Synthesis, stability, and crystal structure of an azulenium cation containing an adamantyl group

Article abstract of DOI:10.1002/ejoc.200800700

Starting from the trimethylsilyl enol ether of 1-acetyl-1,3,5- cycloheptatriene, the title 1H-azulenium cation was synthesized by a five-step sequence that involved a Noyori-Mukaiyama aldol reaction, a Nazarov cyclization, a Shapiro reaction, and a hydride abstraction. The Nazarov reaction of the aldol-type adduct resulted in the formation of an unusual double-bond position isomer, which has never been obtained in similar reactions forming tetrahydroazulenones. The pK_R⁺ value of the title cation was found to be 9.8, which is less than that expected by inductive stabilization from the number of carbons at the 1-position. The X-ray crystal structure of the title cation (ClO₄^- salt) reveals CH-O interactions and deformation of the azulenyl ion part. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800700

FULL PAPER
DOI: 10.1002/ejoc.200800700
Synthesis, Stability, and Crystal Structure of an Azulenium Cation Containing
an Adamantyl Group
Mitsunori Oda,*[a] Nobue Nakajima,[b] Nguyen Chung Thanh,[b] Kazuhiro Kitahara,[a]
Ryuta Miyatake,[b] and Shigeyasu Kuroda[b]
Keywords: Carbocations / Spiro compounds / Nazarov cyclizations
Starting from the trimethylsilyl enol ether of 1-acetyl-1,3,5-
cycloheptatriene, the title 1H-azulenium cation was synthe-
sized by a five-step sequence that involved a Noyori–Mukai-
yama aldol reaction, a Nazarov cyclization, a Shapiro reac-
tion, and a hydride abstraction. The Nazarov reaction of the
aldol-type adduct resulted in the formation of an unusual
double-bond position isomer, which has never been obtained
value of the title cation was found to be 9.8, which is less than
that expected by inductive stabilization from the number of
carbons at the 1-position. The X-ray crystal structure of the
title cation (ClO4 salt) reveals CH–O interactions and defor-
mation of the azulenyl ion part.
–
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
+
in similar reactions forming tetrahydroazulenones. The pKR
position should be more stable, although the effects may
saturate at some large number of carbons. The reason for
the stability of 7–9, which is not compatible with the
number of carbons in the alkyl groups, may be ascribed to
the relative difficulty of solvation of 9 due to congestion
around the 1-position by two slightly bulkier propyl groups.
Therefore, in order to increase the stability of 1,1-substi-
tuted azulenium cations by an inductive effect, the intro-
duction of a compact substituent with a larger number of
carbons is required. Considering this, we designed the
Introduction
The tropylium cation (1) has played an important role in
the historical development of positively charged Huckeloid
aromatic systems.[1,2] The stability of cyclic π-conjugated
+
carbocations, particularly as expressed in pKR values, aids
in understanding the capability of π-conjugation and the
outcome of various structural effects on delocalized carbo-
cations. We previously reported the syntheses of various
1,1-spiro-alkylated 1H-azulenium cations 2–6[3,4] and 1,1-
dialkylated 1H-azulenium cations 7–9[5] (Figure 1). Their
+
pKR values were in the range of 8.6–13.2, which are far
greater than that (3.9)[6] of 1. The enhanced thermodynamic
stability is attributable to the stabilization of both the in-
ductive and σ-π conjugation effects of the exocyclic ring at
the 1-position and the π-π conjugation of the double bond
at the 2,3-positions. The order of stability of the mono-spi-
roalkylated cations increases with the number of carbons of
the exocyclic ring, as 2 Ͻ 3 Ͻ 4.[3] On the other hand, the
order of stability of the dialkylated cations does not corre-
spond with the number of carbons of the alkyl groups at
the 1-position, as 7 Ͻ 9 Ͻ 8.[5] Since the degree of π-π
conjugation is the same in a series of the cations, the order
of stability of these cations should also correspond to the
degree of substitution at the 1-position. In other words, the
cations having more carbons in the substituent at the 1-
[a] Department of Chemistry, Faculty of Science, Shinshu Univer-
sity,
Asahi 3-1-1, Matsumoto, Nagano 390-8621, Japan
Fax: +81-263-37-3343
E-mail: mituoda@shinshu-u.ac.jp
[b] Graduate School of Science and Engineering, University of
Toyama,
Figure 1. Tropylium and azulenium ions with various spiro-car-
bocycles.
Gofuku 3190, Toyama 930-8555, Japan
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M. Oda et al.
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azulenium cation 10, containing an adamantyl group con-
structed with ten carbons. In this paper, we describe its syn-
thesis, stability, and X-ray structural analysis.
Results and Discussion
The title cation was synthesized by the method that we
had developed for synthesizing spiroalkylated cation 3 and
4 (Scheme 1).[3b,5,7] The Noyori–Mukaiyama aldol reac-
tion[8] of trimethylsilyl enol ether 11 with 2,2-dimethoxyad-
amantane in the presence of trimethylsilyl triflate gave 12
in 44% yield. The subsequent Nazarov cyclization[9,10] pro-
vided azulenone 13 in 50% yield. The azulenone 13 was
transformed into the 1,4-dihydroazulene 14 via the tosylhy-
drazone of 13 by the Shapiro reaction.[11] A final hydride
abstraction from 14 with trityl perchlorate resulted in the
desired cation 10 as yellowish brown crystals. The structure
of 10 was characterized by spectroscopic and combustion
analyses. All signals except unresolved peaks for hydrogens
1
in the H NMR spectrum of 10 were assigned by analysis
of H-H COSY and NOE experiments (Figure 2). The chem-
ical shifts of the olefinic protons of 10 along with those of
2, 3, and 4 are listed in Table 1. The protons at the 2- and
8-positions of 10 resonate at a lower magnetic field than
that those of 2, 3, and 4. In addition, the axial Ha and Hb
of the adamantyl group show similar NOEs with H-2 and
H-8, respectively, as was observed in 12, 13, and 14, sug-
gesting a steric compression effect[12] between Ha and H-2
and between Hb and H-8. The UV spectrum of 10 showed
three bands at 224, 246, and 367 nm, as seen in the spectra
of 2–4, and pH-dependent absorptions of the third band
Figure 2. Proton chemical shifts [δ, ppm] in CD3CN of 10 (left)
and the result of NOE experiments (right).
Table 1. Chemical shifts [δ, ppm] of the olefinic protons of cations
2, 3, 4, and 10 in CD3CN.
Entry
H-2
H-3
H-4
H-5
H-6
H-7
H-8
1
2
3
4
2[a] 7.72
3[a] 8.13
4[a] 8.00
7.33
7.49
7.42
7.47
8.96
9.12
8.99
8.94
8.90
9.00
8.90
8.86
8.75
8.85
8.74
8.74
8.77
9.01
8.82
8.74
9.00
9.10
9.07
9.72
10
8.53
+
[a] Data taken from ref.[3b]
.
were applied in its pKR measurement (vide infra).
follows. Calculations at the B3LYP/6-31G(d) level of theory
predict that enol 20 is more stable than 21 for the ada-
mantane-connected system, whereas enol 20 is less stable
than 21 for the cyclohexane-connected system (Figure 3).
The inverted energy difference for the adamatyl system is
mainly due to the short atomic distances (192.3 and
211.5 pm) between H-8 and hydrogens on the adamantyl
group in 21. Besides the theoretical study, the approach of
either a solvent molecule or its conjugate base for the de-
protonation of H-8a in 19 is thought to suffer from steric
repulsion with the adjacent methylene protons at the ada-
mantyl group, judging from the Dreiding model study. In
fact, congestion around H-8a is also seen in the reaction
rate of hydride abstraction from 14; while the reactions of
Scheme 1. Synthesis of 10.
Note that the structure of 13 is unusual; cyclizations of
various cycloheptatrienylethanones 15 under the same reac-
tion conditions yielded 1,2,3,8-tetrahydroazulen-1-ones in-
stead of the 1,2,3,3a-isomer 16 (Scheme 2).[3–5,7] Since the
Nazarov cyclization is believed to proceed through a 4π-
conrotatory electrocyclization of protonated intermediate
18,[10,13] the key process for giving a different product is the
deprotonation of oxyallyl cation intermediate 19
(Scheme 3). The unusual formation of 13 (22) in this study
is rationalized based on density functional theory (DFT)
calculations[14] of possible enol intermediates 20 and 21, as Scheme 2. Nazarov cyclization of 15.
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Adamantyl-Containing Azulenium Cation
1,4-dihydroazulenes with trityl cation were complete within by inductive stabilization of the nine carbons at the 1-posi-
1 h at room temperature, the reaction of 14 requires 17 h at tion. It is thought to be difficult for the adamantyl group
55 °C.
to accumulate the inductive effect because of its intricate
structural nature. Additionally, ineffective solvation due to
congestion around the carbon atom at the 1-position can
also apply to 10, as was suggested for 9.[5] In order to obtain
further structural information on the perchlorate salt of 10,
we examined its X-ray crystal structure.
+
Table 2. pKR values and reduction potentials of 2–4, 7–9, and 10.
Cation pKR value[a]
Reduction potentials (V vs.
SCE)[b]
+
Entry
1
2
3
4
5
6
7
2[c]
3[c]
9.9
10.0
10.4
8.6
10.1
9.2
–0.41
–0.46
–0.54
–0.38
–0.45
–0.46
–0.54
4[c]
7[d]
8[d]
9[d]
10[e]
9.8
[a] For measurements, see the Experimental Section. [b] Irrevers-
ible. [c] Taken from ref.[3b]. [d] Taken from ref.[5]. [e] This study.
Scheme 3. Possible reaction paths for the Nazarov cyclization.
Yellowish prismatic crystals of the perchlorate salt of 10
were obtained by recrystallization from a mixture of n-hex-
ane and dichloromethane. ORTEP drawings and the crystal
packing of 10 are shown in Figure 4. The C–C bond lengths
of the azulenyl part are comparable to those of 3 (Fig-
ure 5).[3b] Bond alternation of the seven-membered ring is
as small as that of 3. Slightly longer C–C bond lengths
(157.2 and 156.7 pm) at the C-1Ј(C-1) of the adamantyl
group imply σ-π conjugation, as seen in 3. The azulenyl
part of the crystal structure is non-planar, and the ada-
mantyl group is not symmetric against the azulenyl plane.
The deviation of carbons of the azulenyl part from its mean
plane is also shown in Figure 5. The average of the devia-
tion is 4.62 pm, which is greater than that of 3 (1.15 and
1.34 pm)[3b] and 5 (0.41 pm),[3d,3e] indicating clear defor-
mation of the azulenyl ring. Since the perchlorate salt of 10
has the same atom arrangement on both sides of the
azulenyl plane and there is sufficient space for the plane to
spread in the crystal cell, as seen in its packing, the defor-
mation of the azulenyl plane can be ascribed neither to the
steric congestion between H-2 and Ha and between H-8 and
Hb nor to the packing of the azulenyl part in the cell. The
distances between perchlorate oxygens and H-2 and H-4
was found to be in the range of 238.1–259.3 pm, which are
Figure 3. Enol intermediates calculated at the B3LYP/6-31G(d)
level of theory. Values in parentheses are relative total energies
[kcalmol–1].
Assuming an equilibrium between a carbocation and its
+
corresponding alcohol [Equation (1)], the pKR value,
which indicates thermodynamic stability for the carbo-
cations, can be determined.[1a]
R+ + H2O h ROH + H+
(1)
+
The pKR value of 10 was determined to be 9.8 by the sufficiently short to suggest CH–O interactions. Thus, the
UV method in 50% aqueous acetonitrile solution. The deformation is rather considered to be derived from these
thermodynamic stability of 10 is greater than that of the interactions, and it is assumed that 10 should have a planar
tropylium cation (1),[6] and is comparable to those of cat- azulenyl part in solution or the gas phase, unlike it does in
ions 2 and 3. The reduction potential of carbocations indi- the crystal structure. Indeed, DFT calculations of cation 10
cates their reluctance for reduction and provides another predict a planar structure (Figure 6), though the structure
empirical stability parameter for carbocations.[15] The re- shows shorter atomic distances between H-2 and Ha and
duction potentials for various azulenium ions measured by between H-8 and Hb. The X-ray and theoretical structures
+
cyclic voltammetry along with pKR values are shown in support the crowding-atom arrangement and the steric
1
Table 2. The reduction potential of 10 is greater than that compression shift in the H NMR spectrum. The average
of 2 or 3, and is the same as that of 4. Both the pKR+ value distances between Ha and H-2 and between Hb and H-8 in
and the reduction potential of 10 are less than that expected the crystal structure are 214.0 and 199.0 pm, respectively.
Eur. J. Org. Chem. 2008, 5301–5307
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M. Oda et al.
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Figure 4. Crystal packing and ORTEP drawings of 10.
Conclusions
We have applied previously developed methodology for
azulenium cations to the synthesis of the novel azulenium
ion 10. The Nazarov reaction of aldol-type adduct 12 pro-
vided a C–C double bond position isomer 13, which has
never been obtained in similar reactions forming other
tetrahydroazulenones. The formation of 13 was discussed
1
based on DFT calculations of enol intermediates. The H
NMR spectrum of 10 showed a clear steric compression
effect between Ha and H-2 and between Hb and H-8. The
pKR value of 10 was determined to be 9.8, which is less
Figure 5. Bond lengths [pm] (left) of 10 and deviations [pm] (right)
of the azulenyl carbons from its mean plane.
+
than that expected by inductive stabilization by the number
of carbons of the exocyclic rings at the 1-position. The X-
ray crystal structure of the perchlorate salt of 10 reveals
CH–O interactions and deformation of the azulenium ion
part.
Experimental Section
General Remarks: Melting points were measured with a Yanaco
MP-3 and are uncorrected. IR spectra were recorded with a Per-
kin–Elmer Spectrum RX I spectrometer. UV spectra were mea-
sured with a Shimadzu UV1600 spectrometer. 1H and 13C NMR
were recorded with tetramethylsilane as an internal standard with
Figure 6. Optimized structure (Chem3D output) of cation 10 and
atomic distances [pm]. Values from the for X-ray analysis are
shown in parentheses.
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Eur. J. Org. Chem. 2008, 5301–5307

Adamantyl-Containing Azulenium Cation
1
a JEOL α400 spectrometer. Mass spectra were measured with a
JMS-700 mass spectrometer. Cyclic voltammograms were recorded
with a Yanaco P11000 instrument. Column chromatography was
performed with Merck Kieselgel 60 Art 7743 or Wako activated
alumina. Diethyl ether was purified from sodium and benzophen-
one by distillation under an argon atmosphere. A diethyl ether solu-
tion of methyllithium was purchased from Kanto Chem. Co. and
was titrated before use. Trimethylsilyl triflate was purchased from
Tokyo Chemical Industry, Inc. The synthesis of 11 was previously
reported.[7] Trityl perchlorate was prepared by the method of
Dauben et al.[16]
m.p. 189–193 °C. H NMR (400 MHz, CDCl3): δ = 1.26 (m, 1 H),
1.30 (m 1 H), 1.55–2.00 (m, 12 H), 2.09 (m, 2 H), 2.41 (s, 3 H),
3.04 (d, J = 16.8 Hz, 1 H), 5.32 (dd, J = 10.1, 5.2 Hz, 1 H), 6.24
(dd, J = 10.1, 5.2 Hz, 1 H), 6.73 (m, 2 H), 6.88 (d, J = 5.6 Hz, 1
H), 7.29 (d, J = 8.1 Hz, 2 H), 7.54 (s, 1 H), 7.85 (d, J = 8.1 Hz, 2
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.6, 26.7, 27.4, 33.56,
33.64, 33.85, 33.89 (2 C), 33.96, 34.3, 38.3, 46.7, 47.6, 118.0, 119.8,
125.7, 128.0, 129.6, 130.5, 131.0, 132.1, 135.4, 144.0, 157.5 ppm.
IR (KBr): ν = 2909 (s), 1162 (s) cm–1. MS (70 eV): m/z (%) = 434
˜
(9) [M]+, 297 (100), 250 (65), 193 (16), 179 (14), 141 (19), 135 (34),
129 (25), 91 (57). C26H30N2O2S (434.6): calcd. C 71.89, H 6.96, N
6.45; found C 71.88, H 7.00, N 6.49.
1-(Cyclohepta-1,3,5-trienyl)-2-(2-methoxyadamant-2-yl)ethanone (12):
A solution of trimethylsilyl triflate (92 µL, 50.0 mmol) in 1 mL of
dichloromethane was added dropwise to a solution of silyl enol ether
11 (1.03 g, 5.00 mmol) and 2,2-dimethoxyadamantane[17] (0.981 g,
5.50 mmol) in dichloromethane (25 mL) at –78 °C under a nitrogen
atmosphere. After being stirred for 12 h, the reaction mixture was
poured into of ice/water (50 mL). The aqueous layer was extracted
with dichloromethane (2ϫ50 mL). The combined organic layers
were washed with saturated aqueous NaHCO3 and brine and then
dried with anhydrous MgSO4. The solvent was removed under re-
duced pressure, and the residue was purified by column chromatog-
raphy (SiO2, 3% ethyl acetate in hexane as the eluent) to give 0.659 g
1Ј,8aЈ-Dihydrospiro[adamantane-2,1Ј-azulene] (14): To a suspension
of 16 (200 mg, 0.461 mmol) in dry diethyl ether (20 mL) at 0 °C
under a nitrogen atmosphere, methyllithium (0.8  diethyl ether
solution, 2.2 mL, 2.3 mmol) was added slowly with a syringe. After
the addition, the mixture was stirred for 12 h. The mixture was
quenched by adding water carefully and was poured into a mixture
of diethyl ether and ice/water. The aqueous layer was extracted with
diethyl ether (2ϫ50 mL). The combined organic layers were
washed with brine and dried with anhydrous MgSO4. The solvent
was removed under reduced pressure, and the residue was purified
by column chromatography (SiO2, hexane as the eluent) to give
1
1
(44% yield) of 12 as a pale yellow solid; m.p. 81–82 °C. H NMR
13 mg (11% yield) of 14 as a pale yellow oil. H NMR (400 MHz,
(400 MHz, CDCl3): δ = 1.49 (dm, J = 12.0 Hz, 2 H), 1.69 (br. s, 2 CDCl3): δ = 1.34 (m, 1 H), 1.56–1.93 (m, 8 H), 1.99 (m, 2 H), 2.09
H), 1.76–1.79 (m, 3 H), 1.86–1.89 (m, 3 H), 2.11–2.13 (m, 4 H), 2.65 (tm, J = 10.6 Hz, 2 H), 2.20 (dm, J = 13.2 Hz, 1 H), 2.35 (d, J =
(d, J = 7.1 Hz, 2 H), 3.09 (s, 2 H), 3.16 (s, 3 H), 5.57 (dt, J = 9.2, 5.0 Hz, 1 H, H-8a), 5.10 (dd, J = 9.6, 5.0 Hz, 1 H, H-8), 6.04 (d, J
7.1 Hz, 1 H), 6.25 (dd, J = 9.2, 5.8 Hz, 1 H), 6.69 (dd, J = 10.9, = 5.6 Hz, 1 H, H-2), 6.11 (dd, J = 10.8, 5.6 Hz, 1 H, H-7), 6.14 (d,
6.0 Hz, 1 H), 6.83 (dd, J = 10.9, 5.8 Hz, 1 H), 7.07 (d, J = 6.0 Hz, J = 5.6 Hz, 1 H, H-3), 6.42 (dd, J = 10.8, 5.6 Hz, 1 H, H-6), 6.60
1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 26.1, 27.0, 27.4, 32.7,
34.5, 34.6, 38.3, 39.1, 48.4, 80.2, 125.9, 126.9, 129.0, 131.1, 133.7, ppm. 13C NMR (100 MHz, CDCl3): δ = 26.8, 27.8, 31.4, 32.5, 33.8,
135.5, 198.9 ppm. IR (KBr): ν = 2910 (s), 2860 (m), 1645 (s), 1162 34.90, 34.92, 38.3, 39.8, 49.0, 56.4, 114.0, 120.1, 124.2, 127.8, 129.1,
(m) cm–1. MS (70 eV): m/z (%) = 298 (1) [M]+, 266 (17), 165 (35), 130.8, 144.6, 148.8 ppm. UV (MeOH): λ = 229, 234 sh, 318 nm.
(dd, J = 10.8, 5.6 Hz, 1 H, H-5), 6.68 (d, J = 5.6 Hz, 1 H, H-4)
˜
122 (12), 119 (20), 118 (100), 91 (45), 90 (33). C20H26O2 (298.4): IR (KBr): ν = 3050 (w), 3017 (m), 2908 (vs), 2856 (s), 1623 (m),
˜
calcd. C 80.50, H 8.78; found C 80.71, H 8.89.
1455 (s), 704 (s) cm–1. MS (70 eV): m/z (%) = 250 (100) [M]+, 193
(20), 179 (18), 154 (32), 135 (63), 128 (42), 115 (18), 91 (17).
HRMS: calcd. for C19H22 [M] 250.1723; found 250.1722.
1Ј,2Ј,3Ј,8aЈ-Tetrahydrospiro[adamantane-2,1Ј-azulen]-3Ј-one (13): A
mixture of 12 (400 mg, 1.34 mmol) in formic acid (10 mL) and
phosphoric acid (10 mL) was heated at 90 °C for 12 h. The resuling
dark brown mixture was then poured into water and was extracted
with diethyl ether (3ϫ50 mL). The combined organic layers were
washed with saturated aqueous NaHCO3 and brine and then dried
with anhydrous MgSO4. The solvent was removed under reduced
pressure, and the residue was purified by column chromatography
(SiO2, 3% ethyl acetate in hexane as the eluent) to give 180 mg
(50% yield) of 13 as yellow microcrystals; m.p. 117–118 °C. 1H
1ЈH-Spiro[adamantane-2,1Ј-azulenium] Perchlorate (10): To a solu-
tion of 14 (101 mg, 0.404 mmol) in acetonitrile (5 mL) under a ni-
trogen atmosphere was added trityl perchlorate (134 mg,
1.00 mmol) in one portion. The mixture was stirred at 55 °C for
17 h. The solvent was removed under reduced pressure, and the
residue was dissolved in the least amount of dichloromethane pos-
sible. Diethyl ether was added to the solution, and solids formed
were collected and washed well with cold diethyl ether to give
NMR (400 MHz, CDCl3): δ = 1.54 (m, 1 H), 1.60–1.88 (m, 11 H), 90 mg of perchlorate salt of 10 as yellowish brown crystals; m.p.
2.08 (dm, J = 13.2 Hz, 1 H), 2.20 (m, 1 H), 2.31 (d, J = 5.2 Hz, 1 180 °C (dec.). 1H NMR (400 MHz, CD3CN): δ = 1.72 (m, 2 H),
H), 2.32 (d, J = 17.6 Hz, 1 H), 2.89 (d, J = 17.6 Hz, 1 H), 5.58 (dt,
J = 9.2, 5.2 Hz, 1 H), 6.37 (dd, J = 9.2, 6.0 Hz, 1 H), 6.84 (dd, J
= 10.4, 6.0 Hz, 1 H), 6.93 (dd, J = 10.4, 6.0 Hz, 1 H), 6.99 (d, J =
6.0 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 26.7, 27.5,
1.92–2.30 (m, 8 H), 2.47 (dm, J = 14.0 Hz, 2 H), 2.72 (dm, J =
14.0 Hz, 2 H), 7.47 (d, J = 6.0 Hz, 1 H), 8.53 (d, J = 6.0 Hz, 1 H),
8.74 (m, 2 H), 8.86 (t, J = 10.6 Hz, 1 H), 8.94 (d, J = 10.6 Hz, 1
H), 9.72 (d, J = 10.6 Hz, 1 H) ppm. 13C NMR (100 MHz, CD3CN):
33.4, 33.5, 33.6, 33.8, 34.4, 34.5, 38.4, 44.3, 45.8, 49.1, 122.3, 123.6, δ = 27.6, 28.9, 34.6, 35.9, 38.0, 40.5, 66.8, 134.7, 145.2, 147.5, 147.8,
126.2, 129.8, 130.4, 135.7, 203.3 ppm. UV (MeOH): λ = 223, 232
149.4, 153.1, 168.7, 171.7, 177.1 ppm. UV (CH3CN): λ = 224, 246,
sh, 294, 317 sh, 372 sh nm. IR (KBr): ν = 2909 (s), 2855 (s), 1701
280 sh, 367 nm. IR (KBr): ν 2917 (s), 1443 (s), 1073 (s) cm–1. MS
˜
˜
(s), 1617 (s), 720 (s) cm–1. MS (70 eV): m/z (%) = 266 (12) [M]+,
224 (17), 118 (100), 90 (66). C19H22O (266.4): calcd. C 85.67, H
8.32; found C 85.67, H 8.56.
(70 eV): m/z (%) = 249 (22) [C19H21]+, 248 (100), 205 (19), 193 (11),
191 (52), 179 (24), 165 (23), 152 (12), 141 (10). C19H21ClO4·
0.2CH2Cl2 (365.8): calcd. C 63.04, H 5.90; found C 63.27, H 6.01.
Synthesis of the Tosylhydrazone of 13: A suspension of 13 (100 mg, X-ray Crystallographic Analysis of 10: One crystal, having approxi-
0.376 mmol), tosylhydrazide (70 mg, 0.38 mmol), and dry THF
(5 mL) was stirred at 50 °C for 96 h. The solids formed were col-
lected by filtration and washed well with diethyl ether to give
137 mg (84% yield) of the tosylhydrazone of 13 as a yellow powder;
mate dimensions of 0.40ϫ0.30ϫ0.50 mm was mounted on a glass
fiber. All measurements were conducted with a Rigaku AFC7R
diffractometer with graphite monochromated Mo-Kα radiation and
a rotating anode generator. Cell constants and an orientation ma-
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M. Oda et al.
FULL PAPER
trix for data collection, obtained from a least-squares refinement
with the setting angles of 25 carefully centered reflections in the
range 25.45 Ͻ 2θ Ͻ 29.46°, corresponded to a primitive monoclinic
cell with dimensions: a = 7.439 (2) Å, b = 17.479 (4) Å, c = 12.878
(1) Å, β = 92.52 (1)°, and V = 1672.9 (4) Å3. For Z = 4 and formula
weight: 348.83, the calculated density was 1.38 gcm–3. Based on a
statistical analysis of the intensity distribution and the successful
solution and refinement of the structure, the space group was
uniquely determined to be P21/c (#14). The data were collected at
a temperature of 23 Ϯ 1 °C with the ω-2θ scan technique to a
maximum 2θ value of 60.0°. Omega scans of several intense reflec-
tions, made prior to data collection, had an average width at a half-
height of 0.26° with a take-off angle of 6.0°. Scans of (1.73 + 0.30
tanθ)° were made at speeds of 8.0° min–1 (in omega). The weak
reflections [I Ͻ 10.0σ(I)] were rescanned (maximum of 5 scans),
and the counts were accumulated to ensure good counting statis-
tics. 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 collima-
tor 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
5.0 mm (vertical). Of the 5396 reflections collected, 4891 were
unique (Rint = 0.028). The intensities of three representative reflec-
tions were measured after every 150 reflections. No decay correc-
tion was applied. The linear absorption coefficient µ for Mo-Kα
radiation was 2.5 cm–1. Azimuthal scans of several reflections indi-
cated no need for an absorption correction. The structure was
solved by direct methods and expanded with 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 4891 observed reflections [I
Ͼ –10.00σ(I)] and 217 variable parameters, and they converged
(largest parameter shift was 0.00 times its esd) with unweighted
and weighted agreement factors: R = 0.120, Rw = 0.211, and R1 =
0.072 for I Ͼ 2.0σ(I) data. The standard deviation of an observa-
tion of unit weight was 1.05. The weighting scheme was based on
counting statistics and included a factor (p = 0.050) to downweight
the intense reflections. Plots of Σw(|Fo| – |Fc|)2 vs. |Fo|, reflection
order in data collection, sinθ/λ, and various classes of indices
showed no unusual trends. The maximum and minimum peaks on
the final difference Fourier map corresponded to 0.98 and –0.71 e–/
Å3, respectively.
nology, Sports and Culture, Japan (Grant-in-Aid for Scientific Re-
search, no. 13640528; to M. O.) from and also by a research grant
from the Faculty of Science at Shinshu University.
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Acknowledgments
We gratefully thank Takao Ike-uchi and Hitoshi Kainuma at the
University of Toyama for their preliminary synthetic efforts. This
study was supported by the Ministry of Education, Science, Tech-
5306
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 5301–5307

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Received: August 7, 2008
Published Online: September 22, 2008
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Eur. J. Org. Chem. 2008, 5301–5307
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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