Preparation, crystal structure, and spectroscopic, chemical, and electrochemical properties of (2E,4E)-1-(3-Guaiazulenyl)-4-(2-thienyl)-1,3- butadiene

Article abstract of DOI:10.1246/bcsj.20130051

Wittig reaction of (E)-2-(2-thienyl)ethylene-1-carbaldehyde with [(3-guaiazulenyl)methyl]triphenylphosphonium bromide in ethanol containing sodium ethoxide (=NaOC₂H₅) at 25°C for 24 h under argon gives the two (2E,4E)- and (2E,4Z)-geometric isomers of a new compound 1-(3-guaiazulenyl)-4-(2-thienyl)-1,3-butadiene, the only title (2E,4E)- form, of which can be isolated as single crystals. Preparation, chemical and spectroscopic properties, crystal structure, and electrochemical behavior of the target (2E,4E)-form, compared with those of (E)-1-(3-guaiazulenyl)-2-(2- thienyl)ethylene and the structurally related new compound (3-guaiazulenyl)[(E)- 2-(2-thienyl)ethenyl]methylium hexafluorophosphate, are documented.

Full text of DOI:10.1246/bcsj.20130051

968
Bull. Chem. Soc. Jpn. Vol. 86, No. 8, 968-982 (2013)
© 2013 The Chemical Society of Japan
Preparation, Crystal Structure, and Spectroscopic,
Chemical, and Electrochemical Properties of
(2E,4E)-1-(3-Guaiazulenyl)-4-(2-thienyl)-1,3-butadiene
Shin-ichi Takekuma,*1 Norihito Kobayashi,1 Toshie Minematsu,2 and Hideko Takekuma1
1Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University,
3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502
2School of Pharmaceutical Sciences, Kinki University, 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502
Received February 19, 2013; E-mail: takekuma@apch.kindai.ac.jp
Wittig reaction of (E)-2-(2-thienyl)ethylene-1-carbaldehyde with [(3-guaiazulenyl)methyl]triphenylphosphonium
bromide in ethanol containing sodium ethoxide (=NaOC2H5) at 25 °C for 24 h under argon gives the two (2E,4E)- and
(2E,4Z)-geometric isomers of a new compound 1-(3-guaiazulenyl)-4-(2-thienyl)-1,3-butadiene, the only title (2E,4E)-
form, of which can be isolated as single crystals. Preparation, chemical and spectroscopic properties, crystal structure, and
electrochemical behavior of the target (2E,4E)-form, compared with those of (E)-1-(3-guaiazulenyl)-2-(2-thienyl)ethylene
and the structurally related new compound (3-guaiazulenyl)[(E)-2-(2-thienyl)ethenyl]methylium hexafluorophosphate, are
documented.
In previous papers,1-20 we reported a facile preparation and
(and 9) was also proposed.19 In relation to our studies on a
preparation and properties of 2E, for example, preparations
and properties of the 2-thienyl- and aryl-substituted (E)-ethyl-
ene23-25 and (2E,4E)-1,3-butadiene26,27 derivatives have been
reported; however, none have really been documented for
the title basic studies. Therefore, our next challenge has quite
recently been focused on the following investigations: namely,
(i) a preparation of the title new extended ³-electron system 1E
(Chart 1) compared with that of 2E;19 (ii) the reaction behavior
of 1E with TCNE in benzene (and in DMF) under the same
reaction conditions as for 2E19 and a reaction mechanism for the
formation of the resulting products; and (iii) the crystal structure
and the characteristic properties of 1E compared with those of
2E and the structurally related new propenium ion derivative 19
with a delocalized ³-electron system (Chart 3). We now wish
to report the detailed basic studies on the above three points (i)-
(iii) with a view to comparative study.
crystal structures as well as spectroscopic, chemical, and
electrochemical properties of new conjugated (and delocalized)
³-electron systems possessing a 3-guaiazulenyl (=5-isopropyl-
3,8-dimethylazulen-1-yl)1-8,10-20 [or an azulen-1-yl7,17 or a
3-(methoxycarbonyl)azulen-1-yl9] group. During the course
of our basic and systematic investigations on naturally occur-
ring guaiazulene (=7-isopropyl-1,4-dimethylazulene)21 (3) and
parent azulene and its derivative, we recently found that the
(E)-ethylene derivative 2E (Chart 1) serves as a stronger one-
electron donor19 and a stronger one-electron acceptor19 than the
starting material 322 and further, that the reactions of 2E with
tetracyanoethylene (=TCNE), which serves as a strong one-
electron acceptor, in benzene [and in N,N-dimethylformamide
(=DMF)] at 25 °C for 24 h under argon give unique products
8 (and 9) (Chart 2), possessing interesting molecular structures,
respectively. A reaction mechanism for the formation of 8
1
Chart 1. For comparative purposes on the H and 13C NMR
signals and the crystal structures of 1E and the previously
reported 2E,19 the numbering schemes of their compounds
were changed as shown in Chart 1, Figure 3, and Figure 4.
Chart 2. The molecular structures of the products 8 (and 9)
yielded from the reactions of 2E with TCNE in benzene
(and in DMF) at 25 °C for 24 h under argon.19
Published on the web May 14, 2013; doi:10.1246/bcsj.20130051

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
969
Chart 3. The structure of a new monocarbenium ion compound 19 with the two representative resonance structures of the
3-guaiazulenylium ion form 19a and the 2-thienylium ion form 19b.
metric isomers 1 (53 mg, 160 ¯mol, 80% yield) thus obtained
was recrystallized from ethanol-chloroform (5:1, vol/vol)
Experimental
General. Melting points were taken on a Yanagimoto MP-
S3 instrument. Elemental analysis of the monocarbenium ion
compound 19 was taken on a Yanako MT-3 CHN corder. EI-
MS and FAB-MS spectra were taken on a JEOL The Tandem
Mstation JMS-700 TKM data system. IR and UV-vis spectra
were taken on a Shimadzu FTIR-8300 grating spectrometer
and a Beckman DU640 spectrophotometer. NMR spectra were
(several times) to provide pure 1E (11 mg, 34 ¯mol, 17% yield)
as single crystals. Along with the above results, each yield of the
(2E,4E)-form 1E (70%) and (2E,4Z)-1-(3-guaiazulenyl)-4-(2-
thienyl)-1,3-butadiene (1Z) (10%) was calculated from relative
intensities for the 700 MHz H NMR signals of an inseparable
mixture of the two geometric isomers 1E and 1Z.
1
Compound 1E: Dark-green needles [Rf = 0.63 on silica gel
TLC (solv. hexane:ethyl acetate = 4:1, vol/vol)]; mp 113 °C;
exact EI-MS (70 eV): found: m/z 332.1599; calcd for C23H24S:
1
recorded with a JNM-ECA500 (500 MHz for H and 125 MHz
1
for 13C) or JNM-ECA700 (700 MHz for H and 176 MHz for
13C) cryospectrometer at 25 °C. 1H NMR spectra were assigned
using computer-assisted simulation (software: gNMR devel-
oped by Adept Scientific plc) on a DELL Dimension 9200 per-
sonal computer with a Pentium IV processor. Cyclic and differ-
ential pulse voltammograms (=CV and DPV) were measured
with an ALS Model 600 electrochemical analyzer.
M+, m/z 332.1573; IR ¯max/cm (KBr): 2954-2866 (C-H),
¹1
975 (-CH=CH-), 1581, 1542 (C=C), and 682 (C-S); UV-vis
-
max/nm (log ¾) in CH2Cl2: 227 (4.34), 251 (4.30), 258 (4.29),
290 (4.33), 345 (4.56), 437 (4.76), and 645 (2.84). Details are
1
shown in Figure 1a; 700 MHz H NMR (benzene-d6): signals
from a 3-guaiazulenyl group: ¤ 1.16 (6H, d, J = 6.7 Hz,
(CH3)2CH-7¤¤), 2.49 (3H, br s, Me-1¤¤), 2.69 (3H, s, Me-4¤¤),
2.69 (1H, sept, J = 6.7 Hz, (CH3)2CH-7¤¤), 6.54 (1H, d, J =
10.4 Hz, H-5¤¤), 6.96 (1H, dd, J = 10.4, 2.0 Hz, H-6¤¤), 7.89
(1H, br s, H-2¤¤), and 7.92 (1H, d, J = 2.0 Hz, H-8¤¤); signals
from a 2-thienyl group: ¤ 6.73 (1H, dd, J = 4.7, 3.4 Hz, H-4¤),
6.75 (1H, br d, J = 4.7 Hz, H-5¤), and 6.81 (1H, br d, J =
3.4 Hz, H-3¤); and signals from a (2E,4E)-1,3-butadiene unit:
¤ 6.69 (1H, d, J = 15.2 Hz, H-1), 6.84 (1H, br dd, J = 15.2,
10.8 Hz, H-2), 7.07 (1H, br dd, J = 15.0, 10.8 Hz, H-3), and
7.57 (1H, d, J = 15.0 Hz, H-4); 176 MHz 13C NMR (benzene-
d6): ¤ 146.5 (C-4¤¤), 144.2 (C-2¤), 141.8 (C-8a¤¤), 141.2 (C-7¤¤),
136.3 (C-2¤¤), 134.9 (C-6¤¤), 133.6 (C-8¤¤), 133.3 (C-3a¤¤),
131.3 (C-3), 130.9 (C-4), 127.7 (C-4¤,5¤¤), 127.5 (C-2), 127.2
(C-3¤¤), 126.7 (C-1¤¤), 125.4 (C-3¤), 123.8 (C-5¤), 123.3 (C-1),
37.9 ((CH3)2CH-7¤¤), 28.4 (Me-4¤¤), 24.4 ((CH3)2CH-7¤¤), and
13.1 (Me-1¤¤). For comparative purposes, the above 1H and
13C NMR signals (¤) are shown in Tables 1 and 2.
Compound 1Z: 700 MHz 1H NMR (benzene-d6): signals
from a 3-guaiazulenyl group: ¤ 1.17 (6H, d, J = 7.0 Hz,
(CH3)2CH-7¤¤), 2.49 (3H, br s, Me-1¤¤), 2.74 (1H, sept, J =
7.0 Hz, (CH3)2CH-7¤¤), 2.77 (3H, s, Me-4¤¤), 6.56 (1H, d, J =
10.4 Hz, H-5¤¤), 6.98 (1H, dd, J = 10.4, 2.0 Hz, H-6¤¤), 7.88
(1H, br s, H-2¤¤), and 7.91 (1H, d, J = 2.0 Hz, H-8¤¤); signals
from a 2-thienyl group: ¤ 6.72 (1H, dd, J = 5.0, 3.4 Hz, H-4¤),
6.77 (1H, br d, J = 5.0 Hz, H-5¤), and 6.78 (1H, br d, J =
3.4 Hz, H-3¤); and signals from a (2E,4Z)-1,3-butadiene unit:
¤ 6.59 (1H, br d, J = 15.2 Hz, H-1), 6.87 (1H, br dd, J = 15.2,
10.6 Hz, H-2), 6.35 (1H, br dd, J = 10.8, 10.6 Hz, H-3), and
7.22 (1H, br d, J = 10.8 Hz, H-4).
Preparation of (E)-2-(2-Thienyl)ethylene-1-carbalde-
hyde28 (7). Preparation of 7 was according to the experimental
procedures documented in Ref. 28: namely, to a mixture of
vinyl acetate (0.02 mL, 216 ¯mol) and thiophene-2-carbalde-
hyde (6) (24 mg, 214 ¯mol) in THF (5 mL) was added slowly
a stirred suspension of Ba(OH)2 (37 mg, 216 ¯mol) in THF
(3 mL) and further, the reaction mixture, which was refluxed
for 8 h. The reaction mixture after cooling was poured into cold
water and then was filtered to remove the insoluble barium salts.
The filtrate was extracted with chloroform (10 mL © 3), and the
obtained organic layer was washed with water, dried (MgSO4),
and concentrated in vacuo. The residue thus obtained was
carefully separated by silica gel column chromatography with
benzene-hexane-ethyl acetate (8:8:1, vol/vol/vol) as an eluant
(several times), providing pure 7 (23 mg, 167 ¯mol, 78% yield).
Preparation of (2E,4E)-1-(3-Guaiazulenyl)-4-(2-thienyl)-
1,3-butadiene (1E). To a solution of (E)-2-(2-thienyl)ethyl-
ene-1-carbaldehyde28 (7) (27 mg, 200 ¯mol) in ethanol (5 mL)
was added a solution of the previously reported [(3-guaiazule-
nyl)methyl]triphenylphosphonium bromide15,16 (5) (110 mg,
200 ¯mol) in ethanol (5 mL) containing sodium ethoxide (27
mg, 400 ¯mol) under argon. 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 (MgSO4), and concentrated in vacuo.
The residue thus obtained was carefully separated by silica
gel column chromatography with hexane-ethyl acetate (4:1,
vol/vol) as an eluant. An inseparable mixture of the two geo-

970
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
A New (2E,4E)-1,3-Butadiene Derivative
¹1
Figure 1. The UV-vis spectra of 1E (a) and 2E (b) in dichloromethane (=CH2Cl2). Concentrations, 1E: 0.10 g L (301 ¯mol),
¹1
2E: 0.10 g L (326 ¯mol). Length of cell, 0.1 cm each. Each log ¾ value is given in parenthesis.
1
Table 1. The H NMR Spectral Data (¤) of 1E, 2E, and 19a)
3-Guaiazulenyl group
Compound
Me-1¤¤
H-2¤¤
Me-4¤¤
H-5¤¤
H-6¤¤
(CH3)2CH-7¤¤
(CH3)2CH-7¤¤
H-8¤¤
1E
2E
19
2.49
2.51
2.52
7.89
7.81
8.18
2.69
2.79
3.27
6.54
6.53
8.34
6.96
6.97
8.29
2.69
2.71
3.43
1.16
1.18
1.43
7.92
7.95
8.52
2-Thienyl group
H-4¤
Butadiene, ethylene, and propenylium units
H-3¤
H-5¤
H-1
H-2
H-3
H-4
1E
2E
19
6.81
6.91
7.56
6.73
6.79
7.19
6.75
6.81
7.75
6.69
7.11
7.85
6.84
8.07
7.63
7.07
®
8.44b)
7.57
®
®
a) Measurement solvent: benzene-d6 (=C6D6) for 1E and 2E; acetonitrile-d3 (=CD3CN) for 19. For comparative
purposes on the 1H NMR chemical shifts (¤) of 1E, 2E, and 19, the numbering scheme of 19 was changed as shown in
Scheme 7. b) HC+-¡.
Reaction of (2E,4E)-1-(3-Guaiazulenyl)-4-(2-thienyl)-1,3-
butadiene (1E) with Tetracyanoethylene (=TCNE). To a
solution of compound 1E (10 mg, 30 ¯mol) in benzene (2 mL)
was added a solution of TCNE (9 mg, 60 ¯mol) in benzene
(2 mL) under argon, turning the green solution of 1E into a blue
solution, rapidly. The mixture was stirred at 25 °C for 24 h under
argon. After the reaction, the reaction solution was evaporated
in vacuo. The residue thus obtained was carefully separated by
silica gel column chromatography with hexane-ethyl acetate-
benzene (2:1:1, vol/vol/vol) as an eluant. The crude prod-
uct cis-4,4,5,5-tetracyano-3-(3-guaiazulenyl)-6-(2-thienyl)-1-
cyclohexene (11) (11 mg, 23 ¯mol, 77% yield) was recrystal-
lized from hexane-benzene (5:1, vol/vol) (several times) to
provide pure 11 (7 mg, 16 ¯mol, 55% yield) as crystals.
group: ¤ 7.19 (1H, dd, J = 5.1, 3.6 Hz, H-4¤), 7.40 (1H, br d,
J = 3.6 Hz, H-3¤), and 7.53 (1H, dd, J = 5.1, 1.1 Hz, H-5¤); and
signals from a cis-3,6-disubstituted 4,4,5,5-tetracyano-1-cyclo-
hexene unit: ¤ 4.96 (1H, ddd, J = 2.5, 2.3, 2.3 Hz, H-3), 5.84
(1H, ddd, J = 2.5, 2.3, 2.3 Hz, H-6), 6.15 (1H, ddd, J = 10.4,
2.5, 2.3 Hz, H-4), and 6.33 (1H, ddd, J = 10.4, 2.5, 2.3 Hz, H-
5); 176 MHz 13C NMR (dichloromethane-d2): ¤ 144.1 (C-4¤¤),
142.4 (C-7¤¤), 139.3 (C-8a¤¤), 137.3 (C-2¤¤), 135.5 (C-6¤¤), 134.7
(C-8¤¤), 134.4 (C-2¤), 133.7 (C-3a¤¤), 130.5 (C-5), 129.6 (C-5¤¤),
129.1 (C-3¤), 127.6 (C-5¤), 127.5 (C-4¤), 125.4 (C-1¤¤), 124.8
(C-4), 115.4 (C-3¤¤), 110.9, 110.7, 109.8, 109.5 (CN each), 47.5
(C-1), 47.4 (C-2), 42.8 (C-3), 40.5 (C-6), 37.4 ((CH3)2CH-7¤¤),
27.5 (Me-4¤¤), 23.9 ((CH3)2CH-7¤¤), and 12.4 (Me-1¤¤). For
1
comparative purposes on the H and 13C NMR chemical shifts
Compound 11: Dark-blue blocks [Rf = 0.33 on silica gel
TLC (solv. hexane:ethyl acetate = 3:1, vol/vol)]; mp 185 °C;
exact EI-MS (70 eV): found: m/z 460.1722; calcd for C29H24-
(¤) of 1E and 11, the H and C numbers of the molecular struc-
ture 11 were changed as above.
Reaction of (2E,4E)-1-(3-Guaiazulenyl)-4-(2-thienyl)-1,3-
butadiene (1E) with Dimethyl Acetylenedicarboxylate
¹1
N4S: M+, m/z 460.1720; IR ¯max/cm (KBr): 2249 (C¸N);
700 MHz 1H NMR (dichloromethane-d2): signals from a 3-
guaiazulenyl group: ¤ 1.39 (6H, d, J = 7.0 Hz, (CH3)2CH-7¤¤),
2.66 (3H, br s, Me-1¤¤), 3.12 (3H, s, Me-4¤¤), 3.14 (1H, sept,
J = 7.0 Hz, (CH3)2CH-7¤¤), 7.17 (1H, d, J = 10.8 Hz, H-5¤¤),
7.58 (1H, dd, J = 10.8, 2.2 Hz, H-6¤¤), 7.76 (1H, br s, H-2¤¤),
and 8.32 (1H, d, J = 2.2 Hz, H-8¤¤); signals from a 2-thienyl
(=DMAD).
To a solution of compound 1E (70 mg, 210
¯mol) in toluene (10 mL) was added a solution of DMAD
(51 ¯L, 420 ¯mol) under argon. The mixture was stirred at
reflux temperature (120 °C) for 24 h under argon. After the
reaction, the reaction solution was evaporated in vacuo. The
residue thus obtained was carefully separated by silica gel col-

S. Takekuma et al.
Table 2. The 13C NMR Spectral Data (¤) of 1E, 2E, and 19a)
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
971
3-Guaiazulenyl group
Compound
C-1¤¤
Me-1¤¤
C-2¤¤
C-3¤¤
C-3a¤¤
C-4¤¤
Me-4¤¤
1E
2E
19
126.7
126.4
143.0
13.1
13.0
13.8
136.3
136.3
139.6
127.2
126.4
138.8
133.3
133.4
151.6
146.5
146.3
156.8
28.4
28.3
29.4
3-Guaiazulenyl group
C-5¤¤
C-6¤¤
C-7¤¤
(CH3)2CH-7¤¤
(CH3)2CH-7¤¤
C-8¤¤
C-8a¤¤
1E
2E
19
127.7
127.8
148.7
134.9
134.8
144.2
141.2
140.9
168.5
37.9
37.9
40.0
24.4
24.4
23.8
133.6
133.6
139.6
141.8
141.4
159.9
2-Thienyl group
C-2¤
C-3¤
C-4¤
C-5¤
1E
2E
19
144.2
145.3
142.5
125.4
124.6
135.0
127.7
127.8
130.5
123.8
122.9
134.3
Butadiene, ethylene, and propenylium units
C-1
C-2
C-3
C-4
1E
2E
19
123.3
120.2
145.3
127.5
126.7
126.8
131.3
®
150.8b)
130.9
®
®
a) Measurement solvent: benzene-d6 (=C6D6) for 1E and 2E; acetonitrile-d3 (=CD3CN) for 19. For comparative
purposes on the 13C NMR chemical shifts (¤) of 1E, 2E, and 19, the numbering scheme of 19 was changed as
shown in Scheme 7. b) HC+-¡.
umn chromatography with hexane-ethyl acetate (4:1, vol/vol)
as an eluant (several times), providing pure dimethyl cis-3-
guaiazulenyl-6-(2-thienyl)-1,4-cyclohexadiene-1,2-dicarboxy-
late (16) (49 mg, 100 ¯mol, 71% yield) as a paste.
Reaction of Dimethyl cis-3-Guaiazulenyl-6-(2-thienyl)-
1,4-cyclohexadiene-1,2-dicarboxylate (16) with 2,3-Di-
chloro-5,6-dicyano-1,4-benzoquinone (=DDQ). To a solu-
tion of compound 16 (78 mg, 160 ¯mol) in benzene (5 mL) was
added a solution of DDQ (54 mg, 160 ¯mol) in benzene (5 mL)
under aerobic conditions. The mixture was stirred at 60 °C for
24 h under aerobic conditions. After the reaction, diethyl ether
(5 mL) was added to the mixture and then, the obtained organic
layer was washed with NaOH aq (1 M, 3 mL) and distilled
water. The extract was dried (MgSO4), and concentrated in
vacuo. The residue thus obtained was carefully separated by
silica gel column chromatography with hexane-ethyl acetate
(1:1, vol/vol) as an eluant. The crude product cis-3-(3-formyl-
5-isopropyl-8-methylazulen-1-yl)-6-(2-thienyl)-1,4-cyclohexa-
diene-1,2-dicarboxylate (18) was recrystallized from hexane-
diethyl ether (5:1, vol/vol) (several times) to provide a pure 18
(8 mg, 17 ¯mol, 11% yield) as crystals.
Compound 18: Dark-purple blocks [Rf = 0.47 on silica gel
TLC (solv. hexane:ethyl acetate = 1:1, vol/vol)]; exact EI-
MS (70 eV): found: m/z 488.1658; calcd for C29H28O5S: M+,
m/z 488.1657; 500 MHz 1H NMR (CD2Cl2): signals based on a
3-substituted 3-formyl-5-isopropyl-8-methylazulen-1-yl: ¤ 1.39
(6H, d, J = 6.9 Hz, (CH3)2CH-7¤¤), 3.15 (3H, s, Me-4¤¤), 3.19
(1H, sept, J = 6.9 Hz, (CH3)2CH-7¤¤), 7.45 (1H, d, J = 10.6 Hz,
H-5¤¤), 7.66 (1H, dd, J = 10.6, 2.2 Hz, H-6¤¤), 8.16 (1H, br s,
H-2¤¤), 9.76 (1H, d, J = 2.2 Hz, H-8¤¤), and 10.19 (1H, s, 1¤¤-
CHO); signals from a 2-thienyl group: ¤ 6.98 (1H, dd, J = 5.0,
4.8 Hz, H-4¤), 7.00 (1H, br d, J = 4.8 Hz, H-3¤), and 7.30 (1H,
dd, J = 5.0, 1.4 Hz, H-5¤); and signals from a cis-3,6-disubsti-
Compound 16: Blue paste [Rf = 0.34 on silica gel TLC
(solv. hexane:ethyl acetate = 4:1, vol/vol)]; exact EI-MS (70
eV): found: m/z 474.1865; calcd for C29H30O4S: M+, m/z
1
474.1869; 700 MHz H NMR (benzene-d6): signals from a 3-
guaiazulenyl group: ¤ 1.18 (6H, d, J = 7.0 Hz, (CH3)2CH-7¤¤),
2.48 (3H, br s, Me-1¤¤), 2.75 (1H, sept, J = 7.0 Hz, (CH3)2CH-
7¤¤), 2.87 (3H, s, Me-4¤¤), 6.71 (1H, d, J = 10.9 Hz, H-5¤¤),
7.11 (1H, dd, J = 10.9, 1.9 Hz, H-6¤¤), 8.05 (1H, d, J = 1.9 Hz,
H-8¤¤), and 8.06 (1H, br s, H-2¤¤); signals based on a 2-thienyl
group: ¤ 6.77 (1H, dd, J = 5.0, 3.2 Hz, C-4¤), 6.90 (1H, dd,
J = 5.0, 1.1 Hz, H-5¤), and 7.01 (1H, br d, J = 3.2 Hz, H-3¤);
signals from a cis-3,6-disubstituted 1,2-dimethoxycarbonyl-
1,4-cyclohexadiene unit: ¤ 3.05, 3.36 (3H each, s, H3COOC-1
or 2), 4.84 (1H, m, H-3), 5.55, 5.57 (1H each, m, H-5 or 6), and
5.74 (1H, m, H-4); 176 MHz 13C NMR (benzene-d6): ¤ 167.9,
167.8 (H3COOC-1 or 2), 145.6 (C-2¤), 144.4 (C-4¤¤), 139.8
(C-2¤¤,7¤¤,8a¤¤), 136.9 (C-2), 134.8 (C-1), 134.3 (C-6¤¤), 133.7
(C-8¤¤), 131.8 (C-3a¤¤), 128.4 (C-4), 127.3 (C-5¤¤), 126.8 (C-4¤),
126.1 (C-3¤), 125.4 (C-1¤¤), 125.1 (C-5¤), 123.2 (C-5), 51.5
(H3COOC-1 and 2) 39.2 (C-3), 38.6 (C-6), 37.8 ((CH3)2CH-
7¤¤), 27.3 (Me-4¤¤), 24.5 ((CH3)2CH-7¤¤), and 13.1 (Me-1¤¤). The
C-3¤¤ carbon signal was included in other carbon signals. For
1
comparative purposes on the H and 13C NMR chemical shifts
(¤) of 1E, 11, and 16, the H and C numbers of the molecular
structure 16 were changed as above.

972
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
A New (2E,4E)-1,3-Butadiene Derivative
(Me-4¤¤), 23.8 ((CH3)2CH-7¤¤), and 13.8 (Me-1¤¤). For compa-
1
rative purposes on the H and 13C NMR chemical shifts (¤) of
1E, 2E, and 19 (Tables 1 and 2), the numbering scheme of 19
was changed as shown in Scheme 7.
Reduction of (3-Guaiazulenyl)[(E)-2-(2-thienyl)ethenyl]-
methylium Hexafluorophosphate (19) with NaBH4. To a
solution of 19 (31 mg, 90 ¯mol) in acetonitrile (2 mL) was
added a solution of NaBH4 (4 mg, 100 ¯mol) in ethanol (1 mL).
The mixture was stirred at 25 °C for 1 h and then, the reaction
solution, of which was evaporated in vacuo. The residue thus
obtained was carefully separated by silica gel column chroma-
tography with hexane-ethyl acetate (4:1, vol/vol) as an eluant
(several times), giving pure (E)-1-[(3-guaiazulenyl)methyl]-2-
(2-thienyl)ethylene (20) as a green paste (20 mg, 56 ¯mol, 63%
yield).
Figure 2. The UV-vis spectrum of 19 in CH3CN. Concen-
tration, 19: 0.10 g L (215 ¯mol). Length of Cell, 0.1 cm.
Each log ¾ value is given in parenthesis.
¹1
Compound 20: Green paste; exact EI-MS (70 eV), found:
m/z 320.1599; calcd for C22H24S: M+, m/z 320.1599; 500
MHz 1H NMR (benzene-d6): signals from a 3-guaiazulenyl-
methyl group: ¤ 1.21 (6H, d, J = 6.8 Hz, (CH3)2CH-7¤¤), 2.57
(3H, br s, Me-1¤¤), 2.75 (3H, s, Me-4¤¤), 2.77 (1H, sept, J =
6.8 Hz, (CH3)2CH-7¤¤), 3.91 (2H, br dd, J = 5.4, 1.8 Hz, 1-
CH2-3¤¤), 6.66 (1H, d, J = 10.3 Hz, H-5¤¤), 7.10 (1H, dd, J =
10.3, 2.3 Hz, H-6¤¤), 7.47 (1H, br s, H-2¤¤), and 8.12 (1H, d,
J = 2.3 Hz, H-8¤¤); signals from a 2-thienyl group: ¤ 6.44 (1H,
br d, J = 3.4 Hz, H-3¤), 6.59 (1H, dd, J = 5.1, 3.4 Hz, H-4¤),
and 6.67 (1H, br d, J = 5.1 Hz, H-5¤); signals based on an (E)-
ethylene unit: ¤ 6.27 (1H, dt, J = 15.7, 1.8 Hz, H-2) and 6.44
(1H, dt, J = 15.7, 5.4 Hz, H-1); 125 MHz 13C NMR (benzene-
d6): ¤ 145.3 (C-4¤¤), 143.4 (C-2¤), 141.2 (C-2¤¤), 138.8 (C-8a¤¤),
138.1 (C-7¤¤), 134.6 (C-6¤¤), 133.7 (C-3a¤¤), 133.4 (C-8¤¤), 127.3
(C-4¤), 126.6 (C-3¤¤), 126.5 (C-5¤¤), 124.9 (C-1,3¤,1¤¤), 124.5
(C-2), 123.3 (C-5¤), 37.9 ((CH3)2CH-7¤¤), 34.7 (2-CH2-3¤¤), 26.4
(Me-4¤¤), 24.6 ((CH3)2CH-7¤¤), and 13.0 (Me-1¤¤).
X-ray Crystal Structure of (2E,4E)-1-(3-Guaiazulenyl)-4-
(2-thienyl)-1,3-butadiene (1E). The X-ray measurement of
the single crystal 1E was made on a Rigaku Saturn CCD area
detector with graphite monochromated Mo K¡ radiation (- =
0.71075 ¡) at ¹173 °C. The structure was solved by direct
methods (SIR92)30 and expanded using Fourier techniques
(DIRDIF99).31 Non-hydrogen atoms were refined anisotropi-
cally. 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 CrystalStructure
crystallographic software package developed by Rigaku corpo-
ration, Japan. Crystallographic data have been deposited with
Cambridge Crystallographic Data Centre: Deposition num-
ber CCDC-795121 for compound No. 1E. 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).
tuted 1,2-dimethoxycarbonyl-1,4-cyclohexadiene unit: ¤ 3.43,
3.66 (3H each, s, H3COOC-1 or 2), 4.85 (1H, m, H-3), 5.49
(1H, m, H-6), 5.81 (1H, m, H-5), and 5.95 (1H, m, H-4). For
comparative purposes on the 1H NMR chemical shifts (¤) of 16
and 18, the H numbers of the molecular structure 18 were
changed as above.
Preparation of (3-Guaiazulenyl)[(E)-2-(2-thienyl)ethen-
yl]methylium Hexafluorophosphate (19).
To a solution
of guaiazulene (3) (90 mg, 450 ¯mol) in methanol (3 mL) was
added a solution of (E)-2-(2-thienyl)ethylene-1-carbaldehyde
(7) (55 mg, 400 ¯mol) in methanol (1 mL) containing hexa-
fluorophosphoric acid (i.e., 65% HPF6 aqueous solution, 0.1
mL). The mixture was stirred at 25 °C for 1 h, precipitating a
dark-green solid of 19 and then, the reaction solution con-
taining a precipitate, which 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, vol/vol) under aerobic conditions (several
times) to provide pure 19 as single crystals (175 mg, 377 ¯mol,
94% yield).
Compound 19: Dark-green blocks; mp >193 °C (decomp);
Found: C, 55.19; H, 4.36%. Calcd for C22H23OF6PS (i.e.,
C22H23S + PF6 + 1/2O2): C, 55.00; H, 4.83%;29 exact FAB-
MS (3-nitrobenzyl alcohol matrix): found: m/z 391.1515; calcd
for C22H23S: [M ¹ PF6]+, m/z 319.1516; IR ¯max/cm¹1 (KBr):
¹
837 and 559 (PF6 ); UV-vis -max/nm (log ¾) in CH3CN: 242
(4.55), 343 (4.24), and 540 (4.76). Details are shown in
1
Figure 2; 700 MHz H NMR (acetonitrile-d3): signals from a
3-guaiazulenylmethylium ion unit: ¤ 1.43 (6H, d, J = 6.7 Hz,
(CH3)2CH-7¤¤), 2.52 (3H, br s, Me-1¤¤), 3.27 (3H, s, Me-4¤¤),
3.43 (1H, sept, J = 6.7 Hz, (CH3)2CH-7¤¤), 8.18 (1H, br s, H-
2¤¤), 8.29 (1H, dd, J = 11.0, 2.2 Hz, H-6¤¤), 8.34 (1H, d, J =
11.0 Hz, H-5¤¤), 8.44 (1H, br d, J = 11.6 Hz, HC+-¡), and 8.52
(1H, d, J = 2.2 Hz, H-8¤¤); signals from an (E)-1-(2-thienyl)-
ethenyl group: ¤ 7.19 (1H, dd, J = 5.0, 3.6 Hz, H-4¤), 7.56 (1H,
br d, J = 3.6 Hz, H-3¤), 7.63 (1H, dd, J = 14.6, 11.6 Hz, H-2),
7.75 (1H, br d, J = 5.0 Hz, H-5¤), and 7.85 (1H, d, J = 14.6
Hz, H-1); 176 MHz 13C NMR (acetonitrile-d3): ¤ 168.5 (C-7¤¤),
159.9 (C-8a¤¤), 156.8 (C-4¤¤), 151.6 (C-3a¤¤), 150.8 (HC+-¡),
148.7 (C-5¤¤), 145.3 (C-1), 144.2 (C-6¤¤), 143.0 (C-1¤¤), 142.5
(C-2¤), 139.6 (C-2¤¤,8¤¤), 138.8 (C-3¤¤), 135.0 (C-3¤), 134.3
(C-5¤), 130.5 (C-4¤), 126.8 (C-2), 40.0 ((CH3)2CH-7¤¤), 29.4
Crystallographic data for 1E: C23H24S (FW = 332.50),
Dark-green needle (crystal size, 0.66 © 0.10 © 0.07 mm3),
ꢀ
triclinic, P1 (#2), a = 9.7363(7) ¡, b = 13.7993(12) ¡, c =
14.7729(10) ¡,
¡ = 77.118(7)°,
¢ = 71.400(6)°,
£ =
¹3
82.803(8)°, V = 1830.6(2) ¡3, Z = 4, Dcalcd = 1.206 g cm
,
®(Mo K¡) = 1.772 cm¹1, measured reflections = 22277, ob-
served reflections = 15514, no. of variables = 482, R1 =
0.0700, wR2 = 0.1508, goodness of fit indicator = 0.978.

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
973
Table 3. The Selected C-C and C-S Bond Lengths (¡) of 1E, 2E, and 19
Atom
1E
2E
19
Atom
1E
2E
19
C1¤¤-C2¤¤
C2¤¤-C3¤¤
C3¤¤-C3a¤¤
C3a¤¤-C4¤¤
C4¤¤-C5¤¤
C5¤¤-C6¤¤
C6¤¤-C7¤¤
C7¤¤-C8¤¤
C8¤¤-C8a¤¤
C8a¤¤-C1¤¤
C8a¤¤-C3a¤¤
1.368(3)
1.430(4)
1.419(3)
1.409(4)
1.395(3)
1.403(3)
1.378(4)
1.405(4)
1.369(3)
1.424(4)
1.505(3)
1.373(5)
1.431(5)
1.414(5)
1.408(5)
1.384(5)
1.408(5)
1.388(5)
1.391(5)
1.383(5)
1.424(5)
1.498(4)
1.363(8)
1.441(8)
1.478(7)
1.362(8)
1.429(8)
1.376(8)
1.378(8)
1.392(7)
1.389(7)
1.446(7)
1.494(7)
C1-C2
C2-C3
C3-C4
1.354(3)
1.426(3)
1.349(3)
1.433(2)
®
1.337(5)
®
®
1.338(8)
1.421(7)a)
®
C1-C2¤
C2-C3¤¤
C4-C3¤¤
C2¤-C3¤
C3¤-C4¤
C4¤-C5¤
S1¤-C2¤
S1¤-C5¤
1.446(5)
1.450(4)
®
1.442(7)
®
1.447(3)
1.405(3)
1.409(3)
1.377(4)
1.728(3)
1.712(2)
1.401(8)b)
1.402(8)
1.434(8)
1.334(9)
1.733(6)
1.719(6)
1.371(5)
1.406(5)
1.350(6)
1.727(4)
1.716(4)
a) C2-C¡. b) C¡-C3¤¤. For comparative purposes on the C-C and C-S bond lengths (¡) of 1E, 2E, and 19, the
numbering scheme of 19 was changed as shown in Figure 5a.
X-ray Crystal Structure of (3-Guaiazulenyl)[(E)-2-
(2-thienyl)ethenyl]methylium Hexafluorophosphate (19).
The X-ray measurement of the single crystal 19 was made on
a Rigaku Saturn CCD area detector with graphite monochro-
mated Mo K¡ radiation (- = 0.71075 ¡) at ¹173 °C. The
structure was solved by direct methods (SIR92)30 and expanded
using Fourier techniques (DIRDIF99).31 Non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were refined
using the riding model. The final cycle of full-matrix least-
squares refinement was based on F2. All calculations were
performed using the CrystalStructure crystallographic software
package developed by Rigaku corporation, Japan. Crystallo-
graphic data have been deposited with Cambridge Crystallo-
graphic Data Centre: Deposition number CCDC-851608 for
compound No. 19.
served by spectral analysis of the product 1 (80% isolated
yield) (Scheme 1), while the isomer 1Z could not be isolated
using silica gel column chromatography and recrystallization
(several times). Thus, each yield of the (2E,4E)-form 1E (70%)
and the (2E,4Z)-form 1Z (10%) was calculated from relative
1
intensities for the 700 MHz H NMR signals of an inseparable
mixture of the two geometric isomers 1E and 1Z.
Reaction of 1E with TCNE. Quite recently, we reported
that the reaction of 2E with 2 equivalents of TCNE in benzene at
25 °C for 24 h under argon gave a unique product 8 (Chart 2),
possessing an interesting molecular structure, in 42% yield as
single crystals,19 while the reaction of 2E with an equivalent
of TCNE in DMF at 25 °C for 24 h under argon afforded a
structurally unique product 9 (Chart 2) in 19% yield as single
crystals which showed dichroism (i.e., the two colors of green
and reddish-orange).19 The molecular structures of the products
8 and 9 were determined by spectroscopic and X-ray crystallo-
graphic analyses and further, a reaction mechanism for the for-
mation of 8 and 9 was proposed.19 For comparative purposes,
the reaction of 1E with 2 equivalents of TCNE in benzene was
carried out under the same reaction conditions as for 2E. As a
result, this reaction did not give a structurally unique product
10, which is a similar molecular structure to 8; however, it
afforded a new [³4 + ³2] cycloaddition product 11, in 55%
isolated yield, as crystals (i.e., dark-blue blocks) (Scheme 2).
The molecular structure of 11 was established on the basis of
exact EI-MS, IR, and 1H and 13C NMR spectroscopic analyses.
Along with the above reaction in benzene, the reaction of 1E
with an equivalent of TCNE in DMF was carried out under the
same reaction conditions as for 2E. As a result, this reaction
did not give a structurally unique product 12, which is a similar
molecular structure to 9, while it also afforded a product 11,
selectively (Scheme 3). We now propose a reaction mechanism
for the formation of 11 according to the following experimental
results: namely, to a solution of 1E in benzene (or in DMF)
was added a solution of TCNE in benzene (or in DMF) under
argon, turning the green solution of 1E into a blue solution of
11, rapidly. Therefore, a reaction pathway for the formation of
11 can be inferred that compound 11 is produced presumably
by the Diels-Alder (i.e., the [³4 + ³2] cycloaddition) reaction
of 1E with TCNE (Schemes 2 and 3) under kinetic control. In
relation to our basic study, in 1990 O’Shea and Foote reported
Crystallographic data for 19: C22H23F6PS (FW = 464.45),
Dark-green plate (crystal size, 0.312 © 0.106 © 0.067 mm3),
ꢀ
triclinic, P1 (#2), a = 8.3551(5) ¡, b = 11.4244(9) ¡, c =
23.3622(19) ¡,
¡ = 82.906(6)°,
¢ = 82.814(6)°,
£ =
¹3
77.307(6)°, V = 2147.7(3) ¡3, Z = 4, Dcalcd = 1.436 g cm
,
¹1
®(Mo K¡) = 2.826 cm
,
measured reflections = 24376,
observed reflections = 6323, no. of variables = 564, R1 =
0.1393, wR2 = 0.3644, goodness of fit indicator = 0.868. For
comparative purposes on the C-C and C-S bond lengths (¡)
of 1E, 2E, and 19 (Table 3), the numbering scheme of 19 was
changed as shown in Figure 5a.
Results and Discussion
Preparation of 1E. Quite recently, we reported the crystal
structures and the spectroscopic, chemical, and electrochemical
properties as well as a preparation of the 2-thienyl- and 3-
guaiazulenyl-substitued (E)-ethylene 2E (Chart 1) (36% yield)
and its Z geometric isomer 2Z (24% yield) using the Wittig
reaction.19 For a comparative purpose, a new 2-thienyl- and
3-guaiazulenyl-substituted (2E,4E)-1,3-butadiene 1E (Chart 1)
was prepared, in 70% yield, using the Wittig reaction shown
in Scheme 1. The molecular structure of 1E was established on
the basis of spectroscopic data [exact EI-MS, IR, UV-vis, and
1H and 13C NMR including 2D NMR (i.e., DQF COSY, HSQC,
and HMBC)]. Along with the above results, the 1H NMR
signals from the other geometric isomer of 1E, i.e., (2E,4Z)-
1-(3-guaiazulenyl)-4-(2-thienyl)-1,3-butadiene (1Z), were ob-

974
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
A New (2E,4E)-1,3-Butadiene Derivative
Scheme 1. The preparations of the Wittig reagent 515,16 and the aldehyde compound 728 and further, the Wittig reaction of 7 with
5 in ethanol (=C2H5OH) in the presence of sodium ethoxide (=NaOC2H5) at 25 °C for 24 h under argon, yielding the product 1 in
80% yield.
Scheme 2. The reaction of 1E with 2 equivalents of TCNE in benzene at 25 °C for 24 h under argon gives 11.
that the reaction of (2E,4E)-2,4-hexadiene with TCNE in
CH2Cl2 at 25 °C yields the Diels-Alder adduct, 1,1,2,2-tetra-
cyano-cis-3,6-dimethyl-4-cyclohexene, quantitatively (>99.5%
yield).32 The partial structure cis-3,6-disubstituted 1,1,2,2-tetra-
cyano-4-cyclohexene, established on the basis of 1H NMR
spectral analysis, coincided with that of 11.
(=DMAD) in toluene at 140 °C for 24 h gives a Diels-
Alder-type cycloaddition product 14, in 83% yield, which
upon oxidation with 2,3-dichloro-5,6-dicyano-p-benzoquinone
(=DDQ) in benzene at 60 °C for 24 h affords a dehydrogen-
ation product 15 in 72% yield (Scheme 4).33 We have been
particularly interested in the above reactions. For comparative
purposes, the reaction of 1E with DMAD at 120 °C for 24 h
under argon was carried out (Scheme 5), the reaction, of which
Reaction of 1E with DMAD. In 2003 Ghosh et al. reported
that the reaction of 13 with dimethyl acetylenedicarboxylate

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
975
Scheme 3. The reaction of 1E with an equivalent of TCNE in DMF at 25 °C for 24 h under argon affords 11.
Scheme 4. The reaction of 13 with DMAD in toluene at 140 °C for 24 h gives 14,33 which upon oxidation with DDQ in benzene at
60 °C for 24 h affords 15.33
of 3-formyl-5-isopropyl-8-methylazulen-1-yl yielded from the
autoxidation of guaiazulene35 (3), a reaction mechanism for
the formation of 18 can be inferred as follows: namely, the
oxygenation product 18 is derived via (i) the charge-transfer
complex 16•+¢DDQ•¹, (ii) the radical 16• species generated by
the deprotonation from the methyl group substituted at the C-1¤¤
position of the cation-radical 16•+ species, owing to thermo-
dynamic control, and finally, (iii) the oxygenation of 16• with
Scheme 5. The reaction of 1E with DMAD in toluene at
oxygen molecule (3O2).20 A preparation of the structurally
120 °C for 24 h under argon gives 16.
unique aromatic compound 17, possessing the 2-thienyl and
3-guaiazulenyl groups at the C-3 and C-6 positions of the 1,2-
yielded a new Diels-Alder adduct 16, in 71% isolated yield, as
a blue paste. The molecular structure of 16 was established on
di(methoxycarbonyl)benzene framework, is further currently
under intensive investigation.
1
the basis of exact EI-MS and H and 13C NMR spectroscopic
Spectroscopic Properties of 1E. The title compound 1E
was obtained as dark-green needles. The spectroscopic prop-
erties of 1E compared with those of 2E19 are described as
follows: namely, the molecular formula C23H24S was deter-
mined by exact EI-MS, whose spectrum showed the M+ ion
peak based on the molecular structure 1E illustrated in Chart 1.
The IR spectrum of 1E showed specific bands from the C-H,
-HC=CH-, C=C, and C-S bonds, the wavenumbers, of which
shifted in comparison with those of 2E.19 The UV-vis spec-
trum of 1E, compared with that of the starting material
guaiazulene36 (3), showed the great difference between the
characteristic absorption bands of 3 and those of 1E, suggesting
the formation of the molecular structure 1E with an extended
³-electron system (Chart 1). The spectral pattern of 1E resem-
bled that of 2E (Figure 1), while a characteristic absorption
band (-max 437 nm, log ¾ = 4.76) of 1E showed a bathochro-
mic shift (¦ 17 nm) and a hyperchromic effect (¦ log ¾ = 0.22)
in comparison with the corresponding absorption band (-max
420 nm, log ¾ = 4.54) of 2E. However, the longest absorption
analyses. In relation to our basic study, in 1994 Coudert et al.
reported that the reactions of the (2E,4E)-1,3-butadiene deriva-
tives with DMAD at 130-150 °C for 15 min-1 h yield similar
Diels-Alder adducts to 16 in 51-82% isolated yields.34 Each
partial structure cis-3,6-disubstituted 1,2-dimethoxycarbonyl-
1
1,4-cyclohexadiene, established on the basis of H NMR spec-
tral analysis, coincided with that of 16.
Reaction of 16 with DDQ.
Similar to Scheme 4, the
oxidation of 16 with DDQ in benzene at 60 °C for 24 h under
aerobic conditions was carried out, the reaction, of which did
not give a similar dehydrogenation product to 15; however, it
afforded a new oxygenation product 18, in 11% isolated yield,
as crystals (i.e., dark-purple blocks) (Scheme 6). The molecular
structure of 18, converting the methyl group substituted at the
C-1 position of the 3-guaiazulenyl (=7-isopropyl-1,4-dimeth-
ylazulen-3-yl) group into a CHO group, was established on the
basis of exact EI-MS and 1H NMR spectroscopic analyses.
Referring the proposed reaction mechanism for the formation

976
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
A New (2E,4E)-1,3-Butadiene Derivative
Scheme 6. The oxidation of 16 with DDQ in benzene at 60 °C for 24 h under aerobic conditions affords 18.
Scheme 7. The reaction of 3 with 7 in methanol (=CH3OH) containing 65% hexafluorophosphoric acid (=HPF6) at 25 °C for 1 h
gives the corresponding monocarbenium ion compound 19, which upon reduction with sodium borohydride (=NaBH4) in a mixed
¹
solvent of ethanol (=C2H5OH) and acetonitrile (=CH3CN) at 25 °C for 1 h affords the H reduction product 20. For comparative
1
purposes on the H and 13C NMR chemical shifts (¤) of 1E, 2E, and 19, the numbering scheme of 19 was changed as shown
in Scheme 7.
band (-max 645 nm, log ¾ = 2.84) of 1E coincided with that
(-max 644 nm, log ¾ = 2.77) of 2E. The H NMR spectrum of
Preparation and Spectroscopic and Chemical Properties
of the Monocarbenium Ion Compound 19. We have been
interested further in the great difference between the spectro-
scopic and electrochemical properties and the crystal struc-
ture of a new conjugated (and delocalized) ³-electron system
19, possessing a propenium ion linkage, and those of the
title conjugated ³-electron system 1E, possessing a (2E,4E)-
1,3-butadiene linkage. The target monocarbenium ion com-
pound 19 was prepared according to the procedure shown
in Scheme 7. The structure of the product 19 was established
on the basis of elemental analysis and spectroscopic data
1
1E showed signals from a 3-guaiazulenyl and 2-thienyl group
and signals from a (2E,4E)-1,3-butadiene unit possessing two
nonequivalent substituents at the C-1 and C-4 positions, all the
signals, of which were carefully assigned using DQF COSY
and computer-assisted simulation based on first-order analysis.
As a result, the proton signals (H-1, H-4, H-3¤, and Me-4¤¤)
of 1E (Chart 1) showed upfield shifts in comparison with the
corresponding signals of 2E, while the proton signals (H-4¤,
H-5¤, and H-2¤¤) of 1E revealed slight chemical shifts in
comparison with those of 2E, presumably owing to the differ-
ence between an influence of a ring current generated from 1E
with a (2E,4E)-1,3-butadiene linkage and that generated from
2E with an (E)-ethylene linkage. Other signals of 1E coincided
with those of 2E (Table 1). The 13C NMR spectrum exhibited
21 carbon signals assigned using HSQC and HMBC. As a
result, a carbon signal (C-2¤) and the five carbon signals (C-1,
C-4, C-3¤, C-5¤, and C-3¤¤) of 1E showed chemical shifts in
comparison with the corresponding signals of 2E, owing to the
1
[exact FAB-MS, IR, UV-vis, and H and 13C NMR including
2D NMR (i.e., DQF COSY, HSQC, and HMBC)].
Compound 19 (94% isolated yield) was obtained as dark-
green blocks, while a solution of 19 in CH3CN was purple.
An elemental analysis confirmed the formula C22H23OF6PS
(i.e., C22H23S + PF6 + 1/2O2).29 The formula C22H23S for the
monocarbenium ion unit ([M ¹ PF6]+) was determined by
exact FAB-MS spectrum. The IR spectrum showed two specific
¹
bands (vmax 837 and 559 cm¹1) from the counter anion (PF6 ).
1
same reason described as the above H NMR chemical shifts.
A characteristic UV-vis absorption band from the formation of
the (3-Guaiazulenyl)[(E)-2-(2-thienyl)ethenyl]methylium ion
moiety, with a delocalized ³-electron system, appeared at an
absorption maximum (-max 540 nm, log ¾ = 4.76) (Figure 2),
whose specific broad band revealed a larger bathochromic shift
Other signals of 1E coincided with those of 2E (Table 2). Thus,
the total spectroscopic analyses for 1E led to the molecular
structure illustrated in Chart 1, the molecular conformation, of
which was supported by NOE measurement.

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
977
(¦ -max 103 nm) in comparison with the corresponding absorp-
tion band (-max 437 nm, log ¾ = 4.76) of 1E (Figure 1a);
however, its molar extinction coefficient (log ¾) of 19 coincided
with that of 1E. The 1H NMR spectrum showed signals from an
(3-Guaiazulenyl)[(E)-2-(2-thienyl)ethenyl]methylium ion moi-
ety, all the signals, of which were carefully assigned using
DQF COSY and computer-assisted simulation based on first-
order analysis (Table 1). The 13C NMR spectrum exhibited 20
carbon signals assigned by HSQC and HMBC (Table 2). Thus,
the elemental analysis and the total spectroscopic analyses
for 19 led to the target structure (3-Guaiazulenyl)[(E)-2-(2-
thienyl)ethenyl]methylium hexafluorophosphate illustrated in
Scheme 7, the structural conformation, of which was supported
that of 20, presumably owing to the formation of a resonance
structure, i.e., the 3-guaiazulenylium ion form, for 1E. The
chemical shifts of other carbon signals for the guaiazulene and
thiophene rings of 1E coincided with those of 20.
X-ray Crystal Structure of 1E. The recrystallization of 1E
from a mixed solvent of chloroform and ethanol (1:5, vol/vol)
provided single crystals suitable for X-ray crystallographic
analysis. The crystal structure of 1E was then determined
by means of X-ray diffraction, producing accurate structural
parameters. Similar to 2E19 (Figure 4b), two molecules of
1E were found to exist in a unit cell of the single crystal
(Figure 3b). An ORTEP drawing of 1E with a numbering
scheme and the two different ORTEP drawings of 1E are
shown in Figures 3a and 3b along with the C-C and C-S
bond lengths compared with those of 2E (Table 3). The crystal
structures of 1E and 2E supported the molecular conformations
illustrated in Chart 1. Previously, it was found that the two
aromatic rings of the 2¤-thienyl and 3¤¤-guaiazulenyl groups of
2E twist by 5 and 20° from the plane of the (E)-HC=CH- unit
(Figure 4a),19 presumably due to an influence of intermolecular
³-stacking. Similar to 2E, each plane of the 2¤-thienyl and 3¤¤-
guaiazulenyl groups of 1E twisted by 6 and 24° from each
plane of the C1-C2 and C3-C4 units, owing to a similar reason
to the case of 2E. The structural parameters of 1E showed that
the average C-C bond lengths of the seven- and five-membered
rings for the 3-guaiazulenyl group of 1E (1.409 and 1.429 ¡)
coincide with those of 2E (1.409 and 1.428 ¡), while the C1-
C2 and C3-C4 bond lengths of 1E (1.354 and 1.349 ¡) are
longer than the C1-C2 bond length of 2E (1.337 ¡). The bond
alternation pattern observed for the 2¤-thienyl and 3¤¤-guaiaz-
ulenyl groups of 1E coincided with that of 2E. Moreover, the
intramolecular S£HC2 distances for the two different ORTEP
drawings of 1E (2.78 and 2.72 ¡) (Figure 3b) and 2E (2.77
and 2.71 ¡) (Figure 4b) were shorter than the sum of the
van der Waals radii of the hydrogen and sulfur atoms (1.2 and
1.85 ¡), the distances, which were suggested to form an intra-
molecular S£HC2 hydrogen bond between them. Besides, an
intermolecular S£S distance of 1E (3.90 ¡) (Figure 3b) was
shorter than that of 2E (4.57 ¡) (Figure 4b), both of which
were suggested to form a S£S configuration interaction. Along
with the ORTEP drawings of 1E and 2E, the crystal packing
diagrams of 1E and 2E (Figures 3c and 4c) revealed that each
average interplane distance between the overlapping mole-
cules, whose directions are the same, is 3.60 (for 1E) or 3.69 ¡
(for 2E), suggesting that each molecule forms a ³-stacking
structure in the single crystal.37
1
by NOE measurement. Furthermore, all the H NMR signals
for the 3-guaiazulenyl and 2-thienyl groups of 19 showed
downfield shifts in comparison with those of 1E (Table 1):
namely, the order of a larger downfield shift was H-5¤¤ (¦ ¤
1.80) > H-6¤¤ (1.33) > H-5¤ (1.00) > H-3¤ (0.75) > (CH3)2CH-
7¤¤ (0.74) > H-8¤¤ (0.60) > Me-4¤¤ (0.58) > H-4¤ (0.46) > H-2¤¤
(0.29) > (CH3)2CH-7¤¤ (0.27) > Me-1¤¤ (0.03). Moreover, the
13C NMR signals for the azulene ring and the thiophene ring
(except the C-2¤ carbon) of 19 revealed downfield shifts in
comparison with those of 1E (Table 2): namely, the order of
a larger downfield shift was C-7¤¤ (¦ ¤ 27.3) > C-5¤¤ (21.0) >
C-3a¤¤ (18.3) > C-8a¤¤ (18.1) > C-1¤¤ (16.3) > C-3¤¤ (11.6) >
C-5¤ (10.5) > C-4¤¤ (10.3) > C-3¤ (9.6) > C-6¤¤ (9.3) > C-8¤¤
(6.0) > C-2¤¤ (3.3) > C-4¤ (2.8) > C-2¤ (¹1.7). Thus, the de-
tailed NMR spectral analyses of 19, compared with those of
1E, suggested the formation of the monocarbenium ion com-
pound 19 with the two representative resonance structures
of 19a and 19b (Chart 3). Along with the above results and
discussion, the reduction of 19 with NaBH4 in a mixed solvent
of ethanol and acetonitrile at 25 °C for 1 h gave the corre-
¹
sponding H reduction product 20 (Scheme 7), in 63% isolated
yield, as a green paste. The molecular formula C22H24S was
1
determined by exact EI-MS spectrum. The H NMR spectrum
showed signals from a 2-thienyl and (3-guaiazulenyl)methyl
group and an (E)-ethylene unit, all the signals, of which were
carefully assigned using similar analyses to those of 19.
The 13C NMR spectrum exhibited 19 carbon signals assigned
using similar analyses to those of 19. Thus, the total spectro-
scopic analyses for 20 led to the molecular structure (E)-1-[(3-
guaiazulenyl)methyl]-2-(2-thienyl)ethylene, in which a hydride
¹
ion (=H ) attached to the C+-¡ position of 19, selectively.
The molecular conformation of 20, illustrated in Scheme 7,
was also supported by NOE measurement. Furthermore, from
comparative studies on the 1H and 13C NMR chemical shifts (¤)
of 19 with those of 20, it can be inferred that a positive charge
of the (3-guaiazulenyl)methylium ion unit of 19 is transferred
to a guaiazulene (or thiophene) ring, generating a representative
resonance structure of 19a (or 19b) (Chart 3). Moreover, from
comparative studies of the 13C NMR chemical shifts of 1E
with those of 20, it was found that the five carbon signals (i.e.,
C-1¤¤, C-4¤¤, C-5¤¤, C-7¤¤, and C-8a¤¤) from the guaiazulene ring
of 1E showed downfield shifts in comparison with those of 20:
namely, the order of a larger downfield shift was C-7¤¤ (¦ ¤
3.1) > C-8a¤¤ (3.0) > C-1¤¤ (1.8) > C-4¤¤ (1.2) and C-5¤¤ (1.2),
while a C-2¤¤ carbon signal from the guaiazulene ring of 1E
revealed a larger upfield shift (¦ ¤ ¹4.9) in comparison with
X-ray Crystal Structure of 19. The recrystallization of
19 from a mixed solvent of acetonitrile and diethyl ether (1:5,
vol/vol) provided stable single crystals suitable for X-ray
crystallographic analysis. The crystal structure of 19 was then
determined by means of X-ray diffraction, producing accurate
structural parameters. An ORTEP drawing of 19 is shown in
Figure 5a along with the C-C and C-S bond lengths compared
with those of 1E (Table 3). As a result, it was found that the
planes of the 2¤-thienyl group and the (3¤¤-guaiazulenyl)-
methylium ion unit of 19 slightly twist by 5 and 2° from the
plane of the (E)-ethylene unit, in comparison with 1E and 2E,
due to formation of a delocalized ³-electron system. The struc-
tural parameters of 19 and 1E showed that the average C-C

978
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
A New (2E,4E)-1,3-Butadiene Derivative
Figure 3. (a, b) The ORTEP drawing (30% probability thermal ellipsoids) of 1E. (c) The crystal packing diagram of 1E.37 Hydrogen
atoms are omitted for reasons of clarity.
Figure 4. (a, b) The ORTEP drawing (30% probability thermal ellipsoids) of 2E. (c) The crystal packing diagram of 2E.37 Hydrogen
atoms are omitted for reasons of clarity.

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
979
Figure 5. (a) The ORTEP drawing of 19 (30% probability thermal ellipsoids). For comparative purposes on the C-C and C-S bond
lengths (¡) of 1E, 2E, and 19, the numbering scheme of 19 was changed as shown in Figure 5a. Top (b) and side (c) views for the
crystal packing diagram of 19.37 Hydrogen atoms are omitted for reasons of clarity.
bond lengths for the seven- and five-membered rings of the
3-guaiazulenyl group of 19 (1.403 and 1.445 ¡) do not coin-
cide with those of 1E (1.409 and 1.429 ¡), presumably because
formation of the three representative resonance structures 19,
19a, and 19b (Chart 3) in a single crystal. The bond alterna-
tion pattern observed for the 2¤-thienyl and 3¤¤-guaiazulenyl
groups of 19 resembled that of 1E, suggesting a contribution
of the resonance structures of the 3-guaiazulenylium and 2-
thienylium ion forms for 1E. Similar to 1E and 2E (Figures 3a
and 4a), the S£HC2 distance for the ORTEP drawing of 19
(2.76 ¡) (Figure 5a) was shorter than the sum of the van der
Waals radii of the hydrogen and sulfur atoms (1.2 and 1.85 ¡),
the distance, of which was suggested to form an intramolecular
S£HC2 hydrogen bond between them. Along with the ORTEP
drawing of 19, the crystal packing diagrams of 19 (Figures 5b
and 5c) revealed that each average interplane distance between
the overlapping molecules, whose directions are the same, is
8.33 ¡ (for the intermolecular S£S distance) or 6.92 ¡ (for
the intermolecular C5¤£C5¤ distance).37 From the results, it can
be inferred that the interplane distances between the over-
lapping molecules of 19 are longer than those of 1E and 2E
(Figures 3b, 3c, 4b, and 4c), because of electrostatic repulsion
between those of 19.
Electrochemical Behavior of 1E. We have been interested
further in a comparative study of the electrochemical properties
of 1E with that of 2E. The electrochemical behavior of 2E
was measured by means of CV (=cyclic voltammogram) and
DPV (=differential pulse voltammogram) [potential (in volt)
vs. SCE] in CH3CN containing 0.1 M [n-Bu4N]BF4 (Figures 6c
and 6d). The two redox potentials observed by DPV were
positioned at the Ep values of +0.50 and ¹1.61 V (Figure 6d),
while the corresponding one irreversible oxidation poten-
tial and one reversible reduction potential determined by CV
were located at +0.50 (Epa), +0.38 (Epc), and ¹1.65 V (E1/2)
(Figure 6c). For comparative purposes, the electrochemical
properties of 1E were measured under the same conditions as
for 2E. Similarly, as in the case of 2E, two redox potentials
observed by DPV were positioned at the Ep values of +0.42
and ¹1.63 V (Figure 6b), while the corresponding one irrever-
sible oxidation potential and one reversible reduction potential
determined by CV were located at +0.41 (Epa), +0.32 (Epc),
and ¹1.65 V (E1/2) (Figure 6a), the results, showed that the
reduction potential/Vof 1E coincides with that of 2E, however
the oxidation potential/V of 1E is slightly lower than that of
2E. Referring to our previous three papers,10,15,20 a redox mech-
anism of 1E based on its CV datum is proposed as illustrated
in Scheme 8: namely, 1E is one-electron-oxidized, generating
a cation-radical a with a representative resonance structure b.
Furthermore, 1E is one-electron-reduced to the anion-radical c.
From the data shown in Figure 6, a similar redox mechanism
to 1E can be inferred for 2E. In conclusion, 1E serves as a
slightly stronger one-electron donor than 2E and a similar one-
electron acceptor to 2E.
Electrochemical Behavior of 19. Along with the elec-
trochemical behavior of 1E and 2E, we have been interested
in the electrochemical properties of 19 for comparative study.
The electrochemical behavior of 19 was then measured by CV
and DPV [potential (in volt) vs. SCE] in CH3CN containing
0.1 M [n-Bu4N]BF4 (Figure 6). One reduction potential ob-
served by DPV was positioned at ¹0.14 V (Figure 7b) and the
corresponding one irreversible reduction potential determined
by CV was located at ¹0.20 V (Epc) (Figure 7a), the results,
of which showed that the reduction potential of the extended
³-electron system 19 coincides with that of the previously
reported (3-guaiazulenyl)(2-thienyl)methylium hexafluoro-
phosphate [i.e., ¹0.16 V (Ep) by DPV and ¹0.22 V (Epc) by

980
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
A New (2E,4E)-1,3-Butadiene Derivative
Figure 6. Cyclic and differential pulse voltammograms (=CV and DPV) of 1E (3.0 mg, 8.9 ¯mol) [see (a), (b)] and 2E (3.0 mg,
9.8 ¯mol) [see (c), (d)] in acetonitrile (=CH3CN) (10 mL) containing 0.1 M tetrabutylammonium tetrafluoroborate (=[n-Bu4N]BF4)
at glassy carbon (inside diameter: 3 mm) and a platinum wire served as working and auxiliary electrodes; scan rates 100 mV s¹1 at
25 °C under argon. For comparative purposes, the oxidation potential using ferrocene as a standard material showed +0.45 V (Ep)
by DPV and +0.42 V (E1/2) by CV under the same electrochemical measurement conditions as for 1E and 2E.
Scheme 8. A proposed redox mechanism based on the CV datum (Figure 6a) of 1E.

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
981
yielded a new Diels-Alder adduct 16, in 71% yield, which upon
oxidation with DDQ in benzene at 60 °C for 24 h under aerobic
conditions provided a new product 18, converting the methyl
group substituted at the C-1 position of the 3-guaiazulenyl
group into a CHO group, selectively; and (iv) the spectroscopic
properties, the crystal structure, and the electrochemical behav-
ior of the title (2E,4E)-1,3-butadiene derivative 1E compared
with those of the structurally related (E)-ethylene derivative 2E
and new propenium ion derivative 19 were documented.
This work was partially supported by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.
References
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S.-i. Takekuma, Y. Hata, T. Nishimoto, E. Nomura, M.
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Lett. Org. Chem. 2009, 684359.
12 S.-i. Takekuma, N. Ijibata, T. Minematsu, H. Takekuma,
Bull. Chem. Soc. Jpn. 2009, 82, 585.
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Takekuma, Bull. Chem. Soc. Jpn. 2009, 82, 879.
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Figure 7. CV and DPV of 19 (3.0 mg, 6.4 ¯mol) [see (a),
(b)] in CH3CN (10 mL) containing 0.1 M [n-Bu4N]BF4 at
glassy carbon (inside diameter: 3 mm) and a platinum wire
served as working and auxiliary electrodes; scan rates 100
¹1
mV s at 25 °C under argon. For comparative purposes,
the oxidation potential using ferrocene as a standard mate-
rial showed +0.42 V (Ep) by DPV and +0.40 V (E1/2) by
CV under the same electrochemical measurement con-
ditions as for 19.
CV].2 From the above results, it can be inferred that the
reduction potential [¹0.25 V (Epc)], observed by the CV of 1E
(Figure 6a), arises from the reduction potential/V of the 1E•+
species generated by the electrochemical oxidation of 1E.
16 S.-i. Takekuma, H. Matsuoka, S. Ogawa, Y. Shibasaki, T.
Minematsu, Bull. Chem. Soc. Jpn. 2010, 83, 1248.
17 S.-i. Takekuma, M. Kaibara, T. Minematsu, H. Takekuma,
Tetrahedron 2011, 67, 4780.
Conclusion
We have reported the following four interesting points for
the title basic studies: namely, (i) the Wittig reaction of the
aldehyde compound 7 with the reagent 5 in ethanol containing
NaOC2H5 at 25 °C for 24 h under argon gave the two (2E,4E)-
and (2E,4Z)-geometric isomers of a new compound 1-(3-
guaiazulenyl)-4-(2-thienyl)-1,3-butadiene (1) in 80% yield, the
only title (2E,4E)-form 1E, of which could be isolated as single
crystals; (ii) the reaction of 1E with TCNE in benzene (or
in DMF) at 25 °C for 24 h under argon afforded a new Diels-
Alder adduct 11, in 77% yield, respectively; (iii) the reaction
of 1E with DMAD in toluene at 120 °C for 24 h under argon
18 S.-i. Takekuma, I. Miyamoto, A. Hamasaki, T. Minematsu,
Tetrahedron 2011, 67, 9719.
19 S.-i. Takekuma, K. Nagata, Y. Yoshioka, H. Obata, T.
Minami, T. Tanaka, K. Yashima, T. Minematsu, H. Takekuma,
Tetrahedron 2012, 68, 6737.
20 S.-i. Takekuma, M. Yamamoto, A. Nakagawa, T. Iwata, T.
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Atta-ur-Rahman, Elsevier, Amsterdam, 1994, Vol. 14, Part. 1,
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Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
A New (2E,4E)-1,3-Butadiene Derivative
provide single crystals containing molecular oxygen.
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33 A. Nayek, M. G. B. Drew, S. Ghosh, Tetrahedron 2003, 59,
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22 Guaiazulene (3): DPV (Ep), +0.65 and ¹1.77 V; CV, +0.69
(Epa) and ¹1.77 (E1/2) V under the same electrochemical measure-
ment conditions as for 1E shown in Figure 6 caption.
23 Z.-q. Liu, Q. Fang, D. Wang, D.-x. Cao, G. Xue, W.-t. Yu,
H. Lei, Chem.®Eur. J. 2003, 9, 5074.
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Nozoe, Bull. Chem. Soc. Jpn. 1987, 60, 1415.
36 Guaiazulene (3): UV-vis -max/nm (log ¾) in CH2Cl2, 244
(4.43), 291 (4.67), 304sh (4.16), 336sh (3.56), 350 (3.71), 366
29 It has been long-known that guaiazulene (3) gradually
undergoes oxygenation even on exposure to air at room tem-
perature.21,35 On the other hand, we quite recently found that the
mono-18 and dicarbenium20 ion compounds, stabilized by the 3-
guaiazulenyl group(s), are recrystallized from acetonitrile-diethyl
ether (1:5, vol/vol) under aerobic conditions (several times) to
provide single crystals, respectively, containing molecular oxygen.
Similar to our previous two papers,18,20 the monocarbenium ion
compound 19, stabilized by a 3-guaiazulenyl group, was recrystal-
lized under the same recrystallization conditions as above to
(3.54), 601 (2.69), 652sh (2.61), and 728sh (2.07); UV-vis -max
/
nm (log ¾) in CH3CN, 213 (4.10), 244 (4.39), 284 (4.61), 301sh
(4.03), 348 (3.65), 365 (3.46), 600 (2.68), 648sh (2.61), and 721sh
(2.20).
37 Although the single crystal of 9 (Chart 2) showed dichro-
ism (i.e., the two colors of green and reddish-orange), the specific
phenomenon, of which could be identified using a polarization
microscope,19 the single crystals of 1E, 2E, and 19 did not show
dichroism.