Azulene-Substituted Donor-Acceptor Polymethines and 1,6’-Bi-, 1,6′;3,6′′-Ter-, and Quinqueazulenes via Zincke Salts: Synthesis, and Structural, Optical, and Electrochemical Properties

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Azulene-Substituted Donor-Acceptor Polymethines and

1,6’-Bi-, 1,6’;3,6’’-Ter-, and Quinqueazulenes via Zincke

Salts: Synthesis, and Structural, Optical, and

Electrochemical Properties

Taku Shoji,*^{[a, b]}Akari Yamazaki,^[a]Yukino Ariga,^[a]Mayumi Uda,^[a]Daichi Ando,^[b]

Nichika Sasahara,^[b]Naohito Kai,^[c]and Shunji Ito^[c]

Dedicated to the late Professor Klaus Hafner for his long-termed contribution to azulene chemistry.

Azulene-substituted donor-acceptor polymethines, bi-, ter-, and

quinqueazulenes composed of the 1,6’-biazulene unit have

been successfully prepared from corresponding Zincke salts.

The synthesis of polymethines through the reaction of Zincke

salts with several amines, followed by a Knoevenagel reaction

with malononitrile, was accomplished in moderate to high

yields (40–92%). Meanwhile, the reaction of Zincke salts with

secondary amines and the subsequent sequential condensa-

tion-cyclization with cyclopentadienide ions, so-called Ziegler-

Hafner method, produced the corresponding 1,6’-biazulenes,

1,6’;3,6’’-terazulenes, and quinqueazulene, respectively. The

structural, optical, and electrochemical properties of the

azulene-substituted donor-acceptor polymethines, bi-, ter-, and

quinqueazulenes were revealed by single-crystal X-ray structure

analysis, UV/vis spectroscopy, voltammetry analysis, spectroe-

lectrochemistry, and theoretical calculations. These results

suggested that the substituents on the azulene ring and their

substitution positions directly affect their reactivities, optical

and electrochemical properties.

Introduction

with donor and acceptor moieties by this method.^[5,6,7]Mean-

while, in the chemistry of azulene, the Zincke salt was applied

to the synthesis of azulenes by Ziegler and Hafner et al., in

which the Zincke salt is treated with amines or anilines, by

following the sequential nucleophilic-cyclization reactions with

cyclopentadienide ion.^[8]Nowadays, this methodology is well

known as Ziegler-Hafner’s azulene synthesis, which has been

approved as the best way to synthesize the parent azulene.^[9]

In recent years, several synthetic methods for 1-pyridyl- or

1,3-di(pyridyl)azulene derivatives have been developed.^[10]Our

group has also established the efficient synthesis of 1-(4-

pyridyl)- and 1,3-di(4-pyridyl)azulenes by the subsequent elec-

trophilic substitution and aromatization reactions.^[11]Although

the pyridine derivative is a promising building block for the

construction of polymethine dyes and azulenes, the reactivity of

1-(4-pyridyl)- and 1,3-di(4-pyridyl)azulenes has been hardly

explored, excluding the N-alkylation reaction of the pyridine

moiety. Since many applications have been found in azulene

derivatives with extended π-conjugated systems, such as

photovoltaics, semiconductors, and stimuli-responsive and

electrochromic materials, the development of the new synthetic

methods for the polymethines and the azulene ring assemblies

starting from the 1-(4-pyridyl)- and 1,3-di(4-pyridyl)azulenes as

precursors and characterization of their properties should

contribute to the field of organic electronics.

Since the discovery of Zincke salts in 1904, the salts which

could be obtained by the reaction of pyridine derivatives with

2,4-dinitrochlorobenzene^[1]are widely used as natural product

synthesis,^[2]substructures of pharmaceuticals,^[3]organic

materials,^[4]and precursors for polymethine dyes.^[5]The poly-

methine dyes, which are bonded donor and acceptor units to

both terminals, can be prepared via the ring-opening reaction

of the Zincke salts with amines. The dyes are an important class

of compounds to elucidate the correlation between the donor-

acceptor chromophores and their electronic and optical

properties.^[6]Hence, there has been a large volume of literature

on the synthesis and characterization of the polymethine dyes

[a] Prof. Dr. T. Shoji, A. Yamazaki, Y. Ariga, M. Uda

Department of Material Science

Graduate School of Science and Technology

Shinshu University

Matsumoto 390-8621,

Nagano (Japan)

E-mail: tshoji@shinshu-u.ac.jp

[b] Prof. Dr. T. Shoji, D. Ando, N. Sasahara

Department of Chemistry

Faculty of Science

Shinshu University

Matsumoto 390-8621,

Nagano (Japan)

In this paper, we report the synthesis of azulene-substituted

polymethines, 1,6’-biazulenes, 1,6’;3,6’’-terazulenes and a quin-

queazulene, utilizing the azulene-substituted Zincke salts as

precursors, which are prepared from 1-(4-pyridyl)- and 1,3-di(4-

pyridyl)azulenes.^[12]The structure of some products was re-

vealed by single-crystal X-ray analysis. The optical and electro-

[c] N. Kai, Prof. Dr. S. Ito

Graduate School of Science and Technology,

Hirosaki University

Hirosaki 036-8561,

Aomori (Japan)

Supporting information for this article is available on the WWW under

https://doi.org/10.1002/cplu.202100174

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chemical properties of the azulene-substituted polymethines,

1,6’-biazulenes and 1,6’;3,6’’-terazulenes were clarified by UV/vis

spectroscopy, voltammetry analysis, spectroelectrochemistry,

and theoretical calculations.

Results and Discussion

Synthesis of azulene-substituted polymethines

As mentioned above, pyridine derivatives are well-known for

the derivation into pyridinium salts and the subsequent

reactions with amines induced into the polymethines through

the ring-opening reactions.^[1–6]Thus, for the synthesis of

azulene-substituted polymethines, we have employed 1-(4-

pyridyl)- and 1,3-di(4-pyridyl)azulenes as starting materials,

which can be efficiently prepared by our method reported

previously.

The conversion of the 1-(4-pyridyl)- and 1,3-di(4-pyridyl)

azulenes to the corresponding pyridinium salts, which become

efficient precursors for the polymethines, was accomplished by

the reaction with 1-chloro-2,4-dinitrobenzene as previously

reported in the synthesis of the parent azulene by Hafner

et al.^[8,9]The reaction of 1a^[11a]with 1- chloro-2,4-dinitrobenzene

in toluene at refluxing temperature afforded Zincke salt 2a⁺

·Cl^{À [12a]}in 90% yield (Scheme 1). Since the Zincke salt 2a⁺·Cl^À

was insoluble toward the reaction solvent, the product was

Scheme 2. Synthesis of azulene-substituted pyridinium salts 4a,b⁺·Cl^–and

5a,b²⁺·2Cl^–.

precipitated during the reaction, which could be easily isolated

[12b]

by simple filtration. The Zincke salts 2b⁺·Cl^À

and 2c⁺·Cl^À

were also prepared from 1-(4-pyridyl)azulenes 1b^[11c]and 1c^[11d]

in a similar manner (Scheme 1).

Subsequently, the preparation of the Zincke salts with two

pyridinium groups at the 1,3-positions of the azulene ring was

examined according to the similar procedure described above.

However, the reaction of 1,3-(4-pyridyl)azulenes 3a and 3b

99% and 99% yields, respectively, from 3a and 3b (Scheme 2).

However, because of the difficulty in purifying the dicationic

products, 5a²⁺·2Cl^Àand 5b²⁺·2Cl^Àwere employed in the next

reaction without further purification.

with 1-chloro-2,4-dinitrobenzene in refluxing toluene produced

The ring-opening of the pyridinium salts 2a–c⁺·Cl^Àwas

conducted by the reaction with several secondary amines, so-

called Zincke reaction (Scheme 3).^[13]The Zincke reaction of 2a⁺

·Cl^Àwith diethylamine, by following the hydrolysis with 10%

HCl, produced the Zincke aldehyde 6a. However, the aldehyde

6a was unstable to show significant decomposition during the

purification by silica gel chromatography. Therefore, the

aldehyde 6a was transformed to 7aa^[12a]by Knoevenagel

reaction with malononitrile without further purification in 57%

as a two-step yield from 2a⁺·Cl^À(Table 1, Entry 1). The similar

ring-opening of 2a⁺·Cl^Àwas also found in the reaction with

morpholine, piperidine, and pyrrolidine, and the subsequent

amine-induced Knoevenagel reaction with malononitrile pro-

duced the corresponding polymethines 7ab–7ad^[12a]in moder-

ate to good yields (Table 1, Entries 3, 5 and 7).

[12b]

Zincke salts 4a⁺·Cl^{À [12b]}and 4b⁺·Cl^À,

which were retained

an unreacted pyridine ring, in 94% and 97% yields, respectively

(Scheme 2). This incompleteness of the reaction should be

attributed to the precipitation of the products 4a⁺·Cl^Àand 4b⁺

·Cl^Àin the reaction solvent. Therefore, to avoid the precipitation

of the products, ethanol was selected as the solvent that

facilitated the dissolution of the pyridinium salts. As a result,

the reaction in ethanol was found to give Zincke salts 5a²⁺

·2Cl^{À [12b]}and 5b²⁺·2Cl^{À [12b]}with the two-pyridinium units in

In 1982, Texier-Boullet and Foucaud reported the Knoevena-

gel reaction of various carbonyl compounds with active meth-

ylene compounds using alumina as a catalyst.^[14]Since their

preparation method is simple to operate and the product yields

are good to excellent, their methodology is adopted for the

synthesis of various donor-acceptor type molecules.^[15]We also

evaluated the Knoevenagel reaction using alumina as a catalyst

Scheme 1. Synthesis of azulene-substituted pyridinium salts 2a–c⁺·Cl^-.

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were difficult to isolate. The alumina-catalyzed Knoevenagel

reaction of the aldehydes with malononitrile gave 8a and 8b in

54% and 57% yields, respectively (Scheme 4).

In general, electron-rich dienes undergo [4+2] cycloaddi-

tion with electron-deficient alkenes, known as Diels-Alder

reaction, to form the corresponding six-membered ring prod-

ucts. Since the obtained polymethines have a triene moiety, the

Diels-Alder reaction with olefins may proceed to afford cyclo-

addition products. Since the polymethines possess both an

amine moiety, which has an electron-donating ability, and a

dicyanovinyl group, which shows an electron-withdrawing

nature, at both termini, the reactivity and reaction site of the

triene with olefins is of great interest. Therefore, the [4+2]

cycloaddition of the polymethines 7aa–ad with maleimide,

which is known as one of the reactive olefins, was examined for

the evaluation of their reactivity (Scheme 5). As a result, the

reaction of 7aa–ad with N-cyclohexyl maleimide in toluene at

Scheme 3. Synthesis of azulene-substituted polymethines 7a–e. For the R

groups on the amine moiety, see Table 1.

°

150 C yielded the azulene-substituted phthalimide 9, which is

obtained by the elimination of the amino group from the

presumed cycloadduct and further addition of the second

maleimide to the dicyanovinyl moiety, instead of the formation

Table 1. Synthesis of azulene-substituted polymethines 7a–e.

Ring-opening reaction

Knoevenagel reaction

additive

Entry

substrate

amine

product, yield [%]^[a]

1

2

3

4

5

6

7

8

2a⁺·Cl^-

2b⁺·Cl^-

2c⁺·Cl^-

4a⁺·Cl^-

4b⁺·Cl^-

Et₂NH

Et₃N

alumina

Et₃N

alumina

Et₃N

7aa, 57

7aa, 64

7ab, 75

7ab, 89

7ac, 40

7ac, 81

7ad, 52

7ad, 66

7b, 80

7b, 76

7c, 92

morpholine

piperidine

pyrrolidine

diethylamine

alumina

Et₃N

alumina

Et₃N

alumina

9

10

11

12

13

7d, 84

7e, 87

[a] two-step yield from the pyridinium salts 2a⁺·Cl^-–2c⁺·Cl^-and 4a,b⁺·Cl^-.

as another condition for the preparation of 7aa–ad because

this might become more useful conditions than those of the

base-catalyzed reaction. As a result, the alumina-catalyzed

Knoevenagel reaction of the Zincke aldehydes with malononi-

trile provided the desired polymethines 7aa–ad in higher yields

than those under the basic conditions (Table 1, Entries 2, 3, 6,

and 8). Furthermore, the alumina catalyst could be easily

removed by filtration at the workup process. The above results

suggest that the alumina-catalyzed Knoevenagel reaction is a

better selection for the preparation of the donor-acceptor type

polymethines. Thus, the ring-opening reaction of the pyridinium

salts 2b,c⁺·Cl^Àand 4a,b⁺·Cl^Àwith diethylamine, by following

the alumina-catalyzed Knoevenagel reaction with malononitrile

also afforded the corresponding polymethines 7b–e in good to

excellent yields without the isolation of 6b–e (Table 1,

Entries 9–13).

Scheme 4. Synthesis of azulene-substituted polymethines 8a,b.

Azulene derivatives 8a,b with two polymethine units were

also obtained by the same method. The Zincke salts 5a²⁺·2Cl^À

and 5b²⁺·2Cl^Àwith two pyridinium groups were treated with

diethylamine to produce the corresponding aldehydes, which

Scheme 5. [4+2] cycloaddition of 7aa–ad with N-cyclohexylmaleimide.

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of the usual simple [4+2] cycloadduct. The structure of 9 is

supported by single-crystal X-ray structure analysis as appeared

later (Figure 2).

The presumed reaction mechanism for the formation of 9 is

shown in Scheme 6. Initially, the usual [4+2] cycloaddition of

maleimide to the polymethine moiety takes place to give the

intermediate A. Subsequently, the amine is eliminated from A

to form the diene B. Additionally, the carbanion C stabilized by

the dicyanomethylene unit is formed by the deprotonation

under the basic conditions, which undergoes conjugate

addition to another maleimide to afford intermediate D. Finally,

the aromatization occurs at the cyclohexadienylidene moiety by

the allyl rearrangement of D to form 9. Since the intermediates

illustrated in Scheme 6 have never been isolated, there might

be still room for argument about the mechanism for the

formation of 9.

Figure 1. ORTEP representation of 7aa (Deposition Number 1838801 con-

tains the supplementary crystallographic data for this paper. These data are

provided free of charge by the joint Cambridge Crystallographic Data Centre

and Fachinformationszentrum Karlsruhe Access Structures service

Spectroscopic properties of azulene-substituted

polymethines

www.ccdc.cam.ac.uk/structures) recrystalized from a mixed solvent of

CH₂Cl₂/MeOH; ellipsoids are shown at the 50% probability level. orthorhom-

bic, Pca2₁(#29), a=10.1071(4) Å, b=15.4777(6) Å, c=11.3725(5) Å,

V=1779.05(13) Å³, Z=4, D_calc=1.222 g/cm³, μ(MoK_α)=0.730 cm^{À 1}, R1

(I>2.00σ)=0.0604, R (All reflections)=0.0747, wR2 (All reflections)=0.1421.

These new compounds were fully characterized based on their

spectral data, as summarized in the Experimental Section. The

NMR spectroscopic assignment of the reported compounds was

confirmed by the COSY experiment (Supporting Information

Figures S1–S48). High-resolution mass spectra showed the

correct molecular ion peaks. The characteristic stretching

vibration band of the C�N moieties of 7, 8, and 9 was observed

at ν_max=2188–2201 cm^{À 1}in their IR spectra. These results are

consistent with the structures of these products.

Since single crystals suitable for the X-ray structure analysis

were obtained, the structures of 7aa and 9 were clarified by the

single-crystal X-ray structure analysis (Figures 1 and 2).^[16]The

triene moiety of 7aa containing diethylamine and

dicyanomethylene takes all-trans and almost planar structure.

The crystal structure analysis of 7aa also revealed a twisted

conformation between the azulene and polymethine planes, in

°

which the dihedral angle was 63.42 (Figure 1). The single bond

in the triene moiety of 7aa was shorter than the general bond

length, while the double bond showed a longer bond distance

compared to that of the normal double bond. This supports the

Figure 2. ORTEP representation of 9 (Deposition Number 1922390 contains

the supplementary crystallographic data for this paper. These data are

provided free of charge by the joint Cambridge Crystallographic Data Centre

and Fachinformationszentrum Karlsruhe Access Structures service

www.ccdc.cam.ac.uk/structures) recrystalized from mixed solvent of CHCl₃/

MeOH; ellipsoids are shown at the 50% probability level. orthorhombic,

Pca2₁(#29), a=33.5514(17) Å, b=6.3927(3) Å, c=31.6001(16) Å,

3

β=110.124(6) , V=6363.9(6) Å , Z=4, D_calc=1.279 g/cm³, μ(MoK_α)_-

°

=0.839 cm^{À 1}, R1 (I>2.00σ)=0.0765, R (All reflections)=0.1339, wR2 (All

reflections)=0.2081.

push-pull resonance effect between the amine and the

dicyanomethylene moieties as represented by the resonance

structures shown in Scheme 7.

To elucidate the optical properties of the azulene-substi-

tuted polymethines, the UV/Vis spectra of the series of 7 and 8

were measured in CH₂Cl₂and 10% CF₃CO₂H (TFA)/CH₂Cl₂. The

Scheme 6. Presumed reaction mechanism for the formation of 9.

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amine moiety disappears by the protonation, the electron

donation is allowed only from the azulene ring, which should

contribute to the absorption band of [7aa+H]⁺with the lower

molar absorption coefficient.

Compounds 7b and 7c with tBu groups on the azulene ring

exhibited a slight red-shift compared to that of 7aa, but the

shift values were almost negligible. These results also imply that

the push-pull effect from the amine moiety to the dicyanometh-

ylene moiety contributes more effectively than that from the

azulene ring. The absorption maxima of 8a and 8b, which have

two polymethine units at the 1,3-positions of azulene, are

almost identical to those of 7aa and 7b, while the molar

absorption coefficients tend to increase with the number of

polymethine units (Figure 4). These phenomena are originated

from the overlap of the absorption bands arising from the

push-pull effect within the two polymethines and the reso-

nance effect between the central 1,3-azulen-di-yl core and the

two dicyanomethylene moieties as represented by the reso-

nance structures shown in Scheme 7.

Scheme 7. Resonance structure and protonation behavior of 7aa.

To clarify the origin of the absorption band of 7aa in the

UV/Vis spectra from

a theoretical aspect, the electronic

UV/Vis spectra of 7aa–ad in CH₂Cl₂showed a strong and broad

absorption band in the visible region, but their absorption

maxima were almost the same from each other (Figure 3). The

absorption maximum of 7aa was observed at λ_max=505 nm in

CH₂Cl₂. This strong absorption band should be explained by the

push-pull effect on both the azulene and amine moieties to the

dicyanomethylene unit as illustrated in Scheme 7. Similarly,

7ab, 7ac, and 7ad showed the maximum absorption wave-

lengths at λ_max=509 nm, 506 nm, and 509 nm, respectively, but

7ab showed a slight decrease in molar absorption coefficient,

although the reason is unclear.

transition of the absorption band and HOMO and LUMO

energies were investigated by time-dependent density func-

tional theory (TD-DFT) calculations at the B3LYP/6-31G**

level.^[17]Since the absorption spectra for the series of 7 and 8

were similar to each other, 7aa was evaluated as a model

compound. The electronic transitions of 7aa derived from the

calculations are summarized in Table 2. The frontier Kohn–Sham

orbitals and their energy levels are represented in Figure 5.

Theoretical calculations revealed that the strong absorption

band at 505 nm of 7aa is mainly composed of π-π* transitions

from azulene to triene (HÀ 1!L+1), triene moiety itself (H!L

+1), and triene to azulene (H!L+2). TD-DFT calculations also

suggest that several transitions are involved in the end

absorption, but their contribution to the absorption band is

negligibly small from the viewpoint of the oscillator strength.

These results support the existence of the push-pull effect both

When the solvent was changed to 10% TFA/CH₂Cl₂from

CH₂Cl₂,

a remarkable decrease in the molar absorption

coefficient was observed for the maximum absorption band of

7aa. In the acidic medium, by the protonation of either the

amine moiety or the dicyanomethylene unit, [7aa+H]⁺and

[7aa’+H]⁺should be generated. Since the donor nature of the

Figure 3. UV/Vis spectra of the polymethines 7aa (blue line), 7ab (red line),

7ac (light-green line), and 7ad (purple line) in CH₂Cl₂and 7aa (light-blue

line) in 10% TFA/CH₂Cl₂.

Figure 4. UV/Vis spectra of the polymethines 7aa (blue line), 7b (red line),

8a (light-green line) and 8b (purple line) in CH₂Cl₂.

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Table 2. The electronic transitions of 7aa derived from the computed values based on the TD-DFT calculations at the B3LYP/6-31G** level.

Experimental

λ_max

[log ɛ]

Computed values

λ_max

[Oscillator Strength]

Sample

7aa

Composition of band

[contribution]

505 (4.86)

552 (0.0049)

H–1!L (0.0486)

H!L (0.8497)

H!L+1 (0.0846)

H–1!L (0.8765)

H–1!L+1 (0.7682)

H!L+1 (0.0741)

H!L+1 (0.2459

H!L+2 (0.6882)

488 (0.0035)

421 (0.1381)

394 (0.1750)

H=HOMO, L=LUMO.

Most of 7a–e and 8a,b were revealed to show irreversible

redox waves by the CV measurements. The irreversibility could

be derived from either the instability of the radical species

generated or structural changes during the electrochemical

redox reaction. The first oxidation and reduction potentials of

these compounds were almost the same, meaning that the

amine moiety on the trienes 7aa–ad has no noticeable effect

on the electronic properties. On the other hand, the tBu groups

at the 1- or 6-positions of the azulene ring increase both the

ox

red

first oxidation and reduction potentials. As a result, ΔE₁À E₁

values of 7b and 7c become almost equal to those of 7aa–ad.

These findings are consistent with the fact that the similarity in

the maximum absorption wavelengths observed in the UV/Vis

ox

red

spectra of 7aa–ad, 7b, and 7c because the ΔE₁À E₁values

should be correlated to the HOMO-LUMO gap. Pyridine-

substituted adducts 7d,e, and bis-adducts 8a,b displayed

ox

red

slightly smaller ΔE₁À E₁values than those of 7aa–ad, 7b,

and 7c, corresponding to the narrower HOMO-LUMO gap due

to the extension of the π-conjugation.

Spectroelectrochemical measurements of 7aa, 7b–e, and

8a,b were performed to verify the electrochromic behavior. In

the spectroscopic electrochemical measurements, 7aa, 7b–e,

except for 7c, and 8a,b exhibited relatively high reversibility in

the redox cycles, meaning that the irreversibility in CV could be

ascribed to the structural changes by the electrochemical

reaction rather than the decomposition of the radical species

produced

When the spectral changes of 7aa were measured under

the electrochemical reduction conditions, generation of broad

absorption bands at around λ_max=450 nm and 550 nm was

observed along with the disappearance of the original

absorption band at around 500 nm. Reverse oxidation of the

reduced species of 7aa recovered the original spectrum, but

incompletely (regeneration 78%). Compound 7b (regeneration

81%) also displayed similar spectral changes to 7aa. However,

the regeneration ratio of the original spectrum by the reverse

oxidation of the reduced species of 7c was rather low

(regeneration 36%). This outcome suggests that the electron-

donating nature of the tBu group at the 1-position of the

azulene ring might significantly destabilize the anionic species

produced by the electrochemical reduction. The spectral

change of 7d was also developed new absorption bands

centered at 480 nm and 580 nm under the electrochemical

Figure 5. Frontier KohnÀ Sham orbitals of 7aa at the B3LYP/6-31G** level.

in the triene unit and in both azulene and triene moieties in

7aa.

To clarify the electrochemical behavior of 7a–e and 8a,b,

redox potentials of these products were examined by cyclic

voltammetry (CV) and differential pulse voltammetry (DPV). The

redox potentials measured by DPV are summarized in Table 3.

Cyclic and differential pulse voltammograms are appeared in

Supporting Information (Figures 123–132).

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Table 3. Redox potentials of the azulene-substituted polymethines 7a–7e and 8a,b measured by DPV.^[a]

red

Sample

E₁^ox[V]

E₂^ox[V]

E₁^red[V]

E₂^red[V]

ΔE₁^ox– E₁

7aa

7ab

7ac

7ad

7b

7c

7d

7e

8a

8b

+0.42

+0.43

+0.42

+0.43

+0.34

+0.36

+0.40

+0.39

+0.38

+1.01

+0.99

+1.00

+0.94

+0.87

+1.16

–

À 1.59

À 1.53

À 1.56

À 1.53

À 1.62

À 1.51

À 1.55

À 1.46

À 1.53

–

2.01

1.96

1.98

1.96

1.98

1.91

1.94

1.84

1.91

À 1.92

À 1.93

–

+1.24

+1.21

À 1.76^[b]

À 1.92

[a] 1 mM in benzonitrile containing Et₄NClO₄(0.1 M), Pt electrode (internal diameter: 1.6 mm), scan rate=20 mVs^{À 1}, and external standard Fc/Fc⁺= +0.15 V.

[b] E₃was also observed at –1.92 V.

red

reduction conditions. In contrast, the electrochemical reduction

of 7e at À 1.80 V generated the broad absorption band spread-

ing into 750 nm. Reverse oxidation of the reduced species

regenerated the original spectra of 7d (regeneration 64%) and

7e (regeneration 79%) to some extent. Di-substituted products

8a and 8b also displayed pronounced spectral changes under

the electrochemical reduction conditions, but the spectral

recovery to the neutral species upon the reverse oxidation was

also rather high, but incomplete (regeneration 8a: 67% and 8b:

94%).

In general, cyanine dyes exhibit electrochromism with low

reversibility due to the thermodynamic instability of the radical

species generated by the electrochemical redox reactions.^[18]

However, 7aa, 7b–e, and 8a,b showed relatively good reversi-

bility in the spectroelectrochemistry, except for 7c, which might

indicate the stabilization of the generated radical species by the

azulene ring on the cyanine moiety through the delocalization

on the whole molecule.

prepared by this method because this method is suitable for

the synthesis of azulenes having no substituting groups on the

five-membered ring.^[19]This method was applied to the syn-

thesis of 5,5’-^[20]and 6,6’-biazulenes^[21]by Hanke and Jutz. After

that, there are no reports on the preparation of biazulenes by

the Ziegler-Hafner method. Recently, terazulenes composed of

2,6’-biazulene core have been revealed the potential as high-

performance n-type organic field-effect transistors,^[22]so the

development of the synthetic methods for biazulenes and

terazulenes has attracted much attention in terms of the

development of organic materials. Therefore, we addressed the

synthesis of 1,6’-biazulene, 1,6’:3,6’’-terazulene derivatives, and

a quinqueazulene by the Ziegler-Hafner method using the

azulene-substituted Zincke salts as promising starting materials.

The synthesis of 1,6’-biazulenes 10a–e was conducted by

the same procedure for the preparation of the parent azulene

reported by Hafner et al. using the pyridinium salts 2a–c⁺·Cl^À

and 4a,b⁺·Cl^Àas starting materials (Table 4). The reaction of

2a–c⁺·Cl^Àand 4a,b⁺·Cl^Àwith diethylamine or pyrrolidine in

EtOH at room temperature afforded the corresponding iminium

salts as brown oils, which were used in the following reactions

without further purification. Recently, Langhals and Eberspächer

have demonstrated that pyrrolidine is the most favorable amine

for the ring-opening reaction of the pyridinium salt in the

preparation of the parent azulene.^[23]Hence, pyrrolidine was

used as an amine for the ring-opening reaction of the

Synthesis of bi-, ter-, and quinqueazulenes

An efficient synthesis of the parent azulene was achieved by

Ziegler and Hafner et al. via condensation of the Zincke salt

with cyclopentadienide ion by the subsequent intramolecular

cyclization reaction. Numerous azulene derivatives have been

Table 4. Synthesis of 1,6’-biazulenes 10a–e.

Entry

substrate

R¹

R²

amine

Base

Product,

yield [%]^[a]

1

2

3

4

5

2a⁺·Cl^-

2b⁺·Cl^-

2c⁺·Cl^-

4a⁺·Cl^-

4b⁺·Cl^-

H

Et₂NH

pyrrolidine

NaOMe

tBuOK

10a, 56^[12b]

10b, 91^[12b]

10c, 90

10d, 47

10e, 92

tBu

H

tBu

4-pyridyl

tBu

[a] isolated yield.

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pyridinium salts 2c⁺·Cl^Àand 4a,b⁺·Cl^À. Condensation of the

Zincke salts with cyclopentadiene (CPD) in the presence of

sodium methoxide (NaOMe) or potassium tert-butoxide (KOtBu)

afforded the corresponding 1,6’-biazulenes 10a–e in moderate

to good yields in two steps from 2a–c⁺·Cl^Àand 4a,b⁺·Cl^À,

respectively. Overall, 2b⁺·Cl^À, 2c⁺·Cl^Àand 4b⁺·Cl^À, which have

a tBu group at the 6-position of the azulene ring, tended to

give 1,6’-biazulenes in higher yields rather than those from 2a⁺

·Cl^Àand 4a⁺·Cl^À.

A plausible reaction mechanism for the formation of the

1,6’-biazulenes 10a–e is shown in Scheme 8. Essentially, this

reaction should be proceeded by the same mechanism as the

formation of the parent azulene reported by Ziegler and Hafner.

First, the ring-opening of the pyridinium salts 2a–c⁺·Cl^Àand

4a,b⁺·Cl^Àtakes place and the subsequent condensation with

diethylamine results in iminium salt E. The following condensa-

tion reaction of the iminium salt E with cyclopentadienide ion

provides pentafulvene intermediate F accompanying the elimi-

nation of diethylamine. Finally, the formation of the hydro-

azulene intermediate G by the electrocyclic reaction of the

fulvene intermediate F and the subsequent aromatization by

deamination to produce 1,6’-biazulenes.

The difference in the yields for the 1,6’-biazulenes could be

explained by the steric bulkiness of the tBu group at the 6-

position of the azulene ring. The iminium intermediate E has a

contribution of the resonance structure E’ where the azulene

ring has a tropylium ion substructure. Therefore, the nucleo-

philic addition of cyclopentadienide ion to the azulene moiety

at the seven-membered ring should take place to lead to the

undesired decomposition in the reaction of 2a⁺·Cl^Àand 4a⁺

·Cl^Àresulting in the low product yields. Whereas the derivatives

with a tBu group at the 6-position may prevent the attack of

the nucleophile to the seven-membered ring owing to the

steric hindrance of E’ by the substituent. Thus, 2b,c⁺·Cl^À, and

4b⁺·Cl^Àhave probably been obtained in higher product yields

compared to those of 2a⁺·Cl^Àand 4a⁺·Cl^À.

Likewise, the preparation of 1,6’-biazulenes 10a–e, the

synthesis of 1,6’;3,6’’-terazulenes 11a,b^[12b]was also investigated

using the corresponding bis-pyridinium derivatives 5a,b²⁺·2Cl^À

as starting materials (Scheme 9). The ring-opening reaction of

5a²⁺·2Cl^Àwith diethylamine, by following the reaction with

cyclopentadienide ion afforded the desired 1,6’;3,6’’-terazulene

(11a), but in low yield (10%). The 6-tert-butyl derivative 11b

was also obtained from 5b²⁺·2Cl^Àby the same method in 17%

yield. The product yields were both low in these cases, but

5b²⁺·2Cl^Àhaving a tBu group at the 6-position of the azulene

ring gave a slightly higher product yield as predicted.

Next, the synthesis of a quinqueazulene was investigated to

extend the scope of the synthetic methodology (Scheme 10).

For the synthesis of the quinqueazulene, it is required to

prepare the azulene derivatives with pyridine substituents as a

precursor. Thus, the pyridinylation of 10a,b was examined by

the method reported by us, previously.^[11]The reaction of 10a,b

with pyridine in the presence of trifluoromethanesulfonic

anhydride (Tf₂O) by following the base-induced aromatization

of the dihydropyridine intermediates with KOH afforded the tri

(4-pyridyl) derivatives 12a and 12b in 60% and 77%,

respectively, as two-step yields. Although 12a could not

convert to the quinqueazulene by the Ziegler-Hafner method

due to the decomposition of the compound, the reaction of

12b under the same conditions gave 13 in 7% yield.

To extend the applicability of this methodology, the

preparation of unsymmetrically substituted 1,6’;3,6’’-terazulene

15 was also investigated (Scheme 11). The electrophilic sub-

stitution reaction of 10d with N-iodosuccinimide gave a diiodo

derivative, which was insoluble in common organic solvents.

Thus, the crude product was employed in the next Suzuki-

Miyaura cross-coupling reaction with 4-tert-butylphenylboronic

acid without further purification. The Suzuki-Miyaura cross-

coupling reaction catalyzed by Pd(dppf)Cl₂provided 14 in 44%

yield, which could be converted to 1,6’;3,6’’-terazulene 15 in

19% yield by the Ziegler-Hafner method.

Spectroscopic properties of bi-, ter-, and quinqueazulenes

Scheme 8. Plausible reaction mechanism for the formation of 1,6’-biazulenes

10a–e by Ziegler-Hafner’s method.

The new compounds were fully characterized based on their

spectral data, as summarized in the Experimental Section. The

NMR spectroscopic assignment of the reported compounds was

confirmed by the COSY experiment (Supporting Information

Figures S49–S83). High-resolution mass spectra showed the

correct molecular ion peaks.

To elucidate the optical properties of a series of 1,6’-

biazulenes, 1,6’;3,6’’-terazulenes and a quinqueazulene prepared

by this study, measurements of the UV/Vis spectra of these

compounds were investigated (Supporting Information Figur-

es S84–S121). The absorption maxima (λ_max) of the series of 10–

15 in CH₂Cl₂and 30% TFA/CH₂Cl₂are summarized in Table 5.

Scheme 9. Synthesis of 1,6’;3,6’’-terazulenes 11a,b.

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Scheme 10. Synthesis of quinqueazulene 13.

Scheme 11. Synthesis of unsymmetrical 1,6’;3,6’’-terazulene 15.

UV/Vis spectra of 1,6’-biazulenes, 1,6’;3,6’’-terazulenes and

the quinqueazulene in CH₂Cl₂showed a characteristic weak

absorption band in the range of 500–600 nm originating from

the π-π* transition of the azulene rings, along with the strong

absorption band at around 430 nm. Although the molar

absorption coefficient increased with the number of azulene

rings in the molecule, the substitution of the tBu group at the

6-position of the azulene ring resulted in a slight blue-shift in

the longest absorption wavelength (Table 5, Figure 6). For

Table 5. Absorption maxima and their coefficients (log ɛ) of 10–15 in

CH₂Cl₂and 30% TFA/CH₂Cl₂.

[a]

Sample

λ_max[log ɛ] in CH₂Cl₂

λ_max[log ɛ] in 30% TFA/CH₂Cl₂

10a

10b

10c

10d

10e

11a

11b

12a

12b

13

430 (4.32), 583 (2.95)

439 (4.33), 572 (3.03)

458 (4.22), 586 (3.04)

419 (4.35), 587 (2.94)

433 (4.24), 578 (3.08)

436 (4.54), 579 (3.20)

446 (4.57), 576 (3.24)

456 (4.26), 590 (3.03)

466 (4.39), 571 (3.23)

456 (4.84)

581 (4.56)

601 (4.61)

421 (3.87), 629 (4.46)

412 (4.30), 552 (4.48)

421 (4.42), 569 (4.47)

575 (4.66)

593 (4.74)

427 (4.69)

424 (4.59)

585 (4.96)

example, the longest absorption wavelength of 10a (λ_max

=

583 nm) displayed a blue-shift by 11 nm compared to that of

10b (λ_max=572 nm). This phenomenon can be explained by

Plattner’s rule, which states that the alkyl groups substituted at

the even-numbered positions of the azulene ring (2-, 4-, 6- and

8-positions) represent a blue-shift of the absorption maxima in

the visible region.^[24]The longest absorption wavelengths of

14

15

421 (4.52), 577 (2.97)

443 (4.58), 592 (3.17)

415 (4.34), 555 (4.52)

579 (4.70)

[a] Shoulder peaks are omitted for clarity.

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Table 6. Their electronic transitions of 10a–c derived from the computed

values based on the TD-DFT calculations at the B3LYP/6-31G** level.

Experimental

λ_max

Computed values

Sample

λ_max

[Oscillator Strength]

Composition of band

(contribution)

10a^[12b]

583 (2.95)

531 (0.0078)

519 (0.0086)

497 (0.0001)

403 (0.4482)

529 (0.0082)

518 (0.0083)

H–1!L (0.9386)

H!L+1 (0.9044)

H!L (0.9819)

430 (4.32)

572 (3.03)

H–1!L+1 (0.8849)

H–1!L (0.9241)

H!L (0.0460)

10b

10c

H!L+1 (0.8750)

H!L (0.9495)

486 (0.0001)

H!L+1 (0.0453)

H–1!L+1 (0.8827)

H–1!L (0.6699)

H!L (0.2596)

439 (4.33),

586 (3.04)

407 (0.5168)

548 (0.0073)

518 (0.0079)

480 (0.0001)

421 (0.4904)

H–1!L+1 (0.2369)

H!L+1 (0.6450)

H–1!L (0.2584)

H!L (0.6961)

Figure 6. UV/Vis spectra of polymethines 10a (blue line), 10b (red line), 11a

(light-green line), 11b (purple line) and 13 (light-blue line) in CH₂Cl₂; the

dotted lines represent those of 10× magnification.

458 (4.22)

H–1!L+1 (0.6360)

H!L+1 (0.2474)

H=HOMO, L=LUMO.

1,6’-biazulenes 10d (λ_max=587 nm), 10e (λ_max=578 nm), 12a

(λ_max=590 nm), 12b (λ_max=571 nm) and 14 (λ_max=577 nm) did

not exhibit any significant difference from those of 10a,b,

suggesting that the pyridine substituents hardly contribute to

the expansion of the π-conjugation. Contrary to the longest

wavelength absorption band, the absorption band at around

430 nm exhibited a red-shift by the substitution of the tBu

group at the 6-position. Quinqueazulene 13 showed a strong

and broad absorption band at λ_max=456 nm, which spreads

into the near-infrared region.

To examine the theoretical aspects of the spectroscopic

properties, molecular orbital calculations were performed on

10a–c by using B3LYP/6-31G** density functional theory.^[17]The

frontier Kohn-Sham orbitals of 10b are shown in Figure 7. The

theoretical calculations suggest that the strong absorption

band of 10a observed at λ_max=430 nm can be explained by the

transition from HOMO-1 to LUMO+1, i.e., the π-π* transition

from 1-azulenyl group to 6-azulenyl group (Table 6). Similar to

10a, the strong absorption band of the compounds 10b and

10c could also be regarded as the transition from the 1-azulenyl

group to the 6-azulenyl group.

The theoretical calculations of the compounds 10a–c

reproduced the absorption maxima according to Plattner’s rule.

As shown in Table 6, the relatively weak absorption band of

10a at λ_max=583 nm originates from the overlap of several π-

π* transitions involving HOMO and HOMOÀ 1 to LUMO and

LUMO+1. The energy levels of HOMO and LUMO of 10b

(HOMO: À 4.98 eV; LUMO: À 1.98 eV) are higher than those of

10a (HOMO: À 5.04 eV; LUMO: À 2.10 eV). This is probably due

to the tBu group on the seven-membered ring of azulene,

which raises both the HOMO and LUMO energy levels, but has

a much pronounced effect on the LUMO level, resulting in a

hypsochromic shift of the longest wavelength absorption band

of 10b compared to that of 10a. According to Plattner’s rule,

the substitution of the electron-donating group at the 1-

position of the azulene ring leads to a bathochromic shift of the

longest wavelength absorption band, so that the absorption

band of 10c was observed in the longest wavelength side

among those of 10a–c despite the substitution of the tBu

group at the 6-position.

Among azulene derivatives, some of them are known to

show a remarkable color change, so-called halochromism, in

acidic solutions.^[25]Recently, we have also reported that azulene

derivatives with extended π-conjugated systems by substitution

or fusion of aromatic rings exhibit pronounced halochromism in

TFA/CH₂Cl₂mixed solvents.^[26]Therefore, the halochromic

behavior of the series of 10–15 was investigated by UV/Vis

spectroscopy in acidic solutions. UV/Vis spectra of 10a, 10c,

10d, and 11a in CH₂Cl₂and 30% TFA/CH₂Cl₂are shown in

Figure 8.

All compounds exhibited a noticeable color change when

TFA was added to the CH₂Cl₂solution (Figure 9). The reverse

neutralization of the acidic solutions with triethylamine (Et₃N)

Figure 7. Frontier KohnÀ Sham orbitals of 10b at the B3LYP/6-31G** level.

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Scheme 12. Protonation behavior of 1,6’-biazulenes 10a–e.

Figure 8. UV/Vis spectra of polymethines 10a (blue line), 10c (red line), 10d

(light-green line) and 11a (purple line) in CH₂Cl₂and 10a (blue dot-line), 10c

(red dot-line), 10d (light-green dot-line) and 11a (purple dot-line) in 30%

TFA/CH₂Cl₂.

LUMO energy gap. Thus, these derivatives exhibited a red-shift

of the absorption band. On the other hand, the 4-pyridyl group

of 10d and 10e is also protonated to produce an electron-

withdrawing pyridinium ion to decrease the HOMO level,

resulting in a blue-shift in the absorption band compared to

those of 10a and 10b.

Measurements of ¹H NMR of 10b in CDCl₃and in 30%

CF₃CO₂D/CDCl₃were also conducted to obtain further informa-

1

tion on the protonated chemical species (Figure 10). In the H

NMR spectra in 30% CF₃CO₂D/CDCl₃, protons at the 1-, 1’-, and

3’-positions disappeared owing to the proton-deuterium ex-

change with CF₃CO₂D. In 30% CF₃CO₂D/CDCl₃compared to in

CDCl₃, most of the proton signals of 10b exhibited a down-field

shift of the chemical shifts in the spectrum, but the shift values

were larger for the 6-azulenyl group than for the 1-azulenyl

group. Furthermore, the proton signal at the 2’-position was

observed in the olefin region in the 30% CF₃CO₂D/CDCl₃mixed

solvent. These facts should support the correctness of the

structure of the protonated species in acidic media represented

in Scheme 12.

Figure 9. Photo of colour change of (a) 10a, (b) 10c, (c) 10d (d) 11a in

CH₂Cl₂(left) and in 30% TFA/CH₂Cl₂(right).

recovered the original color. The maximum absorption wave-

lengths of 10a and 11a in 30% TFA/CH₂Cl₂were observed at

λ_max=581 nm and 575 nm, respectively, in their UV/Vis spectra.

Compound 10c (λ_max=629 nm) revealed the absorption band

in the longest wavelength region among those of 10a–10e. On

the other hand, the longest wavelength absorption bands of

10d (λ_max=552 nm) and 10e (λ_max=569 nm) with 4-pyridyl

group exhibited a blue-shift compared to those of 10a and 10b

(λ_max=601 nm) with their partial structures of 10e and 10d.

These differences in the absorption wavelengths can be

explained by the protonation as illustrated in Scheme 12. The 6-

azulenyl group of 1,6’-biazulenes 10a–c should be protonated

by TFA to form [10a–c+H]⁺, in which the 6-azulenyl group

forms a tropylium ion substructure, resulting in a strong

electron-withdrawing group. As a result, a strong charge-

transfer absorption band between the electron-donating 1-

azulenyl group and the protonated 6-azulenyl group is

observed in the visible region. In the cases of 10b and 10c, the

electron-donating tBu group on the azulene ring increases the

HOMO energy level, resulting in the decrease of the HOMO-

Figure 10. ¹H NMR (500 MHz) of 10b in CDCl₃(bottom) and in 30%

CF₃CO₂D/CDCl₃(top).

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Since some azulene derivatives are known to exhibit

potentials were observed in terazulenes 11a and 11b com-

pared to those of 10a and 10b; these facts imply that the

extension of the π-conjugated system effectively increases the

HOMO level. The increase of the HOMO levels is also supported

by the results of the theoretical calculations as described above.

The lower first oxidation potential of 1,6-biazulene 14 (+0.43 V)

than that of 10d (+0.63 V) indicates that the aryl group on the

1,3-positions of the 6-azulenyl group also contributes to the

extension of the π-conjugated system. The first oxidation

potential of 15 was slightly shifted to the lower potential side

from that of 11a. On the other hand, the substitution of the

pyridinyl group (e.g., 10d and 10e) led to an increase in the

oxidation potential despite the extension of the π-conjugated

system. This phenomenon should be attributed to the decrease

in the HOMO level due to the electron-withdrawing nature of

the substituted pyridinyl group.

The first reduction potentials of 10b (À 1.83 V), 10e

(À 1.74 V) and 11b (À 1.71 V) with a tBu group at the 6-position

exhibited a cathodic shift from those of 10a (À 1.74 V), 10d

(À 1.63 V), and 11a (À 1.68 V), which represented the increment

of the LUMO level due to the electron-donating nature of the

tBu group. Since there was no significant difference between

the first reduction potentials of 10b and 10c (À 1.84 V), the tBu

group at the 6-position should have a much pronounced effect

on the LUMO energy level than that at the 1-position. The lower

first reduction potentials of 14 (À 1.61 V) and 15 (À 1.60 V) than

those of 11a and 11b are probably due to the decrease in the

HOMO-LUMO gap caused by the extension of the π-conjugated

system by the substituted aryl groups.

luminescence in acidic media, the measurement of fluorescence

spectra of 1,6’-biazulenes, 1,6’;3,6’’-terazulenes and a quinquea-

zulene was examined. However, these derivatives did not show

any emission as well as the usual azulene derivatives.

To clarify the electrochemical behavior of 1,6’-biazulenes

10a–e, 11a,b, 14, and 15, redox potentials of these products

were measured by CV and DPV. The redox potentials measured

by DPV are summarized in Table 7. Cyclic and differential pulse

voltammograms are shown in Supporting Information

(Figures 133–141).

Most of the 1,6’-biazulenes showed irreversible redox waves

on the CV, which means the generation of unstable cationic

and anionic species from these derivatives under both electro-

chemical oxidation and reduction conditions. Even though 14

represented a quasi-reversible oxidation wave, exceptionally

(Figure 11), 1,6-biazulenes were extremely unstable toward the

electrochemical oxidation reaction, and insoluble decomposi-

tion products were deposited on the electrode after the

reaction. Since the first oxidation potential of 10c (+0.45 V)

exhibited a more anodic shift than those of 10a (+0.51 V) and

10b (+0.50), the tBu group on the azulene ring should raise

the HOMO level of the molecule. Lower first oxidation

Table 7. Redox potentials of 1,6’-biazulenes 10a–e, 11a,b, 14 and 15

measured by DPV.^[a]

Sample^[27]

E₁^ox[V]

E₂^ox[V]

E₁^red[V]

E₂^red[V]

10a

10b

10c

10d

10e

11a

11b

14

+0.51

+0.50

+0.45

+0.63

+0.62

+0.43

+0.42

+0.43

+0.41

+1.08

+0.91

+0.80

+1.04

+0.94

+1.21

+1.08

+1.24

+0.76

À 1.74

À 1.83

À 1.84

À 1.63

À 1.74

À 1.68

À 1.71

À 1.61

À 1.60

–

We have investigated the preparation of the extended π-

conjugated molecules substituted with 6-azulenyl groups, as

well as their electrochromic behavior.^[28]As a result, these

compounds have been identified to behave as electrochromic

molecules that show significant spectral changes under the

electrochemical redox conditions. The electrochromic behavior

of 10a–e, 11a,b, 14, and 15 was deduced by the spectroelec-

trochemical measurements because 1,6’-biazulenes prepared by

this study may also show large spectral changes under the

redox conditions.

À 1.95

–

À 1.95

À 1.94

À 1.96

15

[a] 1 mM in benzonitrile containing Et₄NClO₄(0.1 M), Pt electrode (internal

diameter: 1.6 mm), scan rate=20 mVs^–1, and external standard Fc/Fc⁺

+0.15 V.

=

On the basis of our previous studies, we expected that

compounds 10a–e, 11a,b, 14, and 15 should exhibit significant

color changes in their absorption spectra in the visible region.

However, the spectral changes of these compounds in the

visible region were not completely reversible, as reflected by

the results on the CV measurements. For example, when the

visible spectrum of 10a was monitored under the electro-

chemical reduction conditions at room temperature, a new

strong absorption band centered at λ_max=600 nm was ap-

peared accompanying an isosbestic point at λ=575 nm. This

obvious spectral change implies the formation of radical anionic

or anionic species from 10a by electrochemical reduction.

However, the reverse oxidation of the reduced species of 10a

did not reconstitute the original spectrum, completely, even

though the newly formed absorption band was decreased

(Figure 12).

Figure 11. Cyclic voltammograms for the oxidation of 14 in benzonitrile

We have also evaluated the electrochromic properties of

10b–e, 11a,b, 14, and 15. As similar to the case of 10a, the

(1 mM) containing Et₄NClO₄(0.1 M) as the supporting electrolyte; V vs. Ag/

AgNO₃and external standard Fc/Fc⁺= +0.15 V.

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desired products in higher yields than the basic conditions

using triethylamine as a catalyst. The Diels-Alder reaction of

polymethines 7aa–7ad with maleimides did not give the

expected [4+2] cycloadduct but yielded phthalimide 9, whose

structure was determined by single-crystal X-ray analysis.

The conversion of the Zincke salts to 1,6’-biazulenes,

1,6’;3,6’’-terazulenes and a quinqueazulene was also investi-

gated. The reaction of the Zinke salts with secondary amines by

following the successive condensation-cyclization reactions

with cyclopentadienide ion, so-called Ziegler-Hafner method,

afforded the corresponding 1,6’-biazulenes, 1,6’;3,6’’-terazulenes

and quinqueazulene. In these series of reactions, Zincke salts

with a tBu group at the 6-position of the azulene ring resulted

in higher yields of the desired products. The rationale for this

was identified in terms of the reaction mechanism.

The optical and electrochemical properties of azulene-

substituted polymethines, 1,6’-biazulenes, 1,6’;3,6’’-terazulenes

and a quinqueazulene obtained by this study were investigated

by UV/Vis spectroscopy, voltammetry analysis, spectroelectro-

chemistry, and theoretical calculations. These results suggested

that the substituents on the azulene ring and their substitution

positions directly affect their reactivities and optical and

electrochemical properties. The present outcomes provide an

efficient method for the preparation of new azulene derivatives,

which are difficult to obtain, and should contribute to the

development of organic electronic materials with azulene

skeletons.

Figure 12. Continuous change in the visible spectrum of 10a: constant

voltage electrochemical reduction at –1.90 V (top) and reverse oxidation of

the reduced species at �0 V (bottom) in benzonitrile containing Et₄NClO₄

(0.1 M) at 30 s intervals.

Experimental Section

General: Melting points were determined with a Yanagimoto MPS3

micromelting apparatus. The HRMS data were obtained with a

Bruker autoflex III TOF/TOF or JEOL JMS-700 spectrometer. IR and

UV/Vis spectra were recorded with JASCO FTIR-4100 and Shimadzu

large spectral changes of 10b–e, 11a,b, 14, and 15 in the

visible region were observed under the reduction conditions,

but again the spectra did not return to the original states,

completely, upon the reverse oxidation of the reduced species.

The spectra obtained by the reverse oxidation of the reduced

species of 10a–e, 11a,b, 14, and 15 exhibited higher absorption

coefficients than those of the original ones, suggesting that the

polymerization reaction might proceed to some extent during

the reduction or reverse oxidation process, although the

generated species could not be isolated.

1

UV-2550 spectrophotometers, respectively. H and ¹³C NMR spectra

were recorded with a JEOL ECA500 spectrometer at 500 MHz and

125 MHz, respectively. The voltammetry measurements were

performed with

a BAS 100B/W electrochemical workstation

equipped with Pt working and auxiliary electrodes and a reference

electrode formed from Ag/AgNO₃(0.01 M) in acetonitrile containing

tetrabutylammonium perchlorate (0.1 M).

Compound 2a⁺·Cl^À: To a solution of 1-(4-pyridinyl)azulene (1a)

(1.03 g, 5.02 mmol) in toluene (20 mL) was added 1-chloro-2,4-

dinitrobenzene (2.02 g, 10.0 mmol). The resulting solution was

stirred and heated at reflux temperature for 24 h. The reaction

mixture was cooled and the precipitated product was collected by

vacuum filtration to afford 2a⁺·Cl^Àas a reddish brown solid

Conclusion

°

(1.83 g, 90% yield). Mp 277–278 C; IR (ATR): ν_max=3108 (w), 3063

(w), 3009 (w), 1628 (s), 1612 (s), 1536 (s), 1513 (s), 1492 (m), 1390 (s),

1343 (s), 1305 (w), 1286 (w), 1229 (w), 1215 (s), 1070 (m), 917 (w),

903 (w), 862 (m), 835 (m), 802 (s), 752 (m), 740 (w), 707 (w), 682 (w)

In conclusion, we have described herein an efficient and

practical procedure for the synthesis of azulene-substituted

donor-acceptor type polymethines and 1,6’-biazulenes, 1,6’;3,6’’-

terazulenes and a quinqueazulene starting from the azulene

substituted Zincke salts.

Azulene-substituted Zincke salts reacted with several

amines, and subsequent Knoevenagel reaction with malononi-

trile afforded azulene-substituted donor-acceptor type polyme-

thines in moderate to excellent yields. In the Knoevenagel

reaction, alumina was revealed as a good catalyst to give the

1

cm^{À 1}; H NMR (500 MHz, CD₃OD): δ_H=9.24 (d, J=2.0 Hz, 1H, 3-H of

benzene), 9.09 (d, J=10.0 Hz, 1H, 8-H of azulene), 8.91 (d, J =

7.5 Hz, 2H, 2,6-H of pyridine), 8.89 (dd, J=9.0, 2.0 Hz, 1H, 5-H of

benzene), 8.67 (d, J=10.0 Hz, 1H, 4-H of azulene), 8.50–8.48 (m, 3H,

2-H of azulene, 3,5-H of pyridine), 8.32 (d, J=9.0 Hz, 1H, 6-H of

benzene), 8.03 (t, J=10.0 Hz, 1H, 6-H of azulene), 7.77 (t, J=

10.0 Hz, 1H, 7-H of azulene), 7.65 (t, J=10.0 Hz, 1H, 5-H of azulene),

7.60 (d, J=4.0 Hz, 1H, 3-H of azulene) ppm; ¹³C NMR (125 MHz,

CD₃OD): δ_C=154.52, 149.45, 147.97, 143.76, 143.59, 141.00, 139.74,

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139.55, 139.10, 138.99, 136.11, 131.51, 129.74, 129.71, 129.44,

123.93, 122.92, 121.91, 121.49 ppm; HRMS (FAB-MS, positive): Calcd

(125 MHz, CD₃OD): δ_C=154.52, 149.57, 149.07, 144.72, 144.02,

143.71, 142.52, 142.33, 141.04, 139.19, 138.94, 137.81, 137.13,

131.45, 130.62, 130.47, 129.98, 129.74, 124.76, 124.62, 122.72,

+

for C₂₁H₁₄N₃O₄[M]⁺372.0984, found: 372.0990.

+

121.96 ppm; HRMS (MALDI-TOF, positive): Calcd for C₂₆H₁₇N₄O₄

Compound 2b⁺·Cl^–: To a solution of 1b (1.05 g, 4.00 mmol) in

toluene (60 mL) was added 1-chloro-2,4-dinitrobenzene (1.62 g,

7.99 mmol). The resulting solution was stirred and heated at reflux

temperature for 14.5 h. The reaction mixture was cooled and the

precipitated product was collected by vacuum filtration to afford

pure 2b⁺·Cl^–(1.80 g, 97% yield) as a reddish brown solid. M.p. 253–

[M]⁺449.1244, found: 449.1236.

Compound 4b⁺·Cl^–: To a solution of 3b (439 mg, 1.30 mmol) in

toluene (15 mL) was added 1-chloro-2,4-dinitrobenzene (786 mg,

3.88 mmol). The mixture solution was stirred and heated at reflux

temperature for 24 h. The reaction mixture was cooled and the

precipitated product was collected by filtration to afford 4b⁺·Cl^–

°

255 C (decomp.); IR (AT–IR): ν_max=2970 (w), 1631 (s), 1614 (s), 1586

°

(m), 1541 (m), 1523 (m), 1509 (m), 1479 (m), 1442 (m), 1397 (s),

1342 (s), 1309 (m), 1289 (m), 1232 (m), 1218 (s), 1124 (w), 1068 (m),

1010 (w), 915 (m), 849 (m), 835 (m), 822 (w), 783 (m), 764 (w), 741

(661 mg, 94% yield) as a reddish brown solid. M.p. 246–249 C; IR

(AT–IR): ν_max=2963 (w), 2926 (w), 2876 (w), 1627 (m), 1607 (s), 1596

(m), 1577 (m), 1540 (s), 1514 (s), 1475 (m), 1434 (s), 1388 (m), 1373

(m), 1341 (m), 1323 (w), 1283 (m), 1253 (w), 1219 (s), 1192 (w), 1143

(w), 1079 (w), 1007 (w), 990 (w), 946 (m), 910 (w), 892 (w), 867 (m),

837 (m), 823 (m), 768 (w), 736 (m), 715 (w), 689 (w), 677 (w), 652

1

(w), 711 (w), 683 (w) cm^{À 1}; H NMR (500 MHz, CD₃OD): δ_H=9.25 (d,

J=2.3 Hz, 1H), 9.10 (d, J=10.9 Hz, 1H), 8.89 (dd, J=8.6, 2.3 Hz, 1H),

8.83 (d, J=6.9 Hz, 2H), 8.64 (d, J=10.3 Hz, 1H), 8.48 (d, J=6.9 Hz,

2H), 8.44 (d, J=4.6 Hz, 1H), 8.28 (d, J=8.6 Hz, 1H), 8.03 (dd, J=10.9,

1.7 Hz, 1H), 7.96 (dd, J=10.6, 2.0 Hz, 1H), 7.54 (d, J=4.0 Hz, 1H),

1.54 (s, 9H) ppm; ¹³C NMR (125 MHz, CD₃OD): δ_C=166.29, 154.34,

149.43, 147.24, 143.84, 143.26, 139.05, 139.01, 138.61, 138.26,

135.33, 131.40, 129.64, 128.35, 128.20, 123.26, 122.51, 121.92,

121.26, 38.74, 30.70 ppm; HRMS (FAB-MS, positive): Calcd for

1

(w), 634 (w) cm^{À 1}; H NMR (500 MHz, CDCl₃): δ_H=9.25 (d, J=2.3 Hz,

1H, 3-H of benzene), 9.17 (d, J=10.9 Hz, 1H, 4-H of azulene), 8.96

(d, J=6.9 Hz, 2H, 2,6-H of pyridinium), 8.90 (dd, J=8.6, 2.3 Hz, 1H,

5-H of benzene), 8.85 (d, J=10.6 Hz, 1H, 8-H of azulene), 8.68 (s, 1H,

2-H of azulene), 8.66 (d, J=6.0 Hz, 2H, 2,6-H of pyridine), 8.58 (d, J=

6.9 Hz, 2H, 3,5-H of pyridinium), 8.33 (d, J=8.6 Hz, 1H, 6-H of

benzene), 8.10 (dd, J=10.7, 1.6 Hz, 1H, 5-H of azulene), 8.04 (dd, J=

10.9, 1.7 Hz, 1H, 7-H of azulene), 7.78 (d, J=6.0 Hz, 2H, 3,5-H of

pyridine), 1.55 (s, 9H, tBu) ppm; ¹³C NMR (125 MHz, CDCl₃): δ_C=

167.76, 154.31, 149.52, 149.22, 144.53, 143.75, 141.72, 140.18,

138.98, 138.24, 136.82, 136.27, 131.51, 129.86, 129.74, 129.18,

124.37, 124.16, 122.26, 121.94, 38.89, 30.64 ppm; HRMS (MALDI-

+

C₂₅H₂₂N₃O₄[M]⁺428.1600, found: 428.1621.

Compound 2c⁺·Cl^–: To a solution of 1c (473 mg, 1.49 mmol) in

toluene (24 mL) was added 1-chloro-2,4-dinitrobenzene (910 mg,

4.49 mmol). The resulting solution was stirred and heated at reflux

temperature for 24 h. The reaction mixture was cooled and the

precipitated product was collected by vacuum filtration to afford

2c⁺·Cl^–(772 mg, 99% yield) as a reddish brown solid. M.p. 210–

+

TOF, positive): Calcd for C₃₀H₂₅N₄O₄[M]⁺505.1870, found:

505.1870.

°

212 C; IR (AT-IR): ν_max=3358 (w), 3034 (w), 2962 (w), 1626 (s), 1602

(m), 1575 (m), 1542 (s), 1519 (s), 1474 (m), 1429 (s), 1371 (s), 1343

(s), 1317 (w), 1279 (w), 1249 (m), 1209 (s), 1079 (w), 1065 (w), 1026

(w), 966 (w), 944 (w), 916 (w), 899 (w), 875 (w), 857 (m), 846 (m), 831

Compound 5a²⁺·2Cl^–: To a solution of 3a (149 mg, 0.53 mmol) in

ethanol (10 mL) was added 1-chloro-2,4-dinitrobenzene (312 mg,

1.54 mmol). The resulting solution was stirred and heated at reflux

temperature for 24 h. The solvent was removed under reduced

pressure and added toluene. The reaction mixture was cooled and

the precipitated product was collected by vacuum filtration to

afford 5a²⁺·2Cl^–(360 mg, 99% yield) as a reddish-brown solid. The

crude product was used in the next reaction without further

purification.

1

(m), 798 (w), 765 (w), 745 (w), 730 (w), 712 (w), 685 (w) cm^–1; H

NMR (500 MHz, CD₃OD): δ_H=9.23 (d, J=2.6 Hz, 1H, 3-H of benzene),

9.02 (d, J=11.0 Hz, 1H, 4-H of azulene), 9.00 (d, J=11.0 Hz, 1H, 8-H

of azulene), 8.88 (dd, J=8.6, 2.6 Hz, 1H, 5-H of benzene), 8.77 (d, J=

7.2 Hz, 2H, 2,6-H of pyridinium), 8.42 (d, J=7.2 Hz, 2H, 3,5-H of

pyridinium), 8.31 (s, 1H, 2-H of azulene), 8.28 (d, J=8.6 Hz, 1H, 6-H

of benzene), 7.92–7.96 (m, 2H, 5,7-H of azulene), 1.64 (s, 9H, tBu),

1.53 (s, 9H, tBu) ppm; ¹³C NMR (125 MHz, CD₃OD): δ_C=166.02,

153.79, 149.37, 143.87, 142.91, 142.82, 142.77, 140.92, 139.09,

137.74, 136.15, 134.85, 131.42, 129.65, 128.59, 128.20, 127.88,

126.76, 123.23, 121.93, 120.63, 38.53, 32.90, 30.65, 30.57 ppm; HRMS

Compound 5b²⁺·2Cl^–: To a solution of 3b (331 mg, 0.98 mmol) in

ethanol (20 mL) was added 1-chloro-2,4-dinitrobenzene (810 mg,

4.00 mmol). The mixture solution was stirred and heated at reflux

temperature for 24 h. The solvent was removed under reduced

pressure and added toluene. The reaction mixture was cooled to

room temperature and the precipitated product was collected by

filtration to afford 5b²⁺·2Cl^–(723 mg, 99% yield) as a reddish-

brown solid. The crude product was used in the next reaction

without further purification.

+

(MALDI-TOF, positive): Calcd for C₂₉H₃₀N₃O₄[M]⁺484.2231, found:

484.2245.

Compound 4a⁺·Cl^–: To a solution of 3a (282 mg, 1.00 mmol) in

toluene (15 mL) was added 1-chloro-2,4-dinitrobenzene (609 mg,

3.01 mmol). The resulting solution was stirred and heated at reflux

temperature for 24 h. The reaction mixture was cooled and the

precipitated product was collected by filtration to afford 4a⁺·Cl^–

Compound 7aa: Preparation by triethylamine-catalyzed Knoevena-

gel reaction: Diethylamine (5 mL) was added to a solution of 2a⁺

·Cl^–(404 mg, 0.99 mmol) in ethanol (3 mL). The resulting solution

was stirred at room temperature for 30 min. The reaction mixture

was poured into 2 M NaOH and extracted with dichloromethane,

dried with Na₂SO₄, and concentrated under reduced pressure.

Triethylamine (2 mL) was added to a solution of the crude Zincke

aldehyde (204 mg, 0.73 mmol) and malononitrile (96 mg,

1.46 mmol) in dichloromethane (5 mL). The resulting solution was

stirred for 2 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 7aa

(184 mg, 57% as two-step yield from 2a⁺·Cl^–) as a deep red solid.

°

(469 mg, 97% yield) as a reddish brown solid. M.p. 218–220 C; IR

(AT-IR): ν_max=3108 (w), 2964 (w), 2926 (w), 1627 (s), 1607 (s), 1596

(m), 1577 (m), 1541 (s), 1514 (s), 1475 (w), 1434 (s), 1388 (w), 1373

(m), 1341 (s), 1323 (w), 1283 (w), 1252 (w), 1219 (s), 1191 (w), 1160

(w), 1143 (w), 1078 (w), 1067 (w), 1027 (w), 1007 (w), 989 (w), 946

(w), 909 (w), 892 (w), 867 (m), 851 (w), 837 (m), 823 (s), 768 (w), 736

(m), 715 (w), 675 (w), 653 (w) cm^{À 1}; ¹H NMR (500 MHz, CD₃OD): δ_H=

9.27 (d, J=2.6 Hz, 1H, 3-H of benzene), 9.19 (d, J=9.8 Hz, 1H, 4-H of

azulene), 9.03 (d, J=7.2 Hz, 2H, 2,6-H of pyridinium), 8.88–8.93 (m,

2H, 5-H of benzene, 8-H of azulene), 8.76 (s, 1H, 2-H of azulene),

8.68 (d, J=6.0 Hz, 2H, 2,6-H of pyridine), 8.61 (d, J=6.9 Hz, 2H, 3,5-

H of pyridinium), 8.34 (d, J=8.6 Hz, 1H, 6-H of benzene), 8.14 (t, J=

9.8 Hz, 1H, 6-H of azulene), 7.86 (t, J=9.8 Hz, 1H, 5-H of azulene),

7.77–7.81 (m, 3H, 7-H of azulene, 3,5-H of pyridine) ppm; ¹³C NMR

Preparation by alumina-catalyzed Knoevenagel reaction: Diethyl-

amine (1 mL) was added to

a

solution of 2a⁺·Cl^–(306 mg,

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0.75 mmol) in ethanol (5 mL). The resulting solution was stirred at

room temperature for 30 min. The reaction mixture was poured

into 2 M NaOH and extracted with dichloromethane, dried with

Na₂SO₄, and concentrated under reduced pressure. Alumina

(568 mg) was added to a solution of the crude Zincke aldehyde

(156 mg, 0.56 mmol) and malononitrile (88 mg, 1.33 mmol) in

dichloromethane (3 mL). The resulting solution was stirred for 1 h

at room temperature. The solvent was removed under reduced

pressure and the residue was purified by column chromatography

on silica gel with EtOAc/hexane (1:1) to give 7aa (158 mg, 64% as

1H, 7-H of azulene), 6.83 (d, J=12.6 Hz, 1H, H of triene), 6.67 (d, J=

12.9 Hz, 1H, H of triene), 6.38 (d, J=12.6 Hz, 1H, H of triene), 5.84 (d,

J=12.9 Hz, 1H, H of triene), 3.67 (br s, 4H, morpholine), 3.23 (br s,

4H, morpholine) ppm; ¹³C NMR (125 MHz, CDCl₃):δ_C=160.04,

157.44, 152.20, 142.04, 139.02, 138.70, 138.14, 138.00, 135.67,

124.67, 124.46, 123.84, 118.04, 117.79, 117.63, 117.27, 115.22,

104.29, 77.35, 77.10, 76.84, 67.23, 66.12, 29.68 ppm; HRMS (FAB-MS,

positive): Calcd for C₂₂H₁₉N₃O [M]⁺341.1528, found: 341.1530.

Compound 7ac: Preparation by triethylamine-catalyzed Knoevena-

gel reaction: Piperidine (2 mL) was added to a solution of 2a⁺·Cl^–

(202 mg, 0.50 mmol) in ethanol (3 mL). The resulting solution was

stirred at room temperature for 30 min. The reaction mixture was

poured into 2 M NaOH and extracted with dichloromethane, dried

with Na₂SO₄, and concentrated under reduced pressure. Triethyl-

amine (0.5 mL) was added to a solution of the crude Zincke

aldehyde (129 mg, 0.44 mmol) and malononitrile (68 mg,

1.03 mmol) in dichloromethane (3 mL). The resulting solution was

stirred for 1 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 7ac

(67 mg, 40% as two-step yield from 2a⁺·Cl^–) as a deep red solid.

+

–

°

two-step yield from 2a ·Cl ) as a deep red solid. M.p. 181–182 C; IR

(AT–IR): ν_max=2982 (w), 2938 (w), 2878 (w), 2194 (s), 1614 (m), 1508

(s), 1488 (s), 1457 (s), 1424 (m), 1397 (w), 1357 (s), 1309 (m), 1287

(m), 1221 (s), 1187 (s), 1176 (s), 1148 (m), 1115 (s), 1078 (m), 1066

(m), 990 (w), 965 (m), 952 (m), 869 (m), 782 (w), 773 (w), 749 (w),

671 (w) cm^{À 1}; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=237 (4.35), 280 (4.61),

1

324 sh (3.90), 340 sh (3.85), 480 sh (4.71), 505 (4.86) nm; H NMR

(500 MHz, CDCl₃): δ_H=8.40 (d, J=10.0 Hz, 1H, 4-H of azulene), 8.40

(d, J=10.0 Hz, 1H, 8-H of azulene), 7.78 (d, J=4.0 Hz, 1H, 2-H of

azulene), 7.67 (t, J=9.5 Hz, 1H, 6-H of azulene), 7.43 (d, J=4.0 Hz,

1H, 3-H of azulene), 7.28 (t, J=10.0 Hz, 1H, 5-H of azulene), 7.21 (d,

J=10.0 Hz, 1H, 7-H of azulene), 6.80 (d, J=13.0 Hz, 1H, H of triene),

6.65 (d, J=13.0 Hz, 1H, H of triene), 6.80 (d, J=13.0 Hz, 1H, H of

triene), 6.48 (d, J=15.0 Hz, 1H, H of triene), 5.79 (d, J=15.0 Hz, 1H,

H of triene), 3.21 (br s, 4H, Et), 1.15 (br s, 6H, Et) ppm; ¹³C NMR

(125 MHz, CDCl₃): δ_C=160.70, 157.09, 152.50, 142.11, 138.98,

138.85, 138.20, 137.95, 135.82, 124.58, 124.33, 124.09, 118.03,

117.59, 117.07, 115.99, 104.00, 64.52, 50.97, 43.21, 14.81, 12.23 ppm;

Preparation by alumina-catalyzed Knoevenagel reaction: Pyrroli-

dine (2 mL) was added to a solution of 2a⁺·Cl^–(96 mg, 0.23 mmol)

in ethanol (2 mL). The resulting solution was stirred at room

temperature for 30 min. The reaction mixture was poured into 2 M

NaOH and extracted with dichloromethane, dried with Na₂SO₄, and

concentrated under reduced pressure. Alumina (234 mg) was

+

HRMS (FAB-MS, positive): Calcd for C₂₂H₂₁N₃[M]⁺327.1735, found:

added to

a solution of the crude Zincke aldehyde (66 mg,

327.1731.

0.23 mmol) and malononitrile (36 mg, 0.55 mmol) in dichloro-

methane (3 mL). The resulting solution was stirred for 1 h at room

temperature. The solvent was removed under reduced pressure

and the residue was purified by column chromatography on silica

gel with EtOAc/hexane (1:1) to give 7ac (65 mg, 0.19 mmol, 81%

Compound 7ab: Preparation by triethylamine-catalyzed Knoeve-

nagel reaction: Morpholine (2 mL) was added to a solution of 2a⁺

·Cl^–(240 mg, 0.59 mmol) in ethanol (3 mL). The resulting solution

was stirred at room temperature for 30 min. The reaction mixture

was poured into 2 M NaOH and extracted with dichloromethane,

dried with Na₂SO₄, and concentrated under reduced pressure.

Triethylamine (0.5 mL) was added to a solution of the crude Zincke

aldehyde (135 mg, 0.46 mmol) and malononitrile (82 mg,

1.24 mmol) in dichloromethane (3 mL). The resulting solution was

stirred for 2 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 7ab

(149 mg, 75% as two-step yield from 2a⁺·Cl^–) as a deep red solid.

+

–

°

as two-step yield from 2a ·Cl ) as a deep red solid. M.p. 85–87 C;

IR (AT–IR): ν_max=2938 (w), 2857 (w), 2199 (m), 1616 (w), 1505 (s),

1458 (m), 1444 (m), 1396 (w), 1361 (m), 1311 (w), 1207 (s), 1186 (s),

1125 (m), 1106 (w), 1021 (w), 999 (w), 942 (w), 853 (w), 782 (w), 748

(w), 673 (w), 664 (w), 637 (w) cm^{À 1}; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=

235 (4.24), 280 (4.49), 323 sh (3.80), 341 (3.75), 481 sh (4.60), 506

(4.75) nm; ¹H NMR (500 MHz, CDCl₃): δ_H=8.41 (d, J=9.5 Hz, 1H, 4-H

of azulene), 8.18 (d, J=9.7 Hz, 1H, 8-H of azulene), 7.78 (d, J=

3.7 Hz, 1H, 2-H of azulene), 7.69 (t, J=9.9 Hz, 1H, 6-H of azulene),

7.43 (d, J=3.7 Hz, 1H, 3-H of azulene), 7.30 (t, J=9.7 Hz, 1H, 5-H of

azulene), 7.22 (d, J=9.7 Hz, 1H, 7-H of azulene), 6.78 (d, J=12.9 Hz,

1H, H of triene), 6.63 (d, J=12.9 Hz, 1H, H of triene), 6.44 (d, J=

12.6 Hz, 1H), 5.84 (d, J=12.6 Hz, 1H, H of triene), 3.31 (br s, 4H,

piperidine), 1.64 (br s, 6H, piperidine) ppm; ¹³C NMR (500 MHz,

CDCl₃): δ_C=161.07, 156.69, 153.21, 141.92, 138.86, 138.71, 138.04,

137.85, 135.68, 124.47, 124.26, 124.04, 118.15, 117.48, 116.67,

116.02, 103.66, 63.49, 55.55, 46.48, 26.38, 25.19, 23.76 ppm; HRMS

Preparation by alumina-catalyzed Knoevenagel reaction: Morpho-

line (1 mL) was added to a solution of 2a⁺·Cl^–(29 mg, 0.072 mmol)

in ethanol (1 mL). The resulting solution was stirred at room

temperature for 30 min. The reaction mixture was poured into 2 M

NaOH and extracted with dichloromethane, dried with Na₂SO₄, and

concentrated under reduced pressure. Alumina (86 mg) was added

to a solution of the crude Zincke aldehyde (24 mg, 0.082 mmol)

and malononitrile (16 mg, 0.24 mmol) in dichloromethane (2 mL).

The resulting solution was stirred for 1 h at room temperature. The

solvent was removed under reduced pressure and the residue was

purified by column chromatography on silica gel with EtOAc/

(FAB-MS, positive): Calcd for C₂₃H₂₁N₃[M]⁺339.1735, found:

+

339.1737.

Compound 7ad: Preparation by triethylamine-catalyzed Knoeve-

nagel reaction: Pyrrolidine (2 mL) was added to a solution of 2a⁺

·Cl^–(206 mg, 0.50 mmol) in ethanol (3 mL). The resulting solution

was stirred at room temperature for 30 min. The reaction mixture

was poured into 2 M NaOH and extracted with dichloromethane,

dried with Na₂SO₄, and concentrated under reduced pressure.

Triethylamine (0.5 mL) was added to a solution of the crude Zincke

aldehyde (101 mg, 0.36 mmol) and malononitrile (66 mg,

1.00 mmol) in dichloromethane (3 mL). The resulting solution was

stirred for 2 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 7ad

(84 mg, 52% as two-step yield from 2a⁺·Cl^–) as a deep red solid.

hexane (1:1) to give 7ab (22 mg, 89% as two-step yield from 2a⁺

–

°

·Cl ) as a deep red solid. M.p. 94–97 C; IR (AT–IR): ν_max=2966 (w),

2917 (w), 2860 (w), 2200 (m), 2187 (m), 1617 (m), 1577 (w), 1487 (s),

1428 (s), 1396 (w), 1364 (m), 1331 (w), 1311 (w), 1287 (w), 1213 (s),

1174 (s), 1153 (s), 1115 (m), 1068 (w), 1020 (m), 960 (w), 943 (m)

cm^{À 1}; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=237 (4.29), 280 (4.57), 325 sh

1

(3.85), 341 (3.81), 477 sh (4.67), 499 (4.74) nm; H NMR (500 MHz,

CDCl₃):δ_H=8.42 (d, J=9.5 Hz, 1H, 4-H of azulene), 8.16 (d, J=9.7 Hz,

1H, 8-H of azulene), 7.78 (d, J=4.0 Hz, 1H, 2-H of azulene), 7.69 (t,

J=9.9 Hz, 1H, 6-H of azulene), 7.43 (d, J=3.7 Hz, 1H, 3-H of

azulene), 7.30 (t, J=9.7 Hz, 1H, 5-H of azulene), 7.22 (d, J=9.7 Hz,

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Preparation by alumina-catalyzed Knoevenagel reaction: Pyrroli-

dine (2 mL) was added to a solution of 2a⁺·Cl^–(80 mg, 0.20 mmol)

in ethanol (2 mL). The resulting solution was stirred at room

temperature for 30 min. The reaction mixture was poured into 2 M

NaOH and extracted with dichloromethane, dried with Na₂SO₄, and

concentrated under reduced pressure. Alumina (146 mg) was

1H, H of triene), 6.63 (d, J=12.9 Hz, 1H, H of triene), 6.53 (s, 1H, H of

triene), 5.78 (d, J=12.3 Hz, 1H, H of triene), 3.36 (s, 2H, Et), 3.09 (s,

2H, Et), 1.47 (s, 9H, tBu), 1.25 (s, 3H, Et), 1.06 (s, 3H, Et) ppm; ¹³C

NMR (500 MHz, CDCl₃): δ_C=163.34, 160.96, 157.36, 152.42, 152.35,

140.89, 138.01, 137.14, 136.99, 134.87, 123.54, 122.74, 118.16,

117.03, 116.09, 104.01, 77.34, 77.09, 76.83, 64.45, 50.91, 43.16, 38.93,

31.96, 14.86, 12.27 ppm; HRMS (FAB-MS, positive): Calcd for

added to

a solution of the crude Zincke aldehyde (39 mg,

+

0.14 mmol) and malononitrile (17 mg, 0.25 mmol) in dichloro-

methane (3 mL). The resulting solution was stirred for 1 h at room

temperature. The solvent was removed under reduced pressure

and the residue was purified by column chromatography on silica

gel with EtOAc/hexane (1: 1) to give 7ad (42 mg, 66% as two-step

C₂₆H₂₉N₃[M]⁺383.2361, found: 383.2351.

Compound 7c: Diethylamine (5 mL) was added to a solution of 2c⁺

·Cl^–(322 mg, 0.62 mmol) in ethanol (5 mL). The resulting solution

was stirred at room temperature for 30 min. The reaction mixture

was poured into 2 M NaOH and extracted with dichloromethane,

dried with Na₂SO₄, and concentrated under reduced pressure.

Alumina (611 mg) was added to a solution of the crude Zincke

aldehyde (235 mg, 0.60 mmol) and malononitrile (81 mg,

1.22 mmol) in dichloromethane (3 mL). The resulting solution was

stirred for 1 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 7c

(251 mg, 92% as two-step yield from 2c⁺·Cl^–) as a deep red solid.

+

–

°

yield from 2a ·Cl ) as a deep red solid. M.p. 102–105 C; IR (AT–IR):

ν

_max=3011 (w), 2975 (w), 2873 (w), 2200 (m), 1614 (w), 1577 (w),

1499 (s), 1473 (m), 1451 (m), 1412 (w), 1396 (w), 1361 (m), 1338 (w),

1313 (m), 1265 (w), 1207 (s), 1194 (s), 1170 (s), 1109 (w), 1033 (w),

944 (w), 864 (w), 780 (w), 750 (m), 668 (w) cm^{À 1}; UV/Vis (CH₂Cl₂):

λ_max(log ɛ)=238 (4.32), 280 (4.58), 323 sh (3.87), 341 (3.82), 482 sh

(4.68), 509 (4.84) nm; ¹H NMR (500 MHz, CDCl₃): δ_H=8.40 (d, J=

9.5 Hz, 1H, 4-H of azulene), 8.18 (d, J=9.7 Hz, 1H, 8-H of azulene),

7.78 (d, J=3.7 Hz, 1H, 2-H of azulene), 7.66 (t, J=9.9 Hz, 1H, 6-H of

azulene), 7.42 (d, J=3.7 Hz, 1H, 3-H of azulene), 7.29 (d, J=9.5 Hz,

1H, 5-H of azulene), 7.20 (t, J=9.7 Hz, 1H, 7-H of azulene), 6.77 (d,

J=12.9 Hz, 1H, H of triene), 6.64 (d, J=12.9 Hz, 2H, H of triene),

5.72 (d, J=11.5 Hz, 1H, H of triene), 3.27 (br s, 4H, pyrrolidine),

1.83–2.00 (m, 4H, pyrrolidine) ppm; ¹³C NMR (500 MHz, CDCl₃): δ_C=

160.61, 156.59, 150.46, 141.81, 138.80, 138.66, 138.00, 137.79,

135.63, 124.38, 124.20, 123.96, 118.14, 117.76, 117.40, 116.88,

116.04, 105.53, 63.29, 52.83, 47.36, 24.92 ppm; HRMS (FAB-MS,

°

M.p. 96–98 C; IR (AT–IR): ν_max=2966 (w), 2879 (w), 2201 (m), 1616

(m), 1509 (s), 1460 (m), 1402 (w), 1360 (m), 1311 (w), 1217 (s), 1198

(s), 1118 (m), 1077 (w), 945 (w), 843 (w), 771 (w), 669 (w), 634 (w)

cm^{À 1}; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=236 (4.29), 286 (4.65), 345 (3.92),

1

478 sh (4.64), 506 (4.82) nm; H NMR (500 MHz, CDCl₃): δ_H=8.36 (d,

J=10.4 Hz, 1H, 4-H of azulene), 8.14 (d, J=10.7 Hz, 1H, 8-H of

azulene), 7.69 (d, J=4.0 Hz, 1H, 2-H of azulene), 7.48 (dd, J=10.4,

1.9 Hz, 1H, 5-H of azulene), 7.41 (d, J=10.7, 1.9 Hz, 1H, 7-H of

azulene), 7.34 (d, J=3.7 Hz, 1H, 3-H of azulene), 6.84 (d, J=12.9 Hz,

1H, H of triene), 6.63 (d, J=12.9 Hz, 1H, H of triene), 6.53 (s, 1H, H of

triene), 5.78 (d, J=12.3 Hz, 1H, H of triene), 3.36 (br s, 2H, Et), 3.09

(br s, 1H, Et), 1.47 (s, 9H, tBu), 1.25 (br s, 3H, Et), 1.06 (br s, 3H, Et)

ppm; ¹³C NMR (500 MHz, CDCl₃): δ_C=163.34, 160.96, 157.36, 152.42,

152.35, 140.89, 138.01, 137.14, 136.99, 134.87, 123.54, 122.74,

118.16, 117.03, 116.09, 104.01, 77.34, 77.09, 76.83, 64.45, 50.91,

43.16, 38.93, 31.96, 14.86, 12.27 ppm; HRMS (FAB-MS, positive):

+

positive): Calcd for C₂₂H₁₉N₃[M]⁺325.1579, found: 325.1571.

Compound 7b: Preparation by triethylamine catalyzed Knoevena-

gel reaction: Diethylamine (2 mL) was added to a solution of 2b⁺

(230 mg, 0.50 mmol) in ethanol (3 mL). The resulting solution was

stirred at room temperature for 30 min. The reaction mixture was

poured into 2 M NaOH and extracted with dichloromethane, dried

with Na₂SO₄, and concentrated under reduced pressure. Triethyl-

amine (0.5 mL) was added to a solution of the crude Zincke

aldehyde (158 mg, 0.47 mmol) and malononitrile (62 mg,

0.94 mmol) in dichloromethane (3 mL). The resulting solution was

stirred for 1 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 7b

(155 mg, 80% as two-step yield from 2b⁺·Cl^–) as a deep red solid.

+

Calcd for C₂₆H₂₉N₃[M]⁺383.2361, found: 383.2351.

Compound 7d: Diethylamine (3 mL) was added to a solution of

2d⁺·Cl^–(272 mg, 0.56 mmol) in ethanol (3 mL). The resulting

solution was stirred at room temperature for 30 min. The reaction

mixture was poured into 2 M NaOH and extracted with dichloro-

methane, dried with Na₂SO₄, and concentrated under reduced

pressure. Alumina (507 mg) was added to a solution of the crude

Zincke aldehyde (182 mg, 0.51 mmol) and malononitrile (71 mg,

1.08 mmol) in dichloromethane (3 mL). The resulting solution was

stirred for 1 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 7d

(190 mg, 84% as two-step yield from 2d⁺·Cl^–) as a deep red solid.

Preparation by alumina-catalyzed Knoevenagel reaction: Diethyl-

amine (2 mL) was added to a solution of 2b⁺·Cl^–(172 mg,

0.37 mmol) in ethanol (2 mL). The resulting solution was stirred at

room temperature for 30 min. The reaction mixture was poured

into 2 M NaOH and extracted with dichloromethane, dried with

Na₂SO₄, and concentrated under reduced pressure. Alumina

(146 mg) was added to a solution of the crude Zincke aldehyde

(114 mg, 0.34 mmol) and malononitrile (47 mg, 0.71 mmol) in

dichloromethane (3 mL). The resulting solution was stirred for

1 hours at room temperature. The solvent was removed under

reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 7b

(161 mg, 86% as two-step yield from 2b⁺·Cl^–) as a deep red solid.

°

M.p. 125–127 C; IR (AT–IR): ν_max=2975 (w), 2200 (m), 1616 (w),

1595 (m), 1577 (w), 1507 (s), 1460 (m), 1361 (m), 1311 (w), 1291 (w),

1215 (s), 1200 (s), 1119 (s), 1077 (m), 992 (w), 945 (w), 864 (w), 824

(w), 774 (w), 751 (w), 696 (w), 676 (w), 652 (w), 633 (w) cm^{À 1}; UV/Vis

(CH₂Cl₂): λ_max(log ɛ)=240 (4.36), 278 sh (4.37), 304 (4.48), 374 (4.03),

480 sh (4.69), 504 (4.81) nm; ¹H NMR (500 MHz, CDCl₃): δ_H=8.72

(dd, J=4.6, 1.6 Hz, 2H, 2,6-H of pyridine), 8.69 (d, J=9.7 Hz, 1H, 4-H

of azulene), 8.24 (d, J=9.7 Hz, 1H, 8-H of azulene), 7.94 (s, 1H, 2-H

of azulene), 7.77 (t, J=9.9 Hz, 1H, 6-H of azulene), 7.56 (dd, J=4.6,

1.6 Hz, 2H, 3,5-H of pyridine), 7.39 (t, J=9.9 Hz, 1H, 5-H of azulene),

7.30 (t, J=9.9 Hz, 1H, 7-H of azulene), 6.81 (d, J=12.8 Hz, 1H, H of

triene), 6.68 (d, J=12.8 Hz, 1H, H of triene), 6.49 (br s, 1H, H of

triene), 5.83 (d, J=10.6 Hz, 1H, H of triene), 3.37 (br s, 2H, Et), 3.09

(br s, 2H, Et), 1.27 (br s, 3H, Et), 1.06 (br s, 3H, Et) ppm; ¹³C NMR

(125 MHz, CDCl₃): δ_C=159.48, 156.84, 152.03, 150.23, 144.16,

140.42, 140.35, 138.29, 137.39, 137.06, 136.60, 127.31, 126.06,

°

M.p. 96–98 C; IR (AT–IR): ν_max=2966 (w), 2879 (w), 2201 (m), 1616

(m), 1509 (s), 1460 (m), 1402 (w), 1360 (m), 1311 (w), 1217 (s), 1198

(s), 1118 (m), 1077 (w), 945 (w), 843 (w), 771 (w), 669 (w), 634 (w)

cm^{À 1}; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=236 (4.29), 286 (4.65), 345 (3.92),

1

478 sh (4.64), 506 (4.82) nm; H NMR (500 MHz, CDCl₃): δ_H=8.36 (d,

J=10.4 Hz, 1H, 4-H of azulene), 8.14 (d, J=10.8 Hz, 1H, 8-H of

azulene), 7.69 (d, J=4.0 Hz, 1H, 2-H of azulene), 7.48 (dd, J=10.4,

1.9 Hz, 1H, 5-H of azulene), 7.41 (dd, J=10.8, 1.9 Hz, 1H, 7-H of

azulene), 7.34 (d, J=3.7 Hz, 1H, 3-H of azulene), 6.84 (d, J=12.9 Hz,

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125.61, 124.31, 117.75, 117.43, 115.67, 104.11, 65.72, 51.09, 43.25,

14.86, 12.27 ppm. One signal is overlapped with other signal. HRMS

(MALDI-TOF, positive): Calcd for C₂₇H₂₄N₄+H⁺[M+H]⁺405.2074,

found: 405.2071.

mixture was poured into 2 M NaOH and extracted with dichloro-

methane, dried with Na₂SO₄, and concentrated under reduced

pressure. Alumina (103 mg) was added to a solution of the crude

Zincke aldehyde (44 mg, 0.09 mmol) and malononitrile (14 mg,

0.21 mmol) in dichloromethane (5 mL). The resulting solution was

stirred for 1 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 8b

(61 mg, 57% as two-step yield from 5b²⁺·2Cl^–) as a deep red solid.

Compound 7e: Diethylamine (3 mL) was added to a solution of

2e⁺·Cl^–(255 mg, 0.47 mmol) in ethanol (3 mL). The resulting

solution was stirred at room temperature for 30 min. The reaction

mixture was poured into 2 M NaOH and extracted with dichloro-

methane, dried with Na₂SO₄, and concentrated under reduced

pressure. Alumina (466 mg) was added to a solution of the crude

Zincke aldehyde (182 mg, 0.44 mmol) and malononitrile (63 mg,

0.95 mmol) in dichloromethane (3 mL). The resulting solution was

stirred for 1 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 7e

(189 mg, 87% as two-step yield from 2e⁺·Cl^–) as a deep red solid.

°

M.p. 288–290 C; IR (AT–IR): ν_max=2975 (w), 2931 (w), 2201 (w), 1618

(w), 1517 (s), 1466 (m), 1449 (w), 1426 (w), 1361 (w), 1311 (w), 1228

(s), 1202 (s), 1122 (w), 1097 (w), 1078 (w), 994 (w), 955 (w), 940 (w),

877 (w), 831 (w), 775 (w), 745 (w), 687 (w), 671 (w), 651 (w), 638 (w),

615 (w) cm^{À 1}; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=237 (4.33), 289 (4.57),

324 sh (4.16), 346 (4.04), 479 (4.99), 499 (4.96) nm; ¹H NMR

(500 MHz, CDCl₃): δ_H=8.20 (d, J=10.3 Hz, 2H, 4,8-H of azulene),

7.53–7.59 (m, 3H, 2,5,7-H of azulene), 6.70 (br s, 4H, H of triene),

6.54 (br s, 2H, H of triene), 5.82 (d, J=12.0 Hz, 2H, H of triene), 3.30

(br s, 8H, Et), 1.50 (s, 9H, tBu), 1.22 (br s, 12H, Et) ppm; ¹³C NMR

(125 MHz, CDCl₃): δ_C=165.87, 160.06, 156.35, 152.40, 138.96,

138.42, 136.36, 124.33, 123.49, 118.09, 116.99, 115.58, 104.13, 64.85,

51.56, 39.29, 31.93, 29.79, 14.62, 12.59 ppm; HRMS (FAB-MS,

°

M.p. 178–180 C; IR (AT–IR): ν_max=2969 (w), 2201 (m), 1615 (m),

1597 (m), 1580 (m), 1509 (s), 1461 (m), 1428 (m), 1361 (m), 1312

(m), 1217 (s), 1201 (s), 1120 (m), 1077 (m), 993 (w), 948 (m), 859 (m),

823 (m), 775 (m), 737 (w), 668 (w), 654 (m), 643 (w), 633 (m) cm^{À 1}

;

UV/Vis (CH₂Cl₂): λ_max(log ɛ)=286 (4.40), 310 (4.50), 324 sh (4.41),

1

378 (4.04), 480 sh (4.66), 505 (4.79) nm; H NMR (500 MHz, CDCl₃):

+

positive): Calcd for C₃₈H₄₂N₆[M]⁺582.3471, found: 582.3464.

δ_H=8.70 (dd, J=4.4, 1.6 Hz, 2H, 2,6-H of pyridine), 8.65 (d, J=

10.9 Hz, 1H, 4-H of azulene), 8.18 (d, J=10.7 Hz, 1H, 8-H of azulene),

7.85 (s, 1H, 2-H of azulene), 7.55–7.59 (m, 3H, 5-H of azulene and

3,5-H of pyridine), 7.48 (dd, J=10.7, 1.9 Hz, 1H, 7-H of azulene), 6.84

(d, J=12.8 Hz, 1H, H of triene), 6.66 (d, J=12.8 Hz, 1H, H of triene),

6.53 (br s, 1H, H of triene), 5.82 (d, J=11.5 Hz, 1H, H of triene), 3.36

(s, 2H, Et), 3.10 (s, 2H, Et), 1.48 (s, 9H, tBu), 1.27 (s, 3H, Et), 1.06 (s,

3H, Et) ppm; ¹³C NMR (125 MHz, CDCl₃): δ_C=165.15, 159.87, 157.02,

152.06, 150.10, 144.40, 139.34, 137.31, 136.09, 135.63, 126.76,

124.44, 124.10, 123.94, 117.92, 115.80, 104.17, 65.36, 51.07, 43.23,

39.09, 31.88, 14.88, 12.26 ppm. Three signals are overlapped with

other signals. HRMS (MALDI-TOF, positive): Calcd for C₃₁H₃₂N₄+H⁺

[M+H]⁺461.2700, found: 461.2713.

Compound 9: Preparation from 7aa: A solution of 7aa (103 mg,

0.31 mmol) in N-cyclohexylmaleimide (154 mg, 0.86 mmol) in

°

toluene was stirred at 150 C for 46 h under an Ar atmosphere. After

the reaction, the solvent was removed under reduced pressure. The

crude product was purified by column chromatography on silica

gel with CHCl₃as an eluent to afford 9 (32 mg, 16% yield) as a

green solid.

Preparation from 7ab: A solution of 7ab (70 mg, 0.21 mmol) in N-

cyclohexylmaleimide (114 mg, 0.64 mmol) in toluene was stirred at

°

150 C for 23.5 h under an Ar atmosphere. After the reaction, the

solvent was removed under reduced pressure. The crude product

was purified by column chromatography on silica gel with CHCl₃as

an eluent to afford 9 (37 mg, 9% yield) as a green solid.

Compound 8a: Diethylamine (2 mL) was added to a solution of

5a²⁺·2Cl^–(111 mg, 0.16 mmol) in ethanol (2 mL). The resulting

solution was stirred at room temperature for 30 min. The reaction

mixture was poured into 2 M NaOH and extracted with dichloro-

methane, dried with Na₂SO₄, and concentrated under reduced

pressure. Alumina (110 mg) was added to a solution of the crude

Zincke aldehyde (43 mg, 0.10 mmol) and malononitrile (16 mg,

0.24 mmol) in dichloromethane (5 mL). The resulting solution was

stirred for 1 h at room temperature. The solvent was removed

under reduced pressure and the residue was purified by column

chromatography on silica gel with EtOAc/hexane (1:1) to give 8a

(46 mg, 54% as two-step yield from 5a²⁺·2Cl^–) as a deep red solid.

Preparation from 7ac: A solution of 7ac (116 mg, 0.34 mmol) in N-

cyclohexylmaleimide (186 mg, 1.03 mmol) in toluene was stirred at

°

150 C for 15.5 h under an Ar atmosphere. After the reaction, the

solvent was removed under reduced pressure. The crude product

was purified by column chromatography on silica gel with CHCl₃as

an eluent to afford 9 (76 mg, 12% yield) as a green solid.

Preparation from 7ad: A solution of 7ad (120 mg, 0.37 mmol) in N-

cyclohexylmaleimide (197 mg, 1.10 mmol) in toluene was stirred at

°

150 C for 16 h under an Ar atmosphere. After the reaction, solvent

was removed under reduced pressure. The crude product was

purified by column chromatography on silica gel with CHCl₃as an

eluent to afford 9 (74 mg, 33% yield) as a green solid. M.p. 229–

°

M.p. 278–279 C; IR (AT–IR): ν_max=2974 (w), 2931 (w), 2198 (m),

2188 (w), 1617 (w), 1508 (s), 1468 (m), 1441 (m), 1422 (w), 1359 (m),

1345 (w), 1311 (m), 1282 (w), 1222 (s), 1200 (s), 1118 (m), 1077 (m),

993 (w), 953 (w), 942 (w), 869 (w), 834 (w), 775 (w), 751 (w), 716 (w),

687 (w), 666 (w), 650 (w), 640 (w), 627 (w), 617 (w) cm^{À 1}; UV/Vis

(CH₂Cl₂): λ_max(log ɛ)=233 (4.17), 281 (4.32), 326 sh (3.89), 342 sh

°

231 C; IR (AT–IR): ν_max=2930 (w), 2852 (w), 2204 (w), 1765 (m),

1699 (s), 1618 (w), 1579 (w), 1530 (m), 1474 (m), 1451 (m), 1423 (m),

1398 (m), 1373 (s), 1347 (m), 1294 (w), 1258 (w), 1230 (m), 1196 (m),

1171 (m), 1145 (m), 1117 (w), 1101 (m), 1077 (w), 1024 (w), 984 (w),

937 (w), 911 (w), 896 (w), 851 (m), 786 (m), 750 (s), 714 (m), 693 (w),

1

(3.79), 477 (4.84), 500 sh (4.79) nm; H NMR (500 MHz, CDCl₃): δ_H=

1

662 (w), 638 (m), 620 (w) cm^{À 1}; H NMR (500 MHz, CDCl₃): δ_H=8.45

8.26 (d, J=9.8 Hz, 2H, 4,8-H of azulene), 7.80 (t, J=9.8 Hz, 1H, 6-H

of azulene), 7.69 (s, 1H, 2-H of azulene), 7.35 (t, J=9.8 Hz, 2H, 5,7-H

of azulene), 6.69 (br s, 4H, H of triene), 6.50 (br s, 2H, H of triene),

5.83 (d, J=12.0 Hz, 2H, H of triene), 3.32 (br s, 8H, Et), 1.22 (br s,

12H, Et) ppm; ¹³C NMR (125 MHz, CDCl₃): δ_C=159.63, 156.18,

152.34, 140.81, 139.84, 139.57, 137.39, 125.96, 117.87, 115.42,

104.12, 65.34, 51.70, 43.52, 14.47, 12.41 ppm; HRMS (FAB-MS,

(d, J=9.5 Hz, 1H, 8-H of azulene), 7.95–8.04 (m, 2H, 4-H of azulene,

Bz), 7.92 (d, J=7.7 Hz, 1H, Bz), 7.76 (dd, J=3.7, 3.6 Hz, 1H, 2-H of

azulene), 7.70 (q, J=9.7 Hz, 1H, 6-H of azulene), 7.52 (dd, J=3.7,

3.6 Hz, 1H, 1-H of azulene), 7.31 (dd, J=9.7 Hz, 1H, 7-H of azulene),

7.23 (dd, J=9.7 Hz, 1H, 5-H of azulene), 4.35 (dd, J=13.5, 4.6 Hz,

1H, cHex), 3.97-4.17 (m, 2H, CH₂), 3.82 (t, J=12.3 Hz, 1H, CH), 3.22

(m, 1H, cHex), 2.53-2.70 (m, 2H, CH₂), 2.18-2.26 (m, 2H, cHex), 1.56-

1.97 (m, 10H, cHex), 1.10–1.44 (m, 8H, cHex) ppm; ¹³C NMR

(125 MHz, CDCl₃): δ_C=172.67, 172.15, 169.70, 167.59, 145.34,

141.91, 138.85, 138.34, 138.15, 138.11, 137.95, 137.51, 136.94,

+

positive): Calcd for C₃₄H₃₄N₆[M]⁺526.2845, found: 526.2853.

Compound 8b: Diethylamine (2 mL) was added to a solution of

5b²⁺·2Cl^–(82 mg, 0.11 mmol) in ethanol (2 mL). The resulting

solution was stirred at room temperature for 30 min. The reaction

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135.13, 135.00, 131.44, 131.24, 131.16, 130.54, 130.20, 125.72,

125.60, 124.72, 124.68, 124.50, 123.37, 118.14, 118.04, 112.88,

112.64, 112.53, 112.22, 52.54, 51.33, 45.41, 45.26, 39.60, 39.48, 32.03,

31.94, 31.67, 29.89, 28.50, 28.46, 26.09, 25.72, 25.19, 24.92 ppm;

HRMS (MALDI-TOF, positive): Calcd for C₃₈H₃₆N₄O₄+H⁺[M+H]⁺

612.2857, found: 612.2878.

was stirred at room temperature for 3.5 h. The reaction mixture was

concentrated under reduced pressure. To the residue was added

cyclopentadiene (57 mg, 0.86 mmol), KOtBu (93 mg, 0.83 mmol),

and pyridine (10 mL) and the mixture was stirred at room temper-

ature for 1 h and refluxed for 17.5 h. The precipitate was separated

by filtration and the solvent was removed under reduced pressure.

The residue was purified by column chromatography on silica gel

with CHCl₃as an eluent to give 10c (223 mg, 90% yield) as green

Compound (10a): Diethylamine (16 mL) was added to a solution of

2a⁺·Cl^–(1.71 g, 4.20 mmol) in ethanol (36 mL). The resulting

solution was stirred at room temperature for 5 h. The reaction

mixture was concentrated under reduced pressure. To the residue

was added cyclopentadiene (333 mg, 5.0 mmol), 2.5 M NaOMe

(2 mL), and pyridine (50 mL) and the mixture was refluxed for 24 h.

The precipitate was separated by filtration and the solvent was

removed under reduced pressure. The residue was purified by

column chromatography on silica gel with CH₂Cl₂as an eluent to

°

oil. M.p. 110–113 C; IR (AT–IR): ν_max=2963 (w), 2904 (w), 2868 (w),

1573 (m), 1548 (w), 1474 (w), 1459 (w), 1424 (w), 1395 (m), 1362 (w),

1235 (w), 1218 (w), 1091 (w), 1055 (w), 952 (w), 878 (w), 850 (m),

837 (m), 822 (w), 752 (s), 682 (w), 667 (w) cm^–1; UV/Vis (CH₂Cl₂): λ_max

(log ɛ)=241 (4.39), 280 (4.61), 301 (4.48), 319 (4.39), 346 sh (4.16),

368 sh (3.79), 458 (4.22), 586 (3.04), 636 sh (2.91), 695 sh (2.56), 751

sh (2.31) nm; UV/Vis (30% CH₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=280 (4.58),

299 (4.47), 318 sh (4.39), 346 sh (4.18), 367 sh (3.93), 457 (4.21), 723

(3.39) nm; UV/Vis (30% CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=308 (4.22),

339 sh (4.04), 370 sh (3.72), 421 (3.87), 629 (4.46) nm; ¹H NMR

(500 MHz, CDCl₃): δ_H=8.78 (d, J=10.6 Hz, 1H, 8-H), 8.65 (d, J=

10.6 Hz, 1H, 4-H), 8.46 (d, J=10.3 Hz, 2H, 4’,8’-H), 8.07 (s, 1H, 2-H),

7.94 (t, J=3.7 Hz, 1H, 2’-H), 7.60 (d, J=10.3 Hz, 2H, 5’,7’-H), 7.48 (d,

J=3.7 Hz, 2H, 1’,3’-H), 7.45–7.36 (m, 2H, 5,7-H), 1.76 (s, 9H, tBu), 1.55

(s, 9H, tBu) ppm; ¹³C NMR (125 MHz, CDCl₃): δ_C=162.38, 147.61,

138.98, 138.37, 136.34, 135.93, 135.82, 135.67, 134.77, 132.25,

125.61, 122.19, 120.27, 118.02, 38.45, 33.37, 32.22, 31.85 ppm; HRMS

°

give 10a (593 mg, 56%) as green crystals. M.p. 135–137 C; IR (AT-

IR): ν_max=3084 (w), 3022 (w), 1571 (s), 1546 (m), 1492 (w), 1471 (w),

1452 (w), 1391 (s), 1293 (w), 1230 (w), 1199 (w), 1150 (w), 1050 (w),

985 (w), 944 (w), 913 (w), 898 (w), 842 (s), 788 (s), 738 (s), 687 (w)

cm^{À 1}; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=238 (4.50), 276 (4.63), 295 (4.54),

313 (4.51), 343 sh (4.21), 430 (4.32), 540 sh (2.88), 583 (2.95), 635 sh

(2.81), 705 sh (2.25) nm; UV/Vis (30% CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=

257 (4.50), 296 (4.31), 338 (4.11), 396 (3.87), 581 (4.56), 600 sh (4.54)

nm; ¹H NMR (500 MHz, CDCl₃): δ_H=8.66 (d, J=10.0 Hz, 1H, 8-H),

8.41 (d, J=10.5 Hz, 2H, 4’,8’-H), 8.40 (d, J=10.0 Hz, 1H, 4-H), 8.13 (d,

J=4.0 Hz, 1H, 2-H), 7.88 (t, J=3.5 Hz, 1H, 2’-H), 7.65 (t, J=10.0 Hz,

1H, 6-H), 7.51 (d, J=10.5 Hz, 2H, 5’,7’-H), 7.47 (d, J=4.0 Hz, 1H, 3-H),

7.41 (d, J=3.5 Hz, 2H, 1’,3’-H), 7.23 (t, J=10.5 Hz, 2H, 5,7-H) ppm;

¹³C NMR (125 MHz, CDCl₃): δ_C=147.10 (C-3a’,8a’), 142.51 (C-8a),

138.60 (C-6), 138.44 (C-2), 138.00 (C-4), 137.70 (C-3a), 136.06 (C-8),

135.93 (C-2’), 135.86 (C-6’), 135.64 (C-4’,8’), 134.79 (C-1), 125.55 (C-

5’,7’), 124.34 (C-5 or C-7), 123.99 (C-5 or C-7), 118.12 (C-1’,3’), 117.89

+

(MALDI-TOF, positive): Calcd for C₂₈H₃₀[M]⁺367.2420, found:

367.2417.

Compound (10d): Pyrrolidine (8 mL) was added to a solution of

4a⁺·Cl^–(968 mg, 1.99 mmol) in ethanol (18 mL). The resulting

solution was stirred at room temperature for 19.5 h. The reaction

mixture was concentrated under reduced pressure. To the residue

was added cyclopentadiene (159 mg, 2.40 mmol), KOtBu (274 mg,

2.44 mmol), and pyridine (30 mL) and the mixture was stirred at

room temperature and refluxed for 24 h. The precipitate was

separated by filtration and the solvent was removed under reduced

pressure. The residue was purified by column chromatography on

silica gel with CHCl₃/EtOAc as an eluent to give 10d (308 mg, 47%

+

(C-3) ppm; HRMS (FAB-MS, positive): Calcd for C₂₀H₁₄[M]⁺

254.1096, found: 254.1105.

Compound (10b): Pyrrolidine (12 mL) was added to a solution of

2b⁺·Cl^–(1.46 g, 3.14 mmol) in ethanol (27 mL). The resulting

solution was stirred at room temperature for 2 h. The reaction

mixture was concentrated under reduced pressure. To the residue

was added cyclopentadiene (284 mg, 4.30 mmol), KOtBu (423 mg,

3.77 mmol), and pyridine (45 mL) and the mixture was stirred at

room temperature for 1 h and refluxed for 19 h. The precipitate was

separated by filtration and the solvent was removed under reduced

pressure. The residue was purified by column chromatography on

silica gel with toluene/EtOAc as an eluent to give 10b (970 mg,

99% yield) as green oil. IR (AT-IR): ν_max=3078 (w), 2964 (w), 2904

(w), 2868 (w), 1568 (s), 1546 (m), 1468 (w), 1444 (w), 1435 (w), 1395

(s), 1362 (w), 1299 (w), 1264 (w), 1242 (w), 1192 (w), 1054 (w), 1014

(w), 982 (w), 915 (w), 873 (w), 840 (s), 825 (m), 751 (m), 738 (m), 715

(w), 666 (w) cm^{À 1}; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=237 (4.48), 268 sh

(4.54), 278 (4.66), 298 (4.55), 314 (4.48), 345 sh (4.25), 439 (4.33), 572

(3.03), 625 sh (2.89), 700 sh (2.33) nm; UV/Vis (30% CF₃CO₂H/

CH₂Cl₂): λ_max(log ɛ)=257 (4.48), 303 (4.36), 340 (4.15), 408 (3.82),

°

yield) as a green solid. M.p. 210–211 C; IR (AT–IR): ν_max=3084 (w),

3041 (w), 1594 (m), 1574 (m), 1547 (m), 1521 (w), 1490 (w), 1472

(w), 1451 (w), 1424 (m), 1406 (m), 1378 (w), 1359 (w), 1319 (w), 1306

(w), 1269 (w), 1245 (w), 1211 (w), 1195 (w), 1154 (w), 1136 (w), 1091

(w), 1050 (w), 1018 (w), 991 (w), 972 (w), 931 (w), 874 (w), 860 (w),

849 (m), 836 (m), 811 (w), 753 (s), 691 (w), 670 (w) cm^–1; UV/Vis

(CH₂Cl₂): λ_max(log ɛ)=237 (4.48), 278 (4.60), 293 (4.60), 310 (4.61),

320 sh (4.60), 346 sh (4.33), 419 (4.35), 587 (2.94), 635 sh (2.83), 710

sh (2.26) nm; UV/Vis (30% CH₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=276 (4.59),

292 (4.54), 320 (4.58), 343 sh (4.40), 415 (4.41), 584 (3.02) nm; UV/Vis

(30% CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=291 (4.26), 334 (4.37), 384 sh

(4.25), 412 (4.30), 526 sh (4.40), 552 (4.48), 581 sh (4.29) nm; ¹H NMR

(500 MHz, CDCl₃): δ_H=8.73 (dd, J=4.4, 1.6 Hz, 2H, 2,6-H of pyridine),

8.69 (d, J=10.0 Hz, 1H, 8-H), 8.65 (d, J=10.0 Hz, 1H, 4-H), 8.43 (d,

J=10.6 Hz, 2H, 4’,8’-H), 8.25 (s, 1H, 2-H), 7.91 (t, J=3.7 Hz, 1H, 2’-H),

7.73 (t, J=9.7 Hz, 1H, 6-H), 7.59 (dd, J=4.4, 1.6 Hz, 2H, 3,5-H of

pyridine), 7.51 (d, J=10.6 Hz, 2H, 5’,7’-H), 7.44 (d, J=3.7 Hz, 2H,

1’,3’-H), 7.31 (m, 2H, 5,7-H) ppm; ¹³C NMR (125 MHz, CDCl₃): δ_C=

150.19, 146.23, 144.58, 140.00, 138.74, 138.19, 137.89, 137.74,

137.17, 136.70, 136.28, 135.73, 134.73, 127.51, 125.58, 125.55,

125.52, 124.37, 118.54 ppm; HRMS (MALDI-TOF, positive): Calcd for

C₂₅H₁₇N+H⁺[M+H]⁺332.1434, found:332.1419

1

575 sh (4.52), 601 (4.61) nm; H NMR (500 MHz, CDCl₃): δ_H=8.77 (d,

J=11.0 Hz, 1H, 8-H), 8.51 (d, J=10.5 Hz, 2H, 4’,8’-H), 8.42 (d, J=

11.0 Hz, 1H, 4-H), 8.18 (d, J=3.5 Hz, 1H, 2-H), 8.05 (t, J=3.5 Hz, 1H,

2’-H), 7.66 (d, J=10.5 Hz, 2H, 5’,7’-H), 7.58 (d, J=3.5 Hz, 2H, 1’,3’-H),

7.55–7.50 (m, 3H, 3,5,7-H), 1.61 (s, 9H, tBu) ppm; ¹³C NMR (125 MHz,

CDCl₃): δ_C=162.51 (C-6), 147.24 (C-6’), 141.31 (C-8a), 138.23 (C-

3a’,8a’), 137.03 (C-2), 136.69 (C-4), 135.65 (C-2’), 135.58 (C-4’,8’),

134.87 (C-8), 134.53 (C-3a), 134.20 (C-1), 125.32 (C-5’,7’), 122.65 (C-5

or C-7), 122.01 (C-5 or C-7), 117.97 (C-1’,3’), 117.44 (C-3), 38.49 (tBu),

Compound (10e): Pyrrolidine (22 mL) was added to a solution of

4b⁺·Cl^–(2.95 g, 5.46 mmol) in ethanol (50 mL). The resulting

solution was stirred at room temperature for 15.5 h. The reaction

mixture was concentrated under reduced pressure. To the residue

was added cyclopentadiene (433 mg, 6.55 mmol), KOtBu (736 mg,

6.55 mmol), and pyridine (75 mL) and the mixture was stirred at

+

31.75 (tBu) ppm; HRMS (FAB-MS, positive): Calcd for C₂₄H₂₂[M]⁺

310.1721, found: 310.1719.

Compound (10c): Pyrrolidine (3 mL) was added to a solution of

2c⁺(352 mg, 0.68 mmol) in ethanol (6 mL). The resulting solution

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room temperature for 1 h and refluxed for 14 h. The precipitate was

separated by filtration and the solvent was removed under reduced

pressure. The residue was purified by column chromatography on

silica gel with toluene/EtOAc as an eluent to give 10e (1.94 g, 92%

(w), 921 (w), 877 (w), 846 (s), 827 (m), 799 (w), 745 (s), 704 (w), 672

(w) cm^{À 1}; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=240 (4.64), 286 (4.92), 325

(4.74), 345 sh (4.55), 373 sh (4.14), 446 (4.57), 576 (3.24), 632 sh

(3.09), 707 sh (2.43) nm; UV/Vis (30% CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=

265 (4.68), 297 (4.42), 342 (4.40), 376 (4.26), 508 sh (4.41), 593 (4.74)

°

yield) as a green solid. M.p. 181–182 C; IR (AT–IR): ν_max=3024 (w),

1

2969 (w), 1567 (s), 1545 (m), 1516 (w), 1491 (w), 1473 (w), 1435 (s),

1396 (s), 1379 (m), 1361 (w), 1318 (w), 1268 (w), 1233 (w), 1211 (w),

1194 (w), 1138 (w), 1052 (w), 989 (w), 967 (w), 932 (w), 906 (w), 850

(s), 822 (m), 806 (s), 781 (w), 758 (m), 714 (w), 964 (w), 682 (w), 667

(w) cm^–1; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=241 (4.44), 278 (4.53), 293 sh

(4.57), 313 (4.65), 322 sh (4.63), 372 sh (4.08), 433 (4.24), 548 sh

(4.05), 578 (3.08), 624 sh (3.01), 690 sh (2.75) nm; UV/Vis (30%

CH₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=277 (4.56), 295 (4.50), 328 (4.56), 341

sh (4.47), 421 (4.42), 569 (4.47) nm; UV/Vis (30% CF₃CO₂H/CH₂Cl₂):

λ_max(log ɛ)=294 (4.26), 340 (4.44), 402 sh (4.30), 413 (4.31), 522 sh

nm; H NMR (500 MHz, CDCl₃): δ_H=8.65 (d, J=11.0 Hz, 2H, 4,8-H),

8.43 (d, J=10.5 Hz, 4H, 4’,8’,4’’,8’’-H), 8.23 (s, 1H, 2-H), 7.88 (t, J=

3.5 Hz, 2H, 2’,2’’-H), 7.56 (d, J=10.5 Hz, 4H, 5’,7’,5’’,7’’-H), 7.46 (d, J=

11.0 Hz, 2H, 5,7-H), 7.42 (d, J=3.5 Hz, 4H, 1’,3’,1’’,3’’-H), 1.48 (s, 9H,

tBu) ppm; ¹³C NMR (125 MHz, CDCl₃): δ_C=164.16 (C-6), 146.61 (C-

6’,6’’), 138.50 (C-3a’,8a’,3a’’,8a’’), 137.76 (C-2), 136.83 (C-3a,8a),

136.16 (C-2’,2’’), 136.04 (C-4,8), 135.65 (C-4’,8’,4’’,8’’), 134.03 (C-1,3),

125.43 (C-5’,7’,5’’,7’’), 123.65 (C-5,7), 118.22 (C-1’,3’,1’’,3’’), 38.76

+

(tBu), 31.78 (tBu) ppm; HRMS (FAB-MS, positive): Calcd for C₃₄H₂₈

[M]⁺436.2191, found: 436.2185.

1

(4.28), 569 (4.47) nm; H NMR (500 MHz, CDCl₃): δ_H=8.70 (dd, J=

Compound (12a): To a solution of 10a (608 mg, 1.95 mmol) and

pyridine (3.08 g, 38.9 mmol) in CH₂Cl₂(10 mL) was added dropwise

a solution of Tf₂O (2.21 g, 7.84 mmol) in CH₂Cl₂(10 mL). The

resulting solution was stirred for 1 h at room temperature and the

solvent was removed under the reduced pressure. The reaction

mixture was passed through silica gel with toluene and the solvent

was removed by evaporation. KOH (500 mg, 8.91 mmol) was added

to a solution of the obtained green-solid in EtOH (30 mL). The

resulting mixture was refluxed for 16.5 h. The reaction mixture was

poured into ice water and the generated precipitate was collected

by filtration to afford 12a (568 mg, 60% yield from 10a) as a brown

4.4, 1.6 Hz, 2H, 2,6-H of pyridine), 8.66 (d, J=10.9 Hz, 1H, 8-H), 8.62

(d, J=10.9 Hz, 1H, 4-H), 8.42 (d, J=10.3 Hz, 2H, 4’,8’-H), 8.18 (s, 1H,

2-H), 7.89 (t, J=3.7 Hz, 1H, 2’-H), 7.61 (dd, J=4.4, 1.6 Hz, 2H, 3,5-H

of pyridine), 7.49–7.53 (m, 4H, 5,7,5’,7’-H), 7.43 (d, J=3.7 Hz, 2H,

1’,3’-H), 1.49 (s, 9H, tBu) ppm; ¹³C NMR (125 MHz, CDCl₃): δ_C=

164.59, 149.65, 146.44, 145.16, 138.69, 137.21, 136.91, 136.71,

136.46, 136.31, 135.74, 135.37, 134.45, 126.89, 125.44, 124.22,

124.08, 123.99, 118.45, 38.90, 31.85 ppm; HRMS (MALDI-TOF,

positive): Calcd for C₂₉H₂₅N⁺[M]⁺388.2060, found: 388.2077.

Compound (11a): Diethylamine (20 mL) was added to a solution of

5a²⁺(3.44 g, 5.00 mmol) in ethanol (50 mL). The resulting solution

was stirred at room temperature for 17 h. The reaction mixture was

concentrated under reduced pressure. To the residue was added

cyclopentadiene (397 mg, 6.00 mmol), KOtBu (673 mg, 6.00 mmol),

and pyridine (70 mL) and the mixture was stirred at room temper-

ature for 1 h and refluxed for 10 h. The precipitate was separated

by filtration and the solvent was removed under reduced pressure.

The residue was purified by column chromatography on silica gel

with toluene/EtOAc as an eluent to give 10e (190 mg, 10% yield)

°

solid. M.p. 290–292 C; IR (AT-IR) : ν_max=3033 (w), 2959 (w), 1593

(m), 1569 (s), 1504 (w), 1491 (w), 1428 (m), 1395 (w), 1371 (w), 1338

(w), 1311 (w), 1250 (w), 1220 (w), 1092 (w), 1061 (w), 992 (w), 947

(w), 892 (w), 854 (w), 813 (m), 760 (m), 734 (m), 697 (w), 682 (w),

661 (m), 632 (m), 616 (w) cm^–1; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=243

(4.55), 309 (4.56), 330 (4.55), 387 sh (4.31), 456 (4.26), 590 (3.03), 650

sh (2.87), 723 (2.22) nm; UV/Vis (30% CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=

255 (4.44), 280 (4.32), 321 (4.32), 346 (4.38), 427 (4.69), 484 sh (4.46),

1

585 sh (3.59) nm; H NMR (500 MHz, CDCl₃): δ_H=8.66–8.75 (m, 10H,

°

as a green solid. M.p. 278–280 C; IR (AT–IR) ν_max=3078 (w), 3022

4,4’,8,8’-H, 2,2’,2’’,6,6’,6’’-H of pyridine), 8.27 (s, 1H, 2-H), 8.15 (s, 1H,

2’-H), 7.78 (t, J=9.7 Hz, 1H, 6-H), 7.66 (d, J=10.6 Hz, 2H, 5’,7’-H),

7.61 (dd, J=4.4, 1.6 Hz, 4H, 3’,3’’,5’,5’’-H of pyridine), 7.57 (dd, J=

4.4, 1.6 Hz, 2H, 3,5-H of pyridine), 7.37 (t, J=9.7 Hz, 2H, 5,7-H) ppm;

¹³C NMR (125 MHz, CDCl₃): δ_C=150.25, 150.22, 149.32, 144.46,

144.27, 140.42, 138.36, 138.31, 137.87, 136.94, 136.65, 136.22,

136.10, 135.43, 133.35, 128.24, 128.15, 128.07, 126.22, 124.34,

124.26 ppm; HRMS (MALDI-TOF, positive): Calcd for C₃₅H₂₃N₃+H⁺

[M+H]⁺486.1970, found:486.1991.

(w), 1569 (s), 1543 (m), 1507 (w), 1471 (w), 1445 (w), 1423 (w), 1395

(s), 1346 (w), 1302 (w), 1267 (w), 1240 (w), 1195 (w), 1041 (w), 993

(w), 847 (s), 831 (m), 759 (m), 739 (s), 673 (w) cm^{À 1}; UV/Vis (CH₂Cl₂):

λ_max(log ɛ)=238 (4.59), 285 (4.81), 321 (4.75), 345 sh (4.50), 436

(4.54), 579 (3.20), 633 sh (3.05), 705 sh (2.49) nm; UV/Vis (30%

CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=266 (4.67), 288 (4.35), 342 (4.32), 368

1

(4.32), 498 sh (4.36), 575 (4.66) nm; H NMR (500 MHz, CDCl₃): δ_H=

8.68 (d, J=10.0 Hz, 2H, 4,8-H), 8.44 (d, J=10.5 Hz, 4H, 4’,8’,4’’,8’’-H),

8.33 (s, 1H, 2-H), 7.90 (t, J=3.5 Hz, 2H, 2’,2’’-H), 7.70 (t, J=10.0 Hz,

1H, 6-H), 7.54 (d, J=10.5 Hz, 4H, 5’,7’,5’’,7’’-H), 7.41 (d, J=3.5 Hz, 4H,

1’,3’,1’’,3’’-H), 7.27 (t, J=10.5 Hz, 2H, 5,7-H) ppm; ¹³C NMR (125 MHz,

CDCl₃): δ_C=146.37 (C-6’,6’’), 139.75 (C-6), 138.69 (C-3a’,8a’,3a’’,8a’’),

138.61 (C-2), 137.94 (C-3a,8a), 136.96 (C-4,8), 136.45 (C-2’,2’’), 135.63

(C-4’,8’,4’’,8’’), 134.37 (C-1,3), 125.53 (C-5’,7’,5’’,7’’), 125.27 (C-5,7),

118.36 (C-1’,3’,1’’,3’’) ppm; HRMS (FAB-MS, positive): Calcd for

Compound (12b): To a solution of 10b (466 mg, 1.50 mmol) and

pyridine (2.37 g, 30.0 mmol) in CH₂Cl₂(10 mL) was added dropwise

a solution of Tf₂O (1.69 g, 6.00 mmol) in CH₂Cl₂(10 mL). The

resulting solution was stirred for 1 h at room temperature and the

solvent was removed under the reduced pressure. The reaction

mixture was passed through silica gel with toluene and the solvent

was removed by evaporation. KOH (842 mg, 15.0 mmol) was added

to a solution of the obtained green-solid in EtOH (30 mL). The

resulting mixture was refluxed for 15 h. The reaction mixture was

poured into ice water and the generated precipitate was collected

by filtration to afford 12b (626 mg, 77% yield from 10b) as a

C₃₀H₂₀[M]⁺380.1565, found: 380.1574.

+

Compound (11b): Diethylamine (15 mL) was added to a solution of

5b²⁺(3.35 g, 4.50 mmol) in ethanol (45 mL). The resulting solution

was stirred at room temperature for 15 h. The reaction mixture was

concentrated under reduced pressure. To the residue was added

cyclopentadiene (331 mg, 5.00 mmol), KOtBu (561 mg, 5.00 mmol),

and pyridine (60 mL) and the mixture was stirred at room temper-

ature for 1 h and refluxed for 12 h. The precipitate was separated

by filtration and the solvent was removed under reduced pressure.

The residue was purified by column chromatography on silica gel

with toluene/EtOAc as an eluent to give 10e (334 mg, 17% yield)

°

brown solid. M.p. 295–297 C; IR (AT–IR): ν_max=3027 (w), 2965 (w),

2868 (w), 1588 (s), 1567 (s), 1550 (w), 1518 (w), 1502 (w), 1487 (w),

1429 (s), 1389 (w), 1383 (w), 1368 (m), 1308 (w), 1245 (w), 1217 (w),

1139 (w), 1110 (w), 1071 (w), 1062 (w), 991 (w), 948 (w), 933 (w),

880 (w), 858 (w), 841 (w), 817 (s), 734 (w), 718 (w), 696 (w), 679 (w),

658 (m) cm^–1; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=244 (4.64), 302 sh (4.66),

316 (4.71), 330 sh (4.67), 360 sh (4.48), 381 sh (4.43), 466 (4.39), 571

(3.23), 629 sh (3.09) nm; UV/Vis (30% CH₃CO₂H/CH₂Cl₂): λ_max(log

ɛ)=284 sh (4.42), 321 sh (4.58), 344 (4.62), 424 (4.59), 465 sh (4.47),

578 sh (3.53) nm; UV/Vis (30% CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=288

°

as a green solid. M.p. 274–275 C; IR (AT–IR) ν_max=3089 (w), 2963

(w), 1568 (s), 1546 (m), 1473 (w), 1429 (m), 1396 (s), 1349 (w), 1302

(w), 1267 (w), 1235 (w), 1192 (w), 1118 (w), 1054 (w), 1028 (w), 982

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(4.45), 321 (4.41), 352 (4.50), 429 (4.76), 479 sh (4.62), 543 sh (4.07),

571 sh (3.81) nm; H NMR (500 MHz, CDCl₃): δ_H=8.70–8.74 (m, 9H,

680 (w), 667 (m) cm^–1; UV/Vis (CH₂Cl₂): λ_max(log ɛ)=234 (4.58), 278

(4.65), 300 sh (4.54), 335 (4.63), 387 (4.60), 421 (4.52), 543 sh (2.92),

577 (2.97), 631 sh (2.91), 697 sh (2.64) nm; UV/Vis (30% CH₃CO₂H/

CH₂Cl₂): λ_max(log ɛ)=277 (4.68), 335 (4.67), 386 (4.62), 419 (4.52)

nm; UV/Vis (30% CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=285 sh (4.40), 331

(4.42), 370 (4.36), 415 (4.34), 534 sh (4.50), 555 (4.52), 587 sh (4.37)

1

4,4’,8’-H, 2,2’,2’’,6,6’,6’’-H of pyridine), 8.65 (d, J=10.9 Hz, 1H, 8-H),

8.22 (s, 1H, 2-H), 8.15 (s, 1H, 2’-H), 7.72 (d, J=10.9 Hz, 2H, 5’,7’-H),

7.65 (dd, J=4.6, 1.7 Hz, 4H, 3’,3’’,5’,5’’-H of pyridine), 7.61 (dd, J=

4.6, 1.4 Hz, 2H, 3,5-H of pyridine), 7.59 (d, J=10.6 Hz, 2H, 5,7-H),

1.50 (s, 9H, tBu) ppm; ¹³C NMR (125 MHz, CDCl₃): δ_C=165.33,

149.80, 149.68, 149.62, 145.09, 144.91, 137.52, 137.44, 136.93,

136.45, 136.11, 135.92, 135.82, 135.51, 132.99, 128.37, 128.09,

127.59, 124.93, 124.85, 124.31, 124.22, 39.05, 31.85 ppm; HRMS

1

nm; H NMR (500 MHz, CDCl₃): δ_H=8.72–8.73 (m, 3H, 4-H, 2,6-H of

pyridine), 8.60–8.63 (m, 3H, 8-H, 4’,8’-H), 8.23 (s, 1H, 2-H), 8.10 (s, 1H,

2’-H), 7.70 (t, J=9.7 Hz, 1H, 6-H), 7.65 (d, J=8.3 Hz, 4H, 4-tBuPh),

7.55–7.58 (m, 6H, 4-tBuPh, 3,5-H of pyridine), 7.38 (d, J=10.6 Hz,

2H, 5’,7’-H), 7.28 (dd, J=9.9, 1.7 Hz, 2H, 5,7-H), 1.44 (s, 18H, tBu)

ppm; ¹³C NMR (125 MHz, CDCl₃): δ_C=150.17, 149.40, 147.63, 144.52,

140.00, 138.21, 137.89, 137.71, 137.14, 136.73, 136.25, 135.33,

135.08, 134.42, 134.40, 131.13, 129.51, 127.58, 125.73, 125.57,

124.33, 34.67, 31.54 ppm; HRMS (MALDI-TOF, positive): Calcd for

C₄₅H₄₁N+H⁺[M+H]⁺596.3312, found: 596.3329.

+

(MALDI-TOF, positive): Calcd for C₃₉H₃₁N₃[M]⁺542.2591, found:

542.2611.

Compound (13): To a solution of 12b (294 mg, 0.54 mmol) in EtOH

(10 mL) was added 1-chloro-2,4-dinitrobenzene (659 mg,

3.25 mmol), then the resulting solution was refluxed for 22.5 h. The

precipitate was collected by filtration to afford pyridinium salt

intermediate as a reddish brown solid. Pyrrolidine (2 mL) was added

to a solution of the pyridinium salt in EtOH (5 mL). The resulting

mixture was stirred at room temperature for 3 h and the solvent

was removed under reduced pressure. To the residue was added

cyclopentadiene (160 mg, 2.42 mmol), KOtBu (252 mg, 2.24 mmol),

and pyridine (8 mL) and the mixture was stirred at room temper-

ature for 1 h and refluxed for 17 h. The precipitate was separated

by filtration and the solvent was removed under reduced pressure.

The residue was purified by column chromatography on silica gel

with toluene as an eluent to give 13 (25 mg, 7% yield) as a brown

Compound (15): To a solution of 14 (159 mg, 0.27 mmol) in toluene

(10 mL) was added 1-chloro-2,4-dinitrobenzene (109 mg,

0.54 mmol) and the solution was reflux for 24 h. The precipitate

was collected by filtration to afford the pyridinium salt (213 mg,

100% yield) as a reddish brown solid. Pyrrolidine (1 mL) was added

to a solution of the pyridinium salt (213 mg, 0.266 mmol) in ethanol

(3 mL). The resulting solution was stirred at room temperature for

2 h. The reaction mixture was concentrated under reduced

pressure. To the residue was added cyclopentadiene (24 mg,

0.36 mmol), KOtBu (35 mg, 0.311 mmol), and pyridine (4 mL) and

the mixture was stirred at room temperature for 1 h and refluxed

for 18 h. The precipitate was separated by filtration and the solvent

was removed under reduced pressure. The residue was purified by

column chromatography on silica gel with toluene as an eluent to

°

solid. M.p. >300 C; IR (AT–IR): ν_max=3079 (w), 2965 (w), 1943 (w),

1795 (w), 1716 (w), 1566 (s), 1545 (w), 1498 (w), 1474 (w), 1427 (s),

1397 (s), 1377 (m), 1345 (w), 1303 (w), 1267 (w), 1243 (w), 1200 (w),

1107 (w), 1051 (w), 985 (w), 919 (w), 905 (w), 878 (w), 843 (s), 800

(w), 784 (w), 748 (m), 705 (w), 680 (w), 664 (w), 652 (w) cm^–1; UV/Vis

(CH₂Cl₂): λ_max(log ɛ)=238 (4.80), 285 (4.97), 314 (4.91), 343 sh (4.79),

378 sh (4.43), 456 (4.84), 583 sh (3.61), 621 sh (3.51), 690 sh (3.03)

nm; UV/Vis (30% CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=300 (4.57), 344

°

give 15 (32 mg, 19% yield) as a green solid. M.p. >300 C; IR (AT–

IR): ν_max=3022 (w), 2959 (w), 2867 (w), 1573 (s), 1548 (w), 1491 (w),

1472 (w), 1429 (m), 1397 (m), 1370 (m), 1350 (w), 1304 (w), 1269

(w), 1230 (w), 1197 (w), 1147 (w), 1113 (w), 1050 (w), 1017 (w), 988

(w), 964 (w), 941 (w), 851 (m), 841 (s), 828 (m), 814 (w), 790 (w), 763

(m), 752 (w), 737 (s), 722 (w), 706 (w), 679 (w), 664 (w), 654 (w) cm^–1;

UV/Vis (CH₂Cl₂): λ_max(log ɛ)=239 (4.65), 283 (4.81), 335 (4.74), 386

sh (4.50), 443 (4.58), 592 (3.17), 633 sh (3.12), 699 sh (2.80) nm; UV/

Vis (30% CH₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=284 (4.80), 336 (4.75), 374

sh (4.56), 395 sh (4.51), 442 (4.57), 709 (3.50) nm; UV/Vis (30%

CF₃CO₂H/CH₂Cl₂): λ_max(log ɛ)=291 sh (4.51), 343 sh (4.47), 369

(4.50), 500 sh (4.45), 547 sh (4.61), 579 (4.70) nm; ¹H NMR (500 MHz,

CDCl₃): δ_H=8.73 (d, J=9.7 Hz, 1H, 4-H), 8.68 (d, J=9.7 Hz, 1H, 8-H),

8.62 (d, J=10.6 Hz, 2H, 4’,8’-H), 8.43 (d, J=10.3 Hz, 2H, 4’’,8’’-H),

8.32 (s, 1H, 2-H), 8.10 (s, 1H, 2’-H), 7.91 (t, J=3.7 Hz, 1H, 2’’-H), 7.70

(d, J=9.7 Hz, 1H, 6-H), 7.66 (d, J=8.3 Hz, 4H, 4-tBuPh), 7.57 (d, J=

8.3 Hz, 4H, 4-tBuPh), 7.53 (d, J=10.6 Hz, 2H, 5’’,7’’-H), 7.44 (m, 4H,

1’’,3’’,5’,7’-H), 7.24–7.29 (m, 3H, 5,7-H), 1.43 (s, 18H, tBu) ppm; ¹³C

NMR (125 MHz, CDCl₃): δ_C=149.37, 147.89, 146.42, 139.92, 138.70,

138.20, 138.09, 137.07, 136.62, 136.57, 135.75, 135.37, 135.05,

134.55, 134.45, 134.16, 131.05, 129.53, 125.86, 125.75, 125.62,

125.48, 125.42, 118.48, 34.69, 31.54 ppm; HRMS (MALDI-TOF,

positive): Calcd for C₅₀H₄₄[M]⁺644.3438, found:644.3441.

1

(4.62), 373 sh (4.46), 411 sh (4.23), 585 (4.96), 610 sh (4.91) nm; H

NMR (500 MHz, CDCl₃): δ_H=8.75 (dd, J=10.7, 5.9 Hz, 3H, 4,4’’’’,8’’’’-

H), 8.67 (d, J=10.3 Hz, 1H, 8-H), 8.47 (d, J=10.6 Hz, 4H, 4’’,4’’’,8’’,8’’’-

H), 8.43 (d, J=10.6 Hz, 2H, 4’,8’-H), 8.29 (s, 2H, 2,2’-H), 7.90 (t, J=

3.7 Hz, 3H, 2’’,2’’’,2’’’’-H), 7.67 (d, J=10.9 Hz, 2H, 5’’’’,7’’’’-H), 7.63 (d,

J=10.3 Hz, 4H, 5’’,5’’’,7’’,7’’’-H), 7.50–7.56 (m, 4H, 1’’’’,3’’’’,5’,7’-H),

7.44 (m, 6H, 1’’, 1’’’,3’’, 3’’,5,7,–H), 1.49 (s, 9H, tBu) ppm. Measure-

ment of ¹³C NMR was hampered by the insolubility of the

compound. HRMS (MALDI-TOF, positive): Calcd for C₅₄H₄₀+H⁺[M+

H]⁺689.3203, found: 689.3190.

Compound (14): NIS (357 mg, 1.40 mmol) was added to a solution

of 10d (155 mg, 0.47 mmol) in CH₂Cl₂(10 mL) and Et₃N (3 drops).

°

The resulting solution was stirred at 0 C for 1 h. The reaction

mixture was concentrated under reduced pressure. The residue was

passed through short column chromatography on alumina with

CHCl₃as an eluent to give the crude diiodo derivative (194 mg,

71% yield) as a brown solid. To a solution of the diiodo derivative

(194 mg, 0.33 mmol), 4-tert-butylphenylboronic acid (177 mg,

0.994 mmol), and K₃PO₄(426 mg, 2.00 mmol) in 1,4-dioxane (5 mL)

and H₂O (0.5 mL) was added PdCl₂(dppf) (12 mg, 0.016 mmol). The

resulting mixture was refluxed for 15.5 h under an Ar atmosphere.

The reaction mixture was poured into aq. NaOH (10%) and

extracted with toluene. The organic layer was washed with sat.

NH₄Cl and brine, dried with Na₂SO₄, and concentrated under

reduced pressure. The residue was purified by column chromatog-

raphy on alumina with CHCl₃/hexane as an eluent to give 14

Acknowledgments

This work was partially supported by the JSPS KAKENHI Grant

Number 17K05780. We also thank Ms. Nanami Iida, Ms. Atsuyo

Yamamoto, Ms. Erika Shimomura, and Mr. Yuta Inoue, Shinshu

University, for their technical assistance. We appreciate late

professor Klaus Hafner for his valuable comments on our research.

°

(87 mg, 44% yield) as a green solid. M.p. 183–185 C; IR (AT–IR):

ν

_max=3024 (w), 2959 (w), 2902 (w), 5865 (w), 1596 (m), 1568 (s),

1543 (w), 1519 (w), 1492 (w), 1460 (w), 1429 (m), 1366 (m), 1317 (w),

1303 (w), 1269 (w), 1223 (w), 1204 (w), 1113 (w), 1017 (w), 992 (w),

939 (w), 874 (w), 830 (s), 777 (w), 741 (m), 723 (w), 701 (w), 688 (w),

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[16] Deposition Numbers 1838801 (for 7 a a ) and 1922390 (for 9 ) contain the

Conflict of Interest

supplementary crystallographic data for this paper. These data are

provided free of charge by the joint Cambridge Crystallographic Data

Centre and Fachinformationszentrum Karlsruhe Access Structures

service www.ccdc.cam.ac.uk/structures.

The authors declare no conflict of interest.

[17] The time-dependence density functional calculations were performed

with Spartan’10, Wave function, Irvine, CA.

Keywords: cyanine dyes

· donor-acceptor compounds ·

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Manuscript received: April 15, 2021

Revised manuscript received: April 26, 2021

Accepted manuscript online: April 27, 2021

ChemPlusChem 2021, 86, 1–22

www.chempluschem.org

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FULL PAPERS

Prof. Dr. T. Shoji*, A. Yamazaki, Y.

Ariga, M. Uda, D. Ando, N. Sasahara,

N. Kai, Prof. Dr. S. Ito

1 – 22

Azulene-Substituted Donor-

Acceptor Polymethines and 1,6’-

Bi-, 1,6’;3,6’’-Ter-, and Quinquea-

zulenes via Zincke Salts:

Synthesis, and Structural, Optical,

and Electrochemical Properties

Azulene-substituted donor-acceptor

polymethines, bi-, ter-, and quinquea-

zulenes composed of the 1,6’-

biazulene unit have been successfully

prepared from Zincke salts with an 1-

azulenyl substituent. The structural,

optical, and electrochemical proper-

ties of the azulene-substituted donor-

acceptor polymethines, bi-, ter-, and

quinqueazulenes were revealed by

single-crystal X-ray structure analysis,

UV/vis spectroscopy, voltammetry

analysis, spectroelectrochemistry, and

theoretical calculations.

Article Doi

Azulene-Substituted Donor-Acceptor Polymethines and 1,6’-Bi-, 1,6′;3,6′′-Ter-, and Quinqueazulenes via Zincke Salts: Synthesis, and Structural, Optical, and Electrochemical Properties

DOI: 10.1002/cplu.202100174

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Authors:

Article abstract of DOI:10.1002/cplu.202100174

Full text of DOI:10.1002/cplu.202100174

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