Control in spin-delocalization into the 2-substituted π-systems in 3-oxophenalenoxyl neutral radicals: evaluation by their dimeric structures and DFT calculations

Article abstract of DOI:10.1016/j.tet.2007.05.018

3-Oxophenalenoxyl derivatives, neutral π-radicals having two oxygen atoms at 1,3-position on a phenalenyl skeleton, possess most of their spin densities at the two oxygen atoms and the 2-position, featuring in easy dimerization at the 2-position. For the decrease in spin density at the 2-position by invoking spin-delocalization into the 2-substituted π-systems, we have designed 2-thienyl-3-hydroxyphenalenone derivatives as synthetic precursors of neutral π-radicals, and conducted their oxidation reactions by using a variety of oxidants. The chemical structures of the dimer obtained were unambiguously determined by FABMS, IR, and NMR spectra with help of density functional theory calculations, showing the formation of the bonds on the thienyl moieties. These observations and DFT calculations illustrate the occurrence of a considerable amount of spin-delocalization into the 2-substituted-thienyl moieties from the 3-oxophenalenoxyl skeletons.

Full text of DOI:10.1016/j.tet.2007.05.018

Tetrahedron 63 (2007) 7690–7695
Control in spin-delocalization into the 2-substituted p-systems in
3-oxophenalenoxyl neutral radicals: evaluation by their dimeric
structures and DFT calculations
a
c
b
Shinsuke Nishida,a,b,y Yasushi Morita,a,c, Tomohiro Ohba, Kozo Fukui, Kazunobu Sato,
*
Takeji Takuib, and Kazuhiro Nakasuji
a,
*
*
aDepartment of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
bDepartment of Chemistry, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
cPRESTO, Japan Science and Technology Agency, Honcho Kawaguchi, Saitama 332-0012, Japan
Received 5 March 2007; revised 2 May 2007; accepted 3 May 2007
Available online 8 May 2007
Abstract—3-Oxophenalenoxyl derivatives, neutral p-radicals having two oxygen atoms at 1,3-position on a phenalenyl skeleton, possess
most of their spin densities at the two oxygen atoms and the 2-position, featuring in easy dimerization at the 2-position. For the decrease
in spin density at the 2-position by invoking spin-delocalization into the 2-substituted p-systems, we have designed 2-thienyl-3-hydroxyphe-
nalenone derivatives as synthetic precursors of neutral p-radicals, and conducted their oxidation reactions by using a variety of oxidants. The
chemical structures of the dimer obtained were unambiguously determined by FABMS, IR, and NMR spectra with help of density functional
theory calculations, showing the formation of the bonds on the thienyl moieties. These observations and DFT calculations illustrate the oc-
currence of a considerable amount of spin-delocalization into the 2-substituted-thienyl moieties from the 3-oxophenalenoxyl skeletons.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
control in spin density distribution.5 In contrast, a 3-oxophe-
nalenoxyl derivative 3 with methoxyphenyl moiety at the 2-
position, a topological isomer of 1 and 2, easily gave dimeric
compound 4 having a C–C bond between the 2- and 20-
positions.6 This indicates that the spin density of 3 domi-
nates at the 2-position, although a appreciable amount is de-
localized into the methoxyphenyl moiety. In order to
decrease the spin density at the 2-position by invoking
spin-delocalization into the 2-substituted p-systems, we
have designed 2-thienyl-substituted 3-oxophenalenoxyl
derivatives 5a and 5b. Thiophene, a well-known five-
membered ring system, is likely to have a co-planar structure
with the 3-oxophenalenoxyl skeleton, which is favorable for
an extension of p-conjugated systems. Oxidation of 3-
hydroxyphenalenone derivatives 6a7 and 6b has given
dimeric compounds 7 and 8. Interestingly, their dimeric
structures feature in the formation of the bonds at the carbon
atoms of their thienyl moieties. In this study, we have eluci-
dated electronic-spin structures of 5a and 5b in terms of the
dimeric structures of 7 and 8 determined by spectroscopic
studies and density functional theory (DFT) calculations
from the theoretical side. These results illustrate that consid-
erable amounts of spin densities are delocalized into the 2-
substituted-thienyl moieties in the neutral p-radicals 5a
and 5b.
Stable organic p-radicals have attracted much attention
for both molecule-based magnetic materials1 and single-
component organic conductors.2 In order to synthesize new
stable organic p-radicals as components of these molecule-
based functionality materials, we have extensively studied
phenalenyl-based p-radicals with spin-delocalized and
highly spin-polarized nature. Some of these p-radicals are
extremely stable in air, and exhibit intriguing magnetic
and optical propeties.3 Oxophenalenoxyl systems are a
new class of neutral p-radicals possessing two oxygen atoms
on a phenalenyl skeleton as substituents. Among these sys-
tems, 6- and 4-oxophenalenoxyls 14 and 25a have high stabil-
ity in air due to extensively spin-delocalized nature on the
phenalenyl p-systems. These two p-radicals are topological
isomers, exhibiting the unique spin density distribution na-
ture depending on the connectivity of the two oxygen atoms
on the phenalenyl skeleton, coined as topological symmetry
Keywords: 3-Oxophenalenoxyl; Neutral radical; Dimeric compounds; Spin
density.
* Corresponding authors. Tel.: +81 6 6850 5393; fax: +81 6 6850 5395;
e-mail: morita@chem.sci.osaka-u.ac.jp
Japan Society for the Promotion of Science fellow PD.
y
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.05.018

S. Nishida et al. / Tetrahedron 63 (2007) 7690–7695
Table 1. Synthesis of dimeric compounds 7 and 8
7691
Entry
6
Oxidant, equiv
Condition
Yield (%)
1a
2a
3b
4
a
a
a
a
PbO2, 21
Ag2CO3, 20
Alkalic K3[Fe(CN)6], 22
p-Benzoquinone, 4.8
rt, 24 h
rt, 25.5 h
rt, 40 h
rt, 15 min;
reflux, 3.5 h
rt, 10 min
rt, 1 h
rt, 1 h
rt, 1 h
rt, 1 h
7, 15
7, 21
7, 29
7, 21
5a
6a
7a
8a
9a
a
b
b
b
b
DDQ, 9.5
PbO2, 10
Ag2CO3, 5.1
p-Benzoquinone, 4.6
DDQ, 4.7
7, 40
8, 70
8, 98
8, 87
8, 79
a
In benzene.
In 10:1 benzene–H2O.
b
however, use of 2,3-dichloro-5,6-dicyanoquinodimethane
(DDQ) as an oxidant gave the highest yield (40%, entry
5). In contrast, the dimer 8 was obtained in high yields
(70–98%) in all cases (entries 6–9).
2.2. Structural determination of 7 and 8
The dimeric structures of 7 and 8 have unambiguously been
determined by a combination of FABMS, IR spectra, and 1H,
13C, HMQC, HMBC, and NOESY NMR spectra.10
The dimeric structure of 7 is depicted in Fig. 1a. FABMS of 7
gave m/z 552, indicating elimination of two protons from
two molecules of 3-oxophenalenoxyl radical 5a. H NMR
2. Results and discussion
1
2.1. Synthesis
spectrum revealed that these protons originated from the
thienyl moieties. 13C NMR spectrum showed a downfield
shift of one thienyl carbon (175.3 ppm) from the other
thienyl carbons (102.5–148.6 ppm), indicating that the car-
bon atom on a thienyl ring is linked with an oxygen atom
(Fig. 1a and Table 2). Furthermore, a long-range coupling
between 6-proton and 9-carbon was observed in HMBC
2-Thienyl-3-hydroxyphenalenone (6a) was prepared by fol-
lowing the procedure described in the literature.7 (5-tert-Bu-
tylthienyl)-3-hydroxyphenalenone (6b) was synthesized
according to the method depicted in Scheme 1. Ester deriv-
ative 10 was obtained in 62% yield by introduction of tert-
butyl group into a thiophene moiety of 9.8 Hydrolysis of
10 with KOH in EtOH–H2O gave an acid derivative 11 in
quantitative yield. The condensation reaction of 11 with
1,8-naphthalic anhydride in the presence of sodium acetate
at 190 ꢀC gave the 3-hydroxyphenalenone derivative 6b.
Scheme 1.
Oxidation of 6a and 6b with a variety of organic or inorganic
oxidants gave dimeric compounds 7 as a dark red powder
and 8 as a yellow powder, respectively (Table 1).9 The dimer
7 was obtained in low yields in the case of entries 1–5,
Figure 1. Chemical structures of 7 (a) and 8 (b), and optimized structures of
7 (c) and 8 (d) calculated by Gaussian 03 at the B3LYP/6-31G(d,p) level of
theory.12

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S. Nishida et al. / Tetrahedron 63 (2007) 7690–7695
Table 3. Observed and calculated 1H and 13C chemical shifts of 8
Table 2. Observed and calculated 1H and 13C chemical shifts of 7
Atom
Chemical shift, ppm
Calcdb
Atom
Chemical shift, ppm
Obsda
Atom
Chemical shift, ppm
Calcdb
Atom
Chemical shift, ppm
Calcdb
Obsda
Calcdb
Obsda
Obsda
H(6)
H(7)
H(13)
H(14)
C(1)
C(2)
C(3)
C(4)
C(5)
7.42
6.84
8.88
7.35
156.7
123.7
180.6
129.0
125.6
6.80
7.06
7.22
7.27
159.8
123.3
176.6
140.3
127.8
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
128.7
121.0
182.8
111.8
184.9
102.5
175.3
134.0
148.6
121.4
127.5
188.7
76.1
190.9
122.6
149.3
115.7
125.3
H(3)
H(6)
H(9)
H(10)
H(13)
C(1)
C(2)
C(3)
C(4)
6.64
1.37
5.83
6.65
7.09
1.30
6.60
6.73
C(5)
C(6)
C(7)
C(8)
35.5
32.2
71.4
131.8
122.2
130.2
161.2
34.4
38.3
30.1
77.8
143.7
120.2
114.7
157.3
37.8
0.39
1.49
C(9)
141.9
123.1
124.8
163.6
133.2
134.1
122.0
159.7
C(10)
C(11)
C(12)
C(13)
31.3
31.3
a
a
These chemical shifts were assigned by HMBC and HMQC measure-
ments in CDCl3 solution at 30 ꢀC.10
These values were calculated at the B3LYP/6-31G(d,p).
These chemical shifts were assigned by HMBC, HMQC, and NOESY
measurements in CD2Cl2–CF3CO2H solution at 30 ꢀC.10
These values were calculated at the B3LYP/6-31G(d,p).
b
b
spectra. These results reveal that the dimeric structure of 7
possesses an ether bond between the oxygen atoms at the
1-position and 12-position, and a C–C bond between the
5- and 9-positions (Fig. 1a).
the dimer 8 has a C–C bond only between the 2- and
7-positions, which indicates a fairly large steric hindrance
inhibiting an intramolecular formation of another bond.
Considering that the upfield shift of tert-butyl protons
H(13) was due to a ring-current effect of the opposite 3-
oxophenalenoxyl ring, a steric effect of the tert-butyl groups
seems to be the main factor.
The dimeric structure of 8 is shown in Figure 1b. FABMS
of 8 gave m/z 666, which is equal to two molecules of 5b.
An absorption band due to a hydroxyl group was observed
in an IR spectrum measured in a CCl4 solution (1.1ꢁ
10ꢂ3 M).10 1H NMR showed the disappearance of a thienyl
proton and upfield shift of protons of a tert-butyl group
(0.39 ppm) from the other one (1.37 ppm). NOESY correla-
tion was observed between a thienyl proton and a proton
on a 3-oxophenalenoxyl moiety.11 On the basis of these
spectroscopic results, the dimeric structure of 8 was deter-
mined, having a C–C bond between the 2- and 7-positions
(Fig. 1b).
These NMR studies reveal that the structures of 7 and 8 are
formed by dimerization reactions at the carbon atoms on
their thienyl moieties, indicating the occurrence of a consid-
erable amount of spin-delocalization into the 2-substituted-
thienyl moieties of 5a and 5b.
2.3. Spin density distributions of 3-oxophenalenoxyls
We have calculated the spin density distribution of 3-oxo-
phenalenoxyl,5a p-methoxyphenyl derivative 3,6b and 5a14
at the UBLYP/6-31G(d,p) level of theory (Fig. 2). These
calculations indicate that 5a possesses a co-planar structure
between the 3-oxophenalenoxyl and thiophene skeletons,
and a smaller spin density on the 2-position (r2) than 3-
oxophenalenoxyl and 3 (Fig. 2c and Table 4). In order to
evaluate the degree of spin-delocalization into the thienyl
moieties of 5a, we have made summation of the absolute
spin densities on the 3-oxophenalenoxyl moieties (Sjr3-
oxoj) and the 2-substituted p-systems (Sjr2-subj) (Table
4).15 These results showed that the percentages of spin-
delocalization into the 2-substituted p-systems were 35%
for 3 and 50% for 5a, illustrating that there occurs a larger
amount of spin-delocalization of 5a into the 2-substituted
p-systems than that of 3. These electronic-spin structures
combined with stereoelectronic effects are responsible for
the difference of the dimeric structures of 4 and 7, 8.
The dimeric structures of 7 and 8 showed that their dimeriz-
ing positions are on their thienyl moieties. In order to eluci-
date a stereoelectronic effect on the structural difference
between these dimers, we have calculated both the opti-
mized structures and chemical shifts of 7 and 8 by Gaussian
03 at B3LYP/6-31G(d,p) level of theory (Fig. 2c and d;
Tables 2 and 3).12 The calculated chemical shifts are in good
agreement with the observed ones.13 The dimer 7 has a thio-
phene-fused eight-membered ring structure formed by two-
step dimerization reactions (Fig. 1c), which may indicate
a low steric hindrance around the reactive site. In contrast,
Table 4. Spin densities at the 2-position (r2), sum of absolute spin densities
on the 3-oxophenalenoxyl moieties (Sjr3-oxoj) and on the 2-substituted p-
systems (Sjr2-subj) calculated for 3-oxophenalenoxyl, 3, and 5a at the
UBLYP/6-31G(d,p) level of theory
Compound
r2
Sjr3-oxoj, %a
1.443, 100
0.780, 65
0.593, 50
Sjr2-subj, %a
—
0.425, 35
0.593, 50
3-Oxophenalenoxyl
3
5a
+0.687
+0.401
+0.321
Figure 2. Spin density distributions of 3-oxophenalenoxyl (a), 3 (b), and 5a
(c) calculated by Gaussian 03 at the UBLYP/6-31G(d,p) level of theory.12
Red and blue robes denote positive and negative spin densities, respectively.
a
Percentage of sum of absolute spin densities to total absolute spin densi-
ties (Sjr3-oxoj+Sjr2-subj).

S. Nishida et al. / Tetrahedron 63 (2007) 7690–7695
7693
3. Conclusion
argon atmosphere. To the mixture was added PbO2 (381 mg,
1.59 mmol), and the mixture was stirred overnight at room
temperature. The reaction mixture was filtered through
Celite column and washed with CHCl3 and concentrated
under reduced pressure. The residue was subjected to col-
umn chromatography with CH2Cl2 as an eluant to give dimer
7 (6.2 mg, 15%).
We have succeeded in increasing the spin-delocalization into
the thienyl moieties with the decrease in the spin densities at
the 2-positions of 2-thienyl-substituted 3-oxophenalenoxyl
derivatives 5a and 5b. Their spin structures feature in the
corresponding dimeric structures 7 and 8 and the spin den-
sity distributions acquired by DFT calculations. The dimeric
structures of 7 and 8 have been determined by a combination
of FABMS, IR, and NMR spectra, revealing that these di-
mers form bonds at the carbon atoms of their thienyl moie-
ties. The DFT calculation of 5a has exhibited a considerable
amount of spin-delocalization into the thienyl moiety and
correspondingly the decrease of the spin density at the 2-
position. This study demonstrates an effective manipulation
of the degree of spin-delocalized nature of open-shell p-
electronic systems by invoking functional substitution, and
provides important criteria to design novel spin-delocalized
p-radicals for realization of novel spin-mediated molecular
functional materials.
4.2.2. Oxidation with Ag2CO3. Compound 6a (19 mg,
0.069 mmol) was placed in a 50-mL round-bottomed flask
and dissolved with benzene (30 mL) under an argon atmo-
sphere. To the mixture was added Ag2CO3 (371 mg,
1.35 mmol), and the mixture was stirred overnight at room
temperature. The reaction mixture was filtered through Cel-
ite column and washed with CHCl3 and concentrated under
reduced pressure. The residue was subjected to column chro-
matography with CH2Cl2 as an eluant to give 7 (3.9 mg,
21%).
4.2.3. Oxidation with K3[Fe(CN)6]. Compound 6a (20 mg,
0.070 mmol) was placed in a 50-mL round-bottomed flask
and dissolved with benzene (30 mL) under an argon atmo-
sphere. To the mixture was added K3[Fe(CN)6] (510 mg,
1.6 mmol, in potassium hydroxide aqueous solution,
5 mL), and the mixture was stirred at room temperature for
2 days. The organic layer was separated and dried over
Na2SO4, then filtered, and concentrated under reduced pres-
sure to give 7 (6 mg, 29%).
4. Experimental
4.1. General
1H and 13C NMR spectra were measured at 270 and
600 MHz with CDCl3 or CD2Cl2–CF3COOH as solvent
and Me4Si or residual solvents as internal standards. Corre-
lation NMR spectra (HMBC, HMQC, and NOESY) were
measured at 600 MHz with CDCl3 or CD2Cl2–CF3COOH
as solvent and Me4Si or residual solvents as internal stan-
dards. Infrared spectra were recorded using KBr plates,
CCl2CCl2 or CCl4 solution. EIMS spectra were recorded at
70 eV, and 3-nitrobenzyl alcohol was used as matrix for
FABMS spectra. Elemental analyses were performed at the
Graduate School of Science, Osaka University. Bulb-to-
bulb short-path distillation was performed by using a glass
tube oven (Kugelrohr). Silica gel 60 (100–200 mesh) was
used for column chromatography. Rf values on TLC were re-
corded on E. Merck precoated (0.25 mm) silica gel 60 F254
plates. The plates were sprayed with a solution of 10% phos-
phomolybdic acid in 95% EtOH and then heated until the
spots became clearly visible. Deactivated silica gel was pre-
pared by mixing with 6% water. CH2Cl2, tert-butyl chloride,
and benzene were dried over CaH2 and distilled under argon
prior to use. EtOH was dried over molecular sieves prior to
use. 2-Thienyl-3-hydroxyphenalenone (6a)7 and active
4.2.4. Oxidation with p-benzoquinone. Compound 6a
(19.0 mg, 0.068 mmol) was placed in a 50-mL round-
bottomed flask and dissolved with benzene (30 mL) under
an argon atmosphere. To the mixture was added p-benzoqui-
none (34 mg, 0.31 mmol), and the mixture was stirred
at room temperature for 6 h and refluxed for 1.5 h. The reac-
tion mixture was concentrated and subjected to column
chromatography with CH2Cl2 as an eluant to give 7 (4 mg,
21%).
4.2.5. Oxidation with 2,3-dichloro-5,6-dicyano-1,4-ben-
zoquinone (DDQ). Compound 6a (19 mg, 0.068 mmol)
was placed in a 50-mL round-bottomed flask and dissolved
with benzene (30 mL) under an argon atmosphere. To the
mixture was added DDQ (145 mg, 0.64 mmol), and the mix-
ture was stirred at room temperature for 10 min. The reaction
mixture was filtered and the residue was rinsed with ben-
zene. The solution was concentrated under reduced pressure
and subjected to column chromatography with CH2Cl2 as an
eluant to give 7 (8 mg, 40%).
16
PbO2 were prepared and purified by the procedure de-
scribed in the literatures. Ethyl 2-thienylacetate 9 was
prepared by esterification of commercially available 2-
thienylacetic acid in EtOH in the presence of concd
H2SO4. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)
was purified by recrystallization of purchased material from
CHCl3. Other reagents were used without purification. All
reactions requiring anhydrous conditions were conducted
under an argon atmosphere.
4.2.6. Physical data of dimer 7. A dark red powder. Mp
1
272–273 ꢀC, TLC Rf 0.29 (CH2Cl2); H NMR (600 MHz,
CDCl3) dH 6.84 (1H, d, J¼5.3 Hz), 7.35 (1H, d, J¼
6.3 Hz), 7.42 (1H, d, J¼5.3 Hz), 7.61 (1H, t, J¼7.8 Hz),
7.70 (1H, t, J¼7.8 Hz), 7.77 (1H, t, J¼8.3 Hz), 7.82 (1H,
t, J¼7.9 Hz), 8.08 (1H, d, J¼8.3 Hz), 8.19 (1H, d, J¼
7.3 Hz), 8.21 (2H, d, J¼7.9 Hz), 8.28 (1H, dd, J¼7.3 and
1.0 Hz), 8.53 (1H, dd, J¼7.3 and 1.0 Hz), 8.65 (1H, dd,
J¼6.9 and 1.3 Hz), 8.75 (1H, dd, J¼7.3 and 1.0 Hz), 8.88
(1H, d, J¼6.3 Hz); 13C NMR (600 MHz, CDCl3) d 184.9
(C), 182.8 (C), 180.6 (C), 175.3 (C), 156.7 (C), 148.6
(CH), 135.2 (C), 134.2 (CH), 134.1 (CH), 134.0 (CH),
133.1 (CH), 132.6 (C), 131.8 (C), 130.7 (CH), 129.9 (C),
4.2. Synthesis of dimeric compound 7
4.2.1. Oxidation with PbO2. 3-Hydroxyphenalenone deriv-
ative 6a (21 mg, 0.076 mmol) was placed in a 50-mL round-
bottomed flask and dissolved with benzene (30 mL) under an

7694
S. Nishida et al. / Tetrahedron 63 (2007) 7690–7695
129.6 (CH), 129.5 (CH), 129.0 (C), 128.7 (CH), 127.8 (C),
127.7 (CH), 127.1 (CH), 127.1 (C), 126.7 (CH), 126.7
(CH), 126.6 (CH), 125.9 (C), 125.6 (C), 123.7 (C), 123.0
2966, 1642, 1585 cmꢂ1; EIMS, m/z (%) 334 (M+, 39), 319
(M+ꢂCH3, 100).
(C), 121.0 (CH), 111.8 (C), 102.5 (C); IR (KBr) (nmax
1655, 1634, 1605, 1578 cmꢂ1
)
)
4.3.4. Oxidation with PbO2. 3-Hydroxyphenalenone deriv-
ative 6b (294 mg, 0.88 mmol) was placed in a 50-mL round-
bottomed flask and dissolved with benzene (300 mL) under
an argon atmosphere. To the mixture was added PbO2
(2.08 g, 8.70 mmol), and the mixture was stirred at room
temperature for 1 h. The reaction mixture was filtered
through Celite column and the residue was rinsed with
CHCl3. The solution was concentrated under reduced pres-
sure and subjected to column chromatography with 100:1
mixture of CH2Cl2 and ethyl acetate as an eluant to give
dimer 8 (205 mg, 70%).
;
IR (CCl4) (nmax
1638 cmꢂ1; FABMS, m/z 552 (M+).
4.3. Synthesis of dimeric compound 8
4.3.1. Ethyl 5-tert-butyl-2-thienylacetate (10). AlCl3
(3.60 g, 27.0 mmol) was placed in a 50-mL round-bottomed
flask and suspended with CH2Cl2 (6 mL). After cooling to
ꢂ78 ꢀC, CH2Cl2 (3 mL) solution of ethyl 2-thienylacetate
9 (4.60 g, 27.0 mmol) was added over 5 min to this mixture
and then stirred at this temperature for 5 min. CH2Cl2 solu-
tion (3 mL) of tert-butyl chloride (3.0 mL, 27.6 mmol) was
added over 15 min to this mixture, and stirred at ꢂ78 ꢀC
for 1 h. This reaction mixture was gradually warmed up to
room temperature and stirred at this temperature for 24 h.
This reaction mixture was poured into ice-water, and then or-
ganic layer was separated. Aqueous layer was extracted with
CH2Cl2 (20 mLꢁ2). The combined organic layers were
washed with H2O (40 mL), 1% KOH aq (30 mL), and H2O
(30 mL), successively. The resulting organic layer was dried
over Na2SO4, filtered, and concentrated under reduced pres-
sure. The residual oil was subjected bulb-to-bulb short-path
distillation (Kugelrohr) to yield tert-butylated ester 10
4.3.5. Oxidation with Ag2CO3. Compound 6b (29 mg,
0.087 mmol) was placed in a 50-mL round-bottomed flask
and dissolved with benzene (30 mL) under an argon atmo-
sphere. To the mixture was added Ag2CO3 (124 mg,
0.45 mmol), and the mixture was stirred at room temperature
for 1 h. The reaction mixture was filtered through Celite col-
umn and the residuewas rinsed with CHCl3. The solution was
concentrated under reduced pressure to give 8 (28 mg, 98%).
4.3.6. Oxidation with p-benzoquinone. Compound 6b
(19 mg, 0.056 mmol) was placed in a 50-mL round-bot-
tomed flask and dissolved with benzene (15 mL) under an ar-
gon atmosphere. To the mixture was added p-benzoquinone
(28 mg, 0.26 mmol), and the mixture was stirred at room
temperature for 1 h. The reaction mixture was concentrated
and subjected to column chromatography with CH2Cl2 as an
eluant to give 8 (16 mg, 87%).
1
(3.76 g, 62%) as colorless oil. TLC Rf 0.47 (benzene); H
NMR (270 MHz, CDCl3) dH 1.28 (3H, t, J¼7.1 Hz), 1.36
(9H, s), 3.75 (2H, d, J¼1.0 Hz), 4.18 (2H, q, J¼7.2 Hz),
6.65 (1H, d, J¼3.3 Hz), 6.72 (1H, d, J¼3.3 Hz).
4.3.2. 5-tert-Butyl-2-thienylacetic acid (11). tert-Butylated
ethyl ester 10 (3.76 g, 16.6 mmol) was placed in a 100-mL
round-bottomed flask and dissolved with EtOH (30 mL).
To this mixture was added aqueous (20 mL) solution of
KOH (7.05 g, 126 mmol) and refluxed for 9 h. After most
of EtOH was removed by distillation, concd HCl was added
at room temperature. The reaction mixture was poured into
a H2O and extracted with CH2Cl2. The organic extracts
were dried over Na2SO4, filtered, and concentrated under re-
duced pressure to give almost pure carboxylic acid 11
(3.34 g, 100%) as a light yellow oil. TLC Rf 0.51 (ethyl ace-
tate); 1H NMR (270 MHz, CDCl3) dH1.36 (9H, s), 3.81 (2H,
d, J¼1.0 Hz), 6.67 (1H, d, J¼3.6 Hz), 6.75 (1H, d,
J¼3.6 Hz).
4.3.7. Oxidation with 2,3-dichloro-5,6-dicyano-1,4-ben-
zoquinone (DDQ). Compound 6b (19 mg, 0.057 mmol)
was placed in a 50-mL round-bottomed flask and dissolved
with benzene (15 mL) under an argon atmosphere. To the
mixture was added DDQ (60 mg, 0.27 mmol), and the mix-
ture was stirred at room temperature for 1 h. The reaction
mixture was filtered and the residue was rinsed with ben-
zene. The solution was concentrated under reduced pressure
and subjected to column chromatography with CH2Cl2 as an
eluant to give 8 (15 mg, 79%).
4.3.8. Physical data of dimer 8. Yellow powder. Mp 197–
1
198 ꢀC; TLC Rf 0.53 (1:1 hexane–ethyl acetate); H NMR
(270 MHz, CD2Cl2–CF3COOH) dH 0.39 (9H, s), 1.37 (9H,
s), 5.83 (1H, d, J¼4.0 Hz), 6.64 (1H, s), 6.65 (1H, d,
J¼4.0 Hz), 7.86 (2H, dd, J¼8.3 and 7.3 Hz), 7.99 (2H, t, J¼
7.8 Hz), 8.38 (2H, dd, J¼8.4 and 1.2 Hz), 8.59 (2H, dd,
J¼8.3 and 1.0 Hz), 8.69 (2H, dd, J¼7.3 and 1.3 Hz), 8.93
(2H, dd, J¼7.8 and 1.2 Hz); 13C NMR (600 MHz,
CD2Cl2–CF3COOH) dC 195.6 (C), 175.6 (C), 163.6 (C),
161.2 (C), 141.9 (C), 140.4 (C), 137.2 (CH), 135.7 (CH),
133.3 (C), 132.3 (CH), 131.8 (CH), 131.5 (C), 130.2
(CH), 128.6 (CH), 127.7 (CH), 126.2 (C), 125.5 (C), 124.8
(CH), 123.1 (C), 122.2 (CH), 71.4 (C), 35.5 (C), 34.4 (C),
32.2 (CH3), 31.3 (CH3); IR (KBr) (nmax) 3444, 3062, 2961,
1686, 1655, 1638, 1578 cmꢂ1; IR (CCl4) (nmax) 3313,
2965, 1669, 1742, 1702, 1669, 1640 cmꢂ1; EIMS, m/z (%)
666 (M+, 31%); FABMS, m/z, 666 (M+); Anal. Calcd (%)
for C42H34O4S2: C, 75.65; H, 5.14; N, 0.00. Found: C,
75.36; H, 5.25; N, 0.00.
4.3.3. 2-(5-tert-Butylthienyl)-3-hydroxyphenalenone
(6b). 1,8-Naphthalic anhydride (1.14 g, 5.75 mmol) was
placed in a 30-mL round-bottomed flask and mixed with
tert-butylated thienylacetic acid 11 (3.34 g, 16.8 mmol)
and NaOAc (0.72 g, 8.73 mmol), and then stirred at
190 ꢀC for 4 h. After cooling to room temperature, the reac-
tion mixture was directly subjected to deactivated silica gel
column chromatography with benzene as an eluant to give
6b (0.87 g, 45%) as a purple solid. TLC Rf 0.41 (CH2Cl2);
1H NMR (270 MHz, CDCl3) dH 1.45 (9H, s), 6.93 (1H, d,
J¼3.6 Hz), 7.02 (1H, s), 7.09 (1H, d, J¼3.6 Hz), 7.68 (1H,
dd, J¼8.3 and 7.3 Hz), 7.76 (1H, dd, J¼8.1 and 7.4 Hz),
8.10 (1H, dd, J¼8.3 and 1.0 Hz), 8.18 (1H, dd, J¼8.1 and
1.2 Hz), 8.36 (1H, dd, J¼7.3 and 1.3 Hz), 8.65 (1H, dd,
J¼7.4 and 1.2 Hz); IR (KBr) (nmax) 3456, 3070, 2962,
1630, 1603, 1553 cmꢂ1; IR (CCl2CCl2) (nmax) 3460, 3063,

S. Nishida et al. / Tetrahedron 63 (2007) 7690–7695
7695
Y.; Fukui, K.; Sato, K.; Shiomi, D.; Takui, T.; Nakasuji, K.
Angew. Chem., Int. Ed. 2005, 44, 7277–7280.
Acknowledgements
5. (a) Morita, Y.; Kawai, J.; Fukui, K.; Nakazawa, S.; Sato, K.;
Shiomi, D.; Takui, T.; Nakasuji, K. Org. Lett. 2003, 5, 3289–
3291; (b) Morita, Y.; Kawai, J.; Nishida, S.; Fukui, K.;
Nakazawa, S.; Sato, K.; Shiomi, D.; Takui, T.; Nakasuji, K.
Polyhedron 2003, 22, 2205–2208.
6. (a) Hatanaka, K.; Morita, Y.; Ohba, T.; Yamaguchi, K.; Takui,
T.; Kinoshita, M.; Nakasuji, K. Tetrahedron Lett. 1996, 37,
873–876; (b) Morita, Y.; Nishida, S.; Fukui, K.; Hatanaka,
K.; Ohba, T.; Sato, K.; Shiomi, D.; Takui, T.; Yamamoto, G.;
Nakasuji, K. Polyhedron 2005, 24, 2194–2199.
This work was partly supported by PRESTO-JST, Grant-in-
Aid for Scientific Research in Priority Areas ‘Application of
Molecular Spins’ (Area No. 769) from Ministry of Educa-
tion, Culture, Sports, Science, and Technology, Japan,
21COE program ‘Creation of Integrated EcoChemistry of
Osaka University’, and Japan Society for the Promotion of
Science.
Supplementary data
7. Minchev, S.; Stoyanov, N. M.; Kashchieva, M. V.; Miteva,
M. I.; Alexiev, B. V. Dokl. Bulg. Akad. Nauk. 1992, 45, 45–48.
8. Ester 10 was prepared according to the method of tert-butyl-
ation of thiophene, see: Belen’kii, L. I.; Yakubov, A. P.
Tetrahedron 1984, 40, 2471–2477.
9. Oxidation of 3-hydroxyphenalenone derivatives 6a and 6b with
PbO2 in 1-methylnaphthalene between 30–170 ꢀC in sealed
ESR tubes gave no ESR signals of the corresponding neutral
radicals 5a and 5b.
1H, 13C, HMQC, and HMBC NMR spectra, IR spectra,
1
calculated H and 13C chemical shifts of 7 and 8, NOESY
1
NMR spectrum of 8, observed and calculated H and 13C
chemical shifts of 4, and the result of DFT calculation of
spin density distribution of 5a. Supplementary data associ-
ated with this article can be found in the online version, at
doi:10.1016/j.tet.2007.05.018.
10. IR and NMR spectra are shown in Supplementary data.
11. NOESY spectra of 8 showed a correlation between the proton
in 10-position and those in the opposite 3-oxophenalenoxyl
moiety; see, Supplementary data.
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