Synthesis, stability and molecular structure of novel hydrocarbon cations consisting of a tropylium cation and two spiro[4.5]deca-2,4-dienes

Article abstract of DOI:10.1016/S0040-4020(03)00369-7

Two novel hydrocarbon cations with a tropylium ion ring fused by two spiro[4,5]deca-2,4-dienes, 9 and 10, were synthesized by a six-step sequence starting from 1,6- and 1,5-diacetyl-1,3,5-cycloheptatrienes, respectively. The pK_R⁺ val

Full text of DOI:10.1016/S0040-4020(03)00369-7

Tetrahedron 59 (2003) 2831–2841
Synthesis, stability and molecular structure of novel hydrocarbon
cations consisting of a tropylium cation and two
spiro[4.5]deca-2,4-dienes
*
Mitsunori Oda, Hitoshi Kainuma, Takuya Uchiyama, Ryuta Miyatake and Shigeyasu Kuroda
Department of Applied Chemistry, Faculty of Engineering, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
Received 4 February 2003; accepted 3 March 2003
Abstract—Two novel hydrocarbon cations with a tropylium ion ring fused by two spiro[4,5]deca-2,4-dienes, 9 and 10, were synthesized by a
six-step sequence starting from 1,6- and 1,5-diacetyl-1,3,5-cycloheptatrienes, respectively. The pKRþ values of 9 and 10 were found to be the
same at 13.2, providing a new access to highly stable cations. The density functional calculations predict that both 9 and 10 have cyclohexane
rings with the chair conformation spread toward molecular edges as the most stable structure. The crystal packing and structure of 9 including
dichloromethane were also elucidated by X-ray crystallographic analysis. q 2003 Elsevier Science Ltd. All rights reserved.
Komatsu and Ito reported the synthesis of stable hydro-
carbon cations 11 and 22 with pKRþ values of 13.0 and 14.3,
respectively. Recently, triarylmethyl cations with hetero-
atomic substituents, such as 3 and 4, were found to show
much greater stability with values of more than 20.3–5
Hydrocarbon cation 1 consists of a tropylium cation and
bicyclo[2.2.2]octenes, and the stability of 1 can be ascribed
to not only the inductive effects but also the s–p
conjugative effects of the bicyclooctene moieties. On the
other hand, hydrocarbon cation 2 has p–p conjugation
throughout all of the substituted azulenes, though all of the
three azulene rings cannot be coplanar concomitantly.2 The
stability of 2 can be ascribed to the extended p–p
conjugation and the inductive effects of the t-butyl groups.
Meanwhile, we reported that spiroalkylated azulenium ions
5a–c6 show greater thermodynamic stability compared with
various disubstituted tropylium cations, such as 1,4-
þ
bis(cyclopropyl)tropylium ion (6, pKR ¼7.63),7 1,2-
bicyclo[2.2.2]octenotropylium ion (7, 8.82),8 and cyclo-
hepta[a]acenaphtylenium ion (8, 8.7).9 The effect of fusion
of a spiro[4,n]alka-2,4-diene unit to a tropylium cation ring
on its stability can be attributed to the p–p conjugation at
the 2,3 position and s–p conjugation between the electron-
deficient p orbitals and the Csp3–Csp3 s-bonds at the 1
position, in addition to an inductive effect of the spiro
carbocycles. Thus, 5a–c should be regarded as a hybrid type
of tropylium cation stabilized by p–p and s–p con-
jugations. The cations, dispiro[cyclohexane-1,10-(10,70-di-
hydrocyclopenta[f]azulenium)-70,100-cyclohexane] perchlorate
Keywords: carbenium ions; azulenes; cyclohexanes; sprio compounds;
X-ray crystal structures.
*
Corresponding author. Tel.: þ81-76-445-6820; fax: þ81-76-445-6819;
e-mail: oda@eng.toyama-u.ac.jp
Chart 1.
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00369-7

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M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
this paper we describe the synthesis of these two
isomeric hydrocarbon carbocations, their thermodynamic
stability, and also the crystal packing and structure of 9
(Charts 1 and 2).10
1. Results and discussion
1.1. Synthesis of dispiro[cyclohexane-1,10-(10,70-dihydro-
cyclopenta[ f ]azulenium)-70,100-cyclohexane] perchlorate
(9) and dispiro[cyclohexane-1,10-(10,50-dihydrocyclo-
penta[ f ]azulenium)-50,100-cyclohexane] perchlorate (10)
Chart 2.
(9) and dispiro[cyclohexane-1,10-(10,50-dihydrocyclo-
penta[ f ]azulenium)-50,100-cyclohexane] perchlorate (10),
whose tropylium ring is fused by two spiro[4,5]deca-2,4-
diene units, are expected to show greater stability than 5. In
The synthesis of 9 was accomplished from 1,6-diacetyl-
1,3,5-cycloheptatriene (11)11 by the method which we
had developed for 5c. The trimethylsilyl enol ether 12
was treated in the presence of trimethylsilyl triflate with
Scheme 1.
Scheme 2.

M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
2833
Scheme 3.
Figure 1. Proton (left) and carbon (right) chemical shift values (d ppm) assigned for 5b, 9 and 10.
1,1-dimethoxycyclohexane to give 13 in 81% yield,12 while
the attempted aldol reaction of 11 with cyclohexanone in the
presence of titanium chloride13 gave none of the desired
aldol product. The double Nazarov cyclization14 of 13 in a
mixture of formic acid and phosphoric acid afforded
the tricyclic diketone 14 in 46% yield. The Shapiro
reaction15 of tosylhydrazone of 14 and subsequent hydride
abstraction of 15 with trityl perchlorate gave 9 as yellow
microcrystals in 10% yield based on 14. The cation 9 was
found to be fairly stable and it can be stored without
appreciable change at room temperature for at least a year
(Scheme 1).
preparing it in a multi-gram quantity. In this study, 22 was
obtained in one pot from 1,3,5-cycloheptatriene 23 by the
regioselective lithiation of the 2 position17 and subsequent
acetylation with N,N-dimethylacetamide (Scheme 3).
1.2. Physical properties of 9 and 10
The structures of 9 and 10 were fully characterized by
spectroscopic and elemental analyses. The assignment of
the proton and carbon signals for 9, 10 and known 5b is
shown in Figure 1. The average chemical shifts of 8.15 and
8.27 ppm for the olefinic protons of 9 and 10, respectively,
are slightly lower than that (8.67 ppm) of 5b, and the same is
The synthesis of 10 was carried out in the same manner
starting from 1,5-diacetyl-1,3,5-cycloheptatriene (17)
through compounds 18–21 as shown in Scheme 2. The
cation 10 was obtained as stable brownish-yellow crystals.
The starting material 17 was prepared by the regioselective
Friedel–Crafts acetylation of 2-acetyl-1,3,5-cyclohepta-
triene (22) as seen in the acetylation of 1-acetyl-1,3,5-
cycloheptatriene into 11.11 Although 22 has been known,
the reported method by Linstrumelle16 is not suitable for
Table 1. Absorption maxima (nm) in the electronic spectra of 5b, 9 and 10
in acetonitrile
Cation
lmax (log 1)
5ba
9
230 (4.24) 270 (4.33)
232 (4.03) 297sh (4.33), 311 (4.46) 364 (4.03), 383 (4.10)
238 (3.96) 282 (4.30), 306 (4.14) 381sh (3.99), 401 (4.12)
360 (4.07)
10
a
Taken from Ref. 6.

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M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
Figure 2. p-Molecular orbitals of the tropylium, vinyltropylium, 1,3-divinyltropylium and 1,4-divinyltropylium cations calculated by the PM3 method (energy
level in eV) and their HOMO–LUMO gaps.
true for the 13C NMR chemical shifts of 144.0 and
144.2 ppm for the secondary trigonal carbons of 9 and 10
which are slightly smaller than that (148.1 ppm) of 5b.
Comparison of the shift values of the cyclopenetaazulene
skeleton hydrogens and carbons except the sp3-hybridized
carbons and the 40 position in 9 and 10 with those of the
corresponding precursor hydrocarbons shows clear down
field shift; the average field shifts are 1.56 and 1.65 ppm for
hydrogens and 18.0 and 19.5 ppm for carbons in 9 and 10,
respectively. It is worthy to note that the five-membered
secondary carbons at the 20 and 60 positions in 9 and 10
resonate at lower field of 157.5–160.8 ppm compared with
the other secondary carbons. These results indicate the
delocalization of the positive charge over the skeletal
carbons of the additionally fused spiro[4,5]deca-2,4-diene
unit. The 1H NMR spectrum of 9 shows five bands of signals
in a range of 1.32–2.21 ppm for the hydrogens at the
cyclohexane rings, while that of 10 indicates unresolved
signals except the signals of the 2 (6) and 200 (600) positions in
the similar region because of its less symmetrical structure.
The axial–axial vicinal coupling (13.3 Hz) and the axial–
equatorial vicinal coupling constant (3.3 Hz)18 observed
between these protons of 9 suggest that 9 has cyclohexane
rings with a fixed chair conformation, as observed in the
crystal structure of 9 (vide infra).
The UV spectra of 9 and 10 in acetonitrile show five bands,
while the spectrum of 5b shows three sharp bands (Table 1).
The longest wavelength absorption maxima of 9 and 10 are
Table 2. The pKRþ values and reduction peak potentials of various cations
þ
Cation
pKR
Reduction potential
V vs SCE
V vs Ag/Agþ
1
2
5a
5b
5c
9
13.0
14.3
9.9
10.0
10.4
13.2
13.2
21.12a
20.91, 21.72b
20.41
20.46
20.54
20.65
20.52
10
a
Taken from Ref. 1.
Taken from Ref. 2.
Figure 3. ORTEP drawings of the cation 9. The perchlorate counter anion
and the dichloromethane included are omitted.
b

M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
2835
˚
Figure 4. Bond lengths (A) in the crystal of the cation 9.
shifted by 23 and 41 nm to longer wavelength compared
with that of 5b. It is only natural that these shifts are mainly
due to p–p conjugation of another C–C double bond
around the tropylium cation ring. The dependence of the
degree of the shift on the position of the double-bond around
a tropylium ring can be rationalized by the following
molecular orbital calculations of 1,3- and 1,4-divinyl-
tropylium cations as simplified models for 9 and 10,
respectively. Figure 2 shows p-molecular orbitals of
tropylium, vinyltropylium, and 1,3- and 1,4-divinyl-
tropylium cations calculated by the semiempirical PM3
method. Both of the degenerated LUMO and HOMO are
split in the substituted cations, and the largest splitting of
HOMO and the next HOMO is expected in the 1,4-
divinyltropylium cation. While the energy level of LUMO is
not changed much by vinyl substitution, the level of HOMO
slightly increases one by one by the substitution. The
HOMO–LUMO gap is expected to be the smallest in 1,4-
divinyltropylium cation among them, thus accounting for
the greater shift of 10 in the UV spectrum.
many efforts single crystals of 10 have not been obtained.
The structure was solved and refined in the space group
P21/n with four pairs of 9 and dichloromethane per unit cell.
ORTEP drawings of 9 without the counter anion and the
solvent are shown in Figure 3 and bond lengths in Figure 4.
The structure shows C1 symmetry, and the dihydrocyclo-
penta[f]azulenyl skeleton is nearly planar; the0 greatest
torsion angle of 48 was observed through the C1(1 )–C90a–
C30a–C4 carbons. Mean deviation from the least-squares
plane of the dihydrocyclopenta[ f ]azulene framework is
˚
0.0271 A and the longest distance from the 0 plane is
˚
observed to be 0.0854 A long for the C1(1 ) carbon
(Table 3). The fairly planar carbon framework should be
related to effective delocalization of the positive charge in 9.
The average C–C bond length of the seven-membered ring
˚
˚
is 1.39 A, which is longer than that (1.35 A) of the tropylium
ion in an inclusion complex with dibenzo-24-crown-819 and
is rather closer to those of substituted tropylium ions, such
20
˚
as acetoxytropylim ion (1.38 A) and 1,11-o-benzeno[2]-
orthcyclo[2](1,2)tropyliophane (1.385 A).21 Deviation from
˚
˚
the average in the crystal structure of 9 is less than 0.04 A.
þ
The pKR values of 9 and 10 were determined by the UV
The average bond angle of the seven-membered ring is
128.18, which is close to the 128.68 expected for a regular
heptagon. One may expect that when the s–p conjugation
in 9 is effective, the Csp3–Csp3 single bonds of the
cyclohexane ring at the spiro juncture should be elongated.
In the crystal structure of 9, the average Csp3–Csp3 bond
method in buffered 50% aqueous acetonitrile solutions to be
the same at 13.2. The reversibility in the pKRþ determination
was confirmed by resumption of the spectra of 9 and 10
from the high pH solution up to 60% of the original intensity
upon acidification with a few drops of concd H2SO4. The
thermodynamic stability of 9 and 10 is comparable to that of
1 and slightly less than that of 2. The difference (6.1) in the
values between 5b (10.0)6 and the tropylium ion (3.9)7 is far
greater than that (3.2) between 9 or 10 and 5b. Thus, a
saturation effect of electronic stabilization by the spiro-
decadiene to the tropylium cation is clearly shown.
Reduction peak potentials for 9 and 10 measured by cyclic
voltammetry was 20.65 and 20.52 V vs SCE, respectively,
designating increased reduction reluctance of 9 and 10
compared with 5b (Table 2).6
0
0
00
˚
distance (1.54 A) at the C1(1 ) and C7 (1 ) carbons is indeed
˚
Table 3. Deviation (A) from the least-squares plane of the cyclopenta-
[f]azulene in 9
Carbon
Distance
esd
1(10)
20
0.0854
20.0095
20.0473
20.0242
20.0193
20.0026
0.0448
0.0120
0.0130
0.0131
0.0137
0.0145
0.0145
0.0119
0.0300
0.0122
0.0118
0.0116
0.0121
0.0127
30
30a
40
40a
50
1.3. X-Ray crystallographic analysis of 9 and density
functional calculations of 9 and 10
60
0.0300
70(100)
700a
8
20.0073
20.0241
20.0269
20.0174
0.0131
The molecular structure of 9 was elucidated by X-ray
crystallographic analysis. Single crystals of 9 containing
dichloromethane were obtained by recrystallization from a
mixture of ether, hexane and dichloromethane. In spite of
90
90a

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M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
Figure 5. The crystal packing of 9 viewed along the c-axis.
˚
greater than that (1.52 A) of the other bonds in the
conformer D is expected to be the most stable. As seen for 9,
the conformer D has a chair form whose seats and backs are
spread to the side of the molecular edges. The short atomic
cyclohexane rings, implying the s–p conjugation of 9,
though further comparison with bond length data of related
compounds is necessary to confirm this.
˚
distances less than 2.2 A between the axial hydrogen of the
cyclohexane ring and the hydrogen at the seven-membered
ring observed in B, C, E, F and G, like 1,3-diaxial
interaction, may be one reason to account for their
instability (Fig. 8).
The crystal packing of 9 along the c-axis is shown in
Figure 5. Four molecules of 9 are located around the c-axis
centered in the unit cell with symmetry of rotation–
reflection. Thus, the two facing cations at the opposite
angular positions are upside down against each other,
making space at the middle of the cell along the axis where
the two dichlromethanes are filled. Other dichloromethanes
are at the unit cell edges and surrounded also by the cations
in other cells. Such large space was not observed in the
crystal cells of 5a and 5b.6 A perspective view piled with
five cells along the c-axis is shown in Figure 6.
As been expected by 1H NMR analysis, the crystal structure
clearly shows that the two cyclohexane rings of 9 have a
chair form whose seats and backs are spread to the side of
the molecular edges. This conformation was found to be the
most stable among three possible conformers, A, B and C in
Figure 7, two of which have at least one chair-formed
cyclohexane ring folded inside the molecule, on the basis of
the hybrid molecular orbital calculations at the B3LYP/
6-31Gp level of theory. Similar calculations for 10, whose
crystal structure is unknown, were also carried out. Among
four possible chair form isomers, D, E, F and G, the
Figure 6. A perspective view along the c-axis.

M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
2837
Figure 7. Possible conformers (Chem3D output) having a chair form cyclohexanes for 9 and their total energies (in a.u.) calculated at the B3LYP/6-31Gp level
of theory. The relative energies (in kcal/mol) to the most stable conformer are in parentheses.
Figure 8. Possible conformers (Chem3D output) having a chair form cyclohexanes for 10 and their total energies (in a.u.) calculated at the B3LYP/6-31Gp
level of theory. The relative energies (in kcal/mol) to the most stable conformer are in parentheses.
2. Summary
enhanced thermodynamic stability comparable to that of 1,
providing a new access to highly stable hydrocarbon
cations. The effect of fusion with a spiro[4,5]decana-2,4-
diene unit at the tropylium cation on stability has
been clearly indicated by the present results of both 9
and 10, though a saturation effect also is shown in plural
fusions. We have also demonstrated the X-ray crystal
structure of 9, as the first example of highly stable
hydrocarbon cations.
In summary, we have established an efficient synthetic
route to the tropylium cations fused with two spiro[4,5]-
decana-2,4-diene units, 9 and 10. Two isomeric dia-
cetyl-1,3,5-cycloheptatrienes were converted into 9 and 10
by a sequence involving the Mukaiyama–Noyori aldol
reaction, the Nazarov cyclization, the Shapiro reaction, and
the final hydride abstraction. The cations 9 and 10 show

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M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
3. Experimental
1H), 6.48 (d, J¼5.7 Hz, 1H), 6.63 (dd, J¼11.5, 5.7 Hz, 1H),
6.79 (d, J¼11.5 Hz, 1H); 13C NMR (CDCl3) d¼0.03, 0.07,
18.2, 92.3, 93.8, 122.2, 122.3, 129.0, 131.1, 132.4, 135.6,
154.9, 155.4. IR (liq. film) n (cm21) 2960s, 1611m, 1584m,
1418w, 1327m, 1286s, 1252s, 1219m, 1086m, 1021s, 846s,
688w; MS (70 eV) m/z (rel. intensity) 320 (Mþ, 8), 248 (12),
205 (35), 115 (10), 73 (100); UV lmax (methanol) 231 nm
(log 1¼4.19), 284 (3.76). Found: 320.1593. Calcd for
C17H28Si2O2: M, 320.1628.
3.1. General
Melting points were measured on a Yanaco MP-3 and are
uncorrected. IR spectra were recorded on a Perkin–Elmer
Spectrum RX I spectrometer. UV spectra were measured on
1
a Shimadzu UV-1600 spectrometer. H NMR (400 MHz)
and 13C NMR (100 Hz) were recorded with tetramethyl-
silane as an internal standard on a JEOL a400. Mass spectra
were measured on a JEOL GC-Mate mass spectrometers.
Cyclic voltammogram was recorded on a Yanako P1100
instrument. Column chromatography was done with Merck
Kieselgel 60 Art 7734. Ethyl ether and THF were purified
just before use by distillation from sodium diphenylketyl
under a nitrogen atmosphere. Trimethylsilyl triflate, 1,1-
dimethoxycyclohexane, acetonitrile and HMPA were pur-
chased from Tokyo Kasei Ind. Co. and were used after
appropriately distillation. A solution of n-butyllithium in
hexane from Aldrich Co. and a solution of methyllithium in
ether from Kanto Chem. Inc. were used after titration.
Sodium t-butoxide was purchased from Wako Chem. Co.
and was used without purification. 1,6-Diacetyl-1,3,5-
cycloheptatriene (11) was prepared by the Vogel method.11
Trityl perchlorate was prepared according to the method in
the literature.22 The density functional calculations were
conducted by using the Gaussian 94 (Revision E.1,
Gaussian, Inc., Pittsburg, Pa, 1995) on an IBM RS6000-
G94RevE computer. Semiempirical molecular orbital
calculations were done by using the MOPAC program
(ver. 6.02) on an IBM RS/6000-397 computer.
3.1.2. 1,6-Bis(3-methoxyl-3,3-pentamethylenepro-
pionyl)-1,3,5-cycloheptatriene (13) and 1,5-bis(3-meth-
oxyl-3,3-pentamethylenepropionyl)-1,3,5-cyclohepta-
triene (19). To a solution of 1.60 g (5.00 mmol) of 12 and
1.66 g (11.0 mmol) of 1,1-dimethoxycyclohexane in 15 ml
of dichloromethane at 2788C under nitrogen atmosphere
was added 92 ml (0.50 mmol) of trimethylsilyl triflate. After
being stirred at the same temperature for 12 h, the reaction
mixture was poured into water and was extracted with ether
(30 ml£3). The combined organic layer was washed with a
saturated sodium hydrogencarbonate solution and dried
with anhydrous Na2SO4. After evaporation of the solvent,
the residual oil was purified by silica gel chromatography to
1
give 1.62 g (81% yield) of 13 as a yellow oil. H NMR
(CDCl3) d¼1.21 (m, 4H), 1.51 (m, 12H), 2.89 (s, 4H), 2.99
(s, 2H), 3.19 (s, 6H), 6.94 (m, 2H), 7.12 (m, 2H); 13C NMR
(CDCl3) d¼21.7, 24.7, 25.4, 34.1, 44.7, 48.8, 75.8, 132.1,
133.8, 135.9, 198.0. IR (liq. film) n (cm21) 2933s, 2857s,
2827m, 1663s, 1591m, 1513m, 1456m, 1362m, 1305m,
1256m, 1191m, 1148m, 1073s, 945w, 927w, 869w, 849w,
742m, 694w, 669w, 607w; MS (70 eV) m/z (rel. intensity)
400 (Mþ, 8), 368 (23), 336 (17), 279 (20), 272 (56), 240
(32), 256 (30), 212 (15), 161 (15), 149 (32), 113 (100), 81
(64), 69 (26); UV lmax (methanol) 245 nm (log 1¼4.48),
256sh (4.41), 312 (4.09). Found: 400.2570. Calcd for
C25H36O4: M, 400.2613.
3.1.1. 1,6-Bis(1-trimethylsilyloxyethenyl)-1,3,5-cyclohep-
tatriene (12) and 1,5-bis(1-trimethylsilyloxyethenyl)-
1,3,5-cycloheptatriene (18).
A solution of 19.2 ml
(150 mmol) of trimethylsilylchloride was added dropwise
to a solution of 8.80 g (50. 0 mmol) of 11 and 42.0 ml
(304 mmol) of triethylamine, followed by addition of a
solution of 22.5 g (150 mmol) of sodium iodide in 150 ml of
acetonitrile. After being stirred at room temperature for
12 h, the reaction mixture was slowly poured into a cold
mixture of 100 ml of hexane and 500 ml of water. The
aqueous layer was extracted with hexane (100 ml£2). The
combined organic layer was washed with brine and dried
with anhydrous K2CO3. After evaporation of the solvent, the
residual dark brown oil was purified by distillation to give
9.76 g (61% yield) of 12 as a pale yellow oil. Bp¼110–
The compound 19 was obtained as yellow oil from 18 in
1
92% yield in the same manner. H NMR (CDCl3) d¼1.3–
1.6 (m, 12H), 1.73 (t-like, 4H), 1.84 (t-like, 4H), 2.77 (d,
J¼7.6 Hz, 2H), 2.82 (s, 2H), 2.85 (s, 2H), 3.16 (s, 3H), 3.21
(s, 3H), 6.46 (t, J¼7.6 Hz, 1H), 6.84 (dd, J¼11.5, 5.9 Hz,
1H), 7.07 (d, J¼5.9 Hz, 1H), 7.45 (d, J¼11.5 Hz, 1H); 13C
NMR (CDCl3) d¼21.7 (2C), 25.30, 25.31, 27.0, 34.3, 34.4,
44.3, 44.5, 48.7, 48.8, 75.6 (2C), 130.3, 132.8, 133.0, 133.2,
134.4, 140.7, 198.1, 198.6. IR (liq. film) n (cm21) 2933s,
2858s, 1721s, 1656s, 1600m, 1534, 1446s, 1365s, 1308s,
1192s, 1074s, 927m, 753m, 610w; MS (70 eV) m/z (rel.
intensity) 400 (Mþ, 9), 368 (25), 336 (47), 272 (55), 241
(82), 212 (68), 177 (13), 149 (32), 145 (37), 113 (100), 81
(65); UV lmax (methanol) 240 nm (log 1¼4.14), 295 (3.63).
Found: 400.2600. Calcd for C25H36O4: M, 400.2613.
1
1158C/2 mm Hg. H NMR (CDCl3) d¼0.18 (s, 18H), 2.53
(s, 2H), 4.45 (d, J¼1.5 Hz, 2H), 4.82 (d, J¼1.5 Hz, 2H),
6.65 (m, 4H); 13C NMR (CDCl3) d¼0.3, 29.2, 93.9, 123.0,
130.1, 130.8, 155.3. IR (liq. film) n (cm21) 3043w, 3014w,
2960m, 2901w, 1612m, 1580s, 1504m, 1356m, 1294s,
1253s, 1216s, 1102m, 1042w, 1016s, 847vs, 749s, 691w;
MS (70 eV) m/z (rel. intensity) 320 (Mþ, 17), 305 (9), 215
(9), 205 (6), 147 (12), 115 (6), 75 (23), 74 (9), 73 (100); UV
lmax (methanol) 245 nm (log 1¼4.48), 321 (3.77). Found:
320.1627. Calcd for C17H28Si2O2: M, 320.1628.
3.1.3. Dispiro[cyclohexane-1,10-(10,20,30,40,50,60,70-hepta-
hydrocyclopenta[ f ]azulene-30,50-dione)-70,100-cyclohex-
ane] (14) and dispiro[cyclohexane-1,10-(10,20,30,40,50,60,70-
heptahydrocyclopenta[f]azulene-30,70-dione)-50,100-cyclo-
hexane] (20). To a solution of 1.60 g (4.00 mmol) of 13 in
30 ml of formic acid was added 30 ml of 85% phosphoric
acid. After being stirred at 908C for 5 h, the reaction mixture
was poured into 200 ml of cold water and was extracted
with chloroform (50 ml£3). The combined organic layer
was washed with a saturated sodium hydrogencarbonate
The compound 18 was obtained as a pale yellow oil in 92%
yield from 22 in the same manner. Bp¼1158C/2.5 mm Hg.
1H NMR (CDCl3) d¼0.21 (s, 18H), 2.56 (d, J¼7.7 Hz, 2H),
4.28 (d, J¼1.2 Hz, 1H), 4.48 (d, J¼1.5 Hz, 1H), 4.82 (d,
J¼1.5 Hz, 1H), 4.82 (d, J¼1.2 Hz, 1H), 5.85 (t, J¼7.7 Hz,

M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
2839
solution and brine, and was dried with anhydrous Mg2SO4.
After evaporation of the solvent, the residual solids were
purified by recrystallization from a mixture of dichloro-
methane and hexane to give 620 mg (46% yield) of 14 as
creamy white prisms. Mp .2508C (dec.) 1H NMR (CDCl3)
d¼1.21 (m, 2H), 1.30 (m, 8H), 1.56 (m, 4H), 1.75 (m, 6H),
2.34 (s, 4H), 3.00 (s, 2H), 6.96 (s, 2H); 13C NMR (CDCl3)
d¼16.1, 23.5, 25.3, 35.8, 44.3, 46.8, 131.1, 135.6, 170.7,
205.2. IR (liq. film) n (cm21) 3030w, 2935s, 2854s, 1691s,
1619m, 1556m, 1455m, 1406m, 1367m, 1329m, 1296w,
1265m, 1195m, 1092m, 992m, 919w, 818m, 754m; MS
(70 eV) m/z (rel. intensity) 336 (Mþ, 100), 293 (5), 279 (7),
141 (7), 115 (6), 81 (5); UV lmax (methanol) 238 nm
(log 1¼4.31), 249 (4.31), 275sh (4.22), 317 (3.68). Bis(2,4-
dinitrophenylhydrazone) of 14; Red prisms. Mp.3008C.
Found: C, 60.05; H, 5.28; N, 15.78%. Calcd for
C35H36N8O8: C, 60.34; H, 5.21; N, 16.08%.
363 (4.00). Found: 304.2191. Calcd for C23H28: M,
304.2218.
The compound 21 was obtained as an air-sensitive pale
1
yellow oil in 18% yield from 20 in the same manner. H
NMR (CDCl3) d¼0.95–1.05 (m. 4H), 1.27–1.92 (m, 16H),
3.04 (s, 2H), 6.21 (d, J¼5.6 Hz, 1H), 6.29 (d, J¼5.6 Hz,
1H), 6.42 (d, J¼11.2 Hz, 1H), 6.45 (d, J¼11.2 Hz, 1H), 6.66
(d, J¼5.6 Hz, 1H), 6.90 (d, J¼5.6 Hz, 1H); 13C NMR
(CDCl3) d¼24.9, 25.2, 26.2, 26.9, 29.4, 29.7, 34.8, 57.1,
58.0, 122.3, 127.9, 129.3 (2C), 129.4, 131.7, 140.3, 142.3,
143.8, 152.6. IR (liq. film) n (cm21) 2925s, 2854s, 1652w,
1541w, 1506w, 1448m, 1034w, 762w, 668w; MS (70 eV)
m/z (rel. intensity) 304 (Mþ, 44), 290 (100), 261 (20), 247
(31), 205 (19), 191 (30), 165 (21), 141 (11), 91 (12), 69 (13);
UV lmax (hexane) 235 nm (log 1¼4.14), 243 (3.83), 274sh
(3.54), 284sh (3.54), 339 (3.29). Found: 304.2207. Calcd for
C23H28: M, 304.2191.
The compound 20 was obtained as a pale yellow oil in 77%
yield from 19 in the same manner. 1H NMR (CDCl3)
d¼1.15–1.34 (m, 12H), 1.75 (m, 8H), 2.38 (s, 2H), 2.40
(s, 2H), 6.77 (d, J¼11.5 Hz, 1H), 7.03 (d, J¼11.5 Hz, 1H);
13C NMR (CDCl3) d¼21.2, 23.2, 23.5, 24.8, 25.2, 34.2,
35.9, 44.4, 46.0, 47.0, 47.1, 126.1, 128.9, 129.8, 135.5,
173.5, 179.5, 204.3, 205.7. IR (liq. film) n (cm21) 2928s,
2855w, 1694s, 1617m, 1450m, 1316m, 1190w, 1025w,
919w, 850w, 754s, 667w; MS (70 eV) m/z (rel. intensity)
336 (Mþ, 100), 281 (14), 240 (19), 165 (13), 141 (19),
115 (14); UV lmax (methanol) 250 nm (log 1¼4.16),
293 (3.63). Found: 336.2093. Calcd for C23H28O2: M,
336.2089.
3.1.5. Dispiro[cyclohexane-1,10-(10,70-dihydrocyclo-
penta[f]azulenium)-70,100-cyclohexane] perchlorate (9)
and dispiro[cyclohexane-1,10-(10,50-dihydrocyclopenta-
[ f ]azulenium)-50,100-cyclohexane] perchlorate (10). To a
solution of 300 mg (0.987 mmol) of 15 in 5 ml of
acetonitrile was added 338 mg (0.990 mmol) of trityl
perchlorate. The mixture was stirred at room temperature
for 0.5 h. To the reaction mixture at 08C was added 25 ml of
ether. Solids formed were collected by filtration and
recrystallized from a mixture of dichloromethane and
ether to give 176 mg (44% yield) of 9 as yellow
microcrystals. Mp¼217–2188C. 1H NMR (CD3CN)
d¼1.32 (dm, J¼13.2 Hz, 4H), 1.56 (qt, J¼13.2, 3.3 Hz,
2H), 1.72 (qt, J¼13.2, 3.3 Hz, 4H), 1.91–2.02 (m, 6H), 2.21
(qt, J¼13.2, 3.3 Hz, 4H), 7.36 (d, J¼5.6 Hz, 2H), 8.06 (d,
J¼5.6 Hz, 2H), 8.70 (s, 2H), 8.89 (s, 1H). IR (KBr) n
(cm21) 2928s, 1651m, 1532m, 1487m, 1458m, 1422m,
1359m, 1085vs, 867w, 846w, 791w, 764m, 701m, 622s; MS
(70 eV) m/z (rel. intensity) 303 (Mþ, 37), 302 (100), 273
(21), 259 (14), 247 (19), 217 (21), 202 (19), 191 (26), 165
(11), 69 (11). Found: C, 65.69; H, 6.72%. Calcd for
C23H27ClO4 0.2H2O: C, 65.84; H, 6.53%.
3.1.4. Dispiro[cyclohexane-1,10-(10,40,70-trihydrocyclo-
penta[f]azulene)-70,100-cyclohexane] (15) and dispiro-
[cyclohexane-1,10-(10,40,50-trihydrocyclopenta[ f ]azul-
ene)-50,100-cyclohexane] (21).
A solution of 2.98 g
(8.87 mmol) of 14 and 3.30 g (17.7 mmol) of tosylhydrazide
in 40 ml of THF was stirred at 608C for 96 h. The solvent
was evaporated and the residual solids were washed well
with ether to give the crude hydrazone product. This sample
was suspended in 200 ml of ether. To this at 08C under
nitrogen atmosphere was added dropwise 65 ml (71 mmol)
of 1.1 M methyllithium etheral solution. After 4 h, the
mixture became homogeneous and the color of the solution
turned dark-red. The mixture was stirred at room tempera-
ture for 12 h. Then, the reaction mixture at 08C was
quenched carefully with 4 ml of water and was poured into
water and extracted with ether (100 ml£2). The organic
layer was dried with anhydrous MgSO4. After evaporation
of the solvent, the residual red oil was purified by silica gel
chromatography with hexane as eluent to give 601 mg (22%
The cation 10 was obtained as a brownish-yellow crystals in
30% yield from 21 in the same manner. Mp¼181–1828C.
1H NMR (CD3CN) d¼1.36 (m, 4H), 1.65 (m, 6H), 2.01 (m,
6H), 2.22–2.41 (m, 4H), 7.39 (d, J¼5.6 Hz, 1H), 7.61 (d,
J¼5.6 Hz, 1H), 7.85 (d, J¼5.6 Hz, 1H), 7.94 (d, J¼5.6 Hz,
1H), 9.00 (d, J¼9.9 Hz, 1H), 9.04 (d, J¼9.9 Hz, 1H), 9.19
(s, 1H). IR (KBr) n (cm21) 2924s, 2854s, 1493m, 1446s,
1295m, 1078s, 806s, 758s, 699s, 606m; MS (70 eV) m/z
(rel. intensity) 303 (Mþ, 31), 302 (100), 273 (20), 259 (24),
247 (30), 217 (42), 202 (42), 191 (50), 165 (20), 69 (20).
Found: C, 68.38; H, 6.93%. Calcd for C23H27ClO4: C,
68.56; H, 6.75%.
1
yield) of 15 as an air-sensitive pale yellow oil. H NMR
(CDCl3) d¼1.00 (dm, J¼13.2 Hz, 4H), 1.32 (qt, J¼13.2,
3.3 Hz, 2H), 1.52 (qt, J¼13.2, 3.3 Hz, 4H), 1.68 (td, J¼13.2,
3.3 Hz, 4H), 1.72–1.84 (m, 6H), 3.19 (s, 2H), 6.21 (d,
J¼5.4 Hz, 2H), 6.35 (s, 2H), 6.89 (d, J¼5.4 Hz, 2H); 13C
NMR (CDCl3) d¼25.9, 26.0, 26.7, 33.3, 58.0, 123.2, 133.6,
133.8, 144.8, 150.0. IR (liq. film) n (cm21) 3052w, 2925s,
2855s, 1661w, 1490w, 1449s, 1378w, 1269w, 1124w,
1031w, 996w, 918w, 901w, 844m, 803w, 745m, 726s; MS
(70 eV) m/z (rel. intensity) 304 (Mþ, 100), 303 (71), 291
(21), 205 (27), 191 (43), 165 (36), 91 (20); UV lmax
(hexane) 253sh nm (log 1¼3.69), 287 (3.80), 276 (3.87),
3.1.6. 2-Acetyl-1,3,5-cycloheptatriene (22). In a 500-ml
round-bottom flask at 2108C under nitrogen atmosphere
was charged 100 ml of 1.5 M n-butyllithium hexane
solution. At the same temperature the solvent was removed
under vacuum. To the residue at 2788C was added 250 ml
of THF, followed by addition of 14.4 g (150 mmol) of
sodium t-butoxide and 13.8 g (150 mmol) of 1,3,5-cyclo-
heptatriene. After this mixture was stirred at 2788C for

2840
M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
24 h, 14.4 g (165 mmol) of N,N-dimethylacetamide at
2508C was added to the mixture. Then, the cooling bath
was removed, and the mixture was stirred at room
temperature for 2 h. The resulted reaction mixture was
poured into water and was extracted with ether (100 ml£3).
The combined organic layer was washed with a saturated
sodium hydrogencarbonate solution and brine, and was
dried with anhydrous MgSO4. After evaporation of the
solvent, the residual oil was purified by flash silica gel
chromatography with ether–hexane (1:9) as eluent to give
scan rate of 0.1 V/s at 258C. The peaks of 9 and 10 are
irreversible.
3.4. X-Ray structural analysis of dispiro[cyclohexane-
1,10-(10,70-dihydrocyclopenta[ f ]azulenium)-70,100-cyclo-
hexane] perchlorate (9)
Pale yellow prismatic crystals of 9 containing dichloro-
methane were obtained by recrystallization from a mixture
of hexane, ether and dichloromethane. One of them having
approximate dimensions of 0.50£0.50£0.50 mm3 was
mounted on a glass fiber. All measurements were made on
a Rigaku AFC7R diffractometer with graphite mono-
chromated Mo Ka radiation and a rotating anode generator.
Cell constants and an orientation matrix for data collection,
obtained from a least-squares refinement using the setting
angles of 25 carefully centered reflections in the range
22.32,2u,24.998, corresponded to a primitive monoclinic
1
3.99 g (19% yield) of 2216 as a colorless oil. H NMR
(CDCl3) d¼2.37 (s, 3H), 2.38 (t, J¼7.3 Hz, 2H), 5.48 (dtd,
J¼9.3, 7.3, 1.7 Hz, 1H), 6.23 (ddd, J¼9.3, 5.4, 0.7 Hz, 1H),
6.35 (t, J¼7.3 Hz, 1H), 6.73 (ddd, J¼11.5, 5.4, 1.7 Hz, 1H),
7.21 (dd, J¼11.5, 0.7 Hz, 1H); 13C NMR (CDCl3) d¼26.4,
27.7, 120.9, 127.6, 127.7, 129.3, 131.9, 138.7, 198.1.
3.1.7. 1,5-Dicetyl-1,3,5-cycloheptatriene (17). A suspen-
sion of 33.0 g (250 mmol) of aluminium chloride in 100 ml
of dichloromethane was refluxed with vigorous stirring. To
this was added dropwise 17.3 g (220 mmol) of acetyl-
chloride, followed by addition of 13.4 g (100 mmol) of 22.
This mixture was refluxed for 4 h and was cooled to 2208C.
To this was added dropwise 10 ml of acetic acid in such
manner that the temperature of the reaction mixture did not
exceed 08C, and then 50 ml of water was added carefully.
The resulted reaction mixture was poured into water and
was extracted with chloroform (100 ml£3). The combined
organic layer was washed with a saturated sodium
hydrogencarbonate solution and brine, and was dried with
anhydrous K2CO3. After evaporation of the solvent, the
residual oil was purified by alumina chromatography to give
˚
˚
cell with dimensions: a¼12.513(3) A, b¼13.079(3) A,
3
˚
˚
c¼15.013(3) A, b¼93.27(2)8, V¼2453.0(9) A . For Z¼4
and formular weight¼487.85, the calculated density is
1.32 g/cm3. Based on the systematic absences of
h01:hþ1–2n and 0k0:k–2n, the space group was uniquely
determined to be P21/n (# 14). The data were collected at a
temperature of 238C using the v–2u scan technique to a
maximum 2u value of 60.08. Omega scans of several intense
reflections, made prior to data collection, had an average
width at half-height of 0.268 with a take-off angle of 6.08.
Scans of (1.63þ0.30 tan u)8 were made at speeds of
32.08/min (in omega). The weak reflections (I,10.0s(I))
were rescanned (maximum of five scans) and the counts
were accumulated to ensure good counting statistics.
Stationary background counts were recorded on each side
of the reflection. The ratio of peak counting time to
background counting time was 2:1. The diameter of the
incident beam collimator was 0.5 mm and the crystal to
detector distance was 235 mm. The computer-controlled
slits were set to 3.0 mm (horizontal) and 3.0 mm (vertical).
Of the 7757 reflections which were collected, 7156 were
unique (Rint¼0.023). The intensities of three representative
reflections were measured after every 150 reflections. No
decay correction was applied. The linear absorption
coefficient, m, for Mo Ka radiation is 4 cm21. An empirical
absorption correction based on azimuthal scans of several
reflections was applied which resulted in transmission
factors ranging from 0.88 to 1.00. The structure was solved
by direct methods and expanded using Fourier techniques.
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
916 observed reflections (I.3.00s(I)) and 280 variable
parameters and converged (largest parameter shift was 0.00
times its esd) with unweighted and weighted agreement
factors of: R¼0.054, Rw¼0.067, and R1¼0.054 for
I.3.0s(I) data. The standard deviation of an observation
of unit weight was 1.54. The weighting scheme was based
1
10.9 g (61% yield) of 17 as a pale yellow oil. H NMR
(CDCl3) d¼2.37 (s, 3H), 2.40 (s, 3H), 2.79 (d, J¼7.6 Hz,
2H), 6.53 (tm, J¼7.6 Hz, 1H), 6.85 (dd, J¼11.5, 5.8 Hz,
1H), 7.10 (d, J¼5.8 Hz, 1H), 7.48 (dd, J¼11.5, 1.2 Hz, 1H);
13C NMR (CDCl3) d¼22.5, 26.0, 26.2, 130.3, 132.6, 132.7,
133.6, 134.2, 139.2, 197.0, 197.3. IR (liq. film) n (cm21
)
3025m, 2927m, 1666s, 1603m, 1538m, 1430m, 1256s,
1211s, 1020m, 975m, 774m; MS (70 eV) m/z (rel. intensity)
176 (Mþ, 100), 161 (22), 133 (15), 105 (22), 91 (36), 63
(18); UV lmax (hexane) 236 nm (log 1¼4.15), 292 (3.59).
Found: 176.0836. Calcd for C11H12O2: M, 176.0837.
1
3.2. Determination of pKR values
The UV spectra in various pH of 50% aqueous acetonitrile
solutions were measured by exactly the same method of
Komatsu et al.1 Observed absorbance at the longest
absorption maxima at 383 nm for 9 and at 400 nm for 10
was plotted against pH to give a classical titration curve,
whose midpoint was taken as the pKRþ. Accuracy is ^0.1.
3.3. Cyclic voltammetry
A standard three-electrode cell configuration was employed
using a glassy carbon disk working electrode, a Pt wire
auxiliary electrode, and an Ag wire as an Ag/Agþ quasi-
reference electrode. The reference electrode was calibrated
at the completion of each measurement on a saturated
calomel electrode (SCE). Cyclic voltammetry was
measured in an acetonitrule solution with tetrabutyl-
ammonium perchlorate as a supporting electrolyte and a
on counting statistics and included a factor (p¼0.050) to
P
downweight the intense reflections. Plots of w(lFol2lFcl)2
vs lFol, reflection order in data collection, sin u/l and
various classes of indices showed no unusual trends. The
maximum and minimum peaks on the final difference
2
3
˚
Fourier map corresponded to 0.13 and 20.17 e /A ,
respectively. Tables of fractional atomic coordinates,

M. Oda et al. / Tetrahedron 59 (2003) 2831–2841
2841
Chem. 1980, 92, 566–567, Angew. Chem. Int. Ed. Engl. 1980,
19, 545–546.
thermal parameters, bond lengths and angles have been
deposited at the Cambridge Crystallographic Data Center,
12 Union Road, Cambridge CB2 1EZ, United Kingdom
(CCDC 172674).
9. Yamamoto, K.; Murata, I. Angew. Chem. 1976, 88, 262.
Angew. Chem. Int. Ed. Engl. 1976, 15, 240–541.
10. A preliminary account of this work has appeared; Oda, M.;
Kainuma, H.; Miyatake, R.; Kuroda, S. Tetrahedron Lett.
2002, 43, 3485–3488.
Acknowledgements
11. Vogel, E.; Deger, H. M.; Sombroek, J.; Palm, J.; Wagner, A.;
Lex, J. Angew. Chem. 1980, 92, 43–45, Angew. Chem. Int. Ed.
Engl. 1980, 19, 41–43; German Patent 2851790.
The present work was supported by a Grant-in-Aid for
Scientific Research (No. 13640528 to M. O.) from the
Ministry of Education, Culture, Sports, Science, and
Technology, Japan.
12. Murata, S.; Suzuki, M.; Noyori, R. Tetrahedron Lett. 1980, 21,
2527–2528.
13. Mukaiyama, T.; Narasaka, K. Org. Synth. 1987, 65, 6–11.
14. For recent results for preparing tetrahydroazulen-1-ones by the
Nazarov cyclization, see; Oda, M.; Yamazaki, T.; Kajioka, T.;
Miyatake, R.; Kuroda, S. Liebigs Ann./Recueil 1997,
2563–2566. Kajioka, T.; Oda, M.; Yamada, S.; Miyatake,
R.; Kuroda, S. Synthesis 1999, 184–187. Oda, M.; Kajioka, T.;
Haramoto, K.; Miyatake, R.; Kuroda, S. Synthesis 1999,
1349–1353. Oda, M.; Kajioka, T.; Ikeshima, K.; Miyakake,
R.; Kuroda, S. Synth. Commun. 2000, 30, 2335–2343.
15. Shapiro, R. H. Org. React. 1976, 23, 405–507.
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