Electrolytic partial fluorination of organic compounds. Part 57: Regioselective anodic monofluorination of nitrogen-containing heterocyclic propargyl sulfides

Article abstract of DOI:10.1016/S0040-4020(01)00866-3

Anodic fluorination of various nitrogen-containing heterocyclic propargyl sulfides using Et₄NF·nHF (n=3,4) or Et₃N·3HF as a supporting electrolyte and fluoride ion source in dimethoxyethane provided the corresponding monofluorinated products in moderate yields. Fluorination took place selectively at the position α to the sulfur atom of the sulfides and the heterocyclic moieties were not fluorinated at all.

Full text of DOI:10.1016/S0040-4020(01)00866-3

TETRAHEDRON
Pergamon
Tetrahedron 57 ꢀ2001) 8817±8821
Electrolytic partial ¯uorination of organic compounds. Part 57:
Regioselective anodic mono¯uorination of nitrogen-containing
heterocyclic propargyl sul®des
q
p
Sayed M. Riyadh, Hideki Ishii and Toshio Fuchigami
Department of Electronic Chemistry, Tokyo Institute of Technology, Nagatsuta, Miduri-Ku, Yokohama 226-8502, Japan
Received 18 July 2001; accepted 27 August 2001
AbstractÐAnodic ¯uorination of various nitrogen-containing heterocyclic propargyl sul®des using Et
4
NF´nHF ꢀnˆ3,4) or Et
3
N´3HF as a
supporting electrolyte and ¯uoride ion source in dimethoxyethane provided the corresponding mono¯uorinated products in moderate yields.
Fluorination took place selectively at the position a to the sulfur atom of the sul®des and the heterocyclic moieties were not ¯uorinated at all.
q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
Previously, we found that electron-withdrawing groups
1
1
markedly promoted anodic a-¯uorination of sul®des.
Pyridyl propargyl sul®des are effective antifungal agents
and have been found to be surprisingly effective in protect-
ing ®nished paint from mildew attack for an extended
Since an acetylenic grouphas also an electron-withdrawing
effect, it was expected that heterocyclic sul®des having an
a-acetylenic groupwould be anodically ¯uorinated.
2
period. Benzothiazolyl propargyl sul®des are useful as
potent antagonists of the Bradykinin B-2 receptors as
3
With these facts in mind, we have comparatively studied
anodic ¯uorination of nitrogen-containing heterocyclic
propargyl sul®des such as 2-pyridyl, 4-pyridyl, 2-pyrimidyl,
2-quinolyl, 2-benzothiazolyl, and 2-ꢀ5-chlorobenzothiazo-
lyl) propargyl sul®des 1±6 in dimethoxyethane ꢀDME)
and acetonitrile ꢀMeCN) containing various ¯uoride salts.
It was found that such nitrogen-containing heterocyclic
propargyl sul®des gave the corresponding a-¯uorinated
products selectively where the ¯uorine atom was regio-
selectively introduced into the position a to the sulfur
atom. Fluorination at the acetylenic groupor heterocyclic
ring did not take place at all.
4
well as antitumor and antipro®lative. They are also well-
5
6
known to exhibit antimicrobial activity. Many potent
clinical important antitumor drugs having a quinoline
7
moiety have been discovered. A large number of quinoline
derivatives are involved in manufacturing a wide variety of
medicines and pharmaceuticals.
On the other hand, the development of highly ef®cient and
selective synthetic methods of organo¯uorine compounds
continues to be of crucial importance in the ®eld of
medicinal and agricultural chemistries due to their unique
8
and pronounced biological properties. The relationships
between molecular structures and biological activities
suggest that introduction of ¯uorine atomꢀs) into an
aromatic ring or its side-chain may have a great enhance-
ment or change of biological activities. However, conven-
tional chemical ¯uorination processes are not always easy to
2. Results and discussion
2.1. Preparation of heterocyclic sul®des
9
undertake and very often require hazardous reagents.
The reaction of appropriate heterocyclic thiols with pro-
pargyl bromide in the presence of K CO or NaOH afforded
the corresponding heterocyclic propargyl sul®des 1±6 in
2
3
On the other hand, anodic ¯uorination has been proved to be
more convenient access to accomplish such objects.
1
0
good yields as shown in Scheme 1.
2.2. Oxidation potentials of heterocyclic propargyl
sul®des
q
See Ref. 1.
Keywords: selective ¯uorination; electrochemical ¯uorination; a-¯uoro
heterocyclic sul®de.
Corresponding author. Tel./fax: 181-45-924-5406;
e-mail: fuchi@echem.titech.ac.jp
In order to investigate the effect of heterocyclic rings on the
oxidation potentials of sul®des, the anodic peak potentials
of heterocyclic propargyl sul®des 1±6 were measured by
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020ꢀ01)00866-3

8818
S. M. Riyadh et al. / Tetrahedron 57 +2001) 8817±8821
Scheme 1.
ox
p
Table 1. Oxidation potentials ꢀpeak potentials, E
pargyl sul®des 1±6
) of heterocyclic pro-
methyl sul®de in spite of no a-electron-withdrawing group
in 1. This may suggest that the electron-transfer would take
place at the sulfur atom of heterocyclic sul®des.
2.3. Anodic mono¯uorination of heterocyclic propargyl
sul®des
ox
Sul®des
E
p
ꢀV vs SSCE)
Firstly, the anodic ¯uorination of 2-pyridyl propargyl
sul®de 1 as a model compound was investigated under
various electrolytic conditions. The results are summarized
in Table 2.
No.
Ar
1
2
3
4
5
6
±
2-Pyridyl
4-Pyridyl
2-Pyrimidyl
2-Quinolyl
2-Benzothiazolyl
2-ꢀ5-Chlorobenzothiazolyl)
Methyl 2-pyridyl sul®de
1.92
1.90
2.2
1.92
1.95
2.04
1.74
As shown in Table 2, anodic ¯uorination of 1 proceeded to
give the corresponding a-mono¯uorinated product 7 in a
moderate yield. Et N´3HF/DME was found to be suitable
3
as a ¯uoride salt/electrolytic solvent system ꢀrun 4). In our
previous work, acetonitrile was suitable for anodic ¯uorina-
tion of 2-pyridyl sul®des having various electron-withdraw-
ing group. However, acetonitrile was not effective for the
anodic ¯uorination of 2-pyridyl propargyl sul®de ꢀrun 1).
4 4
Substrate ꢀ1 mmol) in 0.1 M Bu N´BF /MeCN. Sweeprate: 100´ V/s.
1
2
cyclic voltammetry in an anhydrous acetonitrile solution
containing Bu NBF ꢀ0.1 M) using platinum electrodes
4
4
and SSCE as a reference electrode. All these sul®des
showed irreversible oxidation peaks, the ®rst oxidation
peak potentials Ep of the heterocyclic propargyl sul®des
It is known that anodic ¯uorination of pyridine takes place
at the pyridine ring. We also found anodic ¯uorination at
the pyridine ring of isonicotinic acid ester. Therefore, it
should be noted that ¯uorination took place exclusively at
the a-position to the sulfur atom of simple 2-pyridyl
propargyl sul®de 1.
ox
13
1
4
1
±6 are summarized in Table 1.
Pyridyl propargyl sul®des 1,2 and 2-quinolyl propargyl
sul®de 4 showed almost the same oxidation potentials.
The oxidation potential of propargyl 2-pyrimidyl sul®de 3
was higher than those of 1,2 and 4 due to the effect of two
electron-withdrawing nitrogen atoms in the pyrimidyl ring.
Next, we extended the anodic ¯uorination to other hetero-
cyclic propargyl sul®des 2±4 using Et N´3HF/DME. As
3
2
-ꢀ5-Chlorobenzothiazolyl) propargyl sul®de 6 has a more
positive oxidation potential compared with unsubstituted
-benzothiazolyl propargyl sul®de 5 due to the electron-
shown in Table 3, the anodic ¯uorination proceeded regard-
less of the nature of heterocyclic rings. Anodic ¯uorination
of 4-pyridyl propargyl sul®de 2 proceeded smoothly in a
manner similar to the 2-pyridyl analogue and gave almost
same yield of a-mono¯uorinated product 8. As, 2-pyrimidyl
2
withdrawing effect of a chlorine atom. The oxidation
potential of sul®de 1 is much higher than that of 2-pyridyl
Table 2. Anodic mono¯uorination of 2-pyridyl propargyl sul®de 1 under various electrolytic conditions
a
Yield ꢀ%)
Run
Supporting electrolyte
Solvent
1
2
3
4
Et
Et
Et
Et
4
NF´4HF
4
NF´4HF
4
NF´3HF
3
N´3HF
MeCN
DME
DME
DME
15
35
40
b
55 ꢀ50)
a
19
Calculated on the basis of F NMR.
Isolated yield.
b

S. M. Riyadh et al. / Tetrahedron 57 +2001) 8817±8821
Table 3. Anodic mono¯uorination of heterocyclic propargyl sul®des 2±4
8819
a
Yield ꢀ%)
Sul®des
Charged passed ꢀF/mol)
No.
X
1 2
R ,R
b
4
2
2
-Pyridyl
-Pyrimidyl
-Quinolyl
ꢀ2)
ꢀ3)
ꢀ4)
CH
N
CH
H,H
H,H
ꢀCHvCH)
10
12
12
8
9
10
58ꢀ55)
60ꢀ55)
35ꢀ30)
b
b,c
2
a
b
c
19
Determined by F NMR.
Isolated yield.
A large amount of the starting material 4 was recovered.
propargyl sul®de 3 has a higher oxidation potential
compared with the pyridyl analogus 1 and 2, a larger amount
of electricity was required to complete the electrolysis to
give the corresponding a-mono¯uorinated product 9 in
moderate yield. In contrast, anodic ¯uorination of
Et NF´3HF gave the best result ꢀrun 3). Anodic ¯uorination
4
of 5-chloroderivative 6 using Et NF´3HF gave higher
4
¯uorination yield than that of 5 ꢀrun 4). This substituent
effect on the anodic ¯uorination is similar to the anodic
¯uorination of 2-benzothiazolyl sul®des having various
electron-withdrawing groups such as ester, ketone, and
2
-quinolyl propargyl sul®de 4 under the same electrolytic
1
5
conditions provided much lower yield of the a-mono¯uori-
nated product 10. In this case, a large amount of starting
material 4 was recovered.
cyano groups.
The high regioselectivity in the anodic ¯uorination of
heterocyclic sul®des 1±6 can be explained in terms of the
facile elimination of an a-proton of the ¯uorosulfonium
Moreover, anodic ¯uorination of 2-benzothiazoly propargyl
sul®de 5 was carried out using three kinds of ¯uoride salts as
shown in Table 4. Among the supporting ¯uoride salts used,
1
6
ion intermediate due to a strong electron-withdrawing
propargyl group as shown in Scheme 2.
Table 4. Anodic mono¯uorination of 2-benzothiazolyl and 2-ꢀ5-chlorobenzothiazolyl) propargyl sul®des 5,6
a
Yield ꢀ%)
Run
X
Compound no.
Supporting electrolyte
Charged passed ꢀF/mol)
1
2
3
4
H
H
H
Cl
5
5
5
6
Et
Et
Et
Et
4
3
4
4
NF´4HF
N´3HF
NF´3HF
NF´3HF
10
10
10
12
7
15
22ꢀ20)
35ꢀ30)
b
b
a
19
Determinated by F NMR.
Isolated yield.
b
Scheme 2.

8820
S. M. Riyadh et al. / Tetrahedron 57 +2001) 8817±8821
Scheme 3.
It is well-known that ¯uorinated sul®des can be prepared
from the corresponding sul®des using XeF2 or DAST.
However, the former reagent is costly and the latter one
requires the corresponding sulfoxides as the substrate.
Recently, N-¯uoropyridinium tri¯ates and tetra¯uoroborate
have been shown to be alternative ¯uorination reagents of
activated methylenes and benzenes. However, ¯uorination
of 2-pyridyl sul®de 1 as a model compound with various
types of N-¯uoropyridinium tri¯ates in dichloromethane
either at room temperature or under re¯ux resulted in no
formation of the desired ¯uorinated product ꢀScheme 3).
Therefore, the electrochemical ¯uorination is more advan-
tageous than the conventional chemical method for such
heterocyclic sul®des.
C H NS: C, 64.39; H, 4.73; N, 9.39. Found: C, 64.31; H,
8 7
4.57; N, 9.31.
1
4.1.2. 2-Pyrimidyl propargyl sul®de /3). H NMR d 2.16
ꢀt, 1H, Jˆ3 Hz), 3.91 ꢀd, 2H, Jˆ3 Hz), 6.98 ꢀt, 1H, Jˆ5 Hz),
1
1
8.54 ꢀd, 2H, Jˆ5 Hz). MS m/z 150 ꢀM ), 149 ꢀM 2H).
Anal. Calcd for C H N S: C, 55.97; H, 4.03; N, 18.65.
7 6 2
1
7
Found: C, 55.85; H, 4.18; N, 18.43.
4.1.3. Preparation of 2-quinolyl propargyl sul®de /4). To
a solution of 2-mercaptoquinoline ꢀ0.01 mol) dissolved in
50 ml of 2 M sodium hydroxide solution was added
propargyl bromide ꢀ0.01 M), the reaction mixture was stir-
red at room temperature for 2 h. The product was puri®ed by
column chromatography on silica gel ꢀeluent: hexane/
1
AcOEt ꢀ2:1)) to give the pure product. H NMR d 2.19 ꢀt,
1H, Jˆ2.5 Hz), 4.17 ꢀd, 2H, Jˆ2.5 Hz), 7.25 ꢀd, 1H,
3. Conclusion
Jˆ7 Hz), 7.45 ꢀt, 1H, Jˆ6 Hz), 7.67 ꢀt, 1H, Jˆ8 Hz), 7.73
1
In summary, we have successfully carried out anodic mono-
uorination of nitrogen-containing heterocyclic propargyl
ꢀd, 1H, Jˆ8 Hz) 7.95 ꢀt, 2H, Jˆ7 Hz). MS m/z 199 ꢀM ),
1
¯
198 ꢀM 2H). Anal. Calcd for C12
H
NS: C, 72.33; H, 4.55;
9
sul®des. We have found that this ¯uorination is greatly
affected by the ring system of starting sul®des as well as
supporting ¯uoride salts.
N, 7.03. Found: C, 72.29; H, 4.69; N, 6.97.
4.2. Anodic ¯uorination of heterocyclic propargyl
sul®des
4
. Experimental
The electrolyses were carried out with platinum plate elec-
2
trodes ꢀ3£3 cm ) in Et NF´nHF ꢀnˆ3,4) or Et N´3HF/DME
4
3
Caution. Et NF´3HF is toxic and if in contact with skin
4
or MeCN ꢀ30 ml) containing a sul®de 1±6 ꢀ1 mmol) using
an undivided cell under nitrogen atmosphere at room
causes serious burn, so proper safety precautions should
be taken all the time, it is therefore, recommended to protect
hands with rubber gloves.
2
temperature. Constant current ꢀ5 mA/cm ) was passed
until the starting material 1±6 was consumed ꢀchecked by
TLC). After the electrolysis, the electrolytic solution was
passed through a short column ®lled with silica gel using
AcOEt as an eluent to remove ¯uoride salts. The eluent was
evaporated under reduced pressure, and the residue was
further puri®ed by column chromatography on silica gel
using an appropriate solvent as the eluent.
2
Materials. 4-Pyridyl propargyl sul®de 2, 2-benzothiazolyl
3
propargyl sul®de 5, and 2-ꢀ5-chlorobenzothiazolyl)
3
propargyl sul®de 6 were prepared according to the
literatures.
4
.1. Preparation of propargyl sul®des 1,3
4
.2.1. a-Fluoro-2-pyridyl propargyl sul®de /7). Eluent:
1
To a stirred solution of 2-mercaptopyridine or 2-mercapto-
pyrimidine ꢀ0.01 mol) in 50 ml of DMSO containing 1.5 g
hexane/AcOEt ꢀ1: 2). H NMR d 3.02 ꢀdd, 1H, Jˆ2.5,
3 Hz), 7.45 ꢀd, 1H, Jˆ52 Hz), 7.28 ꢀt, 1H, Jˆ8 Hz), 7.56
ꢀd, 1H, Jˆ7 Hz), 7.62 ꢀt, 1H, Jˆ8 Hz), 8.54 ꢀd, 1H,
ꢀ
ꢀ
0.012 mol) of K CO , was added propargyl bromide
2 3
0.01 mol), and the reaction mixture was stirred at room
1
9
Jˆ7 Hz). F NMR d 267.5 ꢀdd, Jˆ2.5, 52 Hz). MS m/z
1
1
temperature for 2 h. The product was puri®ed by column
chromatography on silica gel ꢀhexane/AcOEtˆ1:1) to
provide the desired product.
167 ꢀM ), 166 ꢀM 2H). HRMS m/z calcd for C H FNS:
8 6
167.0205. Found 167.0105. Anal. Calcd for C H FNS: C,
6
8
57.47; H, 3.62; N, 8.38. Found: C, 57.19; H, 3.86; N, 8.04.
1
4
1
7
.1.1. 2-Pyridyl propargyl sul®de /1). H NMR d 2.2 ꢀt,
H, Jˆ2.8 Hz), 3.9 ꢀd, 2H, Jˆ2.8 Hz), 7.18 ꢀt, 1H, Jˆ8 Hz),
.46 ꢀd, 1H, Jˆ7 Hz), 7.52 ꢀt, 1H, Jˆ8 Hz), 8.44 ꢀd, 1H,
4.2.2. a-Fluoro-4-pyridyl propargyl sul®de /8). Eluent:
1
hexane/AcOEt ꢀ1: 2). H NMR d 2.83 ꢀdd, 1H, Jˆ2.6,
19
3.1 Hz), 6.31 ꢀd, 1H, Jˆ47 Hz), 7.11 ꢀd, 2H, Jˆ5 Hz),
1
1
Jˆ7 Hz). MS m/z 149 ꢀM ), 148 ꢀM 2H). Anal. Calcd for
8.27 ꢀd, 2H, Jˆ5 Hz). F NMR d ±63.8 ꢀdd, Jˆ2.6,

S. M. Riyadh et al. / Tetrahedron 57 +2001) 8817±8821
8821
1
7 Hz). MS m/z 167 ꢀM ), 166 ꢀM 2H). Anal. Calcd for
1
4
C H FNS: C, 57.47; H, 3.62; N, 8.38. Found: C, 57.26; H,
3. Heitsch, H.; Wagner, A.; Scholkens, B. A.; Wirth, K. Bioorg.
Med. Chem. Lett. 1999, 9, 327±332.
8
6
3
.88; N, 8.15.
4. Chua, M. S.; Shi, D. F.; Wrigley, S.; Bradshaw, T. D.;
Hutchinson, I.; Shaw, P. N.; Barrett, D. A.; Stanley, L. A.;
Stevens, M. F. G. J. Med. Chem. 1999, 42, 381±392.
5. Easmon, J.; Heinisch, G.; Hofmann, J.; Langer, T.; Grunicke,
H. H.; Fink, J.; Purstinger, G. Eur. J. Med. Chem. 1997, 32,
397±408.
4
.2.3. a-Fluoro-2-pyrimidyl propargyl sul®de /9). Eluent:
1
benzene. H NMR d 3.02 ꢀdd, 1H, Jˆ2, 4 Hz), 7.1 ꢀt, 1H,
1
9
Jˆ5 Hz), 7.4 ꢀd, 1H, Jˆ48 Hz), 8.61 ꢀd, 2H, Jˆ5 Hz).
F
1
NMR d 267.2 ꢀdd, Jˆ2, 48 Hz) MS m/z 168 ꢀM ), 167
1
M 2H). HRMS m/z calcd for C H FN S: 168.0157.
ꢀ
Found 168.0127.
6. Sutoris, V.; Foltinova, P.; Blockinger, G. Chem. Zvesti. 1997,
31, 92.
7
5
2
7
. ꢀa) Deady, L. W.; Kaye, A. J.; Finaly, G. J.; Baguley, B. C.;
Denny, W. A. J. Med. Chem. 1997, 40, 2040. ꢀb) Scharping,
C. E.; Duke, C. C.; Holder, G. M.; Larden, D. Carcinogenesis
1993, 14, 1041. ꢀc) Moron, J.; Rautureau, M.; Huel, C.; Pierre,
A.; Berthier, L. K.; Atassi, G.; Bisagni, E. Anti-cancer Drug
Des. 1993, 8, 399. ꢀd) Yamato, M.; Takeuchi, Y.; Chang,
M. R.; Hashigaki, K. Chem. Pharm. Bull. 1992, 40, 528.
ꢀe) Takeuchi, Y.; Chang, M. R.; Hashigaki, K.; Tashiro, T.;
Tsuruo, T.; Tsukagoshi, S.; Yamato, M. Chem. Pharm. Bull.
1992, 40, 1481.
4
.2.4. a-Fluoro-2-quinolyl propargyl sul®de /10). Eluent:
1
hexane/AcOEt ꢀ10: 1). H NMR d 3.01 ꢀdd, 1H, Jˆ2,
.2 Hz), 7.26 ꢀd, 1H, Jˆ7 Hz), 7.49 ꢀt, 1H, Jˆ6 Hz), 7.67
t, 1H, Jˆ8 Hz), 7.73 ꢀt, 1H, Jˆ8 Hz), 7.81 ꢀd, 1H,
2
ꢀ
1
9
Jˆ52 Hz), 8.01 ꢀd, 2H, Jˆ7 Hz). F NMR d 267.7 ꢀdd,
1
1
Jˆ2, 52 Hz) MS m/z 217 ꢀM ), 216 ꢀM 2H). HRMS m/z
calcd for C H FNS: 217.0361. Found 217.0312.
1
2
8
4
.2.5. a-Fluoro-2-benzothiazolyl propargyl sul®de /11).
1
Eluent: hexane/AcOEt ꢀ10: 1). H NMR d 3.07 ꢀdd, 1H,
Jˆ2, 2.5 Hz), 7.25 ꢀt, 1H, Jˆ8 Hz), 7.35 ꢀt, 1H, Jˆ8 Hz),
8. ꢀa) Smart, B. E., Ed. Chem. Rev. 1996, 96. ꢀb) Resnati, G.
Tetrahedron 1993, 49, 9385. ꢀc) Biomedical Frontiers of
Fluorine Chemistry; Ojima, I., McCarthy, J. R., Welch, J. T.,
Eds.; American Chemical Society: Washington, DC, 1996.
9. Huddlicky, M., Pavlath, A. E., Eds.; Chemistry of Organic
Fluorine Compounds; American Chemical Society:
Washington, DC, 1995; Vol. II.
7
.45 ꢀd, 1H, Jˆ53 Hz), 7.65 ꢀd, 1H, Jˆ8 Hz), 7.85 ꢀd, 1H,
1
9
Jˆ8 Hz). F NMR d 268.5 ꢀdd, Jˆ2, 53 Hz). MS m/z 223
1
1
ꢀ
M ), 222 ꢀM 2H). HRMS m/z calcd for C H FNS :
10 6 2
2
22.9926. Found 222.9920.
4.2.6. a-Fluoro-2-/5-chlorobenzothiazolyl) propargyl
1
sul®de /12). Eluent: hexane/AcOEt ꢀ10: 1). H NMR d
1
0. ꢀa) Childs, W. V.; Christensen, L.; Klink, F. W.; Kolpin, C. F.
In Organic Electrochemistry; Lund, H., Baizer, M. M., Eds.;
3
.09 ꢀdd, 1H, Jˆ2, 2.5 Hz), 7.24 ꢀd, 1H, Jˆ52 Hz), 7.31
3
rd ed., Marcel Dekker: New York, 1991; Chapter 26.
b) Fuchigami, T. In Organic Electrochemistry; Lund, H.,
ꢀ
d, 1H, Jˆ10 Hz), 7.67 ꢀd, 1H, Jˆ10 Hz), 7.88 ꢀs, 1H).
ꢀ
1
9
1
F NMR d 268.1 ꢀdd, Jˆ2, 52 Hz). MS m/z 258 ꢀM ),
Hammerich, O., Eds.; 4th ed., Marcel Dekker: New York,
2001; Chapter 25. ꢀc) Sawaguchi, M.; Hara, S.; Fukuhara,
T.; Yoneda, N. Isr. J. Chem. 1999, 39, 151.
1
57 ꢀM 2H). Anal. Calcd for C H ClFNS : C, 46.60; H,
.96; N, 5.43. Found: C, 46.46; H, 2.3; N, 5.38.
2
1
1
0
5
2
1
1. ꢀa) Fuchigami, T.; Shimojo, M.; Nakagawa, K. J. Org. Chem.
1
990, 55, 6070. ꢀb) Shaaban, M. R.; Ishii, H.; Fuchigami, T.
Acknowledgements
J. Org. Chem. 2000, 65, 8685. ꢀc) Riyadh, S. M.; Ishii, H.;
Fuchigami, T. Tetrahedron Lett. 2001, 42, 3009.
12. Erian, A. W.; Konno, A.; Fuchigami, T. J. Org. Chem. 1995,
This research was supported by a Grant-in-Aid for Scienti®c
Research on Priority Areas ꢀA) `Exploitation of Multi-
Element Cyclic molecules' from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
60, 7654.
13. Ballinger, J. R.; Teare, F. W. Electrochem. Acta 1985, 30,
1075.
1
4. Fuchigami, T.; Shimojo, M.; Konno, A. J. Fluorine Chem.
997, 87.
15. Hou, Y.; Higashiya, S.; Fuchigami, T. J. Org. Chem. 1997, 62,
173.
1
References
9
1
. Part 56: Shaaban, R. M.; Fuchigami, T. Tetrahedron Lett.,
submitted for publication.
16. Fuchigami, T.; Konno, A.; Nakagawa, K.; Shimojo, M. J. Org.
Chem. 1994, 59, 5937.
2
. Brandman, H. A.; Freudewald, J. E.; Manowitz, M.; Nikawitz,
E. J.; Sharpell, F. H. U.S. 4,170,704. Chem. Abst., 1980, 92,
17. ꢀa) Umemoto, T.; Tomizawa, G. Bull. Chem. Soc. Jpn 1986,
59, 3625. ꢀb) Umemoto, T.; Tomizawa, G. J. Org. Chem.
1995, 60, 6563.
4
1776a.