-stability.11 However, no at-
tempt has made to generate such a stabilized neutral
radical utilizing capto-dative substitution of azulenes, to
our knowledge, although the redox properties of 1,6′-
diazulenyl ketone (1) have been examined for a potential
precursor for such a system (Chart 1).12
CHART 4
We have recently reported the synthesis of tri(1-
azulenyl)methylium hexafluorophosphates (e.g., 2a -c+‚
PF6-) with high thermodynamic stabilities (Chart 2).13
In view of the extreme stabilities of the tri(1-azulenyl)-
SCHEME 1
(5) (a) Birkhofer, H.; Ha¨drich, J .; Beckhous, H.-D.; Ru¨chardt, C.
Angew. Chem., Int. Ed. Engl. 1987, 26, 573-575. (b) Beckhous, H.-D.;
Ru¨chardt, C. Angew. Chem., Int. Ed. Engl. 1987, 26, 770-771.
(6) Nakasuji, K.; Yamaguchi, M.; Murata, I.; Yamaguchi, K.; Fueno,
T.; Ohya-Nishiguchi, H.; Sugano, T.; Kinoshita, M. J . Am. Chem. Soc.
1989, 111, 9265-9267.
(7) Awaga, K.; Sugano, T.; Kinoshita, M. Bull. Chem. Soc. J pn. 1985,
58, 1886-1893.
(8) Ito, S.; Inabe, H.; Morita, N.; Ohta, K.; Kitamura, T.; Imafuku,
K. J . Am. Chem. Soc. 2003, 125, 1669-1680.
(9) (a) Ito, S.; Inabe, H.; Okujima, T.; Morita, N.; Watanabe, M.;
Harada, N.; Imafuku, K. J . Org. Chem. 2001, 66, 7090-7101. (b) Ito,
S.; Okujima, T.; Morita, N. J . Chem. Soc., Perkin Trans. 1 2002, 1896-
1905.
(10) Ito, S.; Nomura, A.; Morita, N.; Kabuto, C.; Kobayashi, H.;
Maejima, S.; Fujimori, K.; Yasunami, M. J . Org. Chem. 2002, 67,
7295-7302.
(11) (a) Monk, P. M. S.; Mortimer, R. J .; Rosseinsky, D. R. Electro-
chromism: Fundamentals and Applications; VCH: Weinheim, Ger-
many, 1995. (b) Komatsu, T.; Ohta, K.; Fujimoto, T.; Yamamoto, I. J .
Mater. Chem. 1994, 4, 533-536. (c) Rosseinsky, D. R.; Monk, D. M. S.
J . Appl. Electrochem. 1994, 24, 1213-1221.
(12) Kurotobi, K.; Takakura, K.; Murafuji, T.; Sugihara, Y. Synthesis
2001, 1346-1350.
methyl cations, we have now prepared stable methyl
cations incorporating a 6-azulenyl substituent, i.e., di(1-
azulenyl)(6-azulenyl)methylium hexafluorophosphates 3a-
c+‚PF6- and azulene-1,3-diylbis[(1-azulenyl)(6-azulenyl)-
methylium] bis(hexafluorophosphate)s 4a,b2+‚2PF6- (Chart
3), which should exhibit high stabilities in both cationic
and anionic states by the contribution of the tropylium
and cyclopentadienide substructures (3+ and 3-) in
addition to the neutral radical by the capto-dative sub-
stituent effect (Chart 4). The formation of a persistent
neutral radical from monocation 3b+ was revealed by
ESR and UV-vis spectroscopies and theoretical calcula-
tions. The present report also describes the generation
of stable monoanion 3b- by the deprotonation of the
corresponding methane derivative.
(13) (a) Ito, S.; Morita, N.; Asao, T. Bull. Chem. Soc. J pn. 1995, 68,
1409-1437. (b) Ito, S.; Kikuchi, S.; Morita, N.; Asao, T. Bull. Chem.
Soc. J pn. 1999, 72, 839-849. (c) Ito, S.; Kikuchi, S.; Morita, N.; Asao,
T. J . Org. Chem. 1999, 64, 5815-5821. (d) Ito, S.; Morita, N.; Asao, T.
Bull. Chem. Soc. J pn. 2000, 73, 1865-1874. (e) Ito, S.; Kikuchi, S.;
Okujima, T.; Morita, N.; Asao, T. J . Org. Chem. 2001, 66, 2470-2479.
9754 J . Org. Chem., Vol. 68, No. 25, 2003

Di(1-azulenyl)(6-azulenyl)methyl Cations
SCHEME 2
TABLE 1. Th e Lon gest Wa velen gth Absor p tion s a n d
Coefficien ts of 3a -c+‚P F 6-, 4a ,b2+‚2P F 6-, a n d 2a -c+‚P F 6
in Aceton itr ile
Resu lts a n d Discu ssion
-
Preparation of the carbaldehyde 714 commenced with
6-phenylethynylazulene 59a,15 and is outlined in Scheme
1. Partial hydrogenation of the alkyne 5 utilizing Pd-
BaSO4 as a catalyst in the presence of quinoline gave an
olefin 616 as a single stereoisomer. However, unequivocal
analysis of the stereochemistry of 6 was hampered by
the chemical shift equivalents of both olefin protons on
sample
λ
max, nm (log ꢀ)
sample
λmax, nm (log ꢀ)
3a +‚PF6
675 (4.42)
4b2+‚2PF6
712 (4.45),
603 (4.21)
614 (4.70)
650 (4.62)
620 (4.87)
-
-
3b+‚PF6-
719 (4.59)
668 (4.53)
718 (4.51),
608 (4.27)
2a +‚PF6-
-
-
3c+‚PF6
2b+‚PF6-
4a 2+‚2PF6
2c+‚PF6
-
1
the H NMR spectrum. The olefin 6 was converted into
7 by oxidative cleavage utilizing OsO4-NaIO4 in 82%
yield from 5.17
The reaction of two molar amounts of azulene (8a ) and
its 1,6-di-tert-butyl (8b) and 6-methoxy (8c) derivatives
with 7 in acetic acid at room temperature afforded 9a -c
in 23-80% yields, along with diastereomeric mixtures
of1,3-bis{(1-azulenyl)[1,3-bis(ethoxycarbonyl)-6-azulenyl]-
methyl}azulenes 10a (19%) and 10b (10%) in the case of
8a and 8c (Scheme 2). The high-pressure reaction (10
kbar)18 of 8c with 7 in a 50% acetic acid solution of
dichloromethane at 40 °C for 1 day slightly increased the
yields of the desired 9c (26%) and 10b (18%).
Synthesis of the monocations 3a -c+ and the dications
4a ,b2+ was accomplished by the hydride abstraction from
9a -c and 10a ,b, respectively. The reaction of 9a -c with
DDQ in dichloromethane at room temperature, followed
by an addition of a 60% aqueous HPF6 solution, yielded
3a -c+ (70-88%) as a hexafluorophosphate (Scheme 2).13
Similarly, the oxidation of 10a and 10b with 2 molar
equiv of DDQ, followed by the addition of an HPF6
solution, afforded the corresponding bis(hexafluorophos-
phate)s 4a ,b2+‚2PF6- in 78% and 75% yields, respectively
F IGURE 1. UV-vis spectra of 3a + (solid line), 4a 2+ (broken
line), and 2a + (dotted line) in acetonitrile.
with M+ - 2PF6 ion peaks in the case of 4a ,b2+‚2PF6
The characteristic bands of hexafluorophosphate were
observed at 841-843 (strong) and 558 (medium) cm-1 in
their IR spectra. These salts showed strong absorption
in the visible region, as did the salts 2a -c+‚PF6-, and
so on.13 Their absorption maxima (nm) and coefficients
(log ꢀ) are summarized in Table 1. UV-vis spectra of 3a +
and 4a 2+ in acetonitrile along with that of 2a + are shown
in Figure 1. The longest wavelength absorption of 3a -
c+ showed an appreciable bathochromic shift by 61, 69,
and 48 nm, respectively, compared with those of 2a -c+.
The UV-vis spectra of 4a ,b2+ in the visible region were
characterized by two strong absorption bands as sum-
marized in Table 1, although 3a -c+ exhibited an absorp-
.
-
-
(Scheme 2). These new salts 3a-c+‚PF6- and 4a,b2+‚2PF6
are stable, deep-colored crystals, and are storable in the
crystalline state.
Mass spectra of 3a -c+‚PF6- and 4a ,b2+‚2PF6- ionized
by FAB showed the correct M+ - PF6 ion peaks, together
(14) Morita, T.; Fujita, T.; Nakadate, T.; Takase, K. Sci. Rep. Tohoku
Uni., Ser. 1 1980, 62, 91-101.
(15) Morita, T.; Fujita, T.; Takase, K. Bull. Chem. Soc. J pn. 1980,
53, 1647-1651.
(16) Matsumura, H.; Nagamura, S. Nippon Kagaku Zasshi 1964,
85, 901-905.
(17) (a) Saito, M.; Morita, T.; Takase, K. Bull. Chem. Soc. J pn. 1980,
53, 3696-3700. (b) Balschukat D.; Dehmlow, E. V. Chem. Ber. 1986,
119, 2272-2288.
(18) Matsumoto, K.; Sera, A.; Uchida, T. Synthesis 1985, 1-26.
J . Org. Chem, Vol. 68, No. 25, 2003 9755

Ito et al.
+
TABLE 2. p KR Va lu esa a n d Red ox P oten tia lsb of 3a -c+, 4a ,b2+, a n d 2a -c+
+
red
red
red
ox
ox
ox
cation
pKR
E1
E2
E3
E1
E2
E3
3a +
3b+
3c+
4a 2+
8.1 ( 0.2 (26%)c
10.1 ( 0.2 (19%)c
9.5 ( 0.3 (68%)c
5.6 ( 0.1, 8.1 ( 0.1
-0.46
-0.56
-0.53
-0.26
-0.22d
-0.34
-0.30d
-0.78
-0.91
-0.88
-0.69
-0.73
(-1.99)
(+1.00)
+0.89
(+1.33)
(+1.29)
(+1.35)
(+1.27)
+1.19d
(+1.24)
+1.23d
(+1.07)
+0.95
(+1.39)
-0.71
(+0.92)
(+1.18)
+1.14d
(+1.05)
+1.02d
(+0.98)
+0.84
(-0.41)
-0.39d
-0.52
(-0.76)
-0.76d
-0.74
4b2+
8.5 ( 0.2
-0.48d
(-1.56)
(-1.72)
(-1.64)
-0.71d
2a +
2b+
2c+
11.3
14.3
>14.0
(+1.50)
(+0.90)
(+0.98)
a
+
b
pKR values were determined spectrophotomerically at 25 °C in a buffered solution prepared in 50% aqueous acetonitrile. Redox
potentials were measured by CV (0.1 M Et4NClO4 in acetonitrile, Pt electrode, scan rate 100 mV s-1, and ferrocene/ferrocenium ) 0.07
V). In the case of irreversible waves, which are given in parentheses, Eox and Ered were calculated as Epa (anodic peak potential) - 0.03
and Epc (cathodic peak potential) + 0.03 V, respectively. c Regenerated absorption maxima (%) of the cations in the visible region by the
immediate acidification of the alkaline solution with HCl after the pKR+ measurement are given in parentheses. Redox potentials measured
d
by DPV.
tion band in this region. The longest wavelength absorp-
tion of 4a ,b2+ showed an appreciable bathochromic shift
by 43 and 44 nm, respectively, compared with those of
3a + and 3c+, similar to the results on the dications
stabilized by 1-azulenyl groups.13d,e The bathochromic
shift of 4a ,b2+ should be attributable to the increase of
the positive charge at the central cationic carbons,
because the two cation units of the dications 4a ,b2+ were
stabilized by three 1-azulenyl groups in contrast to the
stabilization by two 1-azulenyl groups in the case of the
monocations 3a -c+.
1
The H NMR chemical shifts of the methine protons
of 9a -c (9a , 7.03 ppm; 9b, 6.93 ppm; and 9c, 6.89 ppm)
showed a slight upfield shift, compared with those of tri-
(1-azulenyl)methane (7.36 ppm) and its 1,1′,1′′,6,6′,6′′-
hexa-tert-butyl (7.08 ppm) and 6,6′,6′′-trimethoxy (7.15
ppm) derivatives.13a,b Those of 10a and 10b were also
observed at a slight upfield location (10a , 6.96 and 6.93
ppm; and 10b, 7.07 ppm) compared with those of tri(1-
azulenyl)methane and its 6,6′,6′′-trimethoxy derivative.
These signals disappeared on the 1H NMR spectra of 3a -
F IGURE 2. Presumed conformational isomers for 3*.
c+ and 4a ,b2+. Thus, the H NMR spectra also supported
the cationic structure of these compounds.
1
SCHEME 3
It is possible for 3a -c+ to exhibit the three isomeric
propeller conformations excluding enantiomeric forms
(A+, B+, and C+) as illustrated in Figure 2.13a Despite the
presumed stereoisomerism, the 1H and 13C NMR spectra
of 3a -c+ were observed as the time-averaged spectra of
these three conformers at room temperature. In the case
of 4a ,b2+ we could not obtain well-resolved 1H NMR
spectra, probably due to the presumed stereoisomerism.
The spectra are represented in the Supporting Informa-
tion.
Large downfield shifts were observed at H-4′, 5′, 6′, and
c+ (2a +, 157.4 ppm; 2b+, 151.8 ppm; and 2c+, 156.3
7′ protons on 3a -c+ as compared with those of the
ppm).13a,b In analogy with the results on 1H NMR
methane derivatives 9a -c. The largest ∆δ value was
measurements, large ∆δ values were observed at 3′-, 3′a-,
observed at H-5′, i.e., +0.97 ppm for 3a +, +0.98 ppm for
5′-, 7′-, and 8′a-carbons. Therefore, the NMR spectra of
3b+, and +0.86 ppm for 3c+. The large downfield shifts
3a -c+ revealed that most of the positive charge is
in the seven-membered ring protons of 1-azulenyl sub-
delocalized on 1-azulenyl substituents as an azulenylium
stituents are consistent with the azulenylium ion sub-
ion substructure, which contributes to the stability of the
carbocations.
structure of 3a -c+. The upfield shifts of H-8′ in 3a -c+
should be regarded as being the effect of the neighboring
azulenyl substituents. The chemical shifts (13C NMR) of
As a measure of the thermodynamic stability of the
carbocations, the pKR+ values of monocations 3a -c+ and
dications 4b,c2+ were determined spectrophotometrically
at 25 °C in a buffer solution prepared in 50% aqueous
-
the central cationic carbons in 3a -c+‚PF6 (3a +, 164.5
ppm; 3b+, 159.9 ppm; and 3c+,163.2 ppm) were observed
at slightly downfield location compared with those in 2a -
9756 J . Org. Chem., Vol. 68, No. 25, 2003

Di(1-azulenyl)(6-azulenyl)methyl Cations
SCHEME 4
CHART 5
acetonitrile.13,19 The pKR+ scale stands for the carbocation
in aqueous solution (pKR+ ) -log KR+). The KR+ scale is
defined by the equilibrium constant for the reaction of a
carbocation with a water molecule (KR+ ) [ROH][H3O+]/
+
[R+]). Therefore, the larger pKR index indicates higher
stability of the carbocation. The values of 3a -c+ and
4a ,b2+ are summarized in Table 2 along with those of
the corresponding tri(1-azulenyl)methyl cations 2a -c+.
+
The pKR values of 3a -c+ exhibited destabilization
compared with those of 2a -c+ due to the substitution of
in 19-68% (Table 2). The instability of the neutralized
products should be attributed to the production of an
unstable polyolefinic substructure by the attack of the
base to the aromatic core. Indeed, the base treatment of
3b+ afforded a significantly complex mixture, which did
not reproduce the corresponding cation 3b+ anymore.
To clarify the electrochemical property, the redox
behavior of 3a -c+ and 4a ,b2+ was examined by cyclic
voltammetry (CV) and differential pulse voltammetry
(DPV) and compared with those of 2a -c+. Redox poten-
tials (in volts vs Ag/Ag+) of 3a -c+ and 4a ,b2+ are
summarized in Table 2, together with those of 2a -c+.
The reduction waves of 3b+ and 4b2+ are shown in the
Supporting Information. The cyclic voltammogram of 3a -
c+ exhibited two reversible redox waves (E1/2 ) -0.46 to
-0.56 V and -0.69 to -0.73 V upon CV) that should
correspond to two single-electron transfers (Scheme 3).
The formation of neutral radical 3• and anion 3- was
revealed by the ESR observation of 3b•, generation of 3b-
by the reaction of 9b with potasium tert-butoxide, and
also electrochromic analysis of monocation 3b+. The less
negative reduction potential of these cations, compared
with that of 2a -c+, corresponds to the increase of
electron affinity of the cations by the 6-azulenyl sub-
stituent. The potential difference between the first and
the second reduction waves (0.17-0.23 V) is significantly
small as compared with those of 2a -c+ (0.76-0.81 V).
These results indicated the generation of neutral radicals
3a -c• with substantial amphoteric redox property. The
amphoteric redox nature of 3a -c• is significantly higher
the electron-withdrawing 6-azulenyl group. However,
+
3a -c+ still exhibit large pKR values (8.1-10.1), which
provide a criterion of high thermodynamic stability of
these cations. These values are 14.5-16.5 pK units
+
higher than that of the triphenylmethyl cation (pKR
)
-6.4).20 The tert-butyl substituents on each azulene ring
slightly increased the pKR+ value due to their steric effect,
and also by their inductive electronic effect induced by
the C-C hyperconjugation with the systems.
Two cation units in 4a 2+ were neutralized stepwise at
the pH of 5.6 and 8.1, respectively. Thus, the dication
4a 2+ itself is even more destabilized than the monocation
3a + by 2.5 pK units. However, the half-neutralized
monocation of 4a 2+ was as stable as the monocation 3a +.
In the case of 4b2+, two cation units were neutralized
simultaneously at the pH of 8.5. The pH corresponds to
2+
the average of the pKR value for the dication and of
+
the pKR value for the half-neutralized monocation.
The neutralization of these cations is not completely
reversible due to the instability of the neutralized
products under the conditions of the pKR+ measurement.
After the measurement, acidification of the alkaline
solutions of 3a -c+ with HCl regenerated the character-
istic absorption of the carbocations in the visible region
(19) (a) Kerber, R. C.; Hsu, H. M. J . Am. Chem. Soc. 1973, 95, 3239-
3245. (b) Komatsu, K.; Masumoto, K.; Waki, Y.; Okamoto, K. Bull.
Chem. Soc. J pn. 1982, 55, 2470-2479.
(20) Arnett E. M.; Buhick, R. D. J . Am. Chem. Soc. 1964, 86, 1564-
1571.
J . Org. Chem, Vol. 68, No. 25, 2003 9757

Ito et al.
F IGURE 4. ESR spectrum of 3a • generated by the electro-
chemical reduction in acetonitrile at room temperature: (a)
observed ESR spectrum and (b) computer simulation.
F IGURE 3. Continuous change in visible spectra of 3b+ (2
mL; 0.2 × 10-5 M) in acetonitrile containing Et4NClO4 (0.1
M) upon constant-current electrochemical reduction (100 uA)
at 10- (lines 1-7) or 20-s (lines 8-13) intervals.
pared under a vacuum line. The deep-green solution of
3b+ did not indicate any ESR signal, but the multiline
ESR spectrum in Figure 4 appeared with the color change
to deep-blue during the electrochemical reduction. This
fact indicates that the blue color originates from the
radical species of 3b•. The ESR spectrum is apparently
split into 19 lines due to hyperfine interactions. The
simulation with a g-value of 2.0024 and proton hyperfine
coupling (hfc) constants of 0.166 (9H) and 0.083 mT (6H)
well reproduced the observed spectrum.
We have performed a semiempirical UHF (Unre-
stricted Hartree-Fock) molecular orbital calculation
using an AM1 (Austin Model 1) Hamiltonian to estimate
the spin density distribution of 3• without any substitu-
ents.21 The geometry optimizations starting from several
different conformations clarified the presence of three
stereoisomers having a local minimum of potential
surface. Consideration of the stabilities of the stereoiso-
mers based on the calculated heats of formation demon-
strates that conformer C• (Figure 2) is the most stable
stereoisomer, although the difference among them is
small (Supporting Information). The spin density distri-
butions calculated for the conformers A-C• are very
similar to each other, which are characterized by the high
spin density at 2-, 3a-, 5-, 7-, and 8a-carbons and low
density at 1-, 3-, 4-, 6-, and 8-carbons on each azulene
ring regardless of the substituted positions. Therefore,
the observed ESR spectrum is reasonably explained by
the hyperfine interactions from three 2-, 5-, 7-protons and
two 4-, 8-protons on each azulene ring to exhibit nine
large and six small hfc constants, respectively. Thus, the
ESR studies for the neutral radical exhibit that the
unpaired electron delocalizes over the three azulene
rings.
than that of donor- and acceptor-substituted phenalenyl
radical 11• (Chart 5), which showed high redox stability
(E1red - E2red of phenalenyl cation 11+ is reported as 1.09
V).7 The substantial amphoteric redox property of 3a -c•
could be explained by the capto-dative substitution effect
of the azulenyl groups.
The electrochemical reduction of 4a ,b2+ showed a
barely separated, three-step reduction wave, which was
characterized by subsequent two single-electron waves
and a two-electron transfer at E1/2 ) -0.26 to -0.83 V
upon CV. The first two single-electron waves suggest the
redox interaction between the two-cation units. These
waves should correspond to the formation of radical
cation 4•+, diradical (or twitter ionic structure) 4, and
dianionic species 42-, respectively (Scheme 4).
The electrochemical oxidation of 3b+ showed a revers-
ible wave at +0.89 V and an irreversible wave at +1.29
V, due to the oxidation of azulene rings, to give a dication
radical and a tricationic species. The electrochemical
oxidation of cations 3a + and 3c+ exhibited irreversible
waves at +1.00 and +0.92 V, respectively. The oxidation
behavior of 3a -c+ is almost comparable to that of di(1-
azulenyl)phenylmethyl cations.13a The electrochemical
oxidation of 4a ,b2+ also exhibited irreversible waves at
+1.05 to +1.27 V upon CV.
When the UV-vis spectra of 3b+ were measured under
the electrochemical reduction conditions, a new absorp-
tion (602 nm) in the visible region was gradually devel-
oped as shown in Figure 3. The color of the solution
gradually changed from deep-green to deep-blue during
electrochemical reduction. On further reduction the new
band in the visible region gradually decreased accompa-
nied by the change of the deep-blue color to deep-red. The
reverse oxidation of the red-colored solution regenerated
the UV-vis spectra of the deep-green 3b+. Thus, the color
change of the solution should correspond to the formation
of anion 3b- via neutral radical 3b• in two-electron
reduction, as observed upon CV.
(21) The molecular orbital calculations were done with a Gaussian
revision E.2 program package,22 which was installed in an UNIX
workstation under a molecular design support system in IMRAM.
(22) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith, T.; Petersson,
G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Cioslowski, J .;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala,
P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts,
R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, J .;
Stewart, J . P.; Head-Gordon, M.; Gonzalez, C.; Pople, J . A. Gaussian,
revision E.2; Gaussian, Inc.: Pittsburgh, PA, 1995.
Formation of 3b• from 3b+ was confirmed by the ESR
measurements, which were carried out at room temper-
ature with use of a degassed acetonitrile solution pre-
9758 J . Org. Chem., Vol. 68, No. 25, 2003

Di(1-azulenyl)(6-azulenyl)methyl Cations
SCHEME 5
CHART 6
Con clu sion
Several di(1-azulenyl)(6-azulenyl)methyl cations 3a -
c+ and azulene-1,3-diylbis[(1-azulenyl)(6-azulenyl)meth-
yl] dications 4a ,b2+ were prepared by the hydride ab-
straction reaction of the corresponding methane deriva-
tives. These mono- and dications (3a -c+ and 4a ,b2+
)
+
exhibited high stability with large pKR values. The
monocations 3a -c+ were found to behave as a two-stage
reduction property with a small numerical sum of the
first reduction potentials (E1red) and the second one (E2red),
which exhibited the generation of a highly amphoteric
neutral radical in solution. It is noteworthy that the color
depending on the charge of 3b* exhibits three primary
colors, deep-green for monocation 3b+, deep-blue for
neutral radical 3b•, and red for anion 3b-. The dications
4a ,b2+ showed voltammograms, which were character-
ized by subsequent two single-electron waves and a two-
electron transfer upon CV attributable to the formation
of a radical cation, a diradical (or twitter ionic structure),
and a dianionic species, respectively.
The neutral radical was considerably stable probably
due to the protection by the 3′- and 6′-tert-butyl groups
and 1,3-diethoxycarbonyl substituents in addition to the
highly delocalized structure by the capto-dative substitu-
tion. Indeed, the deep blue color of the neutral radical
3b• was persistent even under aerobic conditions at room
temperature (T1/2 ) 39 min). The radical persisted for a
much longer period under degassed conditions (T1/2 ) 4.4
days).
Exp er im en ta l Section
The anion 3b- was generated as a red solution by the
reaction of 9b with potassium tert-butoxide in a tetrahy-
drofuran solution. The anion 3b- was found to be stable
at room temperature in a degassed solution. The UV-
vis spectrum of 3b- in tetrahydrofuran is shown in the
Gen er a l. For general experimental details and instrumen-
tation, see our earlier publication.9b
Dieth yl 6-F or m yla zu len e-1,3-d ica r boxyla te (7). A mix-
ture of 5 (3.72 g, 10.0 mmol), 5 wt % Pd-BaSO4 (501 mg),
and quinoline (511 mg, 3.96 mmol) in THF (150 mL) was
stirred at room temperature for 6 h under an H2 atmosphere.
After the Pd catalyst was removed by filtration, the solvent
was removed under reduced pressure. Purification of the
residue by column chromatography on silica gel with CH2Cl2
afforded 6. To a solution of 6 in 1,4-dioxane (115 mL) and water
(45 mL) was added 2 wt % osmium(VIII) oxide in 1,4-dioxane
(30.2 g, 2.38 mmol). Then, sodium periodate (6.68 g, 31.2 mmol)
was added over a period of 30 min. After the mixture was
stirred at room temperature for 5.5 d, it was poured into water
and extracted with CH2Cl2. The organic layer was washed with
water, dried with MgSO4, and concentrated under reduced
pressure. The residue was purified by column chromatography
on silica gel with CH2Cl2 to afford 7 (2.42 g, 82%) as deep green
powder. Mp 181.1-182.2 °C (hexane); [lit.12 mp 190-191 °C];
MS (70 eV) m/z (rel intensity) 300 (M+, 100%), 255 (M+ - OEt,
61), 227 (M+ - COOEt, 41); IR (KBr disk) νmax 1713 (s, CHO),
1686 (s, CdO) cm-1; UV-vis (CH2Cl2) λmax, nm (log ꢀ) 247
(4.53), 271 sh (4.18), 305 sh (4.66), 317 (4.78), 342 sh (3.84),
352 (3.93), 362 sh (3.85), 379 (3.72), 535 sh (2.57), 579 (2.70),
625 sh (2.61), 690 sh (2.12); 1H NMR (400 MHz, CDCl3) δ 10.21
(s, 1H), 9.91 (d, J ) 10.8 Hz, 2H), 8.94 (s, 1H), 8.18 (d, J )
10.8 Hz, 2H), 4.45 (q, J ) 7.1 Hz, 4H), 1.48 (t, J ) 7.1 Hz,
6H); 13C NMR (100 MHz, CDCl3) δ 193.2, 164.4, 146.7, 144.8,
1
Supporting Information. The time-averaged H and 13C
NMR spectra of 3b-, on which the isomeric propeller
conformations expected in the same way of the cation 3b+
(Figure 2) can be averaged out, were obtained at room
temperature in tetrahydrofuran-d8. The NMR spectra
exhibited large chemical shift differences for the positions
in the 6-azulenyl substituent as compared with those of
the methane derivative 9b, which correspond to most of
the negative charge residing on the 6-azulenyl substitu-
ent.
The relatively low stability of the anion 3b- under
aerobic conditions is attributable to the high reactivity
of 3b- with oxygen to produce bis(3,6-di-tert-butyl-1-
azulenyl)ketone (13) and potassium 1,3-ethoxycarbonyl-
5-formylindenide (14). The indenide 14 was isolated from
the reaction mixture as a mixture of diethyl 5- and
6-formylindene-1,3-dicarboxylate (15a and 15b) by the
treatment with acid (Chart 6). 6-Hydroxyazulene 16 did
not show the rearrangement into the indenide 14 by the
reaction with potassium tert-butoxide in tetrahydrofuran-
d8. Thus, a possible mechanism for the reaction of 3b-
with oxygen molecule could be illustrated as shown in
Scheme 5.
142.2, 138.1, 130.3, 117.8, 60.4, 14.5. Anal. Calcd for C17
16O5: C, 67.99; H, 5.37. Found: C, 67.77; H, 5.30.
Di(1-a zu len yl)(1,3-d iet h oxyca r b on yl-6-a zu len yl)m e-
-
H
th a n e (9a ). A solution of 8a (515 mg, 4.02 mmol) and 7 (601
J . Org. Chem, Vol. 68, No. 25, 2003 9759

Ito et al.
mg, 2.00 mmol) in acetic acid (21 mL) was stirred at room
temperature for 2.5 d under an Ar atmosphere. The solvent
was removed under reduced pressure. The residue was neu-
tralized with saturated NaHCO3 and extracted with CH2Cl2.
The organic layer was washed with water, dried with MgSO4,
and concentrated under reduced pressure. Purification of the
residue by column chromatography on silica gel with CH2Cl2
afforded 9a (301 mg, 28%) as blue crystals, a diastereomeric
mixture of 1,3-bis{(1-azulenyl)[1,3-bis(ethoxycarbonyl)-6-azu-
lenyl]methyl}azulene (10a ) (181 mg, 19%) as deep brown
powder, and the recovered 8a (133 mg, 26%).
142.7, 142.5, 138.4, 138.1, 136.2, 135.0, 134.8, 134.4, 132.2
(2C), 128.6, 119.8, 119.0, 115.9, 59.2, 47.3, 38.3, 33.2, 32.2, 31.8,
14.6. Anal. Calcd for C53H62O4: C, 83.42; H, 8.19. Found: C,
83.18; H, 8.43.
(1,3-Dieth oxycar bon yl-6-azu len yl)bis(6-m eth oxy-1-azu -
len yl)m eth a n e (9c). A Teflon vessel (9.1 mL) was filled with
8c (634 mg, 4.01 mmol), 7 (601 mg, 2.00 mmol), and a solution
of 50% acetic acid/CH2Cl2. The mixture was left at 10 kbar for
24 h (40 °C). The reaction mixture was worked up and
concentrated under reduced pressure. Purification of the
residue by column chromatography on silica gel with CH2Cl2
and GPC with CHCl3 afforded 9c (307 mg, 26%) as deep red
crystals, a diastereomeric mixture of 1,3-bis{[1,3-bis(ethoxy-
carbonyl)-6-azulenyl](6-methoxy-1-azulenyl)methyl}-6-meth-
oxyazulene (10b) (189 mg, 18%) as reddish brown powder, and
the recovered 8c (101 mg, 16%). The reaction of 8c (158 mg,
1.00 mmol) with 7 (149 mg, 0.496 mmol) in acetic acid (5 mL)
at room temperature for 7 h followed by chromatographic
purification on silica gel with CH2Cl2 and GPC with CHCl3
afforded 9c (67 mg, 23%), 10b (25 mg, 10%), and the recovered
8c (52 mg, 33%).
9a : mp 158.1-159.2 °C (ethyl acetate/hexane); MS (70 eV)
m/z (rel intensity) 538 (M+, 87%), 267 (M+ - C16H15O4, 100);
IR (KBr disk) νmax 1688 (s, CdO) cm-1; UV-vis (CH2Cl2) λmax
,
nm (log ꢀ) 236 (4.79), 275 (4.88), 294 (4.92), 312 (4.82), 336 sh
(4.35), 343 sh (4.32), 367 (4.36), 381 sh (4.33), 495 sh (3.08),
1
529 sh (3.03), 588 sh (2.91), 646 sh (2.76), 717 sh (2.29); H
NMR (400 MHz, CDCl3) δ 9.62 (d, J ) 11.0 Hz, 2H), 8.77 (s,
1H), 8.32 (d, J ) 9.8 Hz, 2H), 8.24 (d, J ) 9.8 Hz, 2H), 7.75 (d,
J ) 11.0 Hz, 2H), 7.55 (dd, J ) 10.0, 9.8 Hz, 2H), 7.41 (d, J )
3.8 Hz, 2H), 7.30 (d, J ) 3.8 Hz, 2H), 7.14 (dd, J ) 10.0, 9.8
Hz, 2H), 7.03 (s, 1H), 7.02 (dd, J ) 9.8, 9.8 Hz, 2H), 4.38 (q, J
) 7.1 Hz, 4H), 1.40 (t, J ) 7.1 Hz, 6H); 13C NMR (100 MHz,
CDCl3) δ 165.0, 160.3, 142.8, 142.7, 141.2, 138.4 (2C), 137.8,
137.2, 135.2, 133.7, 132.0, 131.3, 123.2, 122.5, 117.0, 116.2,
59.9, 48.0, 14.5. Anal. Calcd for C37H30O4: C, 82.50; H, 5.61.
Found: C, 82.29; H, 5.84.
9c: mp 173.5-174.4 °C (ethyl acetate/hexane); MS (70 eV)
m/z (rel intensity) 598 (M+, 86%), 442 (M+ - C11H9O + H, 100),
327 (M+ - C16H15O4, 90), 158 (C11H10O+, 50); IR (KBr disk)
ν
max 1688 (s, CdO) cm-1; UV-vis (CH2Cl2) λmax, nm (log ꢀ) 234
(4.69), 278 sh (4.77), 310 (5.06), 366 (4.47), 380 sh (4.35), 430
1
sh (3.54), 494 sh (3.22), 532 sh (3.11), 584 sh (2.76); H NMR
(400 MHz, CDCl3) δ 9.61 (d, J ) 11.3 Hz, 2H), 8.76 (s, 1H),
8.16 (d, J ) 10.8 Hz, 2H), 8.08 (d, J ) 10.9 Hz, 2H), 7.77 (d,
J ) 11.3 Hz, 2H), 7.18 (d, J ) 3.9 Hz, 2H), 7.12 (d, J ) 3.9 Hz,
2H), 6.89 (s, 1H), 6.75 (dd, J ) 10.8, 2.7 Hz, 2H), 6.63 (dd, J
) 10.9, 2.7 Hz, 2H), 4.38 (q, J ) 7.1 Hz, 4H), 3.87 (s, 6H), 1.41
(t, J ) 7.1 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 167.4, 165.1,
160.7, 142.7 (2C), 138.4, 136.7, 136.5, 134.0, 133.1, 132.6,
132.2, 131.1, 117.9, 116.0, 110.2, 109.5, 59.9, 55.8, 48.0, 14.6.
Anal. Calcd for C39H34O6: C, 78.24; H, 5.72. Found: C, 78.18;
H, 5.90.
10a : major (A):minor (B) ) 58:42; mp 216.0-217.0 °C (ethyl
acetate/hexane); MS (FAB) m/z 948 (M+); IR (KBr disk) νmax
1690 (s, CdO) cm-1; UV-vis (CH2Cl2) λmax, nm (log ꢀ) 236
(5.01), 277 (5.08), 296 (5.11), 303 (5.11), 311 sh (5.10), 336 sh
(4.59), 368 (4.61), 380 sh (4.60), 424 sh (3.82), 495 sh (3.39),
1
530 sh (3.27), 592 sh (3.09), 651 sh (2.94), 716 sh (2.51); H
NMR (600 MHz, CDCl3) for A, δ 9.51 (d, J ) 11.1 Hz, 4H),
8.73 (s, 2H), 8.28 (d, J ) 9.5 Hz, 2H), 8.24 (d, J ) 9.7 Hz, 2H),
8.12 (d, J ) 9.7 Hz, 2H), 7.64 (d, J ) 11.1 Hz, 4H), 7.54 (t and
dd, J ) 10.1 Hz and J ) 9.9, 9.9 Hz, 3H), 7.25 or 7.24 (d, J )
3.8 Hz, 2H), 7.20 (d, J ) 3.8 Hz, 2H), 7.14 (dd, J ) 9.9, 9.5 Hz,
2H), 7.04 (s, 1H), 7.01 (dd, J ) 10.1, 9.7 Hz, 2H), 6.97 (dd, J
) 9.9, 9.7 Hz, 2H), 6.96 (s, 2H), 4.38 (q, J ) 7.1 Hz, 8H), 1.40
(t, J ) 7.1 Hz, 12H); 1H NMR (600 MHz, CDCl3) for B, δ 9.50
(d, J ) 11.0 Hz, 4H), 8.76 (s, 2H), 8.27 (d, J ) 9.7 Hz, 2H),
8.23 (d, J ) 9.2 Hz, 2H), 8.02 (d, J ) 9.7 Hz, 2H), 7.62 (d, J )
11.0 Hz, 4H), 7.52 (t, J ) 10.1 Hz, 1H), 7.46 (dd, J ) 9.9, 9.7
Hz, 2H), 7.25 or 7.24 (d, J ) 3.8 Hz, 2H), 7.20 (d, J ) 3.8 Hz,
2H), 7.05 (dd, J ) 9.7, 9.2 Hz, 2H), 7.04 (dd, J ) 10.1, 9.7 Hz,
2H), 6.93 (s, 2H), 6.91 (dd, J ) 9.9, 9.7 Hz, 2H), 6.87 (s, 1H),
4.40 (q, J ) 7.1 Hz, 8H), 1.43 (t, J ) 7.1 Hz, 12H); 13C NMR
(150 MHz, CDCl3) δ 165.0 (2C), 159.9, 159.7, 142.9, 142.8,
142.7, 142.6, 141.2, 141.1, 140.3, 139.8, 138.4, 138.3 (2C or
3C), 138.2 (2C or 1C), 138.1, 137.8 (2C), 137.3, 137.2, 136.3,
136.2, 135.1 (2C), 134.4, 134.2, 133.8, 133.7, 131.9 (2C), 130.8,
130.6, 130.4, 130.3, 123.2 (2C), 123.1 (2C), 122.5, 122.3, 116.9,
116.8, 116.2 (2C), 59.9 (2C), 48.0 (2C), 14.6, 14.5. Anal. Calcd
for C64H52O8: C, 80.99; H, 5.52. Found: C, 80.72; H, 5.80.
Bis(3,6-d i-ter t-bu tyl-1-a zu len yl)(1,3-d ieth oxyca r bon yl-
6-a zu len yl)m eth a n e (9b). The same procedure as was used
for the preparation of 9a was adopted. The reaction of 8b (291
mg, 1.21 mmol) with 7 (181 mg, 0.603 mmol) in acetic acid (6
mL) at room temperature for 3.5 d followed by chromato-
graphic purification on silica gel with CH2Cl2 afforded 9b (369
mg, 80%) as dark green powder. Mp 288.0-294.0 °C dec (ethyl
acetate/hexane); MS (FAB) m/z 762 (M+); IR (KBr disk) νmax
1694 (s, CdO) cm-1; UV-vis (CH2Cl2) λmax, nm (log ꢀ) 236
(4.72), 279 (4.87), 304 (5.02), 339 sh (4.38), 375 (4.34), 435 sh
(3.61), 523 sh (3.20), 602 sh (2.85), 663 sh (2.72), 734 sh (2.22);
1H NMR (400 MHz, CDCl3) δ 9.60 (d, J ) 11.0 Hz, 2H), 8.74
(s, 1H), 8.60 (d, J ) 10.6 Hz, 2H), 8.15 (d, J ) 10.6 Hz, 2H),
7.73 (d, J ) 11.0 Hz, 2H), 7.35 (s, 2H), 7.23 (dd, J ) 10.6, 2.0
Hz, 2H), 7.10 (dd, J ) 10.6, 2.0 Hz, 2H), 6.93 (s, 1H), 4.38 (q,
J ) 7.1 Hz, 4H), 1.50 (s, 18H), 1.41 (t, J ) 7.1 Hz, 6H), 1.40
(s, 18H); 13C NMR (100 MHz, CDCl3) δ 165.2, 161.3, 161.0,
10b: major (A):minor (B) ) 58:42; mp 159.2-161.0 °C (ethyl
acetate/hexane); MS (FAB) m/z 1038 (M+); IR (KBr disk) νmax
1690 (s, CdO) cm-1; UV-vis (CH2Cl2) λmax, nm (log ꢀ) 234
(4.96), 277 (4.96), 311 (5.26), 367 (4.71), 381 sh (4.64), 440 sh
(3.81), 491 sh (3.57), 529 sh (3.39), 584 sh (3.02); 1H NMR (600
MHz, acetone-d6) for A, δ 9.47 (d, J ) 10.0 Hz, 4H), 8.55 (s,
2H), 8.31 (d, J ) 11.1 Hz, 2H), 8.23 (d, J ) 10.9 Hz, 2H), 8.14
(d, J ) 10.7 Hz, 2H), 7.82 (d, J ) 10.0 Hz, 4H), 7.10 (d, J )
3.9 Hz, 2H), 7.07 (s, 2H), 7.07 (d, J ) 3.9 Hz, 2H), 6.97 (s,
1H), 6.78 (dd, J ) 10.7, 2.3 Hz, 2H), 6.71 (d, J ) 11.1 Hz, 2H),
6.69 (dd, J ) 10.9, 2.3 Hz, 2H), 4.31 (q, J ) 7.1 Hz, 8H), 3.89
1
(s, 6H), 3.83 (s, 3H), 1.35 (t, J ) 7.1 Hz, 12H); H NMR (600
MHz, acetone-d6) for B, δ 9.53 (d, J ) 11.0 Hz, 4H), 8.61 (s,
2H), 8.34 (d, J ) 11.1 Hz, 2H), 8.18 (d, J ) 10.9 Hz, 2H), 8.10
(d, J ) 10.7 Hz, 2H), 7.85 (d, J ) 11.0 Hz, 4H), 7.07 (s, 2H),
7.06 (d, J ) 4.1 Hz, 2H), 7.05 (d, J ) 4.1 Hz, 2H), 6.94 (s, 1H),
6.73 (dd, J ) 10.7, 2.5 Hz, 2H), 6.72 (d, J ) 11.1 Hz, 2H), 6.65
(dd, J ) 10.9, 2.5 Hz, 2H), 4.34 (q, J ) 7.1 Hz, 8H), 3.87 (s,
6H), 3.83 (s, 3H), 1.36 (t, J ) 7.1 Hz, 12H); 13C NMR (150 MHz,
acetone-d6) δ 168.9 (2C), 168.5 (2C), 165.0, 164.9, 162.4, 162.3,
143.1 (2C), 142.6 (2C), 139.1, 139.0, 137.6, 137.5, 137.4, 137.3,
136.1, 136.0, 134.9, 134.8, 134.5, 134.3 (2C), 134.1, 133.3,
133.2, 133.0 (2C), 132.8 (4C), 131.9 (2C), 118.7, 118.6, 116.8,
116.7, 111.2, 110.9, 110.7, 110.6, 110.4, 110.0, 60.4, 60.3, 56.4,
56.3, 48.4 (2C), 14.8 (2C). Anal. Calcd for C67H58O11: C, 77.44;
H, 5.63. Found: C, 77.15; H, 5.88.
Di(1-a zu len yl)(1,3-d ieth oxyca r bon yl-6-a zu len yl)m eth -
yliu m Hexa flu or op h osp h a te (3a ‚P F 6-). DDQ (54 mg, 0.238
mmol) was added at room temperature to a solution of 9a (105
mg, 0.195 mmol) in CH2Cl2 (5 mL). After the solution was
stirred at room temperature for 10 min, 60% aqueous HPF6
(2 mL) and water (20 mL) were added to the reaction mixture.
The resulting suspension was filtered with suction. The organic
layer was separated, washed with water, dried with MgSO4,
and concentrated under reduced pressure. The residue was
9760 J . Org. Chem., Vol. 68, No. 25, 2003

Di(1-azulenyl)(6-azulenyl)methyl Cations
dissolved in a small amount of CH2Cl2 and then poured into
ether. The precipitated crystals were collected by filtration,
washed with ether, and dried in vacuo to give 3a ‚PF6- (93 mg,
70%) as a green powder. Mp 150.2-152.0 °C dec; MS (FAB)
m/z 682 (M+), 537 (M+ - PF6); IR (KBr disk) νmax 1690 (s, Cd
712 (4.30). Anal. Calcd for C64H50O8P2F12: C, 62.14; H, 4.07.
Found: C, 62.15; H, 4.23.
6-Meth oxya zu len e-1,3-d iylbis[(1,3-d ieth oxyca r bon yl-
6-a zu len yl)(6-m eth oxy-1-a zu len yl)m eth yliu m ] Bis(h exa -
flu or op h osp h a te) (4b‚2P F 6-). The same procedure as was
used for the preparation of 3a ‚PF6- was adopted. The reaction
of 10b (187 mg, 0.180 mmol) with DDQ (99 mg, 0.44 mmol) in
CH2Cl2 (15 mL) at room temperature for 10 min followed by
the treatment with 60% aqueous HPF6 (2 mL) and water (15
mL) afforded 4b‚2PF6- (179 mg, 75%) as a dark green powder.
Mp 209.5-211.0 °C dec; MS (FAB) m/z 1181 (M+ - PF6), 1036
(M+ - 2PF6); IR (KBr disk) νmax 1692 (s, CdO), 841 (s, PF6-),
558 (m, PF6-) cm-1; UV-vis (MeCN) λmax, nm (log ꢀ) 227 (4.76),
255 (4.77), 301 sh (4.65), 357 (4.78), 421 sh (4.46), 603 (4.21),
712 (4.46). Anal. Calcd for C67H56O11P2F12: C 60.64; H, 4.25.
Found: C, 60.90; H, 4.23.
P otassiu m bis(3,6-di-ter t-bu tyl-1-azu len yl)(1,3-dieth oxy-
ca r bon yl-6-a zu len yl)m eth ylid e (K+‚3b-): 1H NMR (600
MHz, tetrahydrofuran-d8) δ 8.46 (d, J ) 10.4 Hz, 2H), 8.19
(br d, J ) 10.0 Hz, 2H), 7.26 (br s, 2H), 7.16 (dd, J ) 10.4, 1.9
Hz, 2H), 7.13 (s, 1H), 7.12 (br d, J ) 10.0 Hz, 2H), 7.05 (d, J
) 12.6 Hz, 2H), 5.89 (d, J ) 12.6 Hz, 2H), 4.11 (q, J ) 7.1 Hz,
4H), 1.53 (s, 18H), 1.49 (s, 18H), 1.28 (t, J ) 7.1 Hz, 6H); 13C
NMR (150 MHz, tetrahydrofuran-d8) δ 169.0, 161.7, 144.5,
139.7, 139.6, 138.7, 137.6, 135.5, 135.4, 132.6, 128.7, 128.2,
126.4, 121.1, 120.2, 119.0, 114.1, 59.5, 40.0, 35.2, 34.0, 33.5,
16.6. A signal is missing.
Rea ction of K+‚3b- w ith Oxygen . To a solution of 9b (111
mg, 0.145 mmol) in tetrahydrofuran (10 mL) was added
t-BuOK (555 mg, 4.95 mmol). After the solution was stirred
at room temperature for 90 min under an oxygen atmosphere,
the reaction mixture was poured into water and extracted with
CH2Cl2. The organic layer was dried with MgSO4 and concen-
trated under reduced pressure. Purification of the residue by
column chromatography on silica gel with CH2Cl2 afforded bis-
(3,6-di-tert-butyl-1-azulenyl)ketone (13) (40 mg, 54%) as purple
crystals. The aqueous layer was acidified with 2 N HCl and
extracted with CH2Cl2. The organic layer was dried with
MgSO4 and concentrated under reduced pressure. Purification
of the residue by GPC with CHCl3 afforded a mixture of diethyl
5- and 6-formylindene-1,3-dicarboxylate (15a and 15b) (12 mg,
29%).
O), 841 (s, PF6-), 558 (m, PF6-) cm-1; UV-vis (MeCN) λmax
,
nm (log ꢀ) 237 (4.66), 254 (4.66), 293 (4.54), 310 (4.55), 361
(4.53), 376 sh (4.66), 422 sh (4.10), 467 sh (3.87), 675 (4.42);
1H NMR (600 MHz, CDCl3) δ 9.82 (d, J ) 10.5 Hz, 2H), 9.05
(s, 1H), 8.83 (d, J ) 9.6 Hz, 2H), 8.19 (dd, J ) 9.7, 9.7 Hz,
2H), 8.11 (dd, J ) 9.7, 9.6 Hz, 2H), 8.06 (d, J ) 9.7 Hz, 2H),
7.77 (d, J ) 4.5 Hz, 2H), 7.75 (d, J ) 10.5 Hz, 2H), 7.74 (d, J
) 4.5 Hz, 2H), 7.66 (dd, J ) 9.7, 9.7 Hz, 2H), 4.46 (q, J ) 7.1
Hz, 4H), 1.47 (t, J ) 7.1 Hz, 6H); 13C NMR (150 MHz, CDCl3)
δ 164.5 (2C), 154.8, 153.1, 148.1, 146.7, 146.1, 144.4, 143.9,
141.9, 140.3, 137.2, 136.9, 136.3, 134.6, 134.4, 127.9, 118.3,
60.6, 14.5. Anal. Calcd for C37H29O4PF6: C, 65.11; H, 4.28.
Found: C, 64.90; H, 4.38.
Bis(3,6-d i-ter t-bu tyl-1-a zu len yl)(1,3-d ieth oxyca r bon yl-
6-a zu len yl)m eth yliu m Hexa flu or op h osp h a te (3b‚P F 6-).
-
The same procedure as was used for the preparation of 3a ‚PF6
was adopted. The reaction of 9b (380 mg, 0.498 mmol) with
DDQ (136 mg, 0.599 mmol) in CH2Cl2 (50 mL) at room
temperature for 10 min followed by the treatment with 60%
aqueous HPF6 (5 mL) and water (50 mL) afforded 3b‚PF6- (361
mg, 80%) as a deep green powder. Mp >300 °C; MS (FAB) m/z
761 (M+ - PF6); IR (KBr disk) νmax 1694 (s, CdO), 841 (s, PF6-),
558 (m, PF6-) cm-1; UV-vis (MeCN) λmax, nm (log ꢀ) 226 sh
(4.72), 254 (4.80), 330 (4.63), 364 (4.69), 447 sh (4.10), 497 sh
1
(3.87), 720 (4.59); H NMR (600 MHz, CDCl3) δ 9.84 (d, J )
10.5 Hz, 2H), 9.06 (d, J ) 11.0 Hz, 2H), 9.04 (s, 1H), 8.21 (dd,
J ) 11.0, 2.0 Hz, 2H), 7.90 (br d, J ) 10.1 Hz, 2H), 7.80 (br d,
J ) 10.5 Hz, 2H), 7.69 (br d, J ) 10.1 Hz, 2H), 7.36 (br s, 2H),
4.47 (q, J ) 7.1 Hz, 4H), 1.54 (s, 18H), 1.48 (t, J ) 7.1 Hz,
6H), 1.44 (s, 18H); 13C NMR (150 MHz, CDCl3) δ 169.8, 164.7,
159.9, 153.7, 150.0, 148.6 (2C), 146.1, 143.9, 141.9, 139.6,
138.9, 137.3, 134.5, 133.5 (2C), 132.6, 118.0, 60.5, 39.5, 33.4,
31.5, 31.0, 14.5. Anal. Calcd for C53H61O4PF6: C, 70.18; H, 6.78.
Found: C, 70.07; H, 6.78.
Bis(6-m eth oxy-1-azu len yl)(1,3-dieth oxycar bon yl-6-azu -
len yl)m eth yliu m Hexa flu or op h osp h a te (3c‚P F 6-). The
-
same procedure as was used for the preparation of 3a ‚PF6
was adopted. The reaction of 9c (91 mg, 0.15 mmol) with DDQ
(42 mg, 0.19 mmol) in CH2Cl2 (15 mL) at room temperature
for 10 min followed by the treatment with 60% aqueous HPF6
(1.5 mL) and water (15 mL) afforded 3c‚PF6- (99 mg, 88%) as
a green powder. Mp 146.5-147.8 °C dec; MS (FAB) m/z 742
(M+), 597 (M+ - PF6); IR (KBr disk) νmax 1690 (s, CdO), 841
(s, PF6-), 558 (m, PF6-) cm-1; UV-vis (MeCN) λmax, nm (log ꢀ)
225 (4.57), 252 (4.61), 300 (4.46), 348 (4.65), 364 (4.66), 422
13: mp 212.8-214.2 °C; MS (70 eV) m/z (rel intensity) 506
(M+, 100), 491 (M+ - Me, 64), 449 (M+ - t-Bu, 56); IR (KBr
disk) νmax 1582 (s, CdO) cm-1; UV-vis (CH2Cl2) λmax, nm (log
ꢀ) 295 (4.64), 329 (4.49), 427 (4.36), 549 (3.04), 594 sh (2.90),
1
655 sh (2.34); H NMR (400 MHz, CDCl3) δ 9.50 (d, J ) 10.6
Hz, 2H), 8.79 (d, J ) 10.9 Hz, 2H), 8.05 (s, 2H), 7.60 (dd, J )
10.6, 1.9 Hz, 2H), 7.55 (dd, J ) 10.9, 1.9 Hz, 2H), 1.59 (s, 18H),
1.48 (s, 18H); 13C NMR (100 MHz, CDCl3) δ 188.9, 162.9, 140.8,
139.5, 138.2, 137.8, 137.0, 136.2, 126.4, 125.2, 122.8, 38.5, 33.0,
31.9, 31.8. Anal. Calcd for C37H46O: C, 87.69; H, 9.15. Found:
C, 87.81; H, 9.15.
1
sh (4.22), 668 (4.53); H NMR (600 MHz, CDCl3) δ 9.81 (d, J
) 10.7 Hz, 2H), 9.03 (s, 1H), 8.59 (d, J ) 11.2 Hz, 2H), 7.88
(d, J ) 11.2 Hz, 2H), 7.74 (d, J ) 10.8 Hz, 2H), 7.61 (dd, J )
11.2, 2.9 Hz, 2H), 7.51 (d, J ) 4.6 Hz, 2H), 7.37 (d, J ) 4.6 Hz,
2H), 7.16 (dd, J ) 11.2, 2.9 Hz, 2H), 4.46 (q, J ) 7.1 Hz, 4H),
4.07 (s, 6H), 1.47 (t, J ) 7.1 Hz, 6H); 13C NMR (150 MHz,
CDCl3) δ 172.9, 164.6, 163.2, 153.8, 149.5, 146.3, 143.9, 142.4,
141.3, 141.1, 139.8, 137.0, 135.2, 134.8, 127.7, 124.4, 120.7,
118.0, 60.5, 57.6, 14.5. Anal. Calcd for C39H33O6PF6: C, 63.08;
H, 4.48. Found: C, 62.80; H, 4.67.
15a a n d 15b: major [A (15b)]:minor [B (15a )] ) 64:36;
colorless oil; MS (70 eV) m/z (rel intensity) 288 (M+, 92%), 216
(M+ - COOEt + H, 100); IR (neat) νmax 1732 (s, CdO), 1717
(s, CdO), 1700 (s, CdO) cm-1; UV-vis (CH2Cl2) λmax, nm (log
ꢀ) 230 (4.08), 254 (3.96), 290 (3.83), 397 sh (2.24); 1H NMR
(400 MHz, C6D6) for A, δ 9.73 (s, 1H), 8.24 (d, J ) 7.8 Hz, 1H),
8.17 (s, 1H), 7.55 (d, J ) 7.8 Hz, 1H), 7.39 (d, J ) 2.2 Hz, 1H),
4.08-3.98 (m, 3H), 3.84-3.75 (m, 2H), 1.00-0.95 (m, 3H),
0.84-0.80 (m, 3H); 1H NMR (400 MHz, C6D6) for B, δ 9.73 (s,
1H), 8.64 (s, 1H), 7.61 (d, J ) 7.8 Hz, 1H), 7.57 (d, J ) 7.8 Hz,
1H), 7.32 (d, J ) 2.2 Hz, 1H), 4.08-3.98 (m, 3H), 3.84-3.75
(m, 2H), 1.00-0.95 (m, 3H), 0.84-0.80 (m, 3H); 13C NMR (100
MHz, C6D6) δ 191.3, 191.1, 167.3 (2C), 163.0, 162.9, 146.7,
146.1, 145.4, 142.8, 141.6, 141.4, 137.2, 137.0, 136.9, 135.5,
131.1, 127.8, 125.2, 124.8, 124.6, 123.5, 61.7, 60.8, 55.1, 54.8,
14.1, 13.9.
Azu len e-1,3-d iylbis[(1-a zu len yl)(1,3-d ieth oxyca r bon yl-
6-a zu len yl)m et h yliu m ] Bis(h exa flu or op h osp h a t e) (4a ‚
2P F 6-). The same procedure as was used for the preparation
-
of 3a ‚PF6 was adopted. The reaction of 10a (138 mg, 0.145
mmol) with DDQ (81 mg, 0.36 mmol) in CH2Cl2 (15 mL) at
room temperature for 10 min followed by the treatment with
60% aqueous HPF6 (2 mL) and water (20 mL) afforded
-
4a ‚2PF6 (140 mg, 78%) as a dark green powder. Mp 215.2-
216.5 °C dec; MS (FAB) m/z 1091 (M+ - PF6), 946 (M+ - 2PF6);
-
IR (KBr disk) νmax 1692 (s, CdO), 843 (s, PF6-), 558 (m, PF6
)
P ota ssiu m 1,3-eth oxyca r bon yl-5-for m ylin d en id e (14):
1H NMR (400 MHz, tetrahydrofuran-d8) δ 9.82 (s, 1H), 8.53
(s, 1H), 8.09 (d, J ) 8.3 Hz, 1H), 7.96 (s, 1H), 7.36 (d, J ) 8.3
cm-1; UV-vis (MeCN) λmax, nm (log ꢀ) 227 (4.60), 225 (4.61),
301 (4.49), 357 (4.62), 421 sh (4.30), 466 sh (4.23), 603 (4.06),
J . Org. Chem, Vol. 68, No. 25, 2003 9761

Ito et al.
Hz, 1H), 4.23 (q, J ) 6.8 Hz, 2H), 4.21 (q, J ) 6.8 Hz, 2H),
1.32 (t, J ) 6.8 Hz, 2H), 1.31 (t, J ) 6.8 Hz, 2H); 13C NMR
(100 MHz, tetrahydrofuran-d8) δ 193.4, 167.6, 167.4, 139.5,
135.1, 134.2, 128.6, 126.7, 120.5, 118.5, 107.1, 106.1, 58.5 (2C),
15.3 (2C).
Ack n ow led gm en t. The present work was supported
by a Grant-in-Aid for Scientific Research (No. 14540486
to S.I. and No. 15310069 to T.I.) from the Ministry of
Education, Culture, Sports, Science, and Technology,
J apan. T.I. also thanks the Showa Shell Sekiyu Foun-
dation for Promotion of Environmental Research and
the Murata Science Foundation for financial support.
Sp ectr oelectr ogr a m Mea su r em en ts. A sample solution
was prepared by dissolving 3b+‚PF6- in acetonitrile containing
Et4NClO4 (0.1 M) and was degassed through an Ar stream.
Spectroelectrogram measurements of 3b+ were carried out in
a quarts cell (1 × 10 × 35 mm) equipped with a Pt mesh and
a wire as working and counter electrodes, respectively, which
were separated by a grass filter. Electrical current was
monitored by a microampere meter. Spectroelectrograms were
measured on a fiber optic spectrometer at 10- or 20-s intervals.
Su p p or tin g In for m a tion Ava ila ble: CV data for 3b+ and
4b2+, optimized structure of 3b•, 1H NMR spectra of 4a ,b2+
‚
2PF6-, K+‚3b-, a mixture of 15a ,b, and 14, and UV-vis
spectrum of 3b-. This material is available free of charge via
the Internet at http://pubs.acs.org.
J O035053O
9762 J . Org. Chem., Vol. 68, No. 25, 2003