Generation and amphoteric redox properties of novel neutral radicals with the TTF-TCNQ hybrid structure

Article abstract of DOI:10.3987/COM-00-S(I)60

One electron oxidation of 4-(2-tetrathiafulvalenyl)phenyl substituted dicyanomethylides (1^-) gave black solids of the title radicals (1^?). They exhibit quite high electrochemical amphotericity, which may be responsible for their good

Full text of DOI:10.3987/COM-00-S(I)60

HETEROCYCLES, Vol. 54, No. 1, 2001, pp. 387 - 394, Received, 31st May, 2000
GENERATION AND AMPHOTERIC REDOX PROPERTIES OF NOVEL
1
NEUTRAL RADICALS WITH THE TTF-TCNQ HYBRID STRUCTURE
Takanori Suzuki,* Masahiro Yamada, Masakazu Ohkita, and Takashi Tsuji
Division of Chemistry, Graduate School of Science, Hokkaido University,
Sapporo 060-0810, Japan; e-mail: tak@sci.hokudai.ac.jp
Abstract - One electron oxidation of 4-(2-tetrathiafulvalenyl)phenyl substituted
-
dicyanomethylides (1 ) gave black solids of the title radicals (1 ). They exhibit
･
quite high electrochemical amphotericity, which may be responsible for their good
-7
electrical conductivities (σ = ca. 10 S cm ) as a single component. Isomeric
-1
･
radicals (2 ) with a m-phenylene spacer could not be obtained under the similar
conditions probably due to insufficient delocalization of the unpaired electron.
Recently much attention has been focused on multi-stage organic redox systems in the field of materials
2
science. Among them, a series of compounds showing electrochemical amphotericity is of special
3
interest, where one electron-oxidation and reduction occur within an easily accessible potential window.
4
5
Beside the topics as NLO materials or molecular electronic devices, another unique property is
6
electrical conductivity as a single component.
7,8
Graphite is the definitive example that exhibits the
sum
ox red
≡ E + (-E ) = 0. Although it is quite difficult to endow the closed-
ultimate amphotericity with E
sum
3
< 0.5 V), it would be much easily achieved in neutral
shell species with pretty high amphotericity (E
8
radicals as suggested by our previous study. On the basis of these results, we have now designed novel
sum
neutral radicals which may exhibit very high amphotericity (E
< 0.2 V) by incorporating both very
9
strong electron-donating and -accepting subunits. Tetrathiafulvalene (TTF) is an electron-rich skeleton
ox
of choice (E
= +0.36 V), whose donating property is finely tuned by substituents such as Me groups
ox
1
･
= +0.31 V). Phenyldicyanomethyl [PhC(CN) ] is selected as an open-shell
red
(2,3-Me -TTF: E
2
1
2
acceptor. Its electron affinity is as high as tetracyanoquinodimethane (TCNQ) (E
= +0.18 V), which
1
- ox
is shown by measuring the oxidation potential of PhC(CN) [E = +0.19 V (irrev.)]. Connection of
2
･
these two subunits furnishes the novel radicals (1 and 2 ) having a p- or m-phenylene unit,respectively
･
Although the irreversible oxidation wave of
-
PhC(CN) suggests the poor stability of
NC
CN
CN
•
2
•
･
PhC(CN) itself, the newly designed radicals
CN
2
R
R
R
R
S
S
S
S
S
S
S
S
･
with the TTF-TCNQ hydride structure (1 and
1•
2•
･
2 ) are expected to be much more stable due
to delocalization of the unpaired electron over
the enlarged π-syste.

RESULTS AND DISCUSSION
Preparation, structure, and redox properties of (4- and 3-dicyanomethylphenyl)tetrathiafulvalenes
(H1 and H2) with the TTF-TCNQ hydride structure. p- and m-Diiodobenzenes were subjected to
10
Takahashi's arylmalononitrile preparation, and the resultant iodophenylmalononitriles (p-3 and m-3)
11
were coupled with 2-trimethylstannyl-TTF (4a) to give H1a and H2a with the TTF-TCNQ hydride
structure in 34 and 35% yields, respectively (Scheme 1). Similar cross-coupling reactions of 6,7-
dimethyl-2-trimethylstannyl-TTF (4b) with p-3 and m-3 afforded H1b (y. 36%) and H2b (y. 39%),
respectively.
X-Ray structural analysis on H2b at 123 K has revealed that the substituents on TTF cause no significant
distortion of the TTF skeleton (Figure 1). The whole π-electron systemof H2b adoptsaplanar geometry;
the dihedral angle between the TTF unit and the benzene nucleus is 3.7°. Furthermore, the largest
deviation of non-hydrogen atoms from the least-square molecular plane excluding CN groups is only 0.17
Å. Therefore, there exist no steric reasons that may prevent the π-conjugation between the TTF unit and
the phenylene group in the compounds studied here. Another important feature is that the bond length of
the central tetrathio-substituted olefin [1.352(3) Å] is comparable with that of the parent TTF [1.349(3)
13
14
Considering that this bond length is sensitive to the degree of charge-transfer on TTF, the
Å].
15
similarity of these values shows absence of any electronic effects from the dicyanomethyl group in
these neutral donors.
In accord with negligible CT interaction between two subunits, redox behaviors of H1a and H2a
resemble that of the parent TTF (Table 1). Their oxidation potentials measured in MeCN are essentially
identical to each other, indicating that C H CH(CN) moiety gives no effects on the reversible two-stage
2
6
4
one electron-oxidation process of TTF (Scheme 2). This idea was also supported by comparisons among
ox
H1b, H2b, and Me -TTF. Again, the E values are insensitive to the substituted position of
2
dicyanomethyl group on the benzene nucleus. On the contrary, quite different behaviors were observed
-
for the anions (1 and 2 ) having a p- or m-phenylene unit as shown in the next section.
-
Scheme 1
CH(CN)2
•
SnMe3
CH(CN)2
R
R
R
R
S
S
S
S
S
S
S
S
Pd(0)
•
•
•
I
+
4a: R = H
p-3 or m-3
H1a: R = H
H2a: R = H
4b: R = Me
H1b: R = Me
H2b: R = Me
(from p-3)
(from m-3)
Scheme 2
CH(CN)2
e
CH(CN)2
CH(CN)2
e
S
S
S
S
S
+
S
S
+
S
S
•
S
S
+
S
e
e
H1a2+
H1a
ox
H1a+•
ox
E
E

-
Generation and redox properties of 4- and 3-(2-tetrathiafulvalenyl)phenyldicyanomethylides (1
-
and 2 ): the anionic precursors of the radicals. Figure 2 shows the cyclic voltammogram of the anion
-
(1a ) generated in situ by adding 1 eq of Et N to an MeCN solution of H1a. Three pairs of reversible or
3
quasi-reversible waves are observed. The first process was assigned to the one electron-oxidation of
-
-
C H C(CN) moiety by comparisons with the potentials of reference compounds. The TTF unit in 1a
6
4
2
ox
ox
undergoes two-stage one electron-oxidation at E and E (Scheme 3). Stronger donating property of
2
3
-
-
1a than that of PhC(CN) is due to the substitution effect of the electron-rich TTF skeleton. On the
2
-
ox
other hand, slight difficulty in oxidizing TTF unit in 1a at E
is attributable to the strong electron-
2
･
withdrawing effect of C H C(CN) moiety. Similar behavior was observed in the dimethyl derivative
6
4
2
-
ox
ox
-
sum
･
(1b ). The differences between E
and E
in 1 correspond to the E
values of 1 by definition.
1
2
･
-
Thus, the radicals (1 ) derived by the one electron-oxidation of the anionic precursors (1 ) are shown to
sum
･
･
exhibit quite high amphotericity with E
of 0.29 V for 1a and 0.24 V for 1b , respectively.
a
Table 1. Oxidation potentials of neutral
donors (H1 and H2) and TTFs
ox
ox
E
1
E
2
H1a
H1b
H2a
H2b
TTF
+0.37
+0.32
+0.36
+0.32
+0.36
+0.31
+0.72
+0.67
+0.73
+0.68
+0.74
+0.68
Me -TTF
2
a
-3
E / V vs SCE, 0.1 mol dm Et NClO in
4
4
-1
MeCN, 100 mV s . Values in Table 2
were obtained under the same conditions.
Table 2. Oxidation potentials of anionic precursors
-
-
a
(1 and 2 ) generated in situ
ox
ox
ox
E
1
E
2
E
3
-
b
b
1a
+0.12
+0.10
+0.17
+0.18
+0.19
+0.41
+0.34
+0.73
+0.70
-
1b
-
c
c
c
d
d
d
d
2a
2b
(+0.35)
(+0.75)
-
(+0.32)
(+0.69)
-
-
-
PhC(CN)
2
a Anions were generated by addition of 1 eq of Et N
3
b
to H1 or H2, respectively.
Quasi-reversible
c
d
waves. Irreverible waves.
Oxidation potentials
of the products formed at the first oxidation process.

9,16
Although generation and isolation of highly amphoteric molecules have been proven very difficult,
-
electrochemical reversibility observed in the interconversion between 1 and 1 prompted us to
･
-
-
preparative-scale oxidation of 1 . When a brown MeCN solution of 1a generated from H1a and 1.2 eq
Et N was reacted with 1.5 eq I , a black powder precipitated immediately; it weighed 58% of the theory
3
2
･
for the radical (1a ). Similar I -treatment on 1b also afforded a black solid, and the same material was
-
2
obtained by the electrochemical oxidation in MeCN. Although full characterization of these solids was
hampered due to the very low solubility and instability in polar solvents, they were assigned to the
･
desired radicals (1 ) based on the combustion analyses and MS spectra. In the IR spectra, both radicals
-1
show two distinct C≡N stretching bands at 2204 and around 2170 cm , suggesting the contribution of
neutral forms (A and B in Scheme 3) as well as a zwitterionic form (C).
･
The electrical conductivities of 1a or 1b measured by atwo-probemethod at roomtemperatureare 1.1 x
･
-7
-6
-1
10 and 5.7 x 10 S cm , respectively. These values are high as a single component, thus confirming
our idea that the unpaired electrons of neutral radicals can act as conduction electrons in the solid when
8
the amphotericity is high enough. In seeking for a higher conductivity of the radicals, regulation of the
sum
17
electronic structure toward a smaller E
becomes important beside controlling of the crystal packing.
The electronic interaction between the donating and accepting subunits through the p-phenylene spacer
･
results in the lower electron affinity of 1 than PhC(CN) . In the same manner, the donating properties
･
2
･
of 1a or 1b become weaker than TTF or Me -TTF, respectively. This is the reason for much greater
･
2
sum
･
values of 1 than expected by the simple calculation from the redox potentials of reference
E
sum
･
･
compounds (hypothetical E : 0.17 V for 1a and 0.12 V for 1b ).
Scheme 3
CN
-
CN
•
CN
•
CN
CN
CN
R
R
S
S
R
R
S
+
S
S
S
R
R
S
S
S
•
S
S
e
e
S
1-
1• (A)
1+
e
ox
e
ox
E2
E1
ox
E3
e
e
CN
CN
CN
•
CN
-
CN
CN
R
R
S
•
S
R
R
S
+
S
S
S
+
S
R
R
S
•
S
S
+
S
S
1• (B)
12+•
1• (C)
Scheme 4
2e
2e
CN CN
CN CN
CN CN
CN
•
CN
dimerization
CN CN
4+
2e
2e
TTF+2
TTF2+
•
TTF
TTF

･
Accordingly, the m-phenylene derivatives (2 ) with smaller mesomeric interaction between subunits are
･
expected to show higher amphotericity than 1 . In fact, the E values of 2 are much higher than those
ox
-
1
-
-
of 1 and rather close to the value of PhC(CN) itself (Table 2). To our regret, however, the first
2
-
oxidation step is irreversible both in 2a and 2b , indicating the high reactivity of 2 . It should be
-
･
mentioned that two pairs of reversible waves are observed in the more anodic region, which are assigned
･
to the oxidation processes of the products derived from 2 (Table 2). Such voltammograms are best
accounted for by formation of dimer (5) with two TTF moieties (Scheme 4). The limited delocalization
･
of the unpaired electron in 2 cannot afford the sufficient stabilization to the radicals for isolation.
CONCLUSION
･
This work has revealed that the novel TTF derivatives bearing p-C H C(CN ) group could be generated
sum
6
4
2
and isolated as stable solids. They exhibit quite high electrical amphotericity, and their E
values are
･
two of the smallest values ever reported. The radicals (1 ) were formed as insoluble powders, thus
difficult to obtain as crystalline materials for measuring physical properties or crystallographic study. By
introduction of proper substituents and/or slight modification of the framework, however, this class of
9
neutral radicals would serve as good candidates for intramolecular CT materials or conducting magnetic
19
multifuntctional materials.
EXPERIMENTAL
Preparation of iodophenylmalononitriles (p-3 and m-3). Mineral oil of NaH (960 mg, 60%, 24 mmol)
was removed by washing with n-hexane. To its suspension in dry THF (40 mL) was added a solution of
malononitrile (1.38 g, 20.9 mmol) in 10 mL of THF over 10 min at 0 °C under Ar. The mixture was
stirred for 30 min at rt. To the resultant solution of sodium dicyanomethylide were added p-
diiodobenzene (4.98 g, 15.1 mmol) and (Ph P) Pd(II)Cl (550 mg, 0.78 mmol). The whole mixture was
3
2
2
heated at reflux for 34 h under Ar. After quenching by pouring over ice water (100 mL), the basic
aqueous layer was washed with CHCl (50 mL x 3). Unreacted p-diiodobenzene (2.73 g, 55% recovery)
3
was obtained from the combined organic layers. Acidifying the aqueous layer with HCl and extraction
with CHCl (50 mL x 3) gave a gray solid (761 mg) of p-iodophenylmalononitrile (p-3) containing a
3
small amount of p-phenylenebis(malononitrile). Chromatographic separation on SiO (CHCl ) gave pure
2
3
p-3 (605 mg) as faintly yellow crystals in 15% yield. Similar procedure on m-diiodobenzene gave m-
iodophenylmalononitrile (m-3) as a pale yellow solid in 25% yield along with 58% recovery of the
starting material.
1
Data of p-3: mp 99-100.5 °C (EtOH); H NMR (90 MHz, CDCl ) δ 5.00 (1H, s), 7.25 (2H, AA'XX'),
3
7.90 (2H, AA'XX'); IR (KBr) 3432, 3084, 2872, 2256, 1584, 1486, 1402, 1062, 1008, 920, 838, 782,
-1
522, 440 cm ; MS (EI) m/z 268 (M ); Anal. Calcd for C H N I: C, 40.32; H, 1.88; N, 10.45; I, 47.34.
+
9
5 2
Found: C, 40.40; H, 2.08; N, 10.33; I, 47.04. Data of m-3: colorless solid, mp 94.5-96.5 °C (benzene/n-
1
hexane); H NMR (400 MHz, CDCl ) δ 5.02 (1H, s), 7.25 (1H, dd, J = 8.5, 8.5 Hz), 7.50 (1H, d, J = 8.5
3
Hz), 7.85 (1H, d, J = 8.5 Hz), 7.86 (1H, s); IR (KBr) 2888, 2256, 1752, 1588, 1570, 1472, 1420, 1256,
-1
1234, 1166, 1104, 1086, 1068, 1004, 928, 875, 818, 774, 694, 672, 422 cm ; Anal. Calcd for C H N I:
9
5 2
C, 40.32; H, 1.88; N, 10.45; I, 47.34. Found: C, 40.36; H, 2.05; N, 10.36; I, 47.58.

Preparation of (4- and 3-dicyanomethylphenyl)tetrathiafulvalenes (H1a and H2a) and their
18
dimethyl derivatives (H1b and H2b) . Unsubstituted TTF and the 2,3-dimethyl derivative (Me -
2
12
11
TTF) were prepared according to the literature. 2-Trimethylstannyl-TTF (4a) was obtained as an
orange oil via 2-lithio-TTF and used without further purification for the cross-coupling. 2-
Trimethylstannyl-6,7-dimethyl-TTF (4b) was similarly prepared from Me -TTF in nearly quantitative
2
yield. Because of easy destannylation during the purification process, 4b was also used as prepared after
1
checking its purity by H NMR [(90 MHz, CDCl ) δ 0.33 (9H, s), 1.92 (6H, s), 6.23 (1H, s)].
3
To a solution of 2-trimethylstannyl-TTF (4a, 546 mg, 1.49 mmol) in toluene (20 mL) were added p-
iodophenylmalononitrile (p-3, 324 mg, 1.21 mmol) and (Ph P) Pd(0) (142 mg, 0.123 mmol). The
3
4
mixture was heated at reflux for 6 h. After evaporation of solvent, the residue was diluted with AcOEt
(50 mL) and washed with water (50 mL x 3) and brine (50 mL). Drying over Na SO and evaporation of
2
4
solvent gave a brown solid, from which 140 mg of 2-(4-dicyanomethylphenyl)tetrathiafulvalene (H1a)
was obtained as orange crystals in 34 % yield by chromatographic separation on SiO .
2
Similarly, 2-(4-dicyanomethylphenyl)-6,7-dimethyltetrathiafulvalene (H1b), 2-(3-dicyanomethylphenyl)-
tetrathiafulvalene (H2a), 2-(3-dicyanomethylphenyl)-6,7-dimethyltetrathiafulvalene (H2b) were obtained
in 36, 35, and 39% yields, respectively, by the cross-coupling reactions of the following combinations, 4b
with p-3, 4a with m-3, and 4b with m-3.
1
Data of H1a: mp 188.5-190 °C (benzene); H NMR (400 MHz, CDCl ) δ 5.07 (1H, s), 6.35 (2H, s), 6.64
3
(1H, s), 7.51 (2H, AA'BB'), 7.52 (2H, AA'BB'); IR (KBr) 3076, 2904, 2888, 1578, 1538, 1506, 1414,
-1
924, 840, 824, 794, 778, 756, 736, 668, 432 cm ; MS (EI) m/z 344 (M ); Anal. Calcd for C H N S : C,
+
15
8 2 4
52.29; H, 2.34; N, 8.13; S, 37.24. Found: C, 52.14; H, 2.45; N, 7.89; S, 37.04. Data of H1b: brown
1
crystals, mp 189.5-191 °C (benzene/n-hexane); H NMR (400 MHz, CDCl ) δ 1.97 (6H, s), 5.07 (1H, s),
3
6.63 (1H, s), 7.50 (2H, AA'BB'), 7.51 (2H, AA'BB'); IR (KBr) 3064, 2916, 2164, 1570, 1532, 1506,
-1
1436, 1412, 780, 768 cm ; MS (FD) m/z 372 (M ); Anal. Calcd for C H N S : C, 54.80; H, 3.25; N,
+
17 12 2 4
7.52; S, 34.43. Found: C, 54.42; H, 3.45; N, 7.36; S, 33.89. Data of H2a: orange crystals (CHCl ), mp
3
1
149.5-152 °C; H NMR (400 MHz, CDCl ) δ 5.08 (1H, s), 6.35 (2H, s), 6.64 (1H, s), 7.43-7.53 (4H, m);
3
IR (KBr) 3068, 2884, 2856, 1604, 1584, 1564, 1540, 1482, 1436, 1212, 1154, 984, 872, 798, 780, 736,
-1
688, 666, 660, 436 cm ; MS (FD) m/z 344 (M ); Anal. Calcd for C H N S : C, 52.29; H, 2.34; N,
+
15
8 2 4
8.13; S, 37.24. Found: C, 51.70; H, 2.47; N, 7.84; S, 36.92. Data of H2b:orange crystals, mp 151-153.5 °C
1
(benzene); H NMR (400 MHz, CDCl ) δ 1.97 (6H, s), 5.07 (1H, s), 6.63 (1H, s), 7.44-7.52 (4H, m);
3
IR (KBr) 2912, 2888, 1604, 1580, 1556, 1530, 1478, 1440, 1272, 1254, 1210, 1180, 1154, 1090, 994,
-1
912, 892, 872, 848, 802, 780, 742, 684, 650, 624, 586, 438, 418 cm ; MS (FD) m/z 372 (M ); Anal.
+
Calcd for C H N S : C, 54.80; H, 3.25; N, 7.52; S, 34.43. Found: C, 54.79 H, 3.32; N, 7.42; S, 34.40.
17 12 2 4
･
Preparation of 4-(2-tetrathiafulvalenyl)phenyldicyanomethyls (1 ).
To a suspension of neutral
precursor (H1a) (50 mg, 0.145 mmol) in 10 mL dry MeCN was added Et N (25 µL, 0.17 mmol) under
3
Ar. The resulting brown solution turned deep green immediately upon addition of iodine (55 mg, 0.217
･
mmol). After stirring for 1 h, 4-(2-tetrathiafulvalenyl)phenyldicyanomethyl (1a , 29 mg) was obtained as
black precipitates in 58% yield. Similarly, 4-(6,7-dimethyl-2-tetrathiafulvalenyl)phenyldicyanomethyl
･
(1b ) was obtained in quantitative yield.

-
By a constant current electrolysis of the anionic precursor (1b ) in MeCN containing 0.1 mol dm
-3
･
Et NClO , the radical (1b ) was also obtained in 56% yield. In the case of the electrolysis of m-
4
4
-
･
phenylene derivative (2a ), however, the resulting brownish solid is not the desired radical (2a ) but
tentatively assigned to the dimer (5a) (y. 50%) by the doubled molecular weight in the MS spectrum and
absence of strong CN stretching frequencies in IR. Preparation of dimers from the m-phenylene-type
-
anionic precursors (2 ) was difficult to reproduce, probably due to the overoxidation of 5 to polycationic
species.
･
Data of 1a : mp > 300 °C; IR (KBr) 3064, 2204, 2172, 1600, 1548, 1494, 1476, 1436, 1412, 1342, 1200,
-1
+
1184, 1142, 1070, 1018, 830, 798, 780, 704, 652, 466 cm ; MS (FD) m/z 343 (M ); Anal. Calcd for
･
C H N S ･H O: C, 49.47;H, 2.51. Found:C, 49.47 H, 2.33. Data of 1b :black powder, mp 159-161.5 °C;
15
7
2 4
2
-1
IR (KBr) 2204, 2168, 1596, 1522, 1430, 1340, 1202, 1182, 1086, 928, 826, 782, 702 cm ; MS (FD)
+
m/z 372 (M +1); Anal. Calcd for C H N S : C, 54.95; H, 2.98; N, 7.54. Found: C, 54.77; H, 3.11; N,
17 11 2 4
7.71. Data of 5a: mp >240 °C; IR (KBr) 3452, 2068, 1598, 1538, 1488, 1422, 1252, 1212, 1090, 998,
-1
+
850, 798, 780, 748, 698, 658, 622 cm ; MS (FD, relative intensity) m/z 344 (100), 686 (M , 31); Anal.
Calcd for C H N S : C, 52.44; H, 2.05; N, 8.16. Found: C, 51.85; H, 2.39; N, 8.45.
30 14 4 8
ox
red
Measurement of Redox Potentials. Oxidation (E ) and reduction (E ) potentials were measured by
-3
cyclic voltammetry in dry MeCN containing 0.1 mol dm Et NClO as a supporting electrolyte.
4
4
Ferrocene undergoes one electron-oxidation at +0.38 V under the same conditions. All of the values
shown in the text are in E/V vs SCE, and Pt wire was used as a working electrode. In the case of
red
ox
irreversible waves, E and E
were calculated as E
- 0.03 and E
+ 0.03,
(anodic peak)
(cathodic peak)
respectively.
3
X-Ray Analysis of H2b: Red plate, 0.2 x 0.1 x 0.05 mm , C H N S , M 372.54, triclinic P1bar, a =
17 12 2 4
3
6.772(4), b = 8.419(4), c = 14.729(7) Å, α = 78.03(2), β = 81.76(2), γ = 86.62(2)°, V = 812.6(7) Å , ρ (Z
-1
= 2) = 1.522 g cm . A total of 3442 unique data (2θ
= 55°) was measured at T = 123 K with a
max
Rigaku Mercury CCD camera diffractometer (Mo-Kα radiation, λ= 0.71069 Å). Numerical absorption
-1
correction was applied (µ = 5.83 cm ). The structure was solved by the Patterson method and refined by
the full-matrix least-squares method on F with anisotropic temperature factors for non-hydrogen atoms.
All of the hydrogen atoms were picked up from the D-map and refined with isotropic temperature factors.
The final R and Rw values are 0.059 and 0.070 for 3442 non-zero reflections and 255 parameters (GOF =
-3
2.13). Maximum residual electron density is 1.14 e Å .
ACKNOWLEDGMENTS
This work was supported by the Ministry of Education, Science, Sports and Culture, Japan (No.
10146101). Financial support from the Izumi Science and Technology Foundation and a Research Grant
from the Iwatani Naoji Foundation is gratefully acknowledged. We thank Prof. Tamotsu Inabe
(Hokkaido University) for use of the X-Ray structure analysis system. MS spectra were measured by Mr.
Kenji Watanabe and Dr. Eri Fukushi at the GC-MS & NMR Laboratory (Hokkaido University).
REFERENCES AND NOTES
1. Dedicated to celebrate the 77th birthday of Professor Shô Itô of Bunri University of Tokushima.

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