Synthesis, properties, and redox behavior of mono-, bis-, and tris[1,1,4,4,-tetracyano-2-(1-azulenyl)-3-butadienyl] chromophores binding with benzene and thiophene cores

Article abstract of DOI:10.1002/chem.200701981

Mono-, bis-, tris-, and tetrakis(1-azulenylethynyl)benzene and mono- and bis(1-azulenylethynyl)thiophene derivatives 5-10 have been prepared by Pd-catalyzed alkynylation of ethynyl arenes with 1-iodoazulene derivative or the 1-ethynylazulene derivative with tetraiodobenzene and iodothiophenes under Sonogashira-Hagihara conditions. Compounds 5-10 reacted with tetracyanoethylene in a [2+2] cycloaddition reaction to afford the corresponding 1,1,4,4,-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-3-butadienyl chromophores 12-16 in excellent yields, except for the reaction of the tetrakis(1-azulenylethynyl)benzene derivative. 1,1,4,4,-Tetracyano-2,3-bis(1- azulenyl)butadiene (17) was also prepared by the similar reaction of bis(1-azulenyl)acetylene (11) with tetracyanoethylene (TCNE). The redox behavior of novel azulene derivatives 12-17 was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed multistep electrochemical reduction properties. Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions.

Full text of DOI:10.1002/chem.200701981

DOI: 10.1002/chem.200701981
Synthesis, Properties, and Redox Behavior of Mono-, Bis-, and Tris[1,1,4,4,-
tetracyano-2-(1-azulenyl)-3-butadienyl] Chromophores Binding with
Benzene and Thiophene Cores
Taku Shoji,*[a] Shunji Ito,[b] Kozo Toyota,[a] Masafumi Yasunami,[c] and
Noboru Morita*[a]
Abstract: Mono-, bis-, tris-, and tetra-
kis(1-azulenylethynyl)benzene and
the corresponding 1,1,4,4,-tetracyano-2-
(5-isopropyl-3-methoxycarbonyl-1-azu-
lenyl)-3-butadienyl chromophores 12–
16 in excellent yields, except for the re-
action of the tetrakis(1-azulenylethy-
nyl)benzene derivative. 1,1,4,4,-Tetra-
cyano-2,3-bis(1-azulenyl)butadiene (17)
was also prepared by the similar reac-
tion of bis(1-azulenyl)acetylene (11)
with tetracyanoethylene (TCNE). The
redox behavior of novel azulene deriv-
atives 12–17 was examined by cyclic
voltammetry (CV) and differential
pulse voltammetry (DPV), which re-
vealed multistep electrochemical re-
duction properties. Moreover, a signifi-
cant color change was observed by visi-
ble spectroscopy under electrochemical
reduction conditions.
mono- and bis(1-azulenylethynyl)thio-
phene derivatives 5–10 have been pre-
pared by Pd-catalyzed alkynylation of
ethynyl arenes with 1-iodoazulene de-
rivative or the 1-ethynylazulene deriva-
tive with tetraiodobenzene and iodo-
thiophenes under Sonogashira–Hagi-
hara conditions. Compounds 5–10 re-
Keywords: azulenes · cycloaddition ·
electrochemistry · photochromism
acted with tetracyanoethylene in
a
[2+2] cycloaddition reaction to afford
Introduction
rich alkynes with TCNE affords [2+2] cycloaddition prod-
ucts, namely cyclobutene derivatives, which exhibit a ring-
opening reaction to give the corresponding 1,1,4,4-tetracya-
no-1,3-butadienes (TCBDs).[2] Recently, Yamashita and co-
workers reported that 1,3-dithiol-2-ylidene derivatives react
with TCNE to afford the corresponding [2+2] cycloadducts
that show amphoteric redox behavior.[3] Diederich et al. re-
Tetracyanoethylene (TCNE) is known to be a strong organic
electron acceptor. The high reactivity of TCNE toward nu-
cleophiles or electron-rich reagents is frequently used to in-
troduce strong acceptor moieties into organic molecules.[1]
In 1981, Bruce et al. reported that the reaction of electron-
ported that
a variety of N,N-dialkylaniline-substituted
(DAA-substituted) alkynes react with TCNE to give DAA-
donor-substituted TCBDs in excellent yields. They also re-
ported that the new class of chromophores is characterized
by intense intramolecular charge-transfer (CT) interactions
with absorption maxima in the visible region as well as
promising third-order optical nonlinearities.[4]
[a] T. Shoji, Prof. Dr. K. Toyota, Prof. Dr. N. Morita
Department of Chemistry, Graduate School of Science
Tohoku University
Sendai 980-8578 (Japan)
Fax : (+81)22-795-7714
E-mail: shoji-azulene@m.tains.tohoku.ac.jp
nmorita@m.tains.tohoku.ac.jp
Azulene (C10H8) has attracted the interest of many re-
search groups owing to its unusual properties as well as its
beautiful blue color.[5] In the initial studies of Hafner et al.,
it is reported that the reaction of azulene with TCNE gives
1-(1,2,2-tricyanoethenyl)azulene via a CT complex between
azulene and TCNE.[6] Recently, Hafner et al. also reported
the preparation of 1-, 2-, and 5-ethynylazulenes utilizing a
Pd-catalyzed cross-coupling reaction under Sonogashira–
Hagihara conditions and/or a Cory–Fuchs alkyne synthesis.
We have also reported the synthesis of 2- and 6-ethynylazu-
[b] Prof. Dr. S. Ito
Graduate School of Science and Technology
Hirosaki University
Hirosaki 036-8561 (Japan)
[c] Prof. Dr. M. Yasunami
Department of Materials Chemistry and Engineering
College of Engineering
Nihon University
Koriyama 963-8642 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200701981.
8398
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FULL PAPER
lene derivatives using a similar Pd-catalyzed reaction.[7]
However, the reaction between ethynylazulenes and TCNE
has not yet been examined. Similar to the DAA-substituent,
the 1-position of the azulene ring possesses electron-donat-
ing properties with high reactivity toward electrophilic sub-
stitution reactions. Thus, 1-ethynylazulene derivatives should
be expected to afford [2+2] cycloaddition products with
TCNE. Furthermore, azulene-substituted TCBDs may ex-
hibit multistage redox behavior similar to that of DAA-sub-
stituted TCBDs as well as polyelectrochromic electrochemi-
cal reactions.[4]
We describe herein the synthesis of mono-, bis-, tris-, and
tetrakis(1-azulenylethynyl)benzene and mono- and bis
(1-azulenylethynyl)thiophene derivatives under Sonoga-
shira–Hagihara reaction conditions as well as the reactivity
of the products toward the [2+2] cycloaddition reaction
with TCNE to afford the corresponding 1,1,4,4,-tetracyano-
2-(1-azulenyl)-3-butadienyl chromophores. The electronic
properties of the novel azulene derivatives are characterized
by electrochemical analysis and absorption spectroscopy.
thesis of the azulene-substituted TCBDs by considering
their stability and the improvement of solubility.
Preparation of the corresponding poly(1-azulenylethynyl)-
benzene derivatives 5, 6, 7, and 8 was accomplished by a
simple one-pot reaction involving repeated Pd-catalyzed al-
kynylation of the corresponding ethynylbenzenes with 2 or
the 1-ethynylazulene 4 with 1,2,4,5-tetraiodobenzene under
Sonogashira–Hagihara conditions. The cross-coupling reac-
tion of 2 with phenylacetylene using [PdCAHTRE(UNG PPh3)4] as a cata-
lyst and subsequent chromatographic purification on silica
gel afforded the desired methyl 7-isopropyl-3-(phenylethy-
nyl)azulene-1-carboxylate (5) in 95% yield (Scheme 2).
Scheme 2.
Likewise, the reaction of 2 with 1,4-diethynylbenzene
Results and Discussion
ACHTREaUNG fforded 1,4-bis[(5-isopropyl-3-methoxycarbonyl-1-azulenyl)
ethynyl]benzene (6) in 91% yield (Scheme 3). The cross-
Synthesis: Methyl 7-isopropylazulene-1-carboxylate (1),
which can readily be prepared by Yasunami–Takaseꢁs
method using the reaction of 5-isopropyl-3-methoxycarbon-
yl-2H-cyclohepta[b]furan-2-one with acetaldehyde in the
presence of diethylamine,[8] reacted with N-iodosuccineimide
(NIS) in dichloromethane at room temperature to afford
methyl 3-iodo-7-isopropylazulene-1-carboxylate (2) in 92%
yield. The 1-ethynylazulene derivative 4 was synthesized by
the Sonogashira–Hagihara reaction.[9] The cross-coupling re-
action of 2 with trimethylsilylacetylene and [PdACHTRE(UGN PPh3)4] as a
Scheme 3.
catalyst at 508C gave methyl 3-trimethylsilylethynyl-7-iso-
propylazulene-1-carboxylate (3) in 97% yield. Treatment of
3 with K2CO3 in a mixed solvent of MeOH/THF/water af-
forded methyl 3-ethynyl-7-isopropylazulene-1-carboxylate
(4) in 95% yield (Scheme 1). Although 1-iodoazulene and
1-ethynylazulene derivatives are usually unstable com-
pounds, 2, 3, and 4 are stable and showed no decomposition
even after several weeks at room temperature. Thus, these
azulene derivatives are utilized in further studies on the syn-
coupling reaction of 2 with 1,3,5-triethynylbenzene[10] in the
presence of the Pd catalyst afforded 1,3,5-tris[(5-isopropyl-3-
methoxycarbonyl-1-azulenyl)ethynyl]benzene (7) in 84%
yield (Scheme 4). 1,2,4,5-Tetrakis[(5-isopropyl-3-methoxy-
carbonyl-1-azulenyl)ethynyl]benzene (8) was prepared by a
similar Pd-catalyzed reaction of 4 with 1,2,4,5-tetraiodoben-
zene[11] in 77% yield (Scheme 5).
Methyl 7-isopropyl-3-(2-thienylethynyl)azulene-1-carbox-
ylate (9) and 2,5-bis[(5-isopropyl-3-methoxycarbonyl-1-azu-
lenyl)ethynyl]thiophene (10) were also synthesized by Pd-
catalyzed alkynylation of 4 with the corresponding iodothio-
phenes. Reaction of 4 with 2-iodothiophene in the presence
of [Pd
(Scheme 6). Bis-adduct 10 was obtained by the reaction of 4
with 2,5-diiodothiophene in the presence of [Pd(PPh3)4] in
72% yield, along with mono-adduct in 9% yield
A
9
in 93% yield
AHCTREUNG
9
(Scheme 7). A similar Pd-catalyzed reaction of 2 with 4 af-
forded bis(5-isopropyl-3-methoxycarbonyl-1-azulenyl)acety-
lene (11) in 94% yield (Scheme 8). These compounds (5–
11) possess fair solubility in chloroform, dichloromethane,
Scheme 1.
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T. Shoji, N. Morita et al.
Scheme 8.
to the procedure described in the literature to give the azu-
lene-substituted TCBDs.[4] The reaction of 5 with TCNE in
ethyl acetate at room temperature yielded 12 in 96% yield
(Scheme 9). Likewise, the reaction of 6 and 7 with TCNE
Scheme 4.
Scheme 9.
AHCTREaUNG fforded 13 and 14 in 96% and 91% yields, respectively
(Schemes 10 and 11). It is noteworthy that these reactions
readily proceeded under mild conditions, although the elec-
tron-withdrawing group, the methoxycarbonyl group, is sub-
stituted on the azulene ring. The high reactivity can be at-
tributed to the highly electron-donating properties of the
azulene ring at the 1-position.
Scheme 5.
Scheme 6.
Scheme 10.
In contrast to these results, the reaction of 8 with TCNE
formed an insoluble complex mixture. Diederich et al. have
reported that the reaction of o-phenylene derivatives with
TCNE does not produce the expected [2+2] cycloadducts
because of the steric effect that prevents the presumed cy-
cloaddition reaction of alkyne with TCNE.[4b] In the cases of
the reaction of 8, therefore, the formation of a complex mix-
ture should be attributable to similar steric reasons.
Scheme 7.
and so on. Moreover, they are stable and show no decompo-
sition even after several weeks at room temperature.
The [2+2] cycloaddition reaction of mono-, bis-, tris-, and
tetrakis(1-azulenylethynyl)benzene and mono- and bis(1-
azulenylethynyl)thiophene along with bis(1-azulenyl)acety-
lene derivatives 5–11 with TCNE was examined according
Similar to the results of the benzene derivatives, the reac-
tion of 9 and 10 with TCNE afforded 15 and 16 in 86% and
97% yields, respectively (Schemes 12 and 13). The [2+2] cy-
cloaddition reaction of 11 with TCNE also proceeded under
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Azulene Chromophores
FULL PAPER
ꢀ
exhibited characteristic C N stretching at n˜ =2220 or
2222 cmÀ1 in their IR spectra. These results are consistent
with the structure of these products. The UV-visible spectra
of 5–11 showed characteristic weak absorptions arising from
the azulene system in the visible region. The extinction coef-
ficients increased with the number of azulene rings
AHCTREUNG
are shown in Figures 1 and 2, respectively. As expected from
their resonance structures (Scheme 15), TCNE adducts 12–
Scheme 11.
Scheme 12.
Figure 1. UV/Vis spectra of 12 (c), 13 (c), and 14 (a) in dichloro-
methane.
Scheme 13.
mild conditions to give 17 in 97% yield (Scheme 14). These
new compounds 12–17 are stable, deep-colored crystals and
can be stored in the crystalline state at room temperature.
Figure 2. UV/Vis spectra of 15 (c) and 16 (a) in dichloromethane.
17 showed characteristic CT absorption in the visible region.
Their absorption maxima and coefficients (loge) are sum-
marized in Table 1. Compound 12 exhibited two relatively
weak CT absorptions at l=462 and 534(sh) nm. Compound
13 exhibited strong and weak CT absorptions at l=444 and
540(sh) nm, respectively. The longest CT absorption showed
a bathochromic shift of 6 nm compared to that of 12, proba-
bly due to expansion of the p-conjugation. In compound 13,
two strong CT absorptions were observed at l=414 and
550 nm. The longest CT absorption also exhibited a further
bathochromic shift compared to those of 12 and 13. Com-
pound 15 showed a relatively weak CT absorption, com-
Scheme 14.
Spectroscopic properties: Compounds 5–17 were fully char-
acterized by the spectral data as shown in the Experimental
Section. Mass spectra of 5–17 ionized by ESI showed the
correct molecular ion peaks. The characteristic stretching-
vibration band of the ethynyl group of 5–10 was observed at
n˜ =2187–2201 cmÀ1 in their IR spectra. Compounds 12–17
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T. Shoji, N. Morita et al.
mainly concentrated on the azulene moiety and on the cya-
novinyl moiety adjoined to the azulene ring. The LUMO
was concentrated on the benzene ring and included the cya-
novinyl moiety adjoined to the benzene ring. Examination
of the HOMO and the LUMO of 17 also showed a similar
CT character in the HOMO–LUMO transition, although
the LUMO is mostly localized on an azulene ring. Thus, the
longer wavelength absorption in the visible region may in-
clude intramolecular CT character from the azulene ring to
the other connecting group.
Redox potentials: To clarify the electrochemical proper-
ties, the redox behavior of 5–17 was examined by cyclic vol-
tammetry (CV) and differential pulse voltammetry (DPV).
Measurements were carried out with a standard three-elec-
trode configuration. Tetraethylammonium perchlorate
(0.1m) in benzonitrile was used as a supporting electrolyte
with platinum wire auxiliary and working electrodes. All
measurements were carried out under an argon atmosphere,
and potentials were related to an Ag/Ag+ reference elec-
trode and Fc/Fc+ as an internal reference, which discharges
at +0.15 V. The redox potentials (in volts vs Ag/AgNO3) of
12–17 are summarized in Table 3. The redox potentials of 5–
11 and oxidation potentials of 5–17 are summarized in the
Supporting Information.
Scheme 15. Presumed electrochemical behavior of 12.
Table 1. Absorption maxima [nm] and their coefficients (loge) of 5–17 in
dichloromethane.
Sample
lmax (loge)
Sample
lmax (loge)
5
6
7
8
9
10
11
412 (4.04), 572 (2.84)
410 (4.64), 570 (3.23)
416 (4.66), 568 (3.37)
410 (4.79), 568 sh (3.49)
400 (4.04), 572 (2.81)
412 (4.60), 570 (3.27)
416 (4.33), 588 (3.19)
12
13
14
15
16
17
462 (4.04), 534 sh (3.88)
444 (4.44), 540 sh (4.10)
414 (4.60), 550 (4.38)
460 (4.18)
416 sh (4.64), 434 (4.67)
508 (4.32)
Table 3. Redox potentials[a] of TCNE adducts 12–17.
red
red
red
red
red
red
Sample
E1
À0.61
E2
À1.03
E3
E4
E5
E6
pared to those of 16, centered at l=460 nm, which extended
beyond l=600 nm. Broad CT absorptions were observed in
16 centered at l=416(sh) and 434 nm. The CT absorption
band of 16 extended beyond l=700 nm. Cyanovinyl-substi-
tuted compounds have been known to exhibit solvatochro-
mic[12] and vapochromic behavior.[13] Solvatochromism was
studied with 17. The solvent dependence of the absorption
maxima and coefficients (loge) of 17 are summarized in
Table 2. The largest solvent effect was observed when the
solvent was changed from CHCl3 (lmax =510 nm) to ethyl
acetate (lmax =486 nm).
12
G
R
A
(À2.18)
13
14
15
16
17
À1.01
À0.73
À1.95
À1.10
À1.11
À1.02
(À0.45)
(À0.63)
(À1.00)
(À1.09)
A
ACHTREUNG
À0.40
À0.64
À0.31
À0.64
À0.57
À1.03
À0.54
À1.04
(À0.39)
(À0.56)
(À0.72)
(À1.03)
G
ACHTREUNG
(À0.63)
(À1.02)
(À1.93)
ACHTREUNG
(À0.29)
(À0.52)
N
A
(À2.15)
(À0.62)
(À1.02)
U
ACHTREUNG
[a] Redox potentials were measured by CV and DPV [V vs Ag/AgNO3,
1 mm in benzonitrile containing Et4NClO4 (0.1m), Pt electrode (internal
diameter: 1.6 mm), scan rate=100 mVsÀ1, and Fc/Fc+ =+0.15 V]. In the
case of reversible waves, redox potentials measured by CV are presented.
The peak potentials measured by DPV are shown in parentheses.
Table 2. Solvatochromic data for the longest wavelength absorption of
17.
Solvent
lmax (loge)
Solvent
lmax (loge)
CHCl3
CH2Cl2
CH3CN
MeOH
EtOH
510 (4.31)
508 (4.32)
504 (4.30)
497 (4.28)
492 (4.25)
cyclohexane
iPrOH
acetone
THF
492 (4.29)
491 (4.27)
491 (4.26)
490 (4.26)
486 (4.19)
Although (6-azulenylethynyl)benzene derivatives exhibit
reversible reduction waves in their cyclovoltammograms,[15]
(1-azulenylethynyl)benzenes 5–8 and thiophenes 9, 10 and
bis(1-azulenyl)acetylene 11 showed irreversible reduction
waves at À1.52 to À2.18 V upon CV, (see the Supporting In-
formation). Electrochemical reduction of 12 showed a rever-
sible two-step reduction wave at half-wave potentials of
À0.61 and À1.03 V upon CV, which can probably be attrib-
uted to the formation of a radical anionic and a dianionic
species, respectively (Figure 3). Thus, the electrochemical
behavior of 12 could be explained as shown in Scheme 15.
The electrochemical reduction also exhibited irreversible
waves at À1.95 and À2.18 V upon DPV, probably due to the
AcOEt
To obtain the theoretical aspect of the spectroscopic prop-
erties of these compounds, B3LYP/6-31G** density func-
tional calculations of the molecular orbitals of 12 and 17
were performed without any substituents on the azulene
rings.[14] The resulting HOMO and LUMOs of optimized
structures are summarized in the Supporting Information.
Geometry optimizations revealed the substantial deviation
from planarity in these molecules. The HOMO in 12 is
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Azulene Chromophores
FULL PAPER
Figure 5. Cyclic voltammograms of the reduction of 14 (1 mm) in benzo-
nitrile containing Et4NClO4 (0.1m) as a supporting electrolyte; scan
Figure 3. Cyclic voltammograms of the reduction of 12 (1 mm) in benzo-
nitrile containing Et4NClO4 (0.1m) as a supporting electrolyte; scan
rate=100 mVsÀ1
.
rate=100 mVsÀ1
.
reduction of the substituted azulene ring. Bis-adduct 13 ex-
hibited a reversible four-step reduction wave, whose poten-
tials were identified at À0.45, À0.63, À1.00, and À1.09 V by
DPV (Figure 4), which are attributed to the formation of a
TCBD units connected by a 1,3,5-benzentriyl spacer shows a
novel six-stage reversible one-electron reduction within a
narrow potential range of 1.00 V (from À0.69 V to À1.69 V
vs Fc/Fc+).[4b] The reduction of 14 exhibited a reversible
five-stage reduction within a narrower potential range of
0.71 V (from À0.39 V to À1.10 V), and the lower first reduc-
tion potential (E1red =À0.54 V vs Fc/Fc+) is comparable with
the results reported by Diederich et al. The electrochemical
reduction of 15 also showed a reversible three-stage reduc-
tion wave upon CV (À0.64, À1.03, and À1.95 V), attributed
to the formation of up to a trianionic species, including the
reduction of either the azulene or the thiophene ring
(Figure 6). A reversible three-stage wave was observed in 16
upon CV (À0.31, À0.54, and À1.10 V), in which the third re-
duction wave should be concluded to be a two-electron
transfer in one step to form
a tetraanionic species
(Figure 7). The electrochemical reduction of 17 showed a re-
versible two-stage wave upon CV (À0.64 and À1.04 V) at-
tributed to the formation of a dianionic species (Figure 8).
The oxidation of these compound exhibited voltammograms
that were characterized by irreversible waves, probably due
to the oxidation of the azulene rings (see the Supporting
Figure 4. Cyclic voltammograms of the reduction of 13 (1 mm) in benzo-
nitrile containing Et4NClO4 (0.1m) as a supporting electrolyte; scan
rate=100 mVsÀ1
.
AHCTREIUNG nformation).
tetraanionic species. The electrochemical reduction of 14 ex-
hibited a reversible five-step reduction wave, whose poten-
tials were identified at À0.39, À0.56, À0.72, À1.03, and
À1.10 V by DPV, which are attributed to the formation of
up to a pentaanionic species (Figure 5). The first reduction
potentials of 12, 13, and 14 decreased as the number of azu-
lene-substituted TCBD units increased. This indicates that
the TCBD unit reduces the LUMO level and increases the
p-acceptance, in spite of the 1,3,5-arrangement in 14. We
have already reported the redox properties of 9-[bis(6-azule-
nylethynyl)methylene]-9H-fluorene and 9-{bisACHTREU[NG 1,3-bis(hexyl-
oxycarbonyl)-6-azulenylethynyl]methylene}-9H-fluorene.[16]
These fluorenes exhibit a reversible three-stage reduction
within a narrow potential range of 0.54 V (from À1.21 V to
À1.75 V) and 0.40 V (from À1.00 V to À1.40 V), respective-
ly. With respect to the TCBD derivatives, Diederich et al.
reported that the compound with three DAA-substituted
Figure 6. Cyclic voltammograms of the reduction of 15 (1 mm) in benzo-
nitrile containing Et4NClO4 (0.1m) as a supporting electrolyte; scan
rate=100 mVsÀ1
.
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T. Shoji, N. Morita et al.
The red color of the solution of 13 changed to orange
during electrochemical reduction with the development of
new absorptions in the visible region at l=546 and 700 nm.
Reverse oxidation of the orange-colored solution regenerat-
ed the visible spectra of the red-colored 13. On the basis of
a comparison with the results of 12 (see the Supporting In-
formation), the color change of the solution of 13 can thus
be attributed to the formation of up to the dianionic species
via a radical anion. When the UV-visible spectra of 14 were
measured under electrochemical reduction conditions, the
absorption of 14 at 550 nm in the visible region gradually
decreased and a new absorption in the visible region at
700 nm gradually developed. The reverse oxidation de-
creased the new absorption band, but did not regenerate the
absorption band of 14. These results indicate the instability
of anionic species of 14 under the spectroscopic measure-
ment conditions (see the Supporting Information).
Figure 7. Cyclic voltammograms of the reduction of 16 (1 mm) in benzo-
nitrile containing Et4NClO4 (0.1m) as a supporting electrolyte; scan
rate=100 mVsÀ1
.
The significant color changes were also observed in thio-
phene derivatives 15 and 16. When the visible spectral
changes of 15 were measured during the electrochemical re-
duction, the absorption in the visible region at l=460 nm
gradually decreased with the development of new absorp-
tions at l=538 and 696 nm in the visible region. The reverse
oxidation decreased the new absorptions and the absorption
of 15 was regenerated (see the Supporting Information). A
two-stage color change was observed in the visible spectra
of 16 under electrochemical reduction conditions (Figure 9).
At the beginning, new absorptions in the visible region at
l=609 and 740 nm gradually developed and the red color of
the solution changed to blue during electrochemical reduc-
tion. On further reduction, the new bands in the visible
region gradually decreased, accompanied by the develop-
ment of a new absorption in the near-infrared region. On re-
verse oxidation, the new absorption in the IR region de-
creased and the absorptions in the visible region at l=609
and 740 nm were regenerated. Further electrochemical oxi-
dation decreased these absorptions. The two-step color-
change should correspond to the formation of a closed-shell
dianionic species via a radical anion in two steps. The ab-
sorption up to the near-infrared region suggests the forma-
tion of the stabilized dianionic species with thienoquinoide
structure in the two-electron reduction.
Figure 8. Cyclic voltammograms of the reduction of 17 (1 mm) in benzo-
nitrile containing Et4NClO4 (0.1m) as a supporting electrolyte; scan
rate=100 mVsÀ1
.
Electrochromic analysis: Visible spectra of 12–17 were
monitored to clarify the color changes during the electro-
chemical reactions. A constant-current reduction was ap-
plied to the solutions of 12–17 with a platinum mesh as the
working electrode and a wire counterelectrode.
Visible spectra of 12 were measured in benzonitrile con-
taining Et4NClO4 (0.1m) as a supporting electrolyte at room
temperature under electrochemical reduction conditions
(see the Supporting Information). The longest absorption of
12 at l=508(sh) nm gradually decreased and thus the color
of the solution gradually changed from purple to brown
during electrochemical reduction with the development of
new absorptions in the visible region at l=517 and 700 nm.
On further reduction, the new absorption bands gradually
decreased and the color of the solution gradually changed
from brown to orange. However, reverse oxidation of the
brown-colored solution did not regenerate the spectrum of
12, although good reversibility was observed in the two-step
reduction in the cyclovoltammogram. The poor reversibility
of the color changes might be attributable to the instability
of the dianionic species produced by two-electron reduction.
The color of the solution of 17 gradually changed from
purple to orange, and electrochemical reduction led to the
development of a new absorption band at l=700 nm. How-
ever, reverse oxidation of the orange-colored solution did
not completely regenerate the spectrum of 17, although the
new absorption did decrease during electrochemical
oxidation.
Conclusion
Several 1-ethynylazulene derivatives 5–11 were prepared by
the Sonogashira–Hagihara reaction. These compounds read-
ily reacted with tetracyanoethylene to give the correspond-
ing 1,1,4,4,-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-
8404
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 8398 – 8408

Azulene Chromophores
FULL PAPER
1H, J=10.0 Hz, H6), 7.50 (dd, 1H, J=10.0, 10.0 Hz, H5), 3.94 (s, 3H,
CO2Me), 3.21 (sept, 1H, J=6.8 Hz, iPr), 1.40 ppm (d, 6H, J=6.8 Hz,
iPr); 13C NMR (100 MHz, CDCl3): d=165.4, 150.4, 147.3, 144.0, 141.5,
139.4, 139.1, 137.7, 127.8, 117.3, 73.8, 51.6, 39.6, 25.0 ppm; HRMS (ESI)
calcd for [C15H15IO2+Na]+: 377.0014; found 377.0009; elemental analysis
calcd (%) for C15H15IO2: C 50.78, H 4.27; found: C 50.84, H 4.36.
Methyl 7-isopropyl-3-trimethylsilylethynylazulene-1-carboxylate (3): To a
degassed solution of
2 (1.77 g, 5.00 mmol), trimethylsilylacetylene
(737 mg, 7.50 mmol), and CuI (95 mg, 0.50 mmol) in triethylamine
(20 mL) and THF (20 mL) was added tetrakis(triphenylphosphine)palla-
dium(o) (289 mg, 0.25 mmol). The resulting mixture was stirred at 508C
for 2 h under an Ar atmosphere. The reaction mixture was poured into a
10% NH4Cl solution and extracted with toluene. The organic layer was
washed with brine, dried over MgSO4, and concentrated under reduced
pressure. The residue was purified by column chromatography on silica
gel with toluene to give 3 (1.58 g, 97%). Purple crystals; m.p. 71.0–
74.08C (hexane); IR (KBr disk): n˜max =2963 (m), 2145 (m), 1703 (s), 1448
(s), 1439 (s), 1421 (m), 1392 (m), 1369 (m), 1224 (m), 1215 (s), 1167 (m),
1128 (m), 1103 (m), 1053 (m), 920 (m), 881 (m), 846 (s), 806 (m), 775
(m), 769 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (loge)=244 (4.49), 278 (4.57),
302 (4.49), 314 (4.52), 386 (3.98), 400 (3.96), 564 (2.78), 604 nm sh (2.71);
1H NMR (400 MHz, CDCl3): d=9.71 (s, 1H, H8), 8.57 (d, 1H, J=
10.0 Hz, H4), 8.41 (s, 1H, H2), 7.82 (d, 1H, J=10.0 Hz, H6), 7.51 (dd, 1H,
J=10.0, 10.0 Hz, H5), 3.94 (s, 3H, CO2Me), 3.23 (sept, 1H, J=6.8 Hz,
iPr), 1.41 (d, 6H, J=6.8 Hz, iPr), 0.32 ppm (s, 9H, TMS); 13C NMR
(100 MHz, CDCl3): d=164.6, 149.9, 144.7, 142.5, 140.5, 138.8, 137.6,
135.6, 127.1, 114.3, 108.8, 100.2, 97.9, 50.5, 38.7, 24.1, 0.0 ppm; HRMS
(ESI) calcd for [C20H24O2Si+Na]+: 347.1443; found: 347.1438; elemental
analysis calcd (%) for C20H24O2Si: C 74.03, H 7.45; found: C 73.99, H
7.34.
Methyl 3-ethynyl-7-isopropylazulene-1-carboxylate (4): To a solution of 3
(650 mg, 2.00 mmol) in MeOH (10 mL), THF (5 mL), and water (10 mL)
was added K2CO3 (1.38 g, 10.0 mmol). The resulting mixture was stirred
at room temperature for 2 h. The reaction mixture was poured into water
and extracted with hexane. The organic layer was washed with brine,
dried over MgSO4, and concentrated under reduced pressure. The residue
was purified by column chromatography on silica gel with toluene to give
4 (477 mg, 95%). Purple oil; IR (KBr disk): n˜max =3296 (m), 2961 (m),
2098 (w), 1693 (s), 1446 (s), 1421 (m), 1381 (m), 1213 (s), 1170 (m),
1124 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (loge)=242 (4.49), 272 (4.45), 298
(4.49), 310 (4.54), 378 (3.95), 394 (3.95), 560 (2.78), 598 sh (2.72), 666 nm
sh (2.18); 1H NMR (400 MHz, CDCl3): d=9.73 (s, 1H, H8), 8.59 (d, 1H,
J=9.6 Hz, H4), 8.42 (s, 1H, H2), 7.79 (d, 1H, J=10.0 Hz, H6), 7.48 (dd,
1H, J=9.6, 10.0 Hz, H5), 3.94 (s, 3H, CO2Me), 3.43 (s, 1H, CꢀC-H),
3.23 (sept, 1H, J=6.8 Hz, iPr), 1.41 ppm (d, 6H, J=6.8 Hz, iPr);
13C NMR (100 MHz, CDCl3): d=165.5, 150.9, 145.6, 143.4, 141.2, 139.6,
138.5, 136.3, 127.9, 114.9, 108.2, 81.8, 79.5, 51.4, 39.4, 24.9 ppm; HRMS
(ESI) calcd for [C17H16O2+Na]+: 275.1048; found: 275.1043; elemental
analysis calcd (%) for C17H16O2: C 80.93, H 6.39; found: C 80.77, H 6.50.
Figure 9. Continuous change in visible spectra of 16 in acetonitrile (2 mL;
2.9”10À4 m) containing Et4NClO4 (0.1m) upon constant-current electro-
chemical reduction (50 uA) at 1 min intervals.
azulenyl)-3-butadienyl chromophores 12–17 in excellent
yields. Analysis by cyclic voltammetry (CV) and differential
pulse voltammetry (DPV) showed that compounds 12–17
exhibited a multistep reduction wave. Moreover, a signifi-
cant color change was observed during electrochemical re-
duction. Preparation of 1,1,4,4,-tetracyano-2-(5-isopropyl-3-
methoxycarbonyl-1-azulenyl)-3-butadienyl
with different p-electron cores is now in progress in our
ACHTREUNGlaboratory.
chromophores
Methyl 7-isopropyl-3-(phenylethynyl)azulene-1-carboxylate (5): To a de-
gassed solution of
2 (354 mg, 1.00 mmol), phenylacetylene (123 mg,
Experimental Section
1.20 mmol), and CuI (19 mg, 0.10 mmol) in triethylamine (10 mL) and
THF (10 mL) was added tetrakis(triphenylphosphine)palladium(o)
(58 mg, 0.05 mmol). The resulting mixture was stirred at 508C for 2 h
under an Ar atmosphere. The reaction mixture was poured into a 10%
NH4Cl solution and extracted with toluene. The organic layer was
washed with brine, dried over MgSO4, and concentrated under reduced
pressure. The residue was purified by column chromatography on silica
gel with CH2Cl2 to give 5 (312 mg, 95%). Purple crystals; m.p. 92.0–
95.08C (CH2Cl2); IR (KBr disk): n˜max =2957 (m), 2201 (w), 1687 (s), 1487
(m), 1468 (m), 1450 (s), 1423 (m), 1406 (m), 1392 (m), 1381 (m), 1371
(m), 1246 (m), 1211 (s), 1196 (m), 1169 (m), 1118 (m), 1072 (m), 871 (m),
804 (m), 777 (m), 756 (m), 688 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (loge)=
238 (4.44), 248 (4.45), 306 (4.65), 310 (4.65), 334 (4.43), 396 (4.10), 412
(4.04), 572 (2.84), 616 sh (2.76), 690 nm sh (2.17); 1H NMR (400 MHz,
CDCl3): d=9.72 (s, 1H, H8), 8.65 (d, 1H, J=10.0 Hz, H4), 8.46 (s, 1H,
H2), 7.78 (d, 1H, J=10.0 Hz, H6), 7.60 (m, 2H, o-Ph), 7.48 (dd, 1H, J=
10.0, 10.0 Hz, H5), 7.39–7.32 (m, 3H, m-, p-Ph), 3.95 (s, 3H, CO2Me),
General: For general and electrochemical measurement details, see the
Supporting Information. Assignment of peaks in the 1H NMR spectra
was accomplished by decoupling, NOE, and/or COSY experiments.
Methyl 3-iodo-7-isopropylazulene-1-carboxylate (2): To a solution of 1
(3.22 g, 14.1 mmol) in CH2Cl2 (30 mL) was added N-iodosuccinimide
(3.81 g, 16.9 mmol) at room temperature. The resulting mixture was
stirred at the same temperature for 30 min under an Ar atmosphere.
After the solvent was removed under reduced pressure, the crude prod-
uct was purified by column chromatography on silica gel with CH2Cl2 to
give 2 (4.60 g, 92%). Purple crystals; m.p. 67.0–69.08C (CH2Cl2); IR
(KBr disk): n˜max =3246 (s), 2961 (m), 1687 (s), 1452 (s), 1441 (s), 1419
(m), 1217 (s), 1197 (m), 1170 (m), 1124 (m), 1051 cmÀ1 (m); UV/Vis
(CH2Cl2): lmax (loge)=244 (4.44), 298 sh (4.47), 308 (4.54), 372 sh (3.91),
1
486 (3.95), 556 (2.81), 594 nm sh (2.77); H NMR (400 MHz, CDCl3): d=
9.71 (s, 1H, H8), 8.41 (s, 1H, H2), 8.27 (d, 1H, J=10.0 Hz, H4), 7.78 (d,
Chem. Eur. J. 2008, 14, 8398 – 8408
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8405

T. Shoji, N. Morita et al.
3.22 (sept, 1H, J=6.8 Hz, iPr), 1.42 ppm (d, 6H, J=6.8 Hz, iPr);
13C NMR (100 MHz, CDCl3): d=165.8, 150.9, 145.2, 143.1, 141.6, 139.7,
138.6, 136.6, 131.8, 128.9, 128.3, 127.9, 124.4, 115.5, 109.6, 94.2, 85.4, 51.6,
39.6, 25.0 ppm; HRMS (ESI) calcd for [C23H20O2+Na]+: 351.1361; found:
351.1356; elemental analysis calcd (%) for C23H20O2: C 84.12, H 6.14;
found: C 83.99, H 6.17.
Methyl 7-isopropyl-3-(2-thienylethynyl)azulene-1-carboxylate (9): The
procedure used for the preparation of 5 was adopted here. Reaction of 4
(505 mg, 2.00 mmol) with 2-iodothiophene (630 mg, 3.00 mmol) in trie-
thylamine (20 mL) and THF (20 mL) in the presence of CuI (38 mg,
0.10 mmol) and tetrakis(triphenylphosphine)palladium(o) (116 mg,
0.10 mmol) at 508C for 3 h followed by column chromatography on silica
gel with toluene afforded 9 (623 mg, 93%). Green crystals; m.p. 63.0–
65.08C (hexane); IR (KBr disk): n˜max =3107 (m), 2959 (m), 2193 (w),
1687 (s), 1500 (m), 1450 (s), 1415 (s), 1381 (m), 1378 (m), 1236 (s), 1213
(s), 1190 (m), 1167 (m), 1130 (m), 1049 (m), 777 (m), 713 cmÀ1 (m); UV/
Vis (CH2Cl2): lmax (loge)=248 (4.38), 278 (4.40), 314 (4.53), 350 sh
(4.16), 400 (4.04), 420 sh (3.88), 572 nm (2.81); 1H NMR (500 MHz,
CDCl3): d=9.72 (s, 1H, H8), 8.60 (d, 1H, J=9.5 Hz, H4), 8.44 (s, 1H,
H2), 7.78 (d, 1H, J=10.5 Hz, H6), 7.49 (dd, 1H, J=9.5, 10.5 Hz, H5), 7.31
(dd, 1H, J=4.0, 1.0 Hz, Th-H3), 7.28 (dd, 1H, J=4.0, 1.0 Hz, Th-H5),
7.02 (dd, 1H, J=4.0, 1.0 Hz, Th-H4), 3.95 (s, 3H, CO2Me), 3.22 (sept,
1H, J=7.0 Hz, iPr), 1.42 ppm (d, 6H, J=7.0 Hz, iPr); 13C NMR
(100 MHz, CDCl3): d=165.3, 150.6, 145.2, 144.7, 142.6, 141.2, 139.4,
138.3, 136.2, 131.3, 127.5, 127.1, 126.7, 124.0, 115.1, 108.6, 88.5, 86.5, 51.1,
39.2, 24.5 ppm; HRMS (ESI) calcd for [C21H18O2S+Na]+: 357.0925;
found: 357.0920; elemental analysis calcd (%) for C21H18O2S: C 75.42, H
5.43; found: C 75.41, H 5.42.
1,4-Bis[(5-isopropyl-3-methoxycarbonyl-1-azulenyl)ethynyl]benzene (6):
The procedure used for the preparation of 5 was adopted here. Reaction
of 2 (779 mg, 2.20 mmol) with 1,4-diethynylbenzene (126 mg, 1.00 mmol)
in triethylamine (10 mL) and THF (10 mL) in the presence of CuI
(38 mg, 0.20 mmol) and tetrakis(triphenylphosphine)palladium(o)
(116 mg, 0.10 mmol) at 508C for 3 h followed by column chromatography
on silica gel with CH2Cl2 afforded 6 (527 mg, 91%). Black crystals; m.p.
238.0–240.08C (CH2Cl2); IR (KBr disk): n˜max =2961 (m), 2199 (m), 1695
(s), 1491 (m), 1444 (s), 1425 (m), 1408 (m), 1371 (m), 1248 (m), 1209 (s),
1197 (s), 1169 (s), 1072 (m), 1049 (m), 873 (m), 839 (m), 775 cmÀ1 (m);
UV/Vis (CH2Cl2): lmax (loge)=244 (4.71), 276 (4.45), 306 (4.62), 312
(4.76), 356 (4.72), 410 (4.64), 432 sh (4.60), 570 (3.23), 614 sh (3.12),
694 nm sh (2.45); 1H NMR (500 MHz, CDCl3): d=9.72 (s, 2H, H8), 8.67
(d, 2H, J=9.6 Hz, H4), 8.48 (s, 2H, H2), 7.82 (d, 2H, J=10.0 Hz, H6),
7.60 (s, 4H, Bz-H2,3,5,6), 7.53 (dd, 2H, J=9.6, 10.0 Hz, H5), 3.97 (s, 6H,
CO2Me), 3.24 (sept, 2H, J=7.0 Hz, iPr), 1.43 ppm (d, 12H, J=7.0 Hz,
iPr); 13C NMR (100 MHz, CDCl3): d=165.4, 150.7, 144.8, 142.8, 141.4,
139.4, 138.4, 136.2, 131.3, 127.6, 123.2, 115.2, 108.9, 93.7, 86.8, 51.2, 39.3,
24.6 ppm; HRMS (ESI) calcd for [C40H34O4+Na]+: 601.2355; found:
2,5-Bis[(5-isopropyl-3-methoxycarbonyl-1-azulenyl)ethynyl]thiophene
(10): The procedure used for the preparation of 5 was adopted here. Re-
action of
4 (757 mg, 3.00 mmol) with 2,5-iodothiophene (504 mg,
1.50 mmol) in triethylamine (20 mL) and THF (20 mL) in the presence
of CuI (38 mg, 0.20 mmol) and tetrakis(triphenylphosphine)palladium(o)
(116 mg, 0.10 mmol) at 508C for 12 h followed by column chromatogra-
phy on silica gel with toluene afforded 9 (85 mg, 9%) and 10 (633 mg,
72%). Green crystals; m.p. 178.0–179.58C (AcOEt); IR (KBr disk):
n˜max =2957 (m), 2189 (m), 1695 (s), 1498 (m), 1444 (s), 1419 (m), 1371
(m), 1240 (m), 1209 (s), 1167 (m), 804 (m), 775 cmÀ1 (m); UV/Vis
(CH2Cl2): lmax (loge)=244 (4.75), 282 sh (4.70), 294 (4.72), 310 sh (4.69),
601.2349; elemental analysis calcd (%) for C40H34O4·1= H2O: C 82.17, H
3
5.98; found: C 82.19, H 5.92.
1,3,5-Tris[(5-isopropyl-3-methoxycarbonyl-1-azulenyl)ethynyl]benzene
(7): The procedure used for the preparation of 5 was adopted here. Reac-
tion of
2 (1.27 g, 3.60 mmol) with 1,3,5-triethynylbenzene (150 mg,
1.00 mmol) in triethylamine (10 mL) and THF (10 mL) in the presence
of CuI (38 mg, 0.20 mmol) and tetrakis(triphenylphosphine)palladium(o)
(116 mg, 0.10 mmol) at 508C for 2 h followed by column chromatography
on silica gel with toluene afforded 7 (700 mg, 84%). Green crystals; m.p.
200.0–205.08C (AcOEt); IR (KBr disk): n˜max =2957 (m), 2197 (m), 1693
(s), 1578 (m), 1508 (m), 1148 (s), 1414 (s), 1371 (m), 1215 (s), 1165 cmÀ1
(m); UV/Vis (CH2Cl2): lmax (loge)=248 (4.96), 274 sh (4.85), 312 (5.09),
342 (4.92), 400 (4.71), 416 (4.66), 568 (3.37), 608 sh (3.28), 684 nm sh
(2.68); 1H NMR (500 MHz, CDCl3): d=9.76 (dd, 3H, H8), 8.71 (d, 3H,
J=9.5 Hz, H4), 8.50 (s, 3H, H2), 7.84 (d, 3H, J=10.5 Hz, H6), 7.79 (s,
3H, Bz-H2,4,6), 7.57 (dd, 3H, J=9.5, 10.5 Hz, H5), 3.98 (s, 9H, CO2Me),
3.26 (sept, 3H, J=7.0 Hz, iPr), 1.44 ppm (d, 18H, J=7.0 Hz, iPr);
13C NMR (100 MHz, CDCl3): d=165.4, 150.8, 145.0, 142.8, 141.4, 139.4,
138.4, 136.3, 133.0, 127.7, 124.7, 115.2, 108.6, 92.5, 86.0, 51.2, 39.3,
24.6 ppm; HRMS (ESI) calcd for [C57H48O6+Na]+: 851.3349; found:
851.3343; elemental analysis calcd (%) for C57H48O6: C 82.58, H 5.84;
found: C 82.46, H 6.04.
1
382 sh (4.59), 412 (4.60), 570 nm (3.27); H NMR (500 MHz, CDCl3): d=
9.75 (s, 2H, H8), 8.63 (d, 2H, J=10.5 Hz, H4), 8.47 (s, 2H, H2), 7.84 (d,
2H, J=10.5 Hz, H6), 7.55 (dd, 2H, J=10.5, 10.5 Hz, H5), 7.22 (s, 2H, Th-
H
3,4), 3.97 (s, 6H, CO2Me), 3.25 (sept, 2H, J=6.5 Hz, iPr), 1.44 ppm (d,
12H, J=6.5 Hz, iPr); 13C NMR (100 MHz, CDCl3): d=165.3, 150.8,
144.7, 142.6, 141.3, 139.4, 138.3, 136.2, 131.2, 127.7, 124.8, 115.2, 108.3,
89.8, 86.5, 51.1, 39.2, 24.5 ppm; HRMS (ESI) calcd for [C38H32O4S+Na]+:
607.1919; found: 607.1914; elemental analysis calcd (%) for C38H32O4S: C
78.06, H 5.52; found: C 77.90, H 5.49.
Bis(5-isopropyl-3-methoxycarbonyl-1-azulenyl)acetylene (11): The proce-
dure used for the preparation of 5 was adopted here. The reaction of 2
(390 mg, 1.10 mmol) with 4 (252 mg, 1.00 mmol) in triethylamine (10 mL)
and THF (10 mL) in the presence of CuI (38 mg, 0.10 mmol) and tetra-
kis(triphenylphosphine)palladium(o) (116 mg, 0.10 mmol) at 508C for 2 h
followed by column chromatography on silica gel with AcOEt/hexane
(1:4) afforded 11 (449 mg, 94%). Green crystals; m.p. 178.0–179.08C
(AcOEt); IR (KBr disk): n˜max =2951 (m), 1693 (s), 1454 (m), 1441 (m),
1412 (m), 1373 (m), 1207 (s), 1201 (s), 1172 (m), 1151 (m), 1116 (m),
1074 (m), 871 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (loge)=246 (4.68), 288
(4.84), 316 (4.74), 416 (4.33), 452 sh (4.25), 588 nm (3.19); 1H NMR
(500 MHz, CDCl3): d=9.74 (s, 2H, H8), 8.74 (d, 2H, J=9.5 Hz, H4), 8.54
(s, 2H, H2), 7.81 (d, 2H, J=10.5 Hz, H6), 7.52 (dd, 2H, J=9.5, 10.5 Hz,
H5), 3.98 (s, 6H, CO2Me), 3.24 (sept, 2H, J=7.0 Hz, iPr), 1.44 ppm (d,
12H, J=7.0 Hz, iPr); 13C NMR (100 MHz, CDCl3): d=165.5, 150.4,
144.5, 142.6, 141.2, 139.2, 138.2, 136.3, 127.3, 115.1, 109.9, 88.7, 51.2, 39.2,
24.6 ppm; HRMS (ESI) calcd for [C32H30O4+Na]+: 501.2042; found:
501.2036; elemental analysis calcd (%) for C32H30O4: C 80.31, H 6.32;
found: C 80.22, H 6.33.
1,2,4,5-Tetrakis(7-isopropyl-1-methoxycarbonyl-3-azulenylethynyl)ben-
zene (8): The procedure used for the preparation of 5 was adopted here.
Reaction of
4 (887 mg, 3.50 mmol) with 1,2,4,5-tetraiodobenzene
(407 mg, 0.70 mmol) in triethylamine (15 mL) and THF (15 mL) in the
presence of CuI (114 mg, 0.60 mmol) and tetrakis(triphenylphosphine)-
palladium(o) (324 mg, 0.30 mmol) at 508C for 19 h followed by column
chromatography on silica gel with CH2Cl2 afforded 8 (582 mg, 77%).
Brown crystals; m.p.>3008C (AcOEt); IR (KBr disk): n˜max =2955 (m),
2187 (m), 1693 (s), 1682 (s), 1481 (m), 1448 (s), 1421 (m), 1373 (m), 1223
(s), 1196 (m), 1169 (m), 1103 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (loge)=
244 (4.91), 302 (4.95), 354 (4.74), 410 (4.79), 462 (4.49), 568 sh (3.49), 630
sh (3.28), 698 nm sh (2.70); 1H NMR (500 MHz, CDCl3): d=9.73 (s, 4H,
H8), 8.70 (d, 4H, J=9.5 Hz, H4), 8.51 (s, 4H, H2), 7.97 (s, 2H, Bz-H3,6),
7.57 (d, 4H, J=10.5 Hz, H6), 6.93 (dd, 4H, J=9.5, 10.5 Hz, H5), 3.95 (s,
12H, CO2Me), 3.19 (sept, 4H, J=7.0 Hz, iPr), 1.40 ppm (d, 24H, J=
7.0 Hz, iPr); 13C NMR (100 MHz, CDCl3): d=165.4, 150.7, 145.2, 142.9,
141.5, 139.2, 138.2, 136.9, 134.3, 128.0, 124.9, 115.2, 108.7, 92.8, 91.0, 51.2,
39.2, 24.6 ppm; HRMS (ESI) calcd for [C74H62O8+Na]+: 1101.4342;
Methyl 5-isopropyl-1-(1,1,4,4,-tetracyano-2-phenyl-3-butadienyl)azulene-
1-carboxylate (12): To a solution of 5 (164 mg, 0.50 mmol) in ethyl ace-
tate (10 mL) was added TCNE (96 mg, 0.75 mmol). The resulting mixture
was stirred at room temperature for 30 min under an Ar atmosphere.
The solvent was removed under reduced pressure. The residue was puri-
fied by column chromatography on silica gel with ethyl acetate and Bio-
Beads with CH2Cl2 to give 12 (220 mg, 96%). Red crystals; m.p. 175.0–
found: 1101.4337; elemental analysis calcd (%) for C74H62O8·1= H2O: C
3
81.89, H 5.82; found: C 81.94, H 5.82.
8406
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Chem. Eur. J. 2008, 14, 8398 – 8408

Azulene Chromophores
FULL PAPER
178.08C (CH2Cl2); IR (KBr disk): n˜max =2972 (m), 2222 (s), 1698 (s), 1496
(s), 1464 (m), 1439 (s), 1423 (s), 1371 (s), 1282 (m), 1224 (s), 1213 (s),
1176 (s), 1155 (m), 1132 (m), 1086 (m), 1043 (m), 1028 (m), 1001 (m),
(ESI) calcd for [C27H18N4O2S+Na]+: 485.1048; found: 485.1043; elemen-
tal analysis calcd (%) for C27H18N4O2S·1= H2O: C 69.21, H 4.02, N 11.96;
3
found: C 69.26, H 4.01, N 12.01.
904 (m), 796 (m), 777 (m), 767 (m), 735 (m), 715 (m), 694 cmÀ1 (m) cmÀ1
;
2,5-Bis[1,1,4,4,-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-
3-butadienyl]thiophene (16): The procedure used for the preparation of
12 was adopted here. The reaction of 10 (292 mg, 0.347 mmol) with
TCNE (192 mg, 1.50 mmol) in refluxing ethyl acetate (20 mL) for 1 h af-
forded 16 (408 mg, 97%). Reddish brown crystals; m.p. 180.0–186.08C
(AcOEt); IR (KBr disk): n˜max =2963 (m), 2222 (s), 1701 (s), 1529 (s),
1441 (s), 1417 (s), 1398 (s), 1368 (s), 1298 (m), 1238 (s), 1213 (s), 1180 (s),
1136 (m), 1089 (m), 1062 (m), 1049 (m), 1024 (m), 900 (m), 812 (m),
779 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (loge)=244 sh (4.68), 262 (4.71),
UV/Vis (CH2Cl2): lmax (loge)=236 (4.43), 262 (4.44), 284 sh (4.45), 296
(4.47), 332 (4.33), 352 sh (4.22), 392 (4.00), 462 (4.04), 534 nm sh
(3.88) nm; 1H NMR (500 MHz, CDCl3): d=10.03 (s, 1H, H8), 8.47 (d,
1H, J=10.0 Hz, H4), 8.30 (s, 1H, H2), 8.17 (d, 1H, J=10.5 Hz, H6), 7.99
(dd, 1H, J=10.0, 10.5 Hz, H5), 7.83 (d, 2H, J=8.0 Hz, o-Ph), 7.69 (t, 1H,
J=8.0 Hz, p-Ph), 7.60 (t, 2H, J=8.0 Hz, m-Ph), 3.96 (s, 3H, CO2Me),
3.36 (sept, 1H, J=6.5 Hz, iPr), 1.47 ppm (d, 6H, J=6.5 Hz, iPr);
13C NMR (100 MHz, CDCl3): d=169.2, 164.3, 160.6, 156.9, 146.1, 142.5,
142.4, 141.9, 140.7, 137.5, 134.5, 132.2, 132.1, 130.0, 129.7, 119.4, 119.2,
113.6, 112.4, 112.0, 111.2, 87.7, 80.8, 51.6, 39.4, 24.4 ppm; HRMS (ESI)
calcd for [C29H20N4O2+Na]+: 479.1484; found: 479.1478; elemental analy-
sis calcd (%) for C29H20N4O2·H2O: C 73.40, H 4.67, N 11.81; found: C
73.15, H 4.57, N 11.65.
1
334 (4.49), 416 sh (4.64), 434 nm (4.67); H NMR (500 MHz, CDCl3): d=
10.04 (s, 2H, H8), 8.45 (d, 2H, J=10.0 Hz, H4), 8.21 (d, 2H, J=9.5 Hz,
H6), 8.20 (s, 2H, H2), 8.06 (s, 2H, Th-H3,4), 8.04 (dd, 2H, J=9.5, 10.0 Hz,
H5), 3.97 (s, 6H, CO2Me), 3.37 (sept, 2H, J=7.0 Hz, iPr), 1.48 ppm (d,
12H, J=7.0 Hz, iPr); 13C NMR (100 MHz, CDCl3): d=164.1, 157.9,
157.7, 156.9, 146.7, 143.0, 142.8, 142.0, 141.8, 141.1, 137.7, 136.4, 133.0,
120.0, 117.5, 113.0, 112.3, 111.7, 110.8, 85.9, 80.5, 51.7, 39.5, 24.4 ppm;
HRMS (ESI) calcd for [C50H32N8O4S+Na]+: 863.2165; found: 863.2159;
1,4-Bis[1,1,4,4,-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-
3-butadienyl]benzene (13): The procedure used for the preparation of 12
was adopted here. The reaction of 6 (289 mg, 0.50 mmol) with TCNE
(154 mg, 1.20 mmol) in refluxing ethyl acetate (10 mL) for 1 h afforded
13 (402 mg, 96%). Reddish purple crystals; m.p.>3008C (AcOEt); IR
(KBr disk): n˜max =2222 (m), 1701 (s), 1506 (s), 1419 (s), 1366 (s), 1236 (s),
1219 (s), 1182 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (loge)=262 (4.72), 296
(4.74), 334 (4.63), 444 (4.44), 540 nm sh (4.10); 1H NMR (500 MHz,
CDCl3): d=10.07 (d, 2H, J=1.5 Hz, H8), 8.45 (d, 2H, J=10.0, 1.5 Hz,
H4), 8.25 (s, 2H, H2), 8.21 (d, 2H, J=10.0, 1.5 Hz, H6), 8.04 (dd, 2H, J=
10.0, 10.0 Hz, H5), 7.93 (s, 4H, Bz-H2,3,5,6), 3.98 (s, 6H, CO2Me), 3.38
(sept, 2H, J=7.0 Hz, iPr), 1.49 ppm (d, 12H, J=7.0 Hz, iPr); 13C NMR
(100 MHz, CDCl3): d=166.7, 164.2, 159.0, 157.7, 146.5, 143.0, 142.1,
142.0, 141.1, 137.7, 136.4, 132.7, 130.6, 120.0, 118.4, 113.3, 112.5, 111.2,
110.6, 90.8, 80.3, 51.8, 39.5, 24.4 ppm; HRMS (ESI) calcd for
[C52H34N8O4+Na]+: 857.2601; found: 857.2595; elemental analysis calcd
elemental analysis calcd (%) for C50H32N8O4S·3= H2O: C 69.19, H 4.06, N
2
12.91; found: C 69.34, H 4.20, N 12.77.
1,1,4,4,-Tetracyano-2,3-bis(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-
AHCTREbUNG utadiene (17): The procedure used for the preparation of 12 was adopt-
ed here. The reaction of 11 (239 mg, 0.50 mmol) with TCNE (77 mg,
0.60 mmol) in ethyl acetate (10 mL) at room temperature for 1 h afford-
ed 17 (293 mg, 97%). Red crystals; m.p. 164.0–166.08C (AcOEt); IR
(KBr disk): n˜max =2220 (m), 1709 (s), 1689 (s), 1496 (s), 1441 (s), 1419 (s),
1367 (m), 1209 (s), 1178 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (loge)=234
(4.59), 262 (4.59), 300 (4.63), 340 (4.37), 388 (4.27), 508 nm (4.32);
1H NMR (500 MHz, CDCl3): d=10.07 (d, 2H, J=1.5 Hz, H8), 8.60 (s,
2H, H2), 8.53 (dd, 2H, J=10.0, 1.5 Hz, H4), 8.15 (dd, 2H, J=10.0,
1.5 Hz, H6), 7.93 (dd, 2H, J=10.0, 10.0 Hz, H5), 3.96 (s, 6H, CO2Me),
3.37 (sept, 2H, J=7.0 Hz, iPr), 1.49 ppm (d, 12H, J=7.0 Hz, iPr);
13C NMR (100 MHz, CDCl3): d=164.5, 164.5, 156.9, 146.3, 143.4, 142.4,
142.3, 140.7, 137.3, 132.3, 120.8, 119.5, 114.3, 112.6, 80.9, 51.7, 39.5,
24.5 ppm; HRMS (ESI) calcd for [C38H30N4O4+Na]+: 629.2165; found:
(%) for C52H34N8O4·4= H2O: C 73.54, H 4.23, N 13.19; found: C 73.55, H
5
4.36, N 13.15.
1,3,5-Tris[1,1,4,4,-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-azulen-
yl)-3-butadienyl]benzene (14): The procedure used for the preparation of
12 was adopted here. The reaction of 7 (166 mg, 0.20 mmol) with TCNE
(154 mg, 1.20 mmol) in refluxing ethyl acetate (30 mL) for 1 h afforded
14 (221 mg, 91%). Brown crystals; m.p. 210.0–214.08C (AcOEt); IR
(KBr disk): n˜max =2964 (m), 2222 (m), 1705 (s), 1496 (s), 1442 (s), 1419
(s), 1365 (m), 1221 (s), 1180 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (loge)=
242 (4.98), 272 (4.96), 302 (4.93), 414 (4.60), 550 nm (4.38); 1H NMR
(500 MHz, CDCl3): d=10.10 (s, 3H, H8), 8.57 (s, 3H, H2), 8.42 (d, 3H,
J=10.0 Hz, H4), 8.34 (s, 3H, Bz-H2,4,6), 8.20 (d, 3H, J=10.0 Hz, H6), 8.01
(dd, 3H, J=10.0, 10.0 Hz, H5), 3.98 (s, 9H, CO2Me), 3.39 (sept, 3H, J=
7.0 Hz, iPr), 1.50 ppm (d, 18H, J=7.0 Hz, iPr); HRMS (ESI) calcd for
[C75H48N12O6+Na]+: 1235.3717; found: 1235.3712; elemental analysis
calcd (%) for C75H48N12O6·H2O: C 73.45, H 4.38, N 13.44; found: C
73.16, H 4.09, N 13.65. Low solubility hampered the measurement of
13C NMR.
629.2159; elemental analysis calcd (%) for C38H30N4O4·1= H2O: C 74.49,
3
H 5.05, N 9.14; found: C 74.55, H 5.16, N 9.09.
Acknowledgements
S.I. thanks the Fund for the Promotion of International Scientific Re-
search for financial support. This work was partially supported by a
Grant-in-Aid for Scientific Research (Grant 18550026 to S.I.) from the
Ministry of Education, Culture, Sports, Science, and Technology, Japan.
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Received: December 17, 2007
Revised: May 9, 2008
Published online: July 24, 2008
8408
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ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 8398 – 8408