Preparation and structures of new azobenzene derivatives with a 3-guaiazulenylvinyl group

Article abstract of DOI:10.1246/bcsj.82.1398

Wittig reactions of (E)-4-(4-methoxyphenyldiazenyl)benzaldehyde and (E)-4-[4-(dimethylamino)phenyldiazenyl]- benzaldehyde with (3- guaiazulenylmethyl)triphenylphosphonium bromide in ethanol in the presence of sodium ethoxide at 25 °C for 24 h under argon

Full text of DOI:10.1246/bcsj.82.1398

1398 Bull. Chem. Soc. Jpn. Vol. 82, No. 11, 1398–1408 (2009)
© 2009 The Chemical Society of Japan
Preparation and Structures of New Azobenzene Derivatives
with a 3-Guaiazulenylvinyl Group
Shin-ichi Takekuma,*1 Kenji Fukuda,1 Toshie Minematsu,2 and Hideko Takekuma1
1Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University,
3-4-1 Kowakae, Higashi-Osaka 577-8502
2School of Pharmaceutical Sciences, Kinki University, 3-4-1 Kowakae, Higashi-Osaka 577-8502
Received May 8, 2009; E-mail: takekuma@apch.kindai.ac.jp
Wittig reactions of (E)-4-(4-methoxyphenyldiazenyl)benzaldehyde and (E)-4-[4-(dimethylamino)phenyldiazenyl]-
benzaldehyde with (3-guaiazulenylmethyl)triphenylphosphonium bromide in ethanol in the presence of sodium ethoxide at
25 °C for 24 h under argon give only E forms (E)-4-{(E)-4-[2-(3-guaiazulenyl)vinyl]phenyldiazenyl}methoxybenzene and
(E)-N,N-dimethyl-4-{(E)-4-[2-(3-guaiazulenyl)vinyl]phenyldiazenyl}aniline in 71 and 73% yields. Comparative studies
on spectroscopic properties and crystal structures of the two new extended ³-electron systems with those of structurally
related (and delocalized) ³-electron systems (3-guaiazulenyl)[(E)-4-(4-methoxyphenyldiazenyl)phenyl]methylium ion and
{(E)-4-[4-(dimethylamino)phenyldiazenyl]phenyl}(3-guaiazulenyl)methylium ion compounds are reported. Similarly,
Wittig reaction of (E)-diphenyldiazene-4,4¤-dicarbaldehyde with the same reagent under the same reaction conditions
as the above affords only E forms (E)-4-{(E)-4-[2-(3-guaiazulenyl)vinyl]phenyldiazenyl}benzaldehyde and (E)-bis{(E)-4-
[2-(3-guaiazulenyl)vinyl]phenyl}diazene in 7 and 24% yields. Furthermore, reaction of guaiazulene (=7-isopropyl-1,4-
dimethylazulene) with (E)-diphenyldiazene-4,4¤-dicarbaldehyde in methanol in the presence of hexafluorophosphoric acid
at 25 °C for 30 min provides (E)-diphenyldiazene-4,4¤-bis(3-guaiazulenylmethylium) bis(hexafluorophosphate) in 46%
yield which upon reduction with NaBH4 in a mixed solvent of ethanol and acetonitrile at 25 °C for 30 min gives (E)-bis[4-
(3-guaiazulenylmethyl)phenyl]diazene in 88% yield. Comparative studies of spectroscopic properties of a new extended
³-electron system (E)-bis{(E)-4-[2-(3-guaiazulenyl)vinyl]phenyl}diazene with those of a new delocalized ³-electron
system (E)-diphenyldiazene-4,4¤-bis(3-guaiazulenylmethylium) bis(hexafluorophosphate) are documented.
1
In previous papers,1-20 we reported facile preparation and
crystal structures as well as spectroscopic, chemical, and
electrochemical properties of new conjugated ³-electron sys-
tems possessing a 3-guaiazulenyl (=5-isopropyl-3,8-dimethyl-
azulen-1-yl)1-16,18-20 [or an azulen-1-yl8,15 or a 3-(methoxy-
carbonyl)azulen-1-yl17] group. During the course of our basic
and systematic investigations of azulenes, we quite recently
found the following interesting results.21 Namely, the reaction
of naturally occurring guaiazulene22 (9) with (E)-4-(4-hydroxy-
phenyldiazenyl)benzaldehyde in methanol in the presence of
hexafluorophosphoric acid at 25 °C for 2 h gave as high as 94%
yield of 12 (Chart 1). Similarly, reactions of 9 with diazenes 2
and 3 under the same reaction conditions as the above afforded
13 and 14a (Chart 1) in 97 and 95% yields. Reduction of 12
with NaBH4 in a mixed solvent of ethanol and acetonitrile at
25 °C for 30 min gave as high as 85% yield of 15, in which
a hydride ion attached to the HC+-¡ carbon atom of 12,
selectively (Scheme 1). Similarly, NaBH4-reductions of 13
and 14a under the same reaction conditions as for 12 afforded
16 and 17 in 74 and 72% yields (Scheme 1). Along with
azobenzene, the variable-temperature H NMR studies of 14a
in acetonitrile-d3 at 70, 40, 25, 0, and ¹40 °C, supporting the
formation of rotational stereoisomers of 14a¤¤ (Chart 1) were
reported. Although X-ray crystallographic analysis of 12-14a
has not yet been achieved because of difficulty in obtaining a
single crystal suitable for that purpose, the crystal structure of
14b with an equiv of HBF4 (Chart 2) could be determined by
means of X-ray diffraction at ¹75 °C, supporting the formation
of 14b, with similar resonance structures to those of 14a, in the
single crystal.
Moreover, our interest has quite recently been focused on the
structures and the spectroscopic properties of the three
new extended ³-electron systems 4, 5, and 8 (Chart 3)
compared with those of structurally related (and delocalized)
³-electron systems 13, 14a, and 10 (Chart 4). In relation
to extended ³-electron systems with an azulenyl group,
for example, styrylazulenes (=1-azulenyl-2-phenylethylenes)
were prepared by Wittig reactions of azulenecarbaldehydes
with benzyltriphenylphosphonium chloride and further, the
reverse Wittig reaction [i.e., the reaction of benzaldehyde
with (azulenylmethyl)triphenylphosphonium iodide] was
applied to the preparation of styrylazulenes.23,24 On the
other hand, azobenzenes in general are currently drawing
increasing interest from the viewpoint of potential utilities
as photomemories,25,26 optical switching,27-29 and optoelec-
tronics.30,31
1
comparative studies of the H and 13C NMR chemical shifts of
the delocalized ³-electron systems of 12-14a with those of the
hydride reduction products 15-17, apparently indicating the
difference between the delocalized ³-electron system of 14a
and those of 12 and 13 owing to the influence of the substituted
(CH3)2N-, HO-, or CH3O- group at the C4¤¤ position of
Published on the web November 10, 2009; doi:10.1246/bcsj.82.1398

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009) 1399
4"
OH
OH
OH
−
PF6
+
N
N
N
−
+
N
N
N
−
PF6
+
H
H
H
α
PF6
12'
12
12''
4"
OCH3
OCH3
OCH3
−
PF6
+
N
N
N
N
N
N
−
PF6
H
+
H
H
−
PF6
α
+
13'
13
13''
+
4"
N
N
N
−
PF6
−
N
N
N
PF6
N
N
N
+
−
H
H
H
PF6
α
+
14a'
14a''
14a
Chart 1.
4"
R
1
N
1"
N
1
α 4
2
H2C
NaBH4
in a mixed solvent
3'
4'
12−14a
15: R = OH
16: R = OCH3
17: R = N(CH
1'
of EtOH and CH3CN
at r.t. for 30 min
)
3 2
7'
−
15 17
Scheme 1. The reductions of 12-14a with NaBH4 in a mixed solvent of EtOH and CH3CN at 25 °C for 30 min, affording the
corresponding hydride-reduction products 15-17.
We now wish to report the following five interesting points
for the title studies: namely, (i) preparation and spectroscopic
3
3"
6"
properties of 4 and 5; (ii) 1H and 13C NMR spectral parameters
of 13 (and 14a) compared with those of 4 (and 5); (iii) crystal
structures of 4 and 5 compared with that of 14b (Chart 2);
(iv) preparation and spectroscopic properties of 8 and 10 which
upon reduction with NaBH4 gives 11 (Chart 4); and (v) 1H and
13C NMR spectral parameters of 10 compared with those of 11
(and 8).
4"
N
2"
1"
1
−
6
3
BF4
5"
1 N
5
N
2
H +
2
4
α
3'
1
N
4'
6
3
5
4
1
N
1'
2
HBF4
2
7'
Experimental
General. Thermal (TGA and DTA) and elemental analyses
were taken on a Shimadzu DTG-50H thermal analyzer and a
Yanaco MT-3 CHN corder. FAB-MS spectra were taken on a JEOL
Tandem MStation JMS-700 TKM data system. UV-vis and IR
14b
18
Chart 2. For comparative purposes, the numbering scheme
of 14b was changed.

1400 Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009)
New Extended ³-Electron Systems
4'' R
1
N
N 1''
1
2
N
1 N
β
4
α
4'
3'
β
4
4'
α
3'
7'
1'
7'
1'
8
4, 5, and 7
4: R = OCH
3, 5: R = N(CH3)2, 7: R = CHO
1
Chart 3. For comparative purposes for H and 13C NMR signals and crystal structures, the numbering schemes of compounds 4, 5,
and 7 were changed.
+
H
−
PF6
1
1
N
N
−
N
N
PF6
H +
α
4
3'
4
3'
α
4'
4'
1'
1'
7'
7'
10
11
Chart 4.
spectra were taken on a Beckman DU640 spectrophotometer and a
Shimadzu FTIR-4200 Grating spectrometer. NMR spectra were
recorded with a JEOL GX-500 (500 MHz for 1H and 125 MHz for
13C), JEOL JNM-ECA600 (600 MHz for 1H and 150 MHz for
provide pure 4 as stable crystals (65 mg, 149 ¯mol, 71% yield).
Compound 4: Dark green plates, mp 172 °C [determined by
thermal analysis (TGA and DTA: rt ¼ 500 °C/5 °C min¹1)];
Rf = 0.38 on silica gel TLC (solv. hexane-EtOAc = 8:2, v/v);
UV-vis -max/nm (log ¾) in CH2Cl2: 238 (4.45), 276 (4.43), 359
1
13C), and JNM-ECA700 (700 MHz for H and 176 MHz for 13C)
1
¹1
cryospectrometer at 25 °C. The H NMR spectra (¤ and J values)
(4.44), and 481 (4.66); IR ¯max/cm (KBr): 1582 (N=N); exact
were assigned using computer-assisted simulation (software:
gNMR developed by Adept Scientific plc) on a SONY VAIO
PCV-HS80 personal-computer with a Pentium (R) 4 processor.
Preparation of (E)-4-{(E)-4-[2-(3-Guaiazulenyl)vinyl]phen-
EI-MS (70 eV), found: m/z 434.2336 (M+, 100%); calcd for
C30H30ON2: M+, m/z 434.2358; 700 MHz 1H NMR (CD2Cl2):
signals resulting from the 3-guaiazulenylvinyl group: ¤ 1.34 (6H,
d, J = 7.0 Hz, (CH3)2CH-7¤), 2.62 (3H, s, Me-1¤), 3.02 (1H,
sept, J = 7.0 Hz, Me2CH-7¤), 3.08 (3H, s, Me-4¤), 6.92 (1H, d,
J = 10.5 Hz, H-5¤), 7.01 (1H, d, J = 15.8 Hz, H-¡), 7.28 (1H, dd,
J = 10.5, 2.0 Hz, H-6¤), 7.97 (1H, s, H-2¤), 8.03 (1H, d, J = 2.0 Hz,
H-8¤), and 8.17 (1H, d, J = 15.8 Hz, H-¢); signals originating from
4-methoxyazobenzene: ¤ 3.89 (3H, s, MeO-4¤¤), 7.03 (2H, ddd,
J = 9.0, 3.1, 2.0 Hz, H-3¤¤,5¤¤), 7.63 (2H, ddd, J = 8.4, 2.2, 1.7 Hz,
H-3,5), 7.88 (2H, ddd, J = 8.4, 2.2, 1.7 Hz, H-2,6), and 7.92 (2H,
ddd, J = 9.0, 3.1, 2.0 Hz, H-2¤¤,6¤¤); 176 MHz 13C NMR (CD2Cl2):
¤ 161.7 (C-4¤¤), 150.8 (C-1), 146.9 (C-1¤¤), 145.8 (C-4¤), 141.5
(C-7¤), 141.0 (C-4), 140.7 (C-8a¤), 135.0 (C-6¤), 134.7 (C-2¤),
133.5 (C-8¤), 132.8 (C-3a¤), 127.6 (C-5¤), 127.1 (C-¢), 126.3
(C-1¤), 126.0 (C-3,5), 125.5 (C-3¤), 124.8 (C-¡), 124.1 (C-2¤¤,6¤¤),
122.8 (C-2,6), 113.9 (C-3¤¤,5¤¤), 53.2 (MeO-4¤¤), 37.3 (Me2CH-7¤),
yldiazenyl}methoxybenzene (4).
To a solution of (E)-4-(4-
methoxyphenyldiazenyl)benzaldehyde21 (2) (50 mg, 208 ¯mol) in
ethanol (2 mL) was added a solution of 3-(guaiazulenylmethyl)-
triphenylphosphonium bromide32 (1) (117 mg, 211 ¯mol) in
ethanol (2 mL) containing sodium ethoxide (15 mg, 221 ¯mol).
The mixture was stirred at 25 °C for 24 h under argon. After
the reaction, distilled water was added to the mixture, and
then the resulting product was extracted with dichloromethane
(20 mL © 3). The extract was washed with distilled water, dried
(Na2SO4), and evaporated in vacuo. The residue thus obtained was
carefully separated by silica gel column chromatography with
dichloromethane as an eluant. The crude product was recrystallized
from dichloromethane-methanol (1:4, v/v) (several times) to

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009) 1401
28.1 (Me-4¤), 23.8 ((CH3)2CH-7¤), and 12.4 (Me-1¤). For com-
parative purposes on 1H and 13C NMR signals, the numbering
scheme of compound 4 was changed as shown in Chart 3.
X-ray Crystal Structure of (E)-4-{(E)-4-[2-(3-Guaiazulenyl)-
150 MHz 13C NMR (CD2Cl2): ¤ 152.7 (C-4¤¤), 151.9 (C-1), 146.4
(C-4¤), 144.0 (C-1¤¤), 142.0 (C-7¤), 141.3 (C-8a¤), 140.6 (C-4),
135.7 (C-2¤), 135.4 (C-6¤), 134.1 (C-8¤), 133.3 (C-3a¤), 128.1
(C-5¤), 127.2 (C-¢), 126.9 (C-1¤), 126.6 (C-3,5), 126.3 (C-3¤),
125.8 (C-¡), 125.0 (C-2¤¤,6¤¤), 123.0 (C-2,6), 111.8 (C-3¤¤,5¤¤), 40.4
(Me2N-4¤¤), 38.0 (Me2CH-7¤), 28.8 (Me-4¤), 24.4 ((CH3)2CH-7¤),
vinyl]phenyldiazenyl}methoxybenzene (4).
A total 5630
reflections with 2ªmax = 55.0° were collected on a Rigaku
AFC-5R automated four-circle diffractometer with graphite mono-
chromated Mo K¡ radiation (- = 0.71069 ¡, rotating anode:
50 kV, 180 mA) at ¹75 °C. The structure was solved by direct
methods (SIR97)34 and expanded using Fourier techniques
(DIRDIF94).35 Non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included but not refined. The final cycle of
full-matrix least-squares refinement was based on F2. All calcu-
lations were performed using the teXsan crystallographic software
package.36 Crystallographic data have been deposited with
Cambridge Crystallographic Data Center: Deposition number
CCDC-669774 for compound No. 4. Copies of the data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge, CB2 1EZ, U.K.; Fax: +44
1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
1
and 13.1 (Me-1¤). For comparative purposes on H and 13C NMR
signals, the numbering scheme of compound 5 was changed as
shown in Chart 3.
X-ray Crystal Structure of (E)-N,N-Dimethyl-4-{(E)-4-[2-(3-
guaiazulenyl)vinyl]phenyldiazenyl}aniline (5). A total of 3325
reflections with 2ªmax = 55.0° were collected on a Rigaku AFC-5R
automated four-circle diffractometer with graphite monochromated
Mo K¡ radiation (- = 0.71069 ¡, rotating anode: 50 kV, 180 mA)
at ¹75 °C. The structure was solved by direct methods (SIR97)34
and expanded using Fourier techniques (DIRDIF94).35 Non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
were included but not refined. The final cycle of full-matrix least-
squares refinement was based on F2. All calculations were
performed using the teXsan crystallographic software package.36
Deposition number CCDC-669775 for compound No. 5.
Crystallographic data for 5: C31H33N3 (FW: 447.62), dark green
plate (the crystal size, 0.40 © 0.40 © 0.50 mm3), monoclinic,
Crystallographic data for 4: C30H30ON2 (FW: 434.58), dark
green plate (the crystal size, 0.30 © 0.30 © 0.30 mm3), triclinic,
ꢀ
P1 (#2), a = 13.474(2) ¡, b = 15.431(4) ¡, c = 5.746(1) ¡, ¡ =
P21 (#4), a = 13.750(3) ¡, b = 5.921(3) ¡, c = 16.596(3) ¡,
95.11(2)°, ¢ = 95.95(1)°, £ = 96.31(1)°, V = 1174.9(5) ¡3, Z = 2,
¢ = 110.57(1)°, V = 1265.0(6) ¡3, Z = 2, Dcalcd = 1.175 g cm
,
¹3
¹3
¹1
D
calcd = 1.228 g cm
,
®(Mo K¡) = 0.74 cm
,
Scan width:
®(Mo K¡) = 0.69 cm¹1, Scan width: (1.31 + 0.30 tan ª)°, Scan
mode: ½-2ª, Scan rate: 8.0° min¹1, measured reflections: 3325,
observed reflections: 3193, No. of parameters: 307, R1 = 0.064,
wR2 = 0.210, and Goodness of fit indicator: 1.78.
¹1
(1.21 + 0.30 tan ª)°, Scan mode: ½-2ª, Scan rate: 8.0° min
,
measured reflections: 5630, observed reflections: 5399, No. of
parameters: 298, R1 = 0.058, wR2 = 0.188, and Goodness of fit
indicator: 1.27.
Preparation of (E)-{(E)-4-[2-(3-Guaiazulenyl)vinyl]phenyl-
diazenyl}benzaldehyde (7) and (E)-Bis{(E)-4-[2-(3-guaiazul-
enyl)vinyl]phenyl}diazene (8). To a solution of (E)-diphenyl-
diazene-4,4¤-dicarbaldehyde37 (6) (30 mg, 125 ¯mol) in ethanol
(20 mL) was added a solution of 3-(guaiazulenylmethyl)triphenyl-
phosphonium bromide32 (1) (150 mg, 270 ¯mol) in ethanol (5 mL)
containing sodium ethoxide (20 mg, 294 ¯mol). The mixture was
stirred at 25 °C for 24 h under argon. After the reaction, distilled
water was added to the mixture, and then the resulting products
were extracted with dichloromethane (20 mL © 3). The extract was
washed with distilled water, dried (Na2SO4), and evaporated in
vacuo. The residue thus obtained was carefully separated by silica
gel column chromatography with dichloromethane-hexane (6:4,
v/v) as an eluant. The starting material 6 (3 mg, 12 ¯mol, 10%)
was recovered. The separated crude products 7 and 8 were
recrystallized from dichlorometane-methanol (1:4, v/v) (several
times), respectively, to provide pure 7 (4 mg, 9 ¯mol, 7% yield)
and 8 (19 mg, 30 ¯mol, 24% yield).
Compound 7: Dark green prisms, mp 172 °C [determined by
thermal analysis (TGA and DTA: rt ¼ 500 °C/5 °C min¹1)];
Rf = 0.16 on silica gel TLC (solv. dichloromethane-hexane = 6:4,
v/v); UV-vis -max/nm (log ¾) in CH2Cl2: 253 (4.31), 278 (4.39),
330 (4.38), and 528 (4.49); IR ¯max/cm¹1 (KBr): 1701 (C=O) and
1585 (N=N); exact FAB-MS (3-nitrobenzyl alcohol matrix):
found: m/z 432.2177; calcd for C30H28ON2: M+, m/z 432.2203;
700 MHz 1H NMR (CD2Cl2): signals resulting from the 3-guai-
azulenylvinyl group: ¤ 1.35 (6H, d, J = 7.0 Hz, (CH3)2CH-7¤),
2.62 (3H, s, Me-1¤), 3.03 (1H, sept, J = 7.0 Hz, Me2CH-7¤), 3.09
(3H, s, Me-4¤), 6.94 (1H, d, J = 10.5 Hz, H-5¤), 7.03 (1H, d,
J = 15.6 Hz, H-¡), 7.30 (1H, dd, J = 10.5, 2.0 Hz, H-6¤), 7.98
(1H, s, H-2¤), 8.04 (1H, d, J = 2.0 Hz, H-8¤), and 8.23 (1H, d,
J = 15.6 Hz, H-¢); signals resulting from 4-formylazobenzene: ¤
7.66 (2H, ddd, J = 8.4, 2.0, 1.7 Hz, H-3,5), 7.97 (2H, ddd, J = 8.4,
Preparation of (E)-N,N-Dimethyl-4-{(E)-4-[2-(3-guaiazul-
enyl)vinyl]phenyldiazenyl}aniline (5). To a solution of (E)-4-
[4-(dimethylamino)phenyldiazenyl]benzaldehyde21 (3) (50 mg,
197 ¯mol) in ethanol (20 mL) was added a solution of 3-(guai-
azulenylmethyl)triphenylphosphonium bromide32 (1) (110 mg,
198 ¯mol) in ethanol (5 mL) containing sodium ethoxide (15 mg,
221 ¯mol). The mixture was stirred at 25 °C for 24 h under argon.
After the reaction, distilled water was added to the mixture, and
then the resulting product was extracted with dichloromethane
(20 mL © 3). The extract was washed with distilled water, dried
(Na2SO4), and evaporated in vacuo. The residue thus obtained was
carefully separated by silica gel column chromatography with
dichloromethane as an eluant. The crude product was recrystallized
from dichloromethane-methanol (1:4, v/v) (several times) to
provide pure 5 as stable crystals (65 mg, 145 ¯mol, 73% yield).
Compound 5: Dark green plates, mp 233 °C [determined by
thermal analysis (TGA and DTA: rt ¼ 500 °C/5 °C min¹1)];
Rf = 0.30 on silica gel TLC (solv. hexane-EtOAc = 8:2, v/v);
UV-vis -max/nm (log ¾) in CH2Cl2: 255 (4.43), 281 (4.43), and
¹1
493 (4.79); IR ¯max/cm (KBr): 1601 (N=N); exact FAB-MS
(3-nitrobenzyl alcohol matrix), found: m/z 447.2663; calcd for
C31H33N3: M+, m/z 447.2675; 600 MHz 1H NMR (CD2Cl2):
signals resulting from the 3-guaiazulenylvinyl group: ¤ 1.34 (6H,
d, J = 7.0 Hz, (CH3)2CH-7¤), 2.62 (3H, s, Me-1¤), 3.02 (1H, sept,
J = 7.0 Hz, Me2CH-7¤), 3.08 (3H, s, Me-4¤), 6.90 (1H, d,
J = 11.0 Hz, H-5¤), 7.00 (1H, d, J = 15.8 Hz, H-¡), 7.27 (1H,
dd, J = 11.0, 2.0 Hz, H-6¤), 7.96 (1H, s, H-2¤), 8.02 (1H, d,
J = 2.0 Hz, H-8¤), and 8.14 (1H, d, J = 15.8 Hz, H-¢); signals
resulting from 4-(dimethylamino)azobenzene: ¤ 3.08 (6H, s,
Me2N-4¤¤), 6.78 (2H, ddd, J = 9.0, 3.1, 2.0 Hz, H-3¤¤,5¤¤), 7.61
(2H, ddd, J = 8.5, 2.1, 1.6 Hz, H-3,5), 7.83 (2H, ddd, J = 8.5, 2.1,
1.6 Hz, H-2,6), and 7.86 (2H, ddd, J = 9.0, 3.1, 2.0 Hz, H-2¤¤,6¤¤);

1402 Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009)
New Extended ³-Electron Systems
2.0, 1.7 Hz, H-2,6), 8.02 (2H, ddd, J = 8.5, 2.1, 1.1 Hz, H-3¤¤,5¤¤),
8.04 (2H, ddd, J = 8.5, 2.1, 1.1 Hz, H-2¤¤,6¤¤), and 10.08 (1H, s,
OHC-4¤¤); 176 MHz 13C NMR (CD2Cl2): ¤ 191.1 (OHC-4¤¤), 155.9
(C-1¤¤), 150.7 (C-1), 145.8 (C-4¤), 142.7 (C-4), 141.9 (C-7¤), 140.9
(C-8a¤), 136.9 (C-4¤¤), 134.9 (C-2¤), 134.9 (C-6¤), 133.6 (C-8¤),
133.2 (C-3a¤), 130.2 (C-3¤¤,5¤¤), 128.1 (C-5¤), 128.0 (C-¢),
126.5 (C-1¤), 126.0 (C-3,5), 125.4 (C-3¤), 124.4 (C-¡), 123.6
(C-2,6), 122.8 (C-2¤¤,6¤¤), 37.3 (Me2CH-7¤), 28.1 (Me-4¤), 23.7
((CH3)2CH-7¤), and 12.4 (Me-1¤). For comparative purposes on 1H
and 13C NMR signals, the numbering scheme of compound 7 was
changed as shown in Chart 3.
153.7 (C-3a¤), 151.4 (C-5¤), 148.4 (HC+-¡), 147.2 (C-1¤), 145.4
(C-6¤), 141.7 (C-3¤), 141.0 (C-2¤), 140.1 (C-8¤), 139.7 (C-4), 134.8
(C-3,5), 124.6 (C-2,6), 40.3 (Me2CH-7¤), 29.7 (Me-4¤), 23.7
((CH3)2CH-7¤), and 13.9 (Me-1¤).
Reduction of (E)-Diphenyldiazene-4,4¤-bis(3-guaiazulenyl-
methylium) Bis(hexafluorophosphate) (10) with NaBH4. To
a solution of NaBH4 (5 mg, 132 ¯mol) in ethanol (2.0 mL) was
added a solution of 10 (30 mg, 33 ¯mol) in acetonitrile (2.0 mL).
The mixture was stirred at 25 °C for 30 min, and then was
evaporated in vacuo. The residue thus obtained was dissolved in
dichloromethane and filtered. The filtrate was evaporated in vacuo,
giving a green pasty residue, which was carefully separated by
silica gel column chromatography with hexane-ethyl acetate (8:2,
v/v) as an eluant. The crude product thus obtained was recrystal-
lized from dichloromethane-methanol (1:5, v/v) (several times) to
provide pure (E)-bis[4-(3-guaiazulenylmethyl)phenyl]diazene (11)
as stable crystals (18 mg, 29 ¯mol, 88% yield).
Compound 8: Dark green powder, mp 263 °C [determined
by thermal analysis (TGA and DTA: rt ¼ 500 °C/5 °C min¹1)];
Rf = 0.48 on silica gel TLC (solv. dichloromethane-hexane = 6:4,
v/v); UV-vis -max/nm (log ¾) in CH2Cl2: 230 (4.43), 278 (4.50),
¹1
312 (4.47), and 533 (4.71); IR ¯max/cm (KBr): 1585 (N=N);
exact FAB-MS (3-nitrobenzyl alcohol matrix), found: m/z
626.3647; calcd for C46H46N2: M+, m/z 626.3661; 500 MHz
1H NMR (CD2Cl2): signals resulting from two equivalent 3-
guaiazulenylvinyl groups: ¤ 1.34 (12H, d, J = 6.9 Hz, (CH3)2CH-
7¤), 2.62 (6H, s, Me-1¤), 3.02 (2H, sept, J = 6.9 Hz, Me2CH-7¤),
3.09 (6H, s, Me-4¤), 6.93 (2H, d, J = 11.0 Hz, H-5¤), 7.03 (2H, d,
J = 15.8 Hz, H-¡), 7.29 (2H, dd, J = 11.0, 2.2 Hz, H-6¤), 7.98 (2H,
s, H-2¤), 8.03 (2H, d, J = 2.2 Hz, H-8¤), and 8.21 (2H, d,
J = 15.8 Hz, H-¢); signals resulting from two equivalent phenyl
groups of an azobenzene: ¤ 7.65 (4H, ddd, J = 8.5, 2.1, 1.8 Hz,
H-3,5) and 7.92 (4H, ddd, J = 8.5, 2.1, 1.8 Hz, H-2,6); 125 MHz
13C NMR (CD2Cl2): ¤ 151.0 (C-1), 145.8 (C-4¤), 141.6 (C-7¤),
141.3 (C-4), 140.8 (C-8a¤), 135.0 (C-2¤), 134.8 (C-6¤), 133.6 (C-
8¤), 132.9 (C-3a¤), 127.7 (C-5¤), 127.3 (C-¢), 126.4 (C-1¤), 126.0
(C-3,5), 125.6 (C-3¤), 124.8 (C-¡), 123.0 (C-2,6), 37.4 (Me2CH-
7¤), 28.2 (Me-4¤), 23.8 ((CH3)2CH-7¤), and 12.4 (Me-1¤).
Preparation of (E)-Diphenyldiazene-4,4¤-bis(3-guaiazulenyl-
methylium) Bis(hexafluorophosphate) (10). To a solution of
commercially available guaiazulene (9) (50 mg, 252 ¯mol) in
methanol (1.0 mL) was added a solution of (E)-diphenyldiazene-
4,4¤-dicarbaldehyde37 (6) (30 mg, 125 ¯mol) in methanol (3.0 mL)
containing hexafluorophosphoric acid (60% aqueous solution,
0.15 mL). The mixture was stirred at 25 °C for 2 h, precipitating a
dark-red solid of 10, and then was centrifuged at 2.5 krpm for
1 min. The crude product thus obtained was carefully washed with
diethyl ether, and was recrystallized from acetonitrile-diethyl ether
(1:5, v/v) (several times) to provide pure 10 as stable crystals
(52 mg, 58 ¯mol, 46% yield).
Compound 11: Dark green prisms, mp 215 °C [determined by
thermal analysis (TGA and DTA: rt ¼ 500 °C/5 °C min¹1)].
Rf = 0.60 on silica gel TLC (solv. hexane-EtOAc = 8:2, v/v);
¹1
IR ¯max/cm (KBr): 1596 (N=N); exact FAB-MS (3-nitrobenzyl
alcohol matrix), found: m/z 602.3657; calcd for C44H46N2: M+,
m/z 602.3661; 500 MHz 1H NMR (CD2Cl2): signals resulting
from two equivalent 3-guaiazulenylmethyl groups: ¤ 1.34 (12H, d,
J = 6.8 Hz, (CH3)2CH-7¤), 2.61 (6H, s, Me-1¤), 2.82 (6H, s, Me-
4¤), 3.03 (2H, sept, J = 6.8 Hz, Me2CH-7¤), 4.69 (4H, s, CH2-3¤),
6.82 (2H, d, J = 11.0 Hz, H-5¤), 7.28 (2H, dd, J = 11.0, 2.0 Hz, H-
6¤), 7.40 (2H, s, H-2¤), and 8.11 (2H, d, J = 2.0 Hz, H-8¤); signals
resulting from two equivalent phenyl groups of an azobenzene: ¤
7.14 (4H, ddd, J = 8.7, 2.3, 2.0 Hz, H-3,5) and 8.05 (4H, ddd,
J = 8.7, 2.3, 2.0 Hz, H-2,6); 125 MHz 13C NMR (CD2Cl2): ¤ 150.8
(C-1), 145.0 (C-4¤), 144.9 (C-4), 140.6 (C-2¤), 138.9 (C-7¤), 137.5
(C-8a¤), 134.4 (C-6¤), 133.1 (C-8¤), 132.7 (C-3a¤), 128.2 (C-3,5),
126.0 (C-5¤), 125.2 (C-2,6), 124.4 (C-3¤), 123.9 (C-1¤), 37.3
(Me2CH-7¤), 36.5 (CH2-3¤), 26.1 (Me-4¤), 23.9 ((CH3)2CH-7¤), and
12.2 (Me-1¤).
Results and Discussion
Preparation and Spectroscopic Properties of 4 and 5.
The target extended ³-electron systems 4 and 5 were prepared
according to Scheme 2. The structures of the products 4 and 5
were established on the basis of spectroscopic data [UV-vis,
IR, exact MS (EI for 4 and FAB for 5), 1H and 13C NMR
including 2D NMR (i.e., H-H COSY, HMQC, and HMBC)].
Compound 10: Dark red prisms, mp >178 °C [decomp.,
determined by thermal analysis (TGA and DTA: rt ¼ 500 °C/
5 °C min¹1)]. Found: C, 57.46; H, 4.81; N, 3.28%. Calcd for
2C44H44N2F12P2 + 3H2O: C, 57.58; H, 5.16; N, 3.05%; UV-vis
R
N
N
-
max/nm (log ¾) in CH3CN: 233 (4.76), 288 (4.52), 334 (4.46),
OHC
¹1
390sh (4.45), and 499 (4.86); IR ¯max/cm (KBr): 1601 (N=N)
and 837, 556 (PF6 ); exact FAB-MS (3-nitrobenzyl alcohol
2, 3
¹
matrix), found: m/z 600.3509; calcd for C44H44N2: [M ¹
2PF6]2+, m/z 600.3505; 500 MHz 1H NMR (CD3CN): signals
resulting from two equivalent 3-guaiazulenylmethylium substitu-
ents: ¤ 1.46 (12H, d, J = 7.0 Hz, (CH3)2CH-7¤), 2.53 (6H, s, Me-
1¤), 3.39 (6H, s, Me-4¤), 3.51 (2H, sept, J = 7.0 Hz, Me2CH-7¤),
8.02 (2H, s, H-2¤), 8.45 (2H, dd, J = 11.2, 2.2 Hz, H-6¤), 8.58 (2H,
d, J = 11.2 Hz, H-5¤), 8.60 (2H, d, J = 2.2 Hz, H-8¤), and 8.80 (2H,
s, HC+-¡); signals resulting from two equivalent phenyl groups of
an azobenzene: ¤ 8.03 (4H, ddd, J = 8.3, 2.0, 1.7 Hz, H-3,5) and
8.15 (4H, ddd, J = 8.3, 2.0, 1.7 Hz, H-2,6); 125 MHz 13C NMR
(CD3CN): ¤ 172.8 (C-7¤), 162.0 (C-8a¤), 158.4 (C-4¤), 154.6 (C-1),
2: R = OCH , 3: R = N(CH
)
3
3 2
+
P
4, 5
−
EtONa/EtOH
at r.t. for 24 h
under argon
Br
1
Scheme 2. The reactions of 1 with 2 (and 3) in ethanol in the
presence of sodium ethoxide at 25 °C for 24 h under argon,
affording the corresponding azobenezene derivatives 4
(and 5).

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009) 1403
¹1
Figure 1. (a) UV-vis spectra of 4, 5, and 7 in CH2Cl2. Concentrations, 4: 0.11 g L (253 ¯mol L¹1), 5: 0.12 g L¹1 (268 ¯mol L¹1),
and 7: 0.14 g L¹1 (322 ¯mol L¹1). Length of the cell, 0.1 cm each. Each log ¾ value is given in parenthesis. (b) UV-vis spectra of 12,
¹1
¹1
¹1
13, and 14a in CH3CN. Concentrations, 12: 0.10 g L (181 ¯mol L¹1), 13: 0.10 g L (177 ¯mol L¹1), and 14a: 0.10 g L
(173 ¯mol L¹1). Length of the cell, 0.1 cm each. Each log ¾ value is given in parenthesis.
¹1
¹1
Figure 2. (a) UV-vis spectra of 8 in CH2Cl2 and 10 in CH3CN. Concentrations, 8: 0.13 g L (123 ¯mol L¹1), 10: 0.11 g L
(268 ¯mol L¹1). Length of the cell, 0.1 cm each. Each log ¾ value is given in parenthesis. (b) UV-vis spectrum of 9 in CH3CN.
Concentration, 9: 0.075 g L (379 ¯mol L¹1). Length of the cell, 0.1 cm. 9: -max/nm (log ¾), 213 (4.10), 244 (4.39), 284 (4.61),
¹1
301sh (4.03), 348 (3.65), 365 (3.46), 600 (2.68), 648sh (2.61), and 721sh (2.20).
Compound 4 (71% yield) was obtained as dark green plates
(mp 172 °C), while a solution of 4 in CH2Cl2 was red. The UV-
vis spectrum is shown in Figure 1a. The characteristic UV-vis
absorption bands resulting from guaiazulene (Figure 2b) were
not observed and the longest absorption wavelength appeared
at -max 481 nm (log ¾ = 4.66), indicating the formation of 4
with an extended ³-electron system. Although the spectral
pattern for the characteristic UV-vis absorption bands of 4
resembled those of the delocalized ³-electron systems 1221 and
1321 (Chart 1), the longest absorption wavelength of 4 showed
hypsochromic shifts (¦ 17 and 15 nm) and hyperchromic
effects (¦ log ¾ = 0.10 and 0.08) in comparison with those of
12 and 13 (Figure 1b). The IR spectrum showed a specific band
based on N=N at ¯max 1582 cm¹1, which was a low wave-
number shift (¦¯max 19 cm¹1 each) in comparison with those of
1221 and 13.21 The formula C30H30ON2 was determined by
isomer (E)-4-{(Z)-4-[2-(3-guaiazulenyl)vinyl]phenyldiazenyl}-
methoxybenzene.
Compound 5 (73% yield) was obtained as dark green plates
(mp 233 °C), while similar to 4, a solution of 5 in CH2Cl2 was
red. The UV-vis spectrum is shown in Figure 1a. Comparative
studies of the UV-vis spectrum of 5 with those of 4 and 9
showed that similar to 4, no characteristic UV-vis absorption
bands for 9 (Figure 2b) were observed, indicating the forma-
tion of 5 with an extended ³-electron system. Although the
spectral pattern for the characteristic UV-vis absorption bands
of 5 resembled that of 4, the longest absorption wavelength of 5
(-max 493 nm, log ¾ = 4.79) showed a bathochromic shift
(¦ 12 nm) and a hyperchromic effect (¦ log ¾ = 0.13) in
comparison with that of 4. Furthermore, the spectral pattern for
the characteristic UV-vis absorption bands of 5 resembled
that of the delocalized ³-electron system 14a21 (Chart 1),
while the longest absorption wavelength of 5 showed a large
hypsochromic shift (¦ 107 nm) and a slight hyperchromic
effect (¦ log ¾ = 0.05) in comparison with that of 14a
(Figure 1b). The IR spectrum showed a specific band resulting
from N=N at ¯max 1601 cm¹1, which was a high wavenumber
shift (¦¯max 19 cm¹1) in comparison with that of 4; however,
which was a low wavenumber shift (¦¯max 19 cm¹1) in
comparison with that of 14a.21 The molecular formula
1
exact EI-MS spectrum. The H NMR spectrum showed signals
resulting from a (E)-2-(3-guaiazulenyl)vinyl group and a 4-
substituted 4¤-methoxyazobenzene, the signals of which were
carefully assigned using H-H COSY and computer-assisted
simulation based on first-order analysis. The 13C NMR spec-
trum exhibited 25 carbon signals assigned by HMQC and
HMBC. Thus, the spectroscopic data for 4 led to the target
structure illustrated in Chart 3. This reaction did not give the Z

1404 Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009)
New Extended ³-Electron Systems
C31H33N3 was determined by exact FAB-MS spectrum. The
1H NMR spectrum showed signals resulting from a (E)-2-(3-
guaiazulenyl)vinyl group and a 4¤-substituted 4-(dimethyl-
amino)azobenzene, the signals of which were carefully
assigned using similar techniques to those of 4. The 13C NMR
spectrum exhibited 25 carbon signals assigned by HMQC and
HMBC. Thus, the spectroscopic data for 5 led to the target
structure illustrated in Chart 3. This reaction also did not give
the Z isomer (E)-N,N-dimethyl-4-{(Z)-4-[2-(3-guaiazulenyl)-
vinyl]phenyldiazenyl}aniline.
Me2CH-7¤ (0.47) > Me-4¤ (0.28) > (CH3)2CH-7¤ (0.11) > H-
2¤ (0.08). Although the (CH3)2CH-7¤ carbon signal (¤ 24.7) for
the 3-guaiazulenyl group of 14a coincided with that of 5 (24.4),
other 3-guaiazulenyl signals of 14a revealed down-field shifts
in comparison with those of 5. The order of larger down-field
shift was C-7¤ (¦¤ 30.5) > C-5¤ (23.4) > C-3a¤ (21.2) >
C-8a¤ (20.7) > C-1¤ (20.4) > C-3¤ (14.8) > C-4¤ (12.5) >
C-6¤ (10.5) > C-8¤ (6.7) > C-2¤ (6.3) > Me2CH-7¤ (3.2) >
Me-4¤ (1.9) > Me-1¤ (1.7). The observed proton signals for
the 4-(dimethylamino)azobenzene unit of 14a showed that the
H-2,6 proton signal (¤ 7.85) coincided with that of 5 (7.83),
while the H-3,5 proton signal (7.98) was a down-field shift
relative to that of 5 (7.61). Although the C-2,6 carbon signal (¤
120.1) for the 4-(dimethylamino)azobenzene unit of 14a was
up-field compared to that of 5 (123.0), the C-3,5 and Me2N-4¤¤
carbon signals for that of 14a showed down-field shifts in
comparison with those of 5. The order of larger down-field shift
was C-3,5 (¦¤ 10.3) > Me2N-4¤¤ (4.0). Thus, an apparent
difference between the 1H and 13C NMR signals of the
delocalized ³-electron system 14a and those of the extended
³-electron system 5 was observed.
1H and 13C NMR Spectral Parameters of 13 Compared
with Those of 4. Comparative studies of the chemical shifts
1
for the H and 13C NMR signals of the delocalized ³-electron
system 1321 (Chart 1) with those of the extended ³-electron
system 4 revealed that the Me-1¤ proton signal (¤ 2.51) for
the 3-guaiazulenyl group of 13 showed an up-field shift in
comparison with that of 4 (2.62) and the H-2¤ proton signal
(7.98) for the 3-guaiazulenyl group of 13 coincided with that of
4 (7.97). However, other 3-guaiazulenyl signals of 13 revealed
down-field shifts in comparison with those of 4. The order of
larger down-field shift was H-5¤ (¦¤ 1.59) > H-6¤ (1.13) >
H-8¤ (0.53) > Me2CH-7¤ (0.46) > Me-4¤ (0.27) > (CH3)2CH-7¤
(0.11). Although the (CH3)2CH-7¤ carbon signal (¤ 23.7) for the
3-guaiazulenyl group of 13 coincided with that of 4 (23.8),
other 3-guaiazulenyl signals of 13 revealed down-field shifts in
comparison with those of 4. The order of larger down-field
shift was C-7¤ (¦¤ 30.7) > C-5¤ (23.4) > C-8a¤ (21.0) >
C-3a¤ (20.9) > C-1¤ (20.4) > C-3¤ (15.5) > C-4¤ (12.4) >
C-6¤ (10.1) > C-2¤ (6.5) > C-8¤ (6.4) > Me2CH-7¤ (3.0) >
Me-4¤ (1.6) > Me-1¤ (1.5). The H-2¤¤,6¤¤, H-3¤¤,5¤¤, and MeO-
4¤¤ proton signals for the 4-substituted 4¤-methoxyazobenzene
unit of 13 coincided with those of 4, however the other signals
of 13 showed down-field shifts in comparison with those of 4.
The order of larger down-field shift was H-3,5 (¦¤ 0.31) >
H-2,6 (0.11). The C-1, C-2,6, C-3,5, C-1¤¤, C-2¤¤,6¤¤, C-3¤¤,5¤¤,
C-4¤¤, and MeO-4¤¤ carbon signals for the 4-substituted 4¤-
methoxyazobenzene part of 13 showed down-field shifts (¦¤
4.1, 1.2, 9.0, 1.0, 2.0, 1.7, 2.4, and 3.3 for C-1, C-2,6, C-3,5,
C-1¤¤, C-2¤¤,6¤¤, C-3¤¤,5¤¤, C-4¤¤, and MeO-4¤¤) in comparison
with those of 4, while the C-4 carbon signal for that of 13
revealed an up-field shift (¦¤ 2.8) in comparison with that of 4.
Thus, an apparent difference between the 1H and 13C NMR
signals of the delocalized ³-electron system 13 and those of the
extended ³-electron system 4 was observed.
X-ray Crystal Structures of 4 and 5.
The crystal
structures of 4 and 5 were then determined by means of X-ray
diffraction, producing accurate structural parameters. The
ORTEP drawings of 4 and 5, with a numbering scheme,
indicating the molecular structures illustrated in Chart 3, are
shown in Figures 3a and 3c along with selected bond lengths
(Tables 1 and 2). As a result, it was found that from the
dihedral angles between the least-squares planes, the planes of
the 3-guaiazulenyl groups of 4 and 5 twisted by 15.9 and 10.0°
from those of the -HC¡=C¢H-Ph functions, respectively.
Furthermore, the plane of the (4-methoxyphenyl)diazenyl
group of 4 twisted by 45.3° from that of another benzene ring,
while that of the [4-(dimethylamino)phenyl]diazenyl group of 5
twisted by 9.9° from that of another benzene ring. The C¡=C¢
bond length of 4 (1.334 ¡) coincided with that of 5 (1.331 ¡).
The average C-C bond length of the seven-membered ring for
the 3-guaiazulenyl group of 4 (1.409 ¡) coincided with that of
5 (1.410 ¡). The C-C bond length of the five-membered ring
for the 3-guaiazulenyl group of 4 appreciably varied between
1.359 and 1.495 ¡; in particular, the C1¤-C2¤ bond length
(1.359 ¡) was characteristically shorter than the average C-C
bond length for the five-membered ring (1.427 ¡). Similar to 4,
the C-C bond length of the five-membered ring for the 3-
guaiazulenyl group of 5 appreciably varied between 1.375 and
1.511 ¡; in particular, the C1¤-C2¤ bond length (1.375 ¡) was
characteristically shorter than the average C-C bond length for
the five-membered ring (1.435 ¡). Although the N1=N2 bond
length of 4 (1.265 ¡) was longer than that of azobenzene38-40
(18) (1.247 ¡) (Chart 2), that of 5 (1.247 ¡) coincided with
that of 18 (Table 2). The N2-C1¤¤ bond length of 4 (1.430 ¡)
coincided with that of 5 (1.433 ¡) and 18 (1.428 ¡), while the
C1-N1 bond length of 4 (1.419 ¡) was shorter than those of 5
(1.459 ¡) and 18. Thus, an apparent difference between the
crystal structure of 4 and that of 5 was observed, owing to the
influence of the substituted CH3O- or (CH3)2N- group at the
C4¤¤ position of azobenzene. Along with the ORTEP drawings
of 4 and 5, the packing structures of 4 and 5 showed that each
molecule formed a ³-stacking structure in the single crystal,
1H and 13C NMR Spectral Parameters of 14a Compared
with Those of 5. Comparative studies of the chemical shifts
1
for the H and 13C NMR signals of the delocalized ³-electron
system 14a21 with those of the extended ³-electron system 5
showed broadening H-2¤¤,6¤¤ and H-3¤¤,5¤¤ proton signals of
14a, which could not be unambiguously assigned, and further,
the C-1, C-4, C-1¤¤, C-2¤¤,6¤¤, C-3¤¤,5¤¤, and C-4¤¤ carbon signals
of 14a were not observed, suggesting the existence of rotational
stereoisomers for 14a¤¤ (Chart 1), however the corresponding
signals of 5 were observed. The Me-1¤ proton signal (¤ 2.53)
for the 3-guaiazulenyl group of 14a revealed a slight up-field
shift in comparison with that of 5 (2.62), however other
3-guaiazulenyl signals of 14a showed down-field shifts in
comparison with those of 5. The order of larger down-fieled
shift was H-5¤ (¦¤ 1.61) > H-6¤ (1.14) > H-8¤ (0.57) >

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009) 1405
Figure 3. The ORTEP drawings with the numbering scheme (30% probability thermal ellipsoids) of 4 (a) and 5 (c), and the packing
structures of 4 (b) and 5 (d); hydrogen atoms are omitted for reasons of clarity.
Table 1. The Selected C-C Bond Lengths (¡) for the
3-Guaiazulenylvinyl Groups of 4, 5, and 14b
Table 2. The Selected Bond Lengths (¡) for the Azoben-
zene of 4, 5, 14b, and 18
Atom
4
5
14b
Atom
4a)
5a)
14ba)
18
C1¤-C2¤
C2¤-C3¤
C3¤-C3a¤
C3a¤-C4¤
C4¤-C5¤
C5¤-C6¤
C6¤-C7¤
C7¤-C8¤
C8¤-C8a¤
C8a¤-C1¤
C3a¤-C8a¤
C3¤-C¢
C¡-C¢
1.359(4)
1.436(4)
1.416(4)
1.410(4)
1.399(4)
1.383(4)
1.389(4)
1.397(4)
1.385(4)
1.428(4)
1.495(4)
1.442(4)
1.334(4)
1.375(6)
1.430(7)
1.437(7)
1.393(8)
1.398(7)
1.401(8)
1.390(10)
1.386(9)
1.386(7)
1.416(8)
1.511(7)
1.442(7)
1.331(7)
1.348(6)
1.442(6)
1.503(6)
1.390(6)
1.407(6)
1.379(7)
1.412(6)
1.382(6)
1.399(6)
1.446(6)
1.445(6)
1.360(6)a)
®
C¡-C4
C4-C5
C5-C6
C6-C1
C1-C2
C2-C3
C3-C4
C1-N1
N1-N2
N2-C1¤¤
C1¤¤-C2¤¤ 1.392(4)
C2¤¤-C3¤¤ 1.373(4)
C3¤¤-C4¤¤ 1.390(4)
C4¤¤-C5¤¤ 1.378(4)
C5¤¤-C6¤¤ 1.398(4)
C6¤¤-C1¤¤ 1.383(4)
1.460(4)
1.408(4)
1.384(4)
1.400(4)
1.387(4)
1.380(4)
1.396(4)
1.419(4)
1.265(3)
1.430(4)
1.461(7)
1.365(8)
1.387(7)
1.368(8)
1.371(8)
1.393(7)
1.415(8)
1.459(6)
1.247(6)
1.433(6)
1.384(8)
1.378(7)
1.407(8)
1.380(8)
1.376(7)
1.361(8)
1.381(6)
1.439(6)
1.405(6)
1.377(6)
1.393(6)
1.403(6)
1.375(6)
1.405(6)
1.400(5)
1.299(5)
1.324(6)
1.423(6)
1.335(6)
1.446(6)
1.431(7)
1.349(7)
1.438(6)
1.341(6)
®
1.382(3)
1.384(3)
1.387(2)
1.389(2)
1.384(3)
1.391(2)
1.428(2)
1.247(2)
®
®
®
®
®
a) C3¤-C¡ (see Chart 2).
®
®
C4¤¤-N3
®
®
and revealed that each average inter-plane distance between the
overlapping molecules, which were overlapped so that those
dipole moments might be negated mutually, was 3.46 ¡ for 4
(Figure 3b) and 3.55 ¡ for 5 (Figure 3d). Moreover, comparing
the selected bond lengths of 14b21 (Chart 2) to those of
structurally related compounds 4 and 5 are shown in Tables 1
and 2. As a result, it was found that the 3-guaiazulenylmeth-
ylium ion of 14b clearly underwent bond alternation between
single and double bonds, indicating the formation of a similar
resonance structure to 14a¤ (Chart 1), and the 4-[4-(dimethyl-
amino)phenyldiazenyl]phenyl group also clearly underwent
a) For a comparative purpose, the numbering schemes of the
azobenzene of 4, 5, and 14b were changed as shown in
Charts 2 and 3.
bond alternation between the single and double bonds,
indicating the formation of a similar resonance structure to
14a¤¤ (Chart 1).
Preparation and Spectroscopic Properties of 7 and 8.
The target extended ³-electron systems 7 and 8 were prepared
using the Wittig reaction shown in Scheme 3. The structures of

1406 Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009)
New Extended ³-Electron Systems
CHO
7
N
N
OHC
6
9
1
10
6
EtONa/EtOH
at r.t. for 24 h
under argon
in CH3OH
with 60% HPF6
at r.t. for 30 min
8
Scheme 4. The reaction of 6 with 9 in methanol in the
presence of hexafluorophosphoric acid at 25 °C for 30 min,
affording the corresponding dicarbenium ion compound
10.
Scheme 3. The reaction of 1 with 6 in ethanol in the
presence of sodium ethoxide at 25 °C for 24 h under argon,
affording the corresponding azobenezene derivatives 7
and 8.
³-electron system 8, the target compound 10 was prepared
according to Scheme 4. The structure of the product 10 was
established on the basis of elemental analysis and similar
spectroscopic analyses to 8.
the products were established on the basis of similar spectro-
scopic analyses to those of 4 and 5.
Compound 7 (7% yield) was obtained as dark green prisms
(mp 172 °C), while a solution of 7 in CH2Cl2 was reddish-
violet. The UV-vis spectrum is shown in Figure 1a. Although
the spectral pattern of 7 resembled those of 4 and 5 (Figure 1a),
the longest absorption wavelength of 7 (-max 528 nm, log ¾ =
4.49) showed bathochromic shifts (¦ 47 and 35 nm) and
hypochromic effects (¦ log ¾ = 0.17 and 0.30) in comparison
with those of 4 and 5. The IR spectrum showed specific bands
Compound 10 (46% yield) was obtained as dark red prisms
(decomp >178 °C). The UV-vis spectrum is shown in
Figure 2a. Although the spectral pattern of 10 resembled that
of 8, the longest absorption wavelength of 10 (-max 499 nm,
log ¾ = 4.86) showed a hypsochromic shift (¦ 34 nm) and a
hyperchromic effect (¦ log ¾ = 0.15) in comparison with that
of 8. The IR spectrum showed specific bands originating from
N=N at 1601 cm¹1, which was a high wavenumber shift
(¦¯max 16 cm¹1) in comparison with that of 8, and counter
¹1
¹1
resulting from C=O at 1701 cm and N=N at 1585 cm
which coincided with that of 4. The molecular formula
C30H28ON2 was determined by exact FAB-MS spectrum. The
1H NMR spectrum showed signals resulting from a (E)-2-(3-
guaiazulenyl)vinyl group and a 4¤-substituted azobenzene-4-
carbaldehyde, the signals of which were carefully assigned
using H-H COSY and computer-assisted simulation based
on first-order analysis. The 13C NMR spectrum exhibited 25
carbon signals assigned by HMQC and HMBC. Thus, the
spectroscopic data for 7 led to the diazene structure illustrated
in Chart 3.
Compound 8 (24% yield) was obtained as a dark green
powder (mp 263 °C), while similar to 7, a solution of 8 in
CH2Cl2 was reddish-violet. The UV-vis spectrum is shown in
Figure 2a. The characteristic UV-vis absorption bands for 9
(Figure 2b) were not observed, suggesting the formation of
8 with an extended ³-electron system. The longest absorp-
tion wavelength of 8 (-max 533 nm, log ¾ = 4.71) showed a
slight bathochromic shift (¦ 5 nm) and a hyperchromic effect
¹
anion (PF6 ) at 837 and 556 cm¹1, the wavenumbers of which
coincided with those of 12-14a.21 The formula C44H44N2 for
the dicarbenium ion part was determined by exact FAB-MS
spectrum. An elemental analysis confirmed C44H44N2F12P2.
1
The H NMR spectrum showed signals originating from two
equivalent 3-guaiazulenylmethylium ion structures, and re-
vealed signals resulting from a 4,4¤-substituted azobenzene,
the signals of which were carefully assigned using similar
techniques to those of 8. The 13C NMR spectrum exhibited 19
carbon signals assigned by HMQC and HMBC. Thus, the
elemental analysis and the spectroscopic data for 10 led to the
target structure illustrated in Chart 4.
Reduction of 10 with NaBH4 and 1H and 13C NMR
Spectral Parameters of 10 Compared with Those of 11. For
comparative purposes of the 1H and 13C NMR properties of the
delocalized ³-electron system 10 with those of the non-
conjugated ³-electron system 11 which have two 3-guaiazul-
enyl groups and an azobenzene unit (Chart 4), the target
compound 11 was prepared. Namely, the reduction of 10 with
NaBH4 in a mixed solvent of ethanol and acetonitrile at 25 °C
for 30 min gave as high as 88% yield of diazene 11, in which a
hydride ion attached to the two HC+-¡ carbon atoms of 10,
selectively. Comparative studies of the chemical shifts for the
1H and 13C NMR signals of 10 with those of 11 showed that the
Me-1¤ proton signal for the 3-guaiazulenyl group of 10 revealed
a slight up-field shift (¦¤ 0.08) in comparison with that of 11,
however other 3-guaiazulenyl signals of 10 showed down-field
shifts in comparison with those of 11. The order of larger
down-field shift was H-5¤ (¦¤ 1.76) > H-6¤ (1.17) > H-2¤
(0.62) > Me-4¤ (0.57) > H-8¤ (0.49) > Me2CH-7¤ (0.48) >
(CH3)2CH-7¤ (0.12). Although the C-2¤ and (CH3)2CH-7¤
(¦ log ¾ = 0.22) in comparison with that of 7. The IR spectrum
¹1
showed specific bands resulting from N=N at 1585 cm
,
whose wavenumber coincided with that of 7. The molecular
formula C46H46N2 was determined by exact FAB-MS spectrum.
1
The H NMR spectrum showed signals originating from two
equivalent (E)-2-(3-guaiazulenyl)vinyl groups and a 4,4¤-
substituted azobenzene, the signals of which were carefully
assigned using similar spectroscopic analyses to those of 7. The
13C NMR spectrum exhibited 20 carbon signals assigned by
HMQC and HMBC. Thus, the spectroscopic data for 8 led to
the target structure illustrated in Chart 3.
Preparation and Spectroscopic Properties of 10. For
comparative purposes of the spectroscopic properties of the
delocalized ³-electron system 10 with those of the extended

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009) 1407
carbon signals for the 3-guaiazulenyl group of 10 coincided
with those of 11, other 3-guaiazulenyl signals of 10 showed
down-field shifts in comparison with those of 11. The order of
larger down-field shift was C-7¤ (¦¤ 33.9) > C-5¤ (25.4) >
C-8a¤ (24.5) > C-1¤ (23.3) > C-3a¤ (21.0) > C-3¤ (17.3) > C-4¤
(13.4) > C-6¤ (11.0) > C-8¤ (7.0) > Me-4¤ (3.6) > Me2CH-7¤
(3.0) > Me-1¤ (1.7). The H-2,6 proton signal for the 4,4¤-
substituted azobenzene part of 10 showed a slight down-field
shift (¦¤ 1.0) in comparison with that of 11; however, the H-
3,5 proton signal for that of 10 revealed a large down-field shift
(¦¤ 0.89) in comparison with that of 11. The C-1 and C-3,5
carbon signals for the 4,4¤-substituted azobenzene of 10
showed down-field shifts (¦¤ 3.8 and 6.6 for C-1 and C-3,5)
in comparison with that of 11, while the C-2,6 and C-4 carbon
signals for that of 10 revealed up-field shift (¦¤ 0.6 and 5.2 for
C-2,6 and C-4) in comparison with that of 11. Comparing the
1H and 13C NMR chemical shifts of 10 to those of 11, an
apparent difference between the 1H and 13C NMR chemical
shifts of the delocalized ³-electron system 10 and those of the
hydride reduction product 11 was observed.
delocalized) ³-electron systems 13 and 14a, an apparent
difference between the spectroscopic properties of 4 and 5 and
those of the delocalized ³-electron systems 13 and 14a was
reported and further, the crystal structural parameters of 14b
compared with those of 4 and 5 apparently supported the
formation of 14b with similar resonance structures to those of
14a (Chart 1) in the single crystal. (iii) The Wittig reaction of
diazene 6 with the same reagent under the same reaction
conditions as the above afforded only E forms 7 and 8 in 7 and
24% yields. The reaction also did not give the Z isomers. (iv)
The reaction of guaiazulene (9) with 6 in methanol in the
presence of hexafluorophosphoric acid at 25 °C for 30 min
provided 10 in 46% yield which upon reduction with NaBH4
gave diazene 11 in 88% yield, in which a hydride ion attached
to the two HC+-¡ carbon atoms of 10 selectively. (v) Similar to
(ii), comparing the spectroscopic properties of a new extended
³-electron system 8 to those of a new delocalized ³-electron
system 10, an apparent difference between the spectroscopic
properties of 8 and those of 10 was documented.
1H and 13C NMR Spectral Parameters of 10 Compared
with Those of 8. Comparative studies of the chemical shifts
This work was partially supported by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.
1
for the H and 13C NMR signals of the delocalized ³-electron
system 10 with those of the extended ³-electron system 8
revealed that the Me-1¤ proton signal (¤ 2.53) for the 3-
guaiazulenyl group of 10 showed a slight up-field shift in
comparison with that of 8 (2.62), however other 3-guaiazulenyl
signals of 10 revealed down-field shifts in comparison with
those of 8. The order of larger down-field shift was H-5¤ (¦¤
1.65) > H-6¤ (1.16) > H-8¤ (0.57) > Me2CH-7¤ (0.49) > Me-4¤
(0.30) > (CH3)2CH-7¤ (0.12) > H-2¤ (0.04). Although the
(CH3)2CH-7¤ carbon signal for the 3-guaiazulenyl group of
10 coincided with that of 8, other 3-guaiazulenyl signals of 10
revealed down-field shifts in comparison with those of 8. The
order of larger down-field shift was C-7¤ (¦¤ 31.2) > C-5¤
(23.7) > C-8a¤ (21.2) > C-1¤,3a¤ (20.8, each) > C-3¤ (16.1) >
C-4¤ (12.6) > C-6¤ (10.6) > C-8¤ (6.5) > C-2¤ (6.0) > Me2CH-
7¤ (2.9) > Me-1¤,4¤ (1.5, each). All the proton signals for the
4,4¤-substituted azobenzene of 10 showed down-field shifts in
comparison with those of 8. The order of larger down-field shift
was H-3,5 (¦¤ 0.38) > H-2,6 (0.23). The C-1, C-2,6, and C-3,5
carbon signals for the 4,4¤-substituted azobenzene of 10
showed down-field shifts (¦¤ 3.6, 1.6, and 8.8 for C-1, C-
2,6, and C-3,5) in comparison with that of 8, while the C-4
carbon signal for that of 10 revealed up-field shift (¦¤ 1.6)
in comparison with that of 8. Thus, an apparent difference
References
1
S. Takekuma, M. Sasaki, H. Takekuma, H. Yamamoto,
Chem. Lett. 1999, 999.
2
S. Takekuma, S. Takata, M. Sasaki, H. Takekuma,
Tetrahedron Lett. 2001, 42, 5921.
3
S. Takekuma, M. Tanizawa, M. Sasaki, T. Matsumoto, H.
Takekuma, Tetrahedron Lett. 2002, 43, 2073.
M. Sasaki, M. Nakamura, G. Hannita, H. Takekuma, T.
4
Minematsu, M. Yoshihara, S. Takekuma, Tetrahedron Lett. 2003,
44, 275.
5
M. Sasaki, M. Nakamura, T. Uriu, H. Takekuma, T.
Minematsu, M. Yoshihara, S. Takekuma, Tetrahedron 2003, 59,
505.
6
M. Nakamura, M. Sasaki, H. Takekuma, T. Minematsu, S.
Takekuma, Bull. Chem. Soc. Jpn. 2003, 76, 2051.
S. Takekuma, K. Sasaki, M. Nakatsuji, M. Sasaki, T.
Minematsu, H. Takekuma, Bull. Chem. Soc. Jpn. 2004, 77, 379.
M. Nakatsuji, Y. Hata, T. Fujihara, K. Yamamoto, M.
7
8
Sasaki, H. Takekuma, M. Yoshihara, T. Minematsu, S. Takekuma,
Tetrahedron 2004, 60, 5983.
9
S. Takekuma, Y. Hata, T. Nishimoto, E. Nomura, M.
Sasaki, T. Minematsu, H. Takekuma, Tetrahedron 2005, 61, 6892.
10 S. Takekuma, K. Takahashi, A. Sakaguchi, Y. Shibata, M.
Sasaki, T. Minematsu, H. Takekuma, Tetrahedron 2005, 61, 10349.
11 S. Takekuma, K. Takahashi, A. Sakaguchi, M. Sasaki, T.
Minematsu, H. Takekuma, Tetrahedron 2006, 62, 1520.
12 S. Takekuma, M. Hirosawa, S. Morishita, M. Sasaki, T.
Minematsu, H. Takekuma, Tetrahedron 2006, 62, 3732.
13 S. Takekuma, K. Sonoda, C. Fukuhara, T. Minematsu,
Tetrahedron 2007, 63, 2472.
14 S. Takekuma, K. Tone, M. Sasaki, T. Minematsu, H.
Takekuma, Tetrahedron 2007, 63, 2490.
15 S. Takekuma, K. Mizutani, K. Inoue, M. Nakamura, M.
Sasaki, T. Minematsu, K. Sugimoto, H. Takekuma, Tetrahedron
2007, 63, 3882.
1
between the H and 13C NMR signals of the delocalized ³-
electron system 10 and those of the extended ³-electron system
8 was observed.
Conclusion
We have reported the following five interesting points in this
paper. namely: (i) The Wittig reactions of diazenes 2 and 3 with
(3-guaiazulenylmethyl)triphenylphosphonium bromide in etha-
nol in the presence of sodium ethoxide at 25 °C for 24 h under
argon gave only E forms 4 and 5 in 71 and 73% yields. The
reactions did not give the Z isomers. (ii) Comparing the
spectroscopic properties of the two new extended ³-electron
systems 4 and 5 to those of structurally related (and
16 S. Takekuma, M. Tamura, T. Minematsu, H. Takekuma,

1408 Bull. Chem. Soc. Jpn. Vol. 82, No. 11 (2009)
New Extended ³-Electron Systems
Tetrahedron 2007, 63, 12058.
17 S. Takekuma, K. Sonoda, T. Minematsu, H. Takekuma,
Tetrahedron 2008, 64, 3802.
18 S. Takekuma, S. Hori, T. Minematsu, H. Takekuma, Bull.
Chem. Soc. Jpn. 2008, 81, 1472.
19 S. Takekuma, S. Hori, T. Minematsu, H. Takekuma, Res.
Lett. Org. Chem. 2009, 684359.
guaiazulenylmethanol in chloroform (3 mL) was added a solution
of triphenylphosphonium bromide (130 mg, 378 ¯mol) in chloro-
form (3 mL). The mixture was refluxed for 1 h under argon. After
cooling, the reaction mixture was poured into diethyl ether (10 mL)
and then was centrifuged at 2.5 krpm for 1 min. The obtained
product was carefully washed with diethyl ether to provide pure 1
as a blue powder (195 mg, 352 ¯mol, 93% yield).
20 S. Takekuma, N. Ijibata, T. Minematsu, H. Takekuma, Bull.
Chem. Soc. Jpn. 2009, 82, 585.
33 Guaiazulene-3-carbaldehyde was prepared according to the
following procedures: To a solution of commercially available
guaiazulene (9) (100 mg, 504 ¯mol) in N,N-dimethylformamide
(DMF) (3.0 mL) was added a solution of phosphoryl chloride
(100 ¯L). The mixture was stirred at 0 °C for 1 h. After the
reaction, the reaction solution was carefully neutralized with aq
KOH and then the resulting product was extracted with dichloro-
methane (10 mL © 3). The extract was washed with distilled water,
dried (Na2SO4), and evaporated in vacuo. The residue thus
obtained was carefully separated by silica gel column chromatog-
raphy with hexane-ethyl acetate (3:2, v/v). The crude product was
recrystallized from hexane to provide pure guaiazulene-3-carb-
aldehyde as stable crystals (108 mg, 477 ¯mol, 94% yield).
34 SIR97: A. Altomare, M. C. Burla, M. Camalli, G. L.
Cascarano, C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G.
Polidori, R. Spagna, J. Appl. Cryst. 1999, 32, 115.
35 DIRDIF94: P. T. Beurskens, G. Admiraal, G. Beurskens,
W. P. Bosman, R. de Gelder, R. Israel, J. M. M. Smits,
Technical Report of the Crystallography Laboratory, University
of Nijmegan, 1994.
36 teXsan, ver 1.11: Single Crystal Structure Analysis
Software, Molecular Structure Corporation, The Woodlands, TX,
1999.
21 S. Takekuma, K. Fukuda, Y. Kawase, T. Minematsu, H.
Takekuma, Bull. Chem. Soc. Jpn. 2009, 82, 879.
22 Y. Matsubara, H. Yamamoto, T. Nozoe, Studies in Natural
Products Chemistry, in Stereoselective Synthesis (Part I), ed. by
Atta-ur-Rahman, Elsevier, Amsterdam, 1994, Vol. 14, pp. 313-
354.
23 A. A. S. Briquet, H.-J. Hansen, Helv. Chim. Acta 1994, 77,
1921.
24 R. N. McDonald, W. S. Stewart, J. Org. Chem. 1965, 30,
270.
25 N. Liu, D. R. Dunphy, M. A. Rodriguez, S. Singer, J.
Brinker, Chem. Commun. 2003, 1144.
26 Y. Yu, T. Ikeda, Macromol. Chem. Phys. 2005, 206, 1705.
27 A. A. Blevins, G. J. Blanchard, J. Phys. Chem. B 2004,
108, 4962.
28 O. Srinivas, N. Mitra, A. Surolia, N. Jayaraman, J. Am.
Chem. Soc. 2002, 124, 2124.
29 X. Liu, M. Jiang, Angew. Chem., Int. Ed. 2006, 45, 3846.
30 L. Brzozowski, E. H. Sargent, J. Mater. Sci. 2001, 12, 483.
31 A. Natansohn, P. Rochon, Adv. Mater. 1999, 11, 1387.
32 The Wittig reagent 1 was prepared according to the
following procedures: To a powder of NaBH4 (30 mg, 793 ¯mol)
was added a solution of guaiazulene-3-carbaldehyde33 (90 mg,
397 ¯mol) in ethanol (1.5 mL). The mixture was stirred at 25 °C
for 1 h. After the reaction, distilled water (10 mL) was added
to the mixture and then the resulting product was extracted
with dichloromethane (10 mL © 3). The extract was washed with
distilled water, dried (Na2SO4), and evaporated in vacuo to provide
3-guaiazulenylmethanol as a blue paste. To a solution of 3-
37 Compound 6 was prepared according to the procedures
based on the following reference: L. Masciello, P. G. Potvin, Can.
J. Chem. 2003, 81, 209.
38 H. Fliegl, A. Köhn, C. Hättig, R. Ahlrichs, J. Am. Chem.
Soc. 2003, 125, 9821.
39 J. A. Bouwstra, A. Schouten, J. Kroon, Acta Crystallogr.,
Sect. C 1983, 39, 1121.
40 C. J. Brown, Acta Crystallogr. 1966, 21, 146.