Preparation, crystal structures, and properties of new conjugated π-electron systems with 3-guaiazulenyl and 4-(dimethylamino)phenyl groups

Article abstract of DOI:10.1246/bcsj.81.1472

Reaction of guaiazulene with l,2-bis[4-(dimethylamino)phenyl]-l,2- ethanediol in methanol in the presence of hydrochloric acid at 60°C for 3h gives l,l-bis[4-(dimethylamino)phenyl]-2-(3-guaiazulenyl)ethylene, in 81% yield, via pinacol rearrangement and fu

Full text of DOI:10.1246/bcsj.81.1472

1472 Bull. Chem. Soc. Jpn. Vol. 81, No. 11, 1472–1484 (2008)
ꢀ 2008 The Chemical Society of Japan
Preparation, Crystal Structures, and Properties
of New Conjugated ꢀ-Electron Systems
with 3-Guaiazulenyl and 4-(Dimethylamino)phenyl Groups
ꢀ1
Shin-ichi Takekuma, Seiki Hori,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 February 26, 2008; E-mail: takekuma@apch.kindai.ac.jp
Reaction of guaiazulene with 1,2-bis[4-(dimethylamino)phenyl]-1,2-ethanediol in methanol in the presence of
hydrochloric acid at 60 ꢁC for 3 h gives 1,1-bis[4-(dimethylamino)phenyl]-2-(3-guaiazulenyl)ethylene, in 81% yield,
via pinacol rearrangement and further Wittig reaction of 3-formylguaiazulene with [4-(dimethylamino)benzyl]triphenyl-
phosphonium bromide in ethanol containing NaOEt at 25 ꢁC for 24 h under argon affords (E)-2-[4-(dimethylamino)-
phenyl]-1-(3-guaiazulenyl)ethylene in 12% yield. Crystal structures as well as spectroscopic and electrochemical prop-
erties of the products, with a view to comparative study, are reported. Moreover, reactions of the products with 2 equiv
of tetracyanoethylene (TCNE) in benzene at 25 ꢁC for 24 h under argon give 1,1,2,2,11,11,12,12-octacyano-3,3-bis[4-
(dimethylamino)phenyl]-8-isopropyl-5,10-dimethyl-1,2,3,6,9,10a-hexahydro-6,9-ethanobenz[a]azulene and 1,1,2,2,11,-
11,12,12-octacyano-3-[4-(dimethylamino)phenyl]-8-isopropyl-5,10-dimethyl-1,2,3,6,9,10a-hexahydro-6,9-ethanobenz-
[a]azulene in 74 and 41% yields. A plausible reaction pathway for the formation of the unique products, possessing
interesting structures, is submitted.
Azulene and its derivatives have been studied to a consider-
able extent over the past 50 years and an extremely large
number of the studies have been well documented and further,
naturally occurring guaiazulene (=7-isopropyl-1,4-dimethyl-
azulene, 1) has been widely used clinically as an antiinflamma-
tory and antiulcer agent. However, none have really been used
as other industrial materials. As a series of basic studies on
creation and potential utility of novel functional materials
with a 3-guaiazulenyl (=7-isopropyl-1,4-dimethyl-3-azulenyl)
(or another 1-azulenyl) group possessing a large dipole mo-
ment, we have been working on facile preparation and crystal
structures as well as spectroscopic, chemical, and electrochem-
ical properties of delocalized mono- and dicarbenium-ion
compounds stabilized by expanded ꢀ-electron systems with
a 3-guaiazulenyl (or a 1-azulenyl) group.1–16 During the course
of investigation, we found that 3–58 and 68 (Chart 1) serve as
strong electron donors and electron acceptors and 3–5 undergo
stepwise two-electron oxidation by means of CV and DPV,
while (Z)-4-(dimethylamino)phenyl-substituted compound 6
undergoes two-electron oxidation simultaneously. Further-
more, we found that reaction of 5 and 4 with 2 equiv of TCNE,
which serves as a strong electron acceptor,11,12 in benzene
at 25 ꢁC for 24 h under argon gives 1612 and 1712 (Chart 2),
selectively. Along with the above basic studies, our interest
has quite recently been focused on the following five points
for comparative purposes: namely, (i) studies of 1,1-bis[4-
(dimethylamino)phenyl]-substituted compound 9 (Figure 1)
and (E)-4-(dimethylamino)phenyl-substituted compound 13
(Figure 2) compared with those of 6. These compounds can
be expected to serve as a strong three- (or two-) electron donor
for 9 (or 13) and one-electron acceptors; (ii) investigation of a
plausible electron-transfer mechanism based on the redox
potentials of 9 and 13, compared with those of 6, by means
of CV and DPV; (iii) the reactions of 9 and 13 with TCNE
under the same reaction conditions as for 4 and 5, probably
yielding new 17 and 16 analogues 18 and 19 (Figure 10);
RO
N
H
H
H
H
RO
3: R = H
4: R = CH3
6
5
Chart 1.
Published on the web November 12, 2008; doi:10.1246/bcsj.81.1472

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008) 1473
(95 mg, 206 mmol, 81% yield) as stable crystals.
CN
CN
CN
Compound 9: Dark-green plates [Rf ¼ 0:48 on silica-gel TLC
(solv. hexane:ethyl acetate:benzene = 7:2:1, vol/vol/vol)]; mp
201 ꢁC [determined by thermal analysis (TGA and DTA)]; found:
C, 85.73; H, 8.37; N, 6.02%, calcd for C33H38N2: C, 85.67; H,
8.28; N, 6.05%; UV–vis ꢁmax (CH3CN) nm (log "): 204 (4.73),
225 (4.47), 253 (4.50), 287 (4.62), 330sh (4.47), 391 (4.41), and
647 (2.69); IR ꢂmax (KBr) cmꢃ1: 2955–2797 (C–H), 1609, 1520
(C=C), and 1358 (C–N); exact FAB-MS (3-nitrobenzyl alcohol
matrix): found: m=z 462.3050; calcd for C33H38N2: Mþ, m=z
462.3035; 1H NMR (benzene-d6): signals based on the 3-guai-
azulenyl group: ꢃ 1.73 (6H, d, J ¼ 7:0 Hz, (CH3)2CH-7000), 2.31
(3H, s, Me-1000), 2.70 (1H, sept, J ¼ 7:0 Hz, (CH3)2CH-7000),
3.00 (3H, s, Me-4000), 6.59 (1H, d, J ¼ 10:5 Hz, H-5000), 7.00
(1H, dd, J ¼ 10:5, 2.5 Hz, H-6000), 7.60 (3H, s, H-2000), and 7.88
(1H, d, J ¼ 2:5 Hz, H-8000); signals based on the two 4-(dimethyl-
amino)phenyl groups: ꢃ 2.45 (6H, s, (CH3)2N-40), 2.54 (6H, s,
(CH3)2N-400), 6.51 (2H, dd, J ¼ 8:5, 2.5 Hz, H-30,50), 6.67 (2H,
dd, J ¼ 8:5, 2.5 Hz, H-300,500), 7.54 (2H, dd, J ¼ 8:5, 2.5 Hz,
H-20,60), and 7.66 (2H, dd, J ¼ 8:5, 2.5 Hz, H-200,600); and a
signal based on the >C=CH– part: ꢃ 7.81 (1H, s, H-2); 13C NMR
(benzene-d6): ꢃ 150.2 (C-400), 149.6 (C-40), 146.3 (C-4000), 140.8
(C-2000), 139.9 (C-8a000), 139.6 (C-7000), 135.2 (C-3a000), 134.3 (C-
6000), 134.1 (C-200,600), 133.9 (C-10), 133.0 (C-20,60), 132.8 (C-
8000), 129.9 (C-100), 128.3 (C-3000), 126.0 (C-5000), 125.4 (C-2),
125.0 (C-1000), 123.3 (C-1), 112.8 (C-300,500), 112.5 (C-30,50),
40.3 ((CH3)2N-400), 40.0 ((CH3)2N-40), 37.9 (Me2CH-7000), 27.8
(Me-4000), 24.5 ((CH3)2CH-7000), and 12.9 (Me-1000).
CN
CN
CN
NC
NC
16
CN
CN
NC
H3CO
CN
CN
CN
NC
NC
OCH3
17
Chart 2.
(iv) accurate crystal structure determination of 18 and 19.
Because the crystal structure of 16 was determined by means
of X-ray diffraction, accurate structural parameters could not
be obtained because of difficulty in obtaining a stable single
crystal suitable for X-ray crystallographic analysis12 and
further, the crystal structure of 17 has not yet been achieved
for similar reasons; and (v) investigation of a plausible
reaction pathway for the formation of the resulting products
16–19. We now wish to report the detailed studies on the
above five points (i)–(v).
X-ray Crystal Structure of 1,1-Bis[4-(dimethylamino)phen-
yl]-2-(3-guaiazulenyl)ethylene (9). A total of 6527 reflections
with 2ꢄmax ¼ 55:0ꢁ were collected on a Rigaku AFC-5R automat-
ed four-circle diffractometer with graphite monochromated
Experimental
˚
Mo Kꢅ radiation (ꢁ ¼ 0:71069 A, rotating anode: 50 kV,
General. Thermal (TGA/DTA) and elemental analyses were
taken on a Shimadzu DTG-50H thermal analyzer and a Yanaco
MT-3 CHN coder. FAB-MS spectra were taken on a JEOL
The Tandem Mstation JMS-700 TKM data system. UV–vis and
IR 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) and JNM-ECA600 (600 MHz for 1H and 150
MHz for 13C) cryospectrometer at 25 ꢁC. The 1H NMR spectra
were assigned using computer-assisted simulation analysis (soft-
ware: gNMR developed by Adept Scientific plc) on a DELL
Dimension XPS T500 personal computer with a Pentium III
processor. Cyclic and differential pulse voltammograms (CV
and DPV) were measured by an ALS Model 600 electrochemical
analyzer.
Preparation of 1,1-Bis[4-(dimethylamino)phenyl]-2-(3-guai-
azulenyl)ethylene (9). To a solution of commercially available
guaiazulene (1) (50 mg, 253 mmol) in methanol (1.5 mL) was add-
ed a solution of 1,2-bis[4-(dimethylamino)phenyl]-1,2-ethanediol17
(8) (80 mg, 267 mmol) in methanol (1.5 mL) containing 36%
hydrochloric acid (0.2 mL). The mixture was stirred at 60 ꢁC for
3 h. After the reaction, distilled water was added to the mixture
and the resulting product was extracted with diethyl ether
(10 mL ꢂ 3). The extract was washed with distilled water, dried
(MgSO4), and evaporated in vacuo. The residue thus obtained
was carefully separated by silica gel column chromatography
(several times) with hexane–ethyl acetate–benzene (7:2:1, vol/
vol/vol) as an eluant. The crude product was recrystallized
from dichloromethane–hexane (1:5, vol/vol) to provide pure 9
180 mA) at 198 K. The structure was solved by direct methods
(SIR9218) and expanded using Fourier techniques (DIRDIF9419).
The 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.20
Crystallographic data have been deposited with the Cambridge
Crystallographic Data Center: Deposition number CCDC-
621672 for compound No. 9. 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 Center, 12,
Union Road, Cambridge, CB2 1EZ, UK; Fax: +44 1223
336033; e-mail: deposit@ccdc.cam.ac.uk).
Crystallographic data for 9: C33H38N2 (FW: 462.68), dark-
green prism (the crystal size, 0:50 ꢂ 0:30 ꢂ 0:50 mm3), triclinic,
ꢀ
˚
˚
˚
P1 (#2), a ¼ 10:589ð2Þ A, b ¼ 15:368ð2Þ A, c ¼ 8:768ð1Þ A, ꢅ ¼
95:78ð1Þꢁ, ꢆ ¼ 105:56ð1Þꢁ, ꢇ ¼ 79:47ð1Þꢁ, V ¼ 1349:5ð4Þ A ,
3
˚
Z ¼ 2, Dcalcd ¼ 1:139 g cmꢃ3, ꢈ(Mo Kꢅ) = 0.66 cmꢃ1
, scan
width: (1:21 þ 0:30 tan ꢄ)ꢁ, scan mode: !–2ꢄ, scan rate: 16.0ꢁ
minꢃ1, measured reflections: 6527, observed reflections: 5513,
No. of parameters: 316, R1 ¼ 0:057, wR2 ¼ 0:177, and goodness
of fit indicator: 1.92.
Preparation of (E)-2-[4-(Dimethylamino)phenyl]-1-(3-guai-
azulenyl)ethylene (13).
To a solution of 3-formylguaiazu-
lene21,22 (2) (50 mg, 221 mmol) in ethanol (2 mL) was added a
solution of [4-(dimethylamino)benzyl]triphenylphosphonium
bromide23–25 (12) (121 mg, 254 mmol) in ethanol (2 mL) contain-
ing sodium ethoxide (18 mg, 265 mmol). The mixture was stirred
at 25 ꢁC for 24 h under argon. After the reaction, distilled water

1474 Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008)
New Conjugated ꢀ-Electron Systems
15 as stable crystals (237 mg, 0.94 mmol, 79% yield).
was added to the mixture and the resulting product was extracted
with dichloromethane (20 mL ꢂ 3). The extract was washed with
distilled water, dried (MgSO4), and evaporated in vacuo. The res-
idue thus obtained was carefully separated by silica-gel column
chromatography with hexane–ethyl acetate (4:1, vol/vol) as an
eluant. The crude product was recrystallized from ethanol to pro-
vide pure 13 (9 mg, 26 mmol, 12% yield) as stable crystals.
Compound 13: Dark-green plates [Rf ¼ 0:60 on silica-gel TLC
(solv. hexane:ethyl acetate:benzene = 7:2:1, vol/vol/vol)]; mp
155 ꢁC [determined by thermal analysis (TGA and DTA)]; found:
C, 87.56; H, 8.56; N, 4.08%, calcd for C25H29N: C, 87.41; H,
8.51; N, 4.08%; UV–vis ꢁmax (CH3CN) nm (log "): 228 (4.39),
246 (4.33), 287 (4.41), 333 (4.59), 421 (4.61), and 654 (2.80);
IR ꢂmax (KBr) cmꢃ1: 2955–2800 (C–H), 2955, 949 (–HC=CH–),
1612, 1520 (C=C), and 1358 (C–N); exact FAB-MS (3-nitroben-
zyl alcohol matrix): found: m=z 343.2298; calcd for C25H29N: Mþ,
m=z 343.2300; 1H NMR (benzene-d6): signals based on the 3-
guaiazulenyl group: ꢃ 1.20 (6H, d, J ¼ 7:2 Hz, (CH3)2CH-70),
2.56 (3H, s, Me-10), 2.73 (1H, sept, J ¼ 7:2 Hz, (CH3)2CH-70),
2.88 (3H, s, Me-40), 6.56 (1H, d, J ¼ 10:6 Hz, H-50), 7.00 (1H,
dd, J ¼ 10:6, 2.0 Hz, H-60), 7.97 (1H, d, J ¼ 2:0 Hz, H-80), and
8.01 (1H, s, H-20); signals based on the 4-(dimethylamino)phenyl
group: ꢃ 2.56 (6H, s, (CH3)2N-400), 6.67 (2H, dd, J ¼ 8:5, 2.5 Hz,
H-300,500), and 7.57 (2H, dd, J ¼ 8:5, 2.5 Hz, H-200,600); and signals
based on the trans-HC=CH– part: ꢃ 7.15 (1H, d, J ¼ 16:0 Hz,
H-2) and 8.10 (1H, d, J ¼ 16:0 Hz, H-1); 13C NMR (benzene-
d6): ꢃ 149.9 (C-400), 146.2 (C-40), 141.2 (C-8a0), 140.1 (C-70),
136.7 (C-20), 134.6 (C-60), 133.4 (C-80), 132.7 (C-3a0), 128.4
(C-30,100), 128.0 (C-2), 127.4 (C-200,600), 126.9 (C-50), 126.1
(C-10), 123.0 (C-1), 113.2 (C-300,500), 40.2 ((CH3)2N-400), 37.9
((CH3)2CH-70), 28.4 (Me-40), 24.5 ((CH3)2CH-70), and 13.1
(Me-10).
Compound 15: Yellow blocks [Rf ¼ 0:15 on silica-gel TLC
(solve. hexane:ethyl acetate = 4:1, vol/vol)]; mp 114 ꢁC [deter-
mined by thermal analysis (TGA and DTA)]; found: C, 75.39;
H, 6.25; N, 5.52%, calcd for C16H15O2N: C, 75.87; H, 5.97; N,
5.53%; exact EI-MS, found: m=z 253.1096, calcd for C16H15O2N:
Mþ, 253.1143.
X-ray Crystal Structure of 1-[4-(Dimethylamino)phenyl]-2-
phenyl-1,2-ethanedione (15). A total of 3475 reflections with
2ꢄmax ¼ 55:0ꢁ were collected on a Rigaku AFC-5R automated
four-circle diffractometer with graphite monochromated Mo Kꢅ
˚
radiation (ꢁ ¼ 0:71069 A, rotating anode: 50 kV, 180 mA) at
296 K. The structure was solved by direct methods (SIR9726)
and expanded using Fourier techniques (DIRDIF9419). The 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.20
Deposition number CCDC-225122 for compound No. 15.
Crystallographic data for 15: C16H15O2N (FW: 253.30), yellow
prism (the crystal size, 0:80 ꢂ 0:60 ꢂ 0:20 mm3), monoclinic,
˚
˚
˚
P21=c (#14), a ¼ 13:010ð3Þ A, b ¼ 7:710ð4Þ A, c ¼ 14:234ð2Þ A,
ꢆ ¼ 109:14ð1Þ , V ¼ 1348:9ð7Þ A , Z ¼ 4, Dcalcd ¼ 1:247 g cmꢃ3
,
ꢁ
3
˚
ꢈ(Mo Kꢅ) = 0.82 cmꢃ1, scan width: (1:47 þ 0:30 tan ꢄ)ꢁ, scan
mode: !–2ꢄ, scan rate: 8.0ꢁ minꢃ1, measured reflections: 3475,
observed reflections: 1773, No. of parameters: 172, R1 ¼ 0:042,
wR2 ¼ 0:119, and goodness of fit indicator: 1.15.
Reaction of 1,1-Bis[4-(dimethylamino)phenyl]-2-(3-guaiazu-
lenyl)ethylene (9) with Tetracyanoethylene (TCNE). To a
solution of 1,1-bis[4-(dimethylamino)phenyl]-2-(3-guaiazulenyl)-
ethylene (9) (20 mg, 43 mmol) in benzene (1.5 mL) was added a
solution of TCNE (11 mg, 86 mmol) in benzene (1.5 mL) under ar-
gon, turning the dark-green solution into a black solution, rapidly.
The mixture was stirred at 25 ꢁC for 24 h under argon, gradually
giving a white precipitate of 18 and then was centrifuged at
2.5 krpm for 1 min. The crude product thus obtained was carefully
washed with benzene and hexane, and was recrystallized from
ethyl acetate–hexane (1:5, vol/vol) to provide pure 18 (23 mg,
32 mmol, 74% yield) as stable crystals.
X-ray Crystal Structure of (E)-2-[4-(Dimethylamino)phen-
yl]-1-(3-guaiazulenyl)ethylene (13). A total of 5125 reflections
with 2ꢄmax ¼ 55:0ꢁ were collected on a Rigaku AFC-5R automat-
ed four-circle diffractometer with graphite monochromated
˚
Mo Kꢅ radiation (ꢁ ¼ 0:71069 A, rotating anode: 50 kV, 180
mA) at 198 K. The structure was solved by direct methods
(SIR9218) and expanded using Fourier techniques (DIRDIF9419).
The 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.20
Deposition number CCDC-621951 for compound No. 13.
Compound 18: Pale-green plates; mp 147 ꢁC [determined by
thermal analysis (TGA and DTA)]; UV–vis ꢁmax (ethyl acetate)
nm (log "): 270 (4.64), 284 (4.63), and 390 (4.11); IR ꢂmax
(KBr) cmꢃ1: 2253 and 2249 (CꢄN); exact FAB-MS (3-nitro-
benzyl alcohol matrix): found: m=z 719.3324; calcd for C45H39-
N10: ½M þ Hꢅþ, m=z 719.3359. The relative intensity of the
1H NMR signals for the diastereomers 18a and 18b showed a
ration of ca. 7:5.
Crystallographic data for 13: C25H29N (FW: 343.51),
dark-green prism (the crystal size, 0:50 ꢂ 0:30 ꢂ 0:50 mm3),
˚
˚
monoclinic, P21=n (#14), a ¼ 14:545ð8Þ A, b ¼ 9:325ð7Þ A, c ¼
ꢁ
3
1
˚
˚
16:495ð8Þ A, ꢆ ¼ 114:79ð4Þ , V ¼ 2031ð2Þ A , Z ¼ 4, Dcalcd
¼
Compound 18a: H NMR (THF-d8): ꢃ 1.14, 1.15 (3H each, d,
1:123 g cmꢃ3, ꢈ(Mo Kꢅ) = 0.64 cmꢃ1
,
scan width: (1:21 þ
J ¼ 6:7 Hz, (CH3)2CH-8), 2.41 (3H, br s, Me-10), 2.43 (3H, br
s, Me-5), 2.61 (1H, sept d, J ¼ 6:7, 0.8 Hz, (CH3)2CH-8), 4.11
(1H, d, J ¼ 7:9 Hz, H-6), 4.51 (1H, br q, H-10a), 4.68 (1H, d,
J ¼ 1:3 Hz, H-9), 6.42 (1H, ddd, J ¼ 7:9, 1.3, 0.8 Hz, H-7), and
6.726, 6.729 (0.5H, br s, H-4); and signals based on the two 4-(di-
methylamino)phenyl groups: ꢃ 2.90, 2.97 (6H each, s, (CH3)2N-
40,400), 6.57, 6.77 (2H each, dd, J ¼ 8:5, 2.5 Hz, H-20,60,200,600),
and 7.27, 7.47 (2H each, dd, J ¼ 8:5, 2.5 Hz, H-30,50,300,500).
0:30 tan ꢄ)ꢁ, scan mode: !–2ꢄ, scan rate: 16.0ꢁ minꢃ1, measured
reflections: 5125, observed reflections: 3928, No. of parameters:
235, R1 ¼ 0:073, wR2 ¼ 0:216, and goodness of fit indicator:
1.95.
Preparation of 1-[4-(Dimethylamino)phenyl]-2-phenyl-1,2-
ethanedione (15). To a solid of copper sulfate (505 mg, 3.17
mmol) was added a solution of commercially available 4-(di-
methylamino)benzoin (14) (304 mg, 1.19 mmol) in a mixed sol-
vent of pyridine (2 mL) and distilled water (2 mL). The mixture
was refluxed for 5 h and cooled, precipitating a yellow solid,
and was then centrifuged at 2.5 krpm for 1 min. The crude product
thus obtained was washed with distilled water and hexane, and
was recrystallized from ethanol (several times) to provide pure
1
Compound 18b: H NMR (THF-d8): ꢃ 1.18, 1.23 (3H each, d,
J ¼ 6:8 Hz, (CH3)2CH-8), 2.36 (3H, br s, Me-10), 2.42 (3H, br
s, Me-5), 2.56 (1H, sept d, J ¼ 6:8, 0.7 Hz, (CH3)2CH-8), 4.13
(1H, d, J ¼ 8:0 Hz, H-6), 4.26 (1H, br q, H-10a), 4.74 (1H, d,
J ¼ 1:4 Hz, H-9), 6.37 (1H, ddd, J ¼ 8:0, 1.4, 0.7 Hz, H-7), and
6.893, 6.897 (0.5H, br s, H-4); and signals based on the two 4-(di-

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008) 1475
N
4'
1'''
HO
OH
7'''
1'
3'''
1
1
2
4'''
in CH3OH
1''
H
in the presence of HCl
N
N
4''
at 60 °C for 3 h
N
8
9
Figure 1. The reaction of 1 with 8 in methanol in the presence of hydrochloric acid at 60 ꢁC for 3 h.
ꢁ
˚
˚
˚
methylamino)phenyl groups: ꢃ 2.87, 2.97 (6H each, s, (CH3)2N-
40,400), 6.51, 6.78 (2H each, dd, J ¼ 8:5, 2.5 Hz, H-20,60,200,600),
and 7.32, 7.62 (2H each, dd, J ¼ 8:5, 2.5 Hz, H-30,50,300,500).
Reaction of (E)-2-[4-(Dimethylamino)phenyl]-1-(3-guai-
azulenyl)ethylene (13) with Tetracyanoethylene (TCNE). To
a solution of (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazule-
nyl)ethylene (13) (10 mg, 29 mmol) in benzene (1.5 mL) was
added a solution of TCNE (8 mg, 63 mmol) in benzene (1.5 mL)
under argon, turning the dark-green solution into a black solution,
rapidly. The mixture was stirred at 25 ꢁC for 24 h under argon,
gradually giving a white precipitate of 19 and then was centri-
fuged at 2.5 krpm for 1 min. The crude product thus obtained
was carefully washed with benzene and hexane, and was recrystal-
lized from ethyl acetate–hexane (1:5, vol/vol) to provide pure 19
(7 mg, 12 mmol, 41% yield) as stable crystals.
12:865ð8Þ A, b ¼ 23:45ð1Þ A, c ¼ 13:219ð9Þ A, ꢆ ¼ 105:67ð5Þ ,
V ¼ 3839ð3Þ A , Z ¼ 4, Dcalcd ¼ 1:190 g cmꢃ3, ꢈ(Mo Kꢅ) =
3
˚
0.77 cmꢃ1, scan width: (1:37 þ 0:30 tan ꢄ)ꢁ, scan mode: !–2ꢄ,
scan rate: 16.0ꢁ minꢃ1, measured reflections: 9431, observed
reflections: 6778, No. of parameters: 469, R1 ¼ 0:055, wR2 ¼
0:163, and goodness of fit indicator: 1.22.
Results and Discussion
Preparation and Spectroscopic Properties of 9 Com-
pared with Those of 4. In 2004 we reported that the reaction
of 1 with 1,2-bis(4-methoxyphenyl)-1,2-ethanediol in metha-
nol in the presence of hydrochloric acid at 60 ꢁC for 3 h gave
4, in 97% yield, via pinacol rearrangement. The reaction of
1 with 1-[4-(dimethylamino)phenyl]-2-phenyl-1,2-ethanediol
under the same reaction conditions as the above however af-
forded numerous products and an only compound 6, without
pinacol rearrangement, could be isolated in 17% yield. A
plausible reaction pathway for the formation of 4 and 6 was
submitted.8 For comparative purposes, the reaction of 1 with
8 under the same reaction conditions as the above was carried
out as shown in Figure 1, yielding a new 4 analogue 9 in 81%
yield, via pinacol rearrangement. Therefore, an apparent dif-
ference between the reactions of 1 with 1-[4-(dimethylamino)-
phenyl]-2-phenyl-1,2-ethanediol and 1,2-bis[4-(dimethyl-
amino)phenyl]-1,2-ethanediol (8) was observed. The molecu-
lar structure of 9 was established on the basis of elemental
analysis and spectroscopic data [UV–vis, IR, exact FAB-MS,
and 1H and 13C NMR including NOE and 2D NMR (i.e., H–H
COSY, HMQC, and HMBC)].
Compound 9 was obtained as dark-green plates. The spec-
troscopic properties of 9 compared with those of 4, possessing
a similar framework, are described as follows (Tables 1–3).
The UV–vis spectrum of 9 resembled that of 4, while the long-
est absorption wavelength of 9 revealed a slight bathochromic
shift (ꢁ 12 nm) and a slight hyperchromic effect (ꢁ log " ¼
0:15). These visible data corresponded to the ꢁ ꢀ-HOMO ꢃ
ꢀ-LUMO/eV levels27,28 of 4 and 9 (Table 1). The IR spectrum
showed specific bands resulting from the C–N, aromatic C=C,
and C–H bonds. The molecular formula C33H38N2 was deter-
mined by exact FAB-MS. Elemental analysis confirmed the
Compound 19: Colorless plates [Rf ¼ 0:34 on silica-gel
TLC (solv. hexane:ethyl acetate = 7:3, vol/vol)]; mp >135 ꢁC
[decomp., determined by thermal analysis (TGA and DTA)];
UV–vis ꢁmax (ethyl acetate) nm (log "): 276 (4.47); IR ꢂmax
(KBr) cmꢃ1: 2253 and 2249 (CꢄN); exact FAB-MS (3-nitroben-
zyl alcohol matrix): found: m=z 600.2614; calcd for C37H30N9:
½M þ Hꢅþ, m=z 600.2625; 1H NMR (THF-d8): ꢃ 1.164, 1.168
(3H each, d, J ¼ 7:0 Hz, (CH3)2CH-8), 2.29 (3H, br s, Me-5),
2.43 (3H, br s, Me-10), 2.62 (1H, sept d, J ¼ 7:0, 1.0 Hz,
(CH3)2CH-8), 4.10 (1H, d, J ¼ 7:9 Hz, H-6), 4.44 (1H, br q,
H-10a), 4.69 (1H, d, J ¼ 1:4 Hz, H-9), 4.891, 4.897 (0.5H each,
br d, J ¼ 2:6 Hz, H-3), 6.434 (1H, ddd, J ¼ 7:9, 1.4, 1.0 Hz,
H-7), and 7.066, 7.071 (0.5H each, br d, J ¼ 2:6 Hz, H-4); and
signals based on the 4-(dimethylamino)phenyl group: ꢃ 2.97
(6H, s, (CH3)2N-40), 6.73 (2H, dd, J ¼ 8:5, 2.5 Hz, H-20,60), and
7.27 (2H, dd, J ¼ 8:5, 2.5 Hz, H-30,50).
X-ray Crystal Structure of 1,1,2,2,11,11,12,12-Octacyano-3-
[4-(dimethylamino)phenyl]-8-isopropyl-5,10-dimethyl-1,2,3,6,-
9,10a-hexahydro-6,9-ethanobenz[a]azulene (19).
A total of
9431 reflections with 2ꢄmax ¼ 55:0ꢁ were collected on a Rigaku
AFC-5R automated four-circle diffractometer with graphite
˚
monochromated Mo Kꢅ radiation (ꢁ ¼ 0:71069 A, rotating
anode: 50 kV, 180 mA) at 198 K. The structure was solved by di-
rect methods (SIR9218) and expanded using Fourier techniques
(DIRDIF9419). The 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 teXsan crystallographic
software package.20 Deposition number CCDC-622803 for com-
pound No. 19.
1
molecular formula C33H38N2. The H NMR spectrum showed
signals consistent with a 3-guaiazulenyl group, signals consis-
tent with two non-equivalent 4-(dimethylamino)phenyl groups,
and a signal based on an ethylene group (>C=CH–), the
signals of which were carefully assigned using NOE and
H–H COSY techniques and computer-assisted simulation
Crystallographic data for 19: C41H37O2N9 (C37H29N9 +
CH3COOC2H5, FW: 687.80), colorless prism (the crystal size,
0:30 ꢂ 0:20 ꢂ 0:50 mm3), monoclinic, P21=a (#14), a ¼

1476 Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008)
New Conjugated ꢀ-Electron Systems
Table 1. Comparative Studies on the Longest Wavelength Absorption Maxima, the Energy Levels,27,28 and the Redox Potentialsa) of 4,
5, 9, and 13
Compound
ꢁ
max/nm (log ")
ꢀ-HOMO/eV
ꢀ-LUMO/eV
ꢁ ꢀ-HOMO ꢃ ꢀ-LUMO/eV
E1ox/V
E1red/V
4
5
9
13
635 (2.54)
661 (3.13)
647 (2.69)
654 (2.80)
ꢃ7:714
ꢃ7:372
ꢃ7:417
ꢃ7:464
ꢃ1:155
ꢃ1:090
ꢃ0:916
ꢃ1:032
ꢃ6:559
ꢃ6:282
ꢃ6:501
ꢃ6:432
0.52
0.20
0.32
0.33
ꢃ1:73
ꢃ1:71
ꢃ1:75
ꢃ1:68
a) CV data.
Table 2. Comparative Studies on Selected 1H NMR Spectra
(ꢃ, ppm) of the 3-Guaiazulenyla) and Vinyl Groups of 4, 5,
9, and 13
Table 3. Comparative Studies on Selected 13C NMR Spec-
tra (ꢃ, ppm) of the 3-Guaiazulenyla) and Vinyl Groups
of 4, 5, 9, and 13
Azulenyl group
Vinyl group
C=CH–Gu3
Azulenyl group
C-5 C-6
Vinyl group
C=CH–Gu3
Compound
Compound
H-2
H-5
H-6
H-8
C-2
C-8
4
5
9
13
7.44
8.14
7.60
8.01
6.63
6.56
6.59
6.56
7.02
6.99
7.00
7.00
7.91
7.97
7.88
7.97
7.77
8.12
7.81
8.10
4
5
9
13
140.4 126.5 134.6 133.2
136.1 126.8 134.6 133.2
140.8 126.0 134.3 132.8
136.7 126.9 134.6 133.4
125.6
125.2
125.4
123.0
a) Gu3: 3-guaiazulenyl group.
a) Gu3: 3-guaiazulenyl group.
CHO
1'
7'
3'
H
2
2
1
P
+
Z form
4'
N
+
1''
H
NaOEt/EtOH
in ethanol at 25 °C
−
Br
4''
for 24 h
under argon
N
12
13
Figure 2. The Wittig reaction of 2 with 12 in ethanol in the presence of sodium ethoxide at 25 ꢁC for 24 h under argon.
based on first-order analysis. Although the H-2000 proton signal
of 9 showed an apparent down-field shift as a result of steric
hindrance and repulsion between the H-2000 hydrogen atom
and the (Z)-4-(dimethylamino)phenyl group along with influ-
ence from the ring current of the (Z)-4-(dimethylamino)phenyl
group, the signals (H-5000, H-6000, H-8000, and >C=CH–) of 9
coincided with those of 4 (Table 2). The 13C NMR spectrum
exhibited 26 carbon signals assigned by HMQC and HMBC
techniques. The carbon signals (C-2000, C-5000, C-6000, C-8000,
and >C=CH–) of 9 coincided with those of 4 (Table 3). Thus,
the spectroscopic data for 9 led to the molecular structure
1,1-bis[4-(dimethylamino)phenyl]-2-(3-guaiazulenyl)ethylene.
Comparing the chemical shifts for the proton and carbon
signals and the UV–vis spectrum of 9 to those of 4 and 1,29
it can be inferred that the azulene ring of 9 twists from the
plane of the >C=CH– structure as a result of steric hindrance
and repulsion between the 3-guaiazulenyl and (Z)-4-(dimethyl-
amino)phenyl groups. A similar reaction pathway to that of 48
can be inferred for the formation of 9.
amino)phenyl]-substituted compound 9. For comparative pur-
poses, the (E)-4-(dimethylamino)phenyl-substituted compound
13 was prepared in 12% yield, using the Wittig reaction as
shown in Figure 2. The molecular structure was established
on the basis of analysis similar to that of 9. Although the
presumed Z isomer30 of 13 was observed by silica gel TLC
of the reaction mixture, it could not be isolated using silica
gel column chromatography and recrystallization.
Compound 13 was obtained as dark-green plates. The spec-
troscopic properties of 13, compared with those of 9 and 5,8
are as follows (Tables 1–3). The UV–vis spectrum of 13 re-
sembled those of 9 and 5, while the longest absorption wave-
length revealed a slight bathochromic shift (ꢁ 7 nm) and a
slight hyperchromic effect (ꢁ log " ¼ 0:11) in comparison
with that of 9, and revealed a slight hypsochromic shift
(ꢁ 7 nm) and a hypochromic effect (ꢁ log " ¼ 0:33) in com-
parison with that of 5. These visible data correspond to the
ꢁ ꢀ-HOMO ꢃ ꢀ-LUMO/eV levels27,28 of 5, 9, and 13
(Table 1). The IR spectrum showed specific bands from the
C–N, aromatic C=C, and C–H bonds, whose wavenumbers
coincided with those of 9, and the –HC=CH– bonds,
whose wavenumbers coincided with those of 5. The molecular
formula C25H29N was determined by exact FAB-MS. Elemen-
Preparation and Spectroscopic Properties of 13 Com-
pared with Those of 9 and 5. We reported preparation
and spectroscopic properties of the (Z)-4-(dimethylamino)-
phenyl-substituted compound 68 and the 1,1-bis[4-(dimethyl-

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008) 1477
Figure 3. The ORTEP drawings with the numbering scheme (30% probability thermal ellipsoids) of 9 and 6.
˚
˚
Table 4. Selected C–C Bond Lengths (A) for the 3-Guaia-
Table 5. Selected C–C and C–N Bond Lengths (A) for the
zulenylethylene Moieties of 4–6, 9, and 13a)
4-(Dimethylamino)phenyl Groups of 6, 9, 13, and 15a)
Atom
4
5
6
9
13
Atom
6
9
13
15
C1–C2
1.343(4) 1.32(1)
1.347(4) 1.348(3) 1.328(4)
C1–C10 1.463(4) 1.495(3)b) 1.487(3)c) 1.458(4) 1.448(4)
C10–C20 1.395(4) 1.391(3)b) 1.401(3)c) 1.391(4) 1.394(3)
C20–C30 1.372(4) 1.390(3)b) 1.376(3)c) 1.379(5) 1.366(4)
C30–C40 1.389(4) 1.400(3)b) 1.406(3)c) 1.382(5) 1.410(3)
C40–C50 1.394(4) 1.409(3)b) 1.396(3)c) 1.408(5) 1.411(3)
C50–C60 1.364(4) 1.386(3)b) 1.385(3)c) 1.371(5) 1.368(4)
C60–C10 1.392(4) 1.385(3)b) 1.403(3)c) 1.389(5) 1.399(3)
C2–C30
C10–C20
C20–C30
1.464(4) 1.444(8) 1.489(4) 1.468(3) 1.457(4)
1.382(5) 1.378(8) 1.373(4) 1.370(3) 1.374(4)
1.407(5) 1.452(8) 1.420(4) 1.420(3) 1.418(4)
C30–C3a0 1.416(5) 1.391(7) 1.404(4) 1.413(3) 1.408(4)
C3a0–C40 1.393(4) 1.404(8) 1.410(4) 1.409(3) 1.412(4)
C40–C50
C50–C60
C60–C70
C70–C80
C80–C8a0 1.382(4) 1.351(8) 1.394(4) 1.376(3) 1.379(4)
C8a0–C10 1.413(5) 1.388(8) 1.397(4) 1.423(3) 1.421(4)
C3a0–C8a0 1.515(4) 1.533(8) 1.502(4) 1.503(3) 1.503(4)
1.390(5) 1.369(9) 1.382(4) 1.393(3) 1.381(5)
1.388(5) 1.40(1) 1.399(4) 1.402(3) 1.403(5)
1.383(4) 1.362(10) 1.386(5) 1.381(3) 1.372(5)
1.384(5) 1.397(9) 1.384(4) 1.408(3) 1.398(4)
C40–N0
1.382(3) 1.384(3)b) 1.378(3)c) 1.375(4) 1.360(3)
a) For comparative purposes, the numbering schemes for the
4-(dimethylamino)phenyl groups of 6 and 13 (see Figure 3
and Figure 4) were changed as shown in Table 5. b) 40-(Di-
methylamino)phenyl group. c) 400-(Dimethylamino)phenyl
group (see Figure 3).
a) For comparative purposes, the numbering schemes
for the 3-guaiazulenylethylene moieties of 4–6, 9, and 13
(see Figure 3 and Figure 4) were changed as shown in
Table 4.
60, and C-80) of 13 coincided with those of 5 (Table 3). From
the spectroscopic data for 13 the molecular structure (E)-2-[4-
(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene was de-
duced.
tal analysis confirmed the molecular formula C25H29N. The
1H NMR spectrum showed signals from 3-guaiazulenyl and
4-(dimethylamino)phenyl groups and signals from a trans-
HC=CH– moiety, the signals of which were carefully assigned
using similar techniques to those used for 9. Although the pro-
ton signals [H-20 and –HC=CH–Gu3 (Gu3: 3-guaiazulenyl)]
of 13 showed apparent down-field shift in comparison with
the signals (H-2000 and >C=CH–Gu3) of 9, the signals (H-50,
H-60, and H-80) of 13 coincided with the signals (H-5000,
H-6000, and H-8000) of 9, and although the H-20 signal of 13
showed an apparent up-field shift in comparison with that
of 5, the signals (H-50, H-60, H-80, and –HC=CH–Gu3) of 13
coincided with those of 5 (Table 2). The 13C NMR spectrum
exhibited 20 carbon signals assigned using similar techniques
to those used for 9. Although the carbon signals (C-20 and
–HC=CH–Gu3) of 13 showed apparent up-field shifts in
comparison to the signals (C-2000 and >C=CH–) of 9, the
signals (C-50, C-60, and C-80) of 13 coincided with the signals
(C-5000, C-6000, and C-8000) of 9. The –HC=CH–Gu3 signal of 13
showed an apparent up-field shift in comparison with the
–HC=CH– signal of 5, however the signals (C-20, C-50, C-
X-ray Crystal Structure of 9 Compared with Those of 4
and 6. The recrystallization of 9 from a mixed solvent of
dichloromethane and hexane (1:5, vol/vol) provided stable
single crystals suitable for X-ray crystallographic analysis.
The crystal structure of 9 was then determined by means of
X-ray diffraction, producing accurate structural parameters.
The ORTEP drawing of 9 with a numbering scheme is shown
in Figure 3a along with selected bond lengths (Tables 4 and
5). The structural parameters of 9 revealed that the C–C bond
length between the >C=CH– group of 9 coincided with
those of 48 and 68 and the C1–C10, C1–C100, and C2–C3000 bond
lengths of 9 coincided with those of 4. Similar to 4 and 6
(Figure 3b), the aromatic rings of the two 40- and 400-(di-
methylamino)phenyl and 3000-guaiazulenyl groups of 9 twisted
by 49, 30, and 66ꢁ from the >C=CH– plane as a result of large
steric hindrance and repulsion between the rings. The average
C–C bond lengths for the seven- and five-membered rings of
˚
the 3-guaiazulenyl group (1.410 and 1.426 A) coincided with
˚
˚
those of 4 (1.405 and 1.427 A) and 6 (1.409 and 1.420 A).
Thus, the crystal structure of 9 supported the molecular struc-
ture established on the basis of spectroscopic data.

1478 Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008)
New Conjugated ꢀ-Electron Systems
Figure 4. The ORTEP drawings with the numbering scheme (30% probability thermal ellipsoids) of 13 and 5.
O
O
O
O
N
N
Figure 5. The ORTEP drawing with the numbering
scheme (30% probability thermal ellipsoids) of 15. The
15
15'
Chart 3.
˚
bond lengths (A) of 15 are as follows: C1–C2; 1.526(4),
C1–O1; 1.231(3), C1–C10; 1.448(4), C10–C20; 1.394(3),
C20–C30; 1.366(4), C30–C40; 1.410(3), C40–C50;
1.411(3), C50–C60; 1.368(4), C60–C10; 1.399(3), C40–N;
1.360(3), N–C70; 1.437(4), N–C80; 1.444(3), C2–O2;
1.218(3), C2–C100; 1.473(4), C100–C200; 1.379(3), C200–
C300; 1.372(4), C300–C400; 1.371(5), C400–C500; 1.372(5),
C500–C600; 1.383(4), and C600–C100; 1.385(4).
X-ray Crystal Structure of 13 Compared with Those of
5 and 9. Recrystallization of 13 from ethanol provided stable
single crystals suitable for X-ray crystallographic analysis. The
ORTEP drawing of 13 is shown in Figure 4a along with select-
ed bond lengths (Tables 4 and 5). The structural parameters of
13 revealed that the C–C bond length of the trans-HC=CH–
moiety of 13 coincided with that of 5,8 however the bond
length was shorter than the >C=CH– of 9. Although the
C1–C30 and C2–C100 bond lengths of 13 were longer than
the C1–C30 bond length of 5, they were shorter than the C2–
C3000 and C1–C100 bond lengths of 9. The crystal structure of
5 was planar (Figure 4b), however the aromatic rings of the
400-(dimethylamino)phenyl and 30-guaiazulenyl groups twisted
by 1 and 23ꢁ from the plane of the trans-HC=CH– group, pre-
sumably due to the influence of inter-molecular stacking, and
the average C–C bond lengths for the seven- and five-mem-
bered rings of the 3-guaiazulenyl group of 13 (1.407 and
with that of 15, probably possessing contribution of intra-mo-
lecular charge-separated structure 150 with a quinoid structure
(Chart 3), are noteworthy. Recrystallization of 15 from ethanol
was carried out, providing stable single crystals suitable for
X-ray crystallographic analysis. The crystal structure of 15
was determined by means of X-ray diffraction, producing
accurate structural parameters, the results of which enabled
comparison with those of 6, 9, and 13 (Table 5). An ORTEP
drawing of 15 is shown in Figure 5 together with selected bond
lengths. The structural parameters of 15 reveal that the plane
of the 4-(dimethylamino)phenyl ketone is twisted by 104ꢁ
from that of the phenyl ketone, owing to the influence of
non-bonded lone pair–lone pair repulsions in the ꢅ-diketones31
and that the bond lengths and their alternation pattern observed
for the 4-(dimethylamino)phenyl ketone, compared with those
observed for the phenyl ketone, indicate an apparent contribu-
tion of 150. It was found that the bond lengths observed for
the 4-(dimethylamino)phenyl groups of 6, 9, and 13 did not
completely coincide with those of 15, while their bond alterna-
tion pattern did, suggesting a small contribution of the quinoid
form.
˚
˚
1.425 A) coincided with those of 5 (1.403 and 1.429 A) and
9. As with 9, the crystal structure of 13 supported the molecu-
lar structure established on the basis of spectroscopic data.
X-ray Crystal Structure of 15 Compared with Those of
6, 9, and 13. In 2003 we reported the unique crystal structure
of [4-(dimethylamino)phenyl]-3-guaiazulenylmethylium tetra-
fluoroborate with two representative resonance forms of the
3-guaiazulenylium and quinoid structures.5 In relation to this
study, our interest has been focused on the crystal structures
of 6, 9, and 13, with resonance forms of similar quinoid struc-
tures to the above, due to the influence of a dipole between the
4-(dimethylamino)phenylethylene group, which serves as a
strong electron donor,8 and the 3-guaiazulenyl group, which
serves as both an electron acceptor and a strong electron do-
nor.8 Studies of the crystal structures of 6, 9, and 13, compared
Electrochemical Properties of 9 and 13 Compared with
Those of 6 and 5. The electrochemical properties of 9 were
measured by means of CV and DPV [Potential (in volts) vs.
SCE] in CH3CN containing 0.1 M [n-Bu4N]BF4 as a support-

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008) 1479
Figure 6. Cyclic (a) and differential pulse (b) voltammo-
grams of 9 (3.0 mg, 6.5 mmol) in 0.1 M [n-Bu4N]BF4,
CH3CN (10 mL) at a glassy carbon (ID: 3 mm) and a plat-
inum wire served as the working and auxiliary electrodes;
scan rates 100 mV sꢃ1 at 25 ꢁC under argon. For compara-
tive purposes, the oxidation potential using ferrocene as a
standard material showed +0.45 (Ep) V by DPV and
+0.42 (E1=2) V by CV under the same electrochemical
measurement conditions as for 9.
Figure 7. Cyclic (a) and differential pulse (b) voltammo-
grams of 6 (3.0 mg, 7.1 mmol) under the same electro-
chemical measurement conditions as for 9.
of 9b is oxidized to the cation-radical at a potential of +1.13 V
by CV (+1.16 V by DPV), generating an electrochemically
stable trication-radical 9c. Along with the oxidation potentials,
9 is reduced to the anion-radical 9d at a potential of ꢃ1:75 V
by CV (ꢃ1:71 V by DPV).
For comparative purposes, the electrochemical properties of
13 were measured under the same conditions as for 9. Three
redox potentials observed by DPV were positioned at the Ep
values of +0.49, +0.34, and ꢃ1:67 V, and the corresponding
three reversible redox potentials determined by CV were locat-
ed at the values of +0.46, +0.33, and ꢃ1:68 V (E1=2 each) as
shown in Figure 8. It was found that 13 was slightly more sus-
ceptible to reduction than 9, whose potentials corresponded to
the ꢀ-LUMO/eV levels27,28 of 13 and 9 (Table 1). The reduc-
tion potential of 13 coincided with the first reduction potential
(E1red) of the E form 5 (Figure 9)8 and as in the case of 5, 13
underwent stepwise two-electron oxidation. From the differ-
ence between the two-electron oxidation potential patterns of
the Z form 6 and the E form 13, a plausible electron-transfer
mechanism for 9 via 9a, 9a0, and 9b, illustrated in Scheme 1,
is suggested. Although 13 was more susceptible to oxidation
than 4, 13 was less susceptible to oxidation than 5 (Figure 9)8
and 9, the potentials of which corresponded to the ꢀ-HOMO/
eV levels27,28 of 4, 5, 9, and 13 (Table 1). Thus, a plausible
electron-transfer mechanism of 13 based on CV and DPV data
can be inferred as illustrated in Scheme 2. Namely, 13 under-
goes stepwise two-electron oxidation at +0.33 and +0.46 V by
CV (+0.34 and +0.49 V by DPV), generating an electro-
chemically stable dication 13b via the cation-radical 13a.
Along with the oxidation potentials, 13 is reduced to anion-
ing electrolyte. Three redox potentials observed by DPV were
positioned at +1.16, +0.33, and ꢃ1:71 V, and the correspond-
ing three reversible redox potentials determined by CV were
+1.13, +0.32, and ꢃ1:75 V (E1=2 each) as shown in Figure 6.
It was found that the reduction potential of 9 coincided with
that of 6 and that as with 6, underwent two-electron oxidation,
however 9 was more susceptible to two-electron oxidation than
6 (Figure 7)8 and the generated dication further underwent
one-electron oxidation. On the other hand, in 1996 Nozoe
et al. reported that 3,30-biguaiazulene underwent stepwise
ox
two-electron oxidation at +0.40 V (E1ox) and +0.54 V (E2
)
by CV, generating a dication species via a cation-radical.32
In relation to this study, in 2002 Ito et al. reported that 1,10-bi-
azulene underwent stepwise two-electron oxidation and reduc-
tion at +0.30 V (E1ox), +0.62 V (E2ox), ꢃ1:88 V (E1red), and
ꢃ2:16 V (E2red) by CV, generating a dication species via a cat-
ion-radical and a dianion via an anion-radical.33 Thus, a plau-
sible electron-transfer mechanism of 9 based on its CV and
DPV data can be inferred as illustrated in Scheme 1. Namely,
9 undergoes two-electron oxidation at +0.32 V by CV
(+0.33 V by DPV), generating an electrochemically stable di-
cation 9b, occurring between the (Z)-4-(dimethylamino)phenyl
and 3-guaiazulenyl groups via cation-radical 9a and resonance
form 9a0, and further, the (E)-4-(dimethylamino)phenyl group

1480 Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008)
New Conjugated ꢀ-Electron Systems
N
N
N
N
+0.32 V (E1/2
)
−
−e
−
+e
H
H
H
N
N
9
9a
9a'
−1.75 V (E1/2
+e
)
+0.32 V (E1/2
−e
)
−
−
−
−
−e
+e
N
N
N
N
N
N
+1.13 V (E1/2
)
−
+e
−
−e
H
H
H
9d
9c
9b
Scheme 1. A plausible electron-transfer mechanism based on the CV and DPV data of 9.
Figure 8. Cyclic (a) and differential pulse (b) voltammo-
grams of 13 (3.0 mg, 8.7 mmol) under the same electro-
chemical measurement conditions as for 9.
Figure 9. Cyclic (a) and differential pulse (b) voltammo-
grams of 5 (3.0 mg, 7.1 mmol) under the same electro-
chemical measurement conditions as for 9.

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008) 1481
NC
NC
R1
CN
CN
TCNE
CN
CN
R1
R2
NC
NC
in benzene
R2
at 25 °C for 24 h
under argon
H
18: R1 = R2 = 4-(CH3)2NC6H4−
19: R1 = H, R2 = 4-(CH3)2NC6H4−
9: R1 = R2 = 4-(CH3)2NC6H4−
13: R1 = H, R2 = 4-(CH3)2NC6H4−
Figure 10. The reaction of 9 (or 13) with 2 equiv of TCNE in benzene at 25 ꢁC for 24 h under argon.
Figure 11. The molecular structure of 19 and its ORTEP drawing with the numbering scheme (30% probability thermal ellipsoids).
and the longest visible absorption wavelength appeared at
ꢁmax 390 nm (log " ¼ 4:11). The IR spectrum showed two
+0.33 V (E1/2
)
−
−e
specific bands corresponding to the –CꢄN group, whose wave-
numbers coincided with those of 1612 and 17.12 The protonated
molecular formula C45H39N10 was determined by exact
FAB-MS. The 1H NMR spectrum showed signals consistent
with 8-isopropyl-5,10-dimethyl-1,2,3,6,9,10a-hexahydrobenz-
[a]azulene possessing two 4-(dimethylamino)phenyl groups
at the C-3 position, the signals of which were carefully as-
signed using conventional methodology. Careful study of the
1H NMR signals suggested a ca. 7:5, mixture of chromato-
graphically inseparable diastereomers. Comparative studies
of detailed spectroscopic data indicated a similar structure to
that of 17, 1,1,2,2,11,11,12,12-octacyano-3,3-bis[4-(dimethyl-
amino)phenyl]-8-isopropyl-5,10-dimethyl-1,2,3,6,9,10a-hexa-
hydro-6,9-ethanobenz[a]azulene.
H
H
−
+e
H
H
N
N
13a
13
−1.68 V (E1/2
+e
)
+0.46 V (E1/2
)
−
−
−
−
−e
−e
+e
H
H
H
H
Reaction of 13 with TCNE. For comparative purposes,
the reaction of 13 with TCNE was carried out under the same
reaction conditions as for 512 (Figure 10), affording a new 16
analogue 19 in 41% yield, the molecular structure of which
was established on the basis of spectroscopic analyses.
Compound 19 was obtained as colorless plates. The charac-
teristic UV–vis absorption bands of 13 were not observed and
the longest UV absorption wavelength appeared at ꢁmax
276 nm (log " ¼ 4:47). The IR spectrum showed two specific
bands from the –CꢄN group, whose wavenumbers coincided
with those of 16–18. The protonated molecular formula
C37H30N9 was determined by exact FAB-MS. The 1H NMR
spectrum showed signals consistent with 8-isopropyl-5,10-di-
methyl-1,2,3,6,9,10a-hexahydrobenz[a]azulene possessing a
4-(dimethylamino)phenyl group at the C-3 position, whose sig-
nals were carefully assigned using conventional methodology.
Comparative studies of detailed spectroscopic data suggested a
N
N
13c
13b
Scheme 2. A plausible electron-transfer mechanism based
on the CV and DPV data of 13.
radical 13c at a potential of ꢃ1:68 V by CV (ꢃ1:67 V by
DPV). In conclusion, the redox potentials of 9 and 13 indicate
that both of them serve as strong two-electron donors and
one-electron acceptors.
Reaction of 9 with TCNE. For comparative purposes,
the reaction of 9 with TCNE was carried out under the same
reaction conditions as for 412 (Figure 10), giving a new 17
analogue 18 in 74% yield, whose molecular structure was
established on the basis of spectroscopic analyses.
Compound 18 was obtained as pale-green plates. The
characteristic UV–vis absorption bands of 9 were not observed

1482 Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008)
New Conjugated ꢀ-Electron Systems
R1
R2
R1
NC
NC
CN
CN
R1
R2
CN
CN
CN
CN
H
NC
NC
CN
CN
R2
H
H
H
9 (or 13)
a
b
CN
CN
CN
NC CN
NC
NC
CN
CN
NC
NC
TCNE
R1
R2
b
NC
[π4 + π2]
R1
R2
H
c
18 (or 19)
9, 18: R1 = R2 = 4-(CH3)2NC6H4–
13, 19: R1 = H, R2 = 4-(CH3)2NC6H4–
Scheme 3. A plausible reaction pathway for the formation of 18 (or 19).
structure similar to that of 16, 1,1,2,2,11,11,12,12-octacyano-
3-[4-(dimethylamino)phenyl]-8-isopropyl-5,10-dimethyl-1,2,-
3,6,9,10a-hexahydro-6,9-ethanobenz[a]azulene.
Although the crystal structure of 18 has not yet been ob-
tained because of difficulty in obtaining a single crystal suita-
ble for analysis, recrystallization of 19 from a mixed solvent of
ethyl acetate and hexane (1:5, vol/vol) provided stable single
crystals suitable for that purpose. An ORTEP drawing of 19
with a numbering scheme, indicating the molecular structure
illustrated in Figure 11a, is shown in Figure 11b.
CN
CN
CN
NC CN
NC
NC
CN
NC
NC
R1
R2
CN
NC
R1
R2
H
d
e
d, e: R1 = R2 = 2-thienyl group
Chart 4.
A Plausible Reaction Pathway for the Formation of 18
and 19. In 2006 we suggested a plausible reaction pathway
for the formation of 16 and 17.12 From the molecular structures
of the resulting products 18 and 19, a plausible reaction path-
way for formation can be inferred as illustrated in Scheme 3.
To a solution of TCNE in benzene was added a solution of 9
(or 13) in benzene under argon, turning the dark-green solution
of 9 (or 13) into a black solution, rapidly. This suggests that
reaction of 9 (or 13) with TCNE gives the corresponding
charge-transfer (CT) complex a. Following addition, the reac-
tion mixture was stirred at 25 ꢁC for 24 h under argon, gradual-
ly precipitating a white solid of 18 (or 19). As it so happens,
azulenes are insusceptible to Diels–Alder reactions. Thus,
these results suggest that CT complex a is converted to 18
(or 19), presumably via the biradical b, intermediate c, and
[ꢀ4 þ ꢀ2] cycloaddition of c with TCNE. Quite recently, we
found that the reaction of 2-(3-guaiazulenyl)-1,1-bis(2-thie-
nyl)ethylene with TCNE under the same reaction conditions
gave product d (Chart 4), similar to intermediate c, and fur-
ther, reaction of d with TCNE under the same conditions as
the above rapidly afforded product e (Chart 4), similar to 18,
presumably by [ꢀ4 þ ꢀ2] cycloaddition.34 Therefore, a similar
reaction pathway to that of 18 and 19 can be inferred for the
formation of 16 and 17.12 Isolation, structure determination,
and properties of a and c are currently under intensive inves-
tigation.
Conclusion
We have reported the following seven points in this paper:
namely, (i) the reaction of 1 with 8 in methanol in the presence
of hydrochloric acid at 60 ꢁC for 3 h gave 9 in 81% yield,
via pinacol rearrangement; (ii) the Wittig reaction of 2 with
12 in ethanol containing NaOEt at 25 ꢁC for 24 h under argon
afforded 13 in 12% yield; (iii) the longest absorption wave-
lengths of 9 and 13 corresponded to their ꢁ ꢀ-HOMO ꢃ
ꢀ-LUMO/eV levels; (iv) the crystal structures of 9 and 13
were determined, supporting molecular structures established
on the basis of spectroscopic data; (v) the electrochemical
properties of 9 and 13 showed that both serve as strong
two-electron donors and one-electron acceptors, whose redox
potentials corresponded to their ꢀ-HOMO and ꢀ-LUMO/eV
levels and further, a plausible electron-transfer mechanism
based on the redox potentials of these compounds was
proposed; (vi) reaction of 9 and 13 with 2 equiv of TCNE in
benzene at 25 ꢁC for 24 h under argon gave unique products
18 and 19, possessing interesting structures, in 74 and 41%
yields and further, a plausible reaction pathway for the forma-
tion of 16–19 was suggested; and (vii) along with the spectro-
scopic properties of 18 and 19, the crystal structure of 19
was determined.

S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008) 1483
(6H, s, (CH3)2N-40,400), 4.59 (2H, s, H-1,2), 6.71 (4H, dd, J ¼
7:5, 2.5 Hz, H-30,50,300,500), and 7.19 (4H, dd, J ¼ 7:5, 2.5 Hz,
H-20,60,200,600); 8b: 1H NMR (methanol-d4): ꢃ 2.89 (6H, s,
(CH3)2N-40,400), 6.61 (4H, dd, J ¼ 7:6, 2.5 Hz, H-30,50,300,500),
and 6.94 (4H, dd, J ¼ 7:6, 2.5 Hz, H-20,60,200,600). The OH and
H-1,2 signals of 8b could not be observed.
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
1
Chem. Lett. 1999, 999.
S. Takekuma, M. Sasaki, H. Takekuma, H. Yamamoto,
18 SIR92: A. Altomare, G. Cascarano, C. Giacovazzo, A.
Guagliardi, M. C. Burla, G. Polidori, M. Camalli, J. Appl. Crystal-
logr. 1994, 27, 435.
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W. P. Bosman, R. de Gelder, R. Israel, J. M. M. Smits, Technical
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2
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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.
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5 M. Sasaki, M. Nakamura, T. Uriu, H. Takekuma, T.
Minematsu, M. Yoshihara, S. Takekuma, Tetrahedron 2003, 59,
20 teXsan, ver 1.11: Single Crystal Structure Analysis Soft-
ware, Molecular Structure Corporation, The Woodlands, TX,
1999.
21 3-Formylguaiazulene (2) was prepared according to the
following procedures.22 To a solution of commercially available
guaiazulene (1) (100 mg, 505 mmol) in N,N-dimethylformamide
(DMF) (3.0 mL) was added a solution of phosphoryl chloride
(100 mL). The mixture was stirred at 0 ꢁC for 1 h. After the
reaction, the reaction solution was carefully neutralized with aq.
KOH and the resulting product was extracted with dichloro-
methane (10 mL ꢂ 3). The extract was washed with distilled wa-
ter, dried (MgSO4), and evaporated in vacuo. The residue thus ob-
tained was carefully separated by silica gel column chromatogra-
phy with hexane–ethyl acetate (9:1, vol/vol). The crude product
was recrystallized from hexane to provide pure 2 (108 mg,
478 mmol, 95%) as stable crystals.
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.
22 K. Hafner, C. Bernhard, Liebigs Ann. Chem. 1959, 625,
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.
108.
23 4-(Dimethylamino)benzyl alcohol (11) was prepared ac-
cording to the following procedures. To a powder of NaBH4
(15 mg, 396 mmol) was added a solution of 4-(dimethylamino)-
benzaldehyde (10) (50 mg, 336 mmol) in ethanol (1.5 mL). The
mixture was stirred at 25 ꢁC for 3 h. After the reaction, distilled
water (10 mL) was added to the mixture and the resulting product
was extracted with diethyl ether (10 mL ꢂ 3). The extract was
washed with distilled water, dried (MgSO4), and evaporated in
vacuo, providing pure 11 (41 mg, 272 mmol, 81% yield) as a pale
yellow oil.
16 S. Takekuma, M. Tamura, T. Minematsu, H. Takekuma,
Tetrahedron 2007, 63, 12058.
24 [4-(Dimethylamino)benzyl]triphenylphosphonium bromide
(12) was prepared according to the following procedures.25 To
a solution of 4-(dimethylamino)benzyl alcohol (11) (120 mg,
795 mmol) in chloroform (3 mL) was added a solution of triphen-
ylphosphine hydrobromide (273 mg, 795 mmol) in chloroform
(3 mL). The mixture was stirred at reflux temperature for 1 h
under argon. After the reaction, diethyl ether (10 mL) was added
to the reaction mixture and then centrifuged at 2.5 krpm for
1 min. The crude product was carefully washed with diethyl
ether, providing pure 12 (340 mg, 714 mmol, 90% yield) as a white
powder.
25 S.-S. P. Chou, Y.-H. Yeh, Tetrahedron Lett. 2001, 42,
1309.
26 Program for the Solution of Crystal Structures: A.
Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.
Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R.
Spagna, J. Appl. Crystallogr. 1999, 32, 115.
17 1,2-Bis[4-(dimethylamino)phenyl]-1,2-ethanediol (8) was
prepared according to the following procedures. To a solution of
NaBH4 (10 mg, 264 mmol) in ethanol (1.5 mL) was added a solu-
tion of commercially available 1,2-bis[4-(dimethylamino)phenyl]-
1,2-ethanedione (7) (50 mg, 169 mmol) in dichloromethane (1.5
mL). The mixture was stirred at 25 ꢁC for 3 h then distilled water
(10 mL) was added. The resulting product was extracted with
dichloromethane (10 mL ꢂ 3), washed with distilled water, dried
(MgSO4), and evaporated in vacuo. The obtained residue was
recrystallized from ethanol, providing pure product 8 (46 mg,
153 mmol, 91% yield) as stable crystals. Compound 8: Colorless
plates [Rf ¼ 0:12 on silica gel TLC (solv. hexane:ethyl acetate:
benzene = 7:2:1, vol/vol/vol)]; IR ꢂmax (KBr) cmꢃ1: 3341 (O–
H), 2955–2797 (C–H), 1612, 1516 (C=C), 1315 (C–N), and
1034 (C–O); exact FAB-MS (3-nitrobenzyl alcohol matrix):
found: m=z 301.1897; Calcd for C18H25N2O2: ½M þ Hꢅþ, m=z
301.1916; The relative intensity of the 1H NMR signals for 8
showed a ca. 20:1 mixture of the meso-8a and enantiomeric 8b
forms. 8a: 1H NMR (methanol-d4): ꢃ 1.95 (2H, br s, OH), 2.93
27 The accurate parameters for the crystal structures of 4, 5, 9,
and 13 were transferred to a WinMOPAC (Ver. 3.0) program28
and their energy levels were calculated. A keyword (1 SCF)
was used.

1484 Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008)
New Conjugated ꢀ-Electron Systems
28 The computer program was developed by Fujitsu Ltd.,
Japan.
CV, +0.69 V (Epa) and ꢃ1:79 V (E1=2) under the same electro-
chemical measurement conditions as for 9.
29 Guaiazulene (1): UV–vis ꢁmax (CH3CN) nm (log "): 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); 1H NMR (ben-
zene-d6): ꢃ 1.22 (6H, d, J ¼ 7:0 Hz, (CH3)2CH-7), 2.615 (3H, s,
Me-4), 2.624 (3H, br s, Me-1), 2.83 (1H, sept, J ¼ 7:0 Hz,
Me2CH-7), 6.79 (1H, d, J ¼ 11:0 Hz, H-5), 7.22 (1H, dd,
J ¼ 11:0, 2.0 Hz, H-6), 7.31 (1H, d, J ¼ 4:0 Hz, H-3), 7.69 (1H,
d, J ¼ 4:0 Hz, H-2), and 8.22 (1H, d, J ¼ 2:0 Hz, H-8); 13C NMR
(benzene-d6): ꢃ 144.1 (C-4), 139.7 (C-7), 138.1 (C-8a), 137.2
(C-3a), 136.7 (C-2), 134.6 (C-6), 133.2 (C-8), 125.4 (C-1),
125.2 (C-5), 113.5 (C-3), 38.5 (Me2CH-7), 24.8 ((CH3)2CH-7),
24.0 (Me-4), and 13.0 (Me-1); DPV (Ep), +0.65 and ꢃ1:77 V;
30 The presumed Z isomer of 13: Green paste [Rf ¼ 0:66
on silica gel TLC (solv. hexane:ethyl acetate:benzene = 7:2:1,
vol/vol/vol) under the same conditions as for 13].
31 G. J. Palenik, A. E. Koziol, A. R. Katritzky, W.-Q. Fan,
J. Chem. Soc., Chem. Commun. 1990, 715.
32 T. Kurihara, T. Suzuki, H. Wakabayashi, S. Ishikawa, K.
Shindo, Y. Shimada, H. Chiba, T. Miyashi, M. Yasunami, T.
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33 S. Ito, A. Nomura, N. Morita, C. Kabuto, H. Kobayashi,
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34 Details will be reported elsewhere.