Electrolytic Partial Fluorination of Organic Compounds. 22. Highly Regioselective Anodic Monofluorination of Oxindole and 3-Oxo-1,2,3,4-tetrahydroisoquinoline Derivatives: Effects of Supporting Fluoride Salts and Anode Materials

Article abstract of DOI:10.1021/jo971173i

Highly regioselective monofluorination of 1-aryl-3-(phenylthio)oxindoles and 2-substituted-3-oxo-4-(phenylthio)-1,2,3,4-tetrahydroisoquinolines can be successfully carried out in the presence of Me₄NF·4HF or Et₄NF·-3HF as a supporting electrolyte to provide the corresponding 3-fluorinated oxindole and 4-fluorinated isoquinoline derivatives in good yields. Carbon anodes as well as a platinum anode were found to be effective for the fluorination when Me₄NF·4HF was used as the supporting electrolyte.

Full text of DOI:10.1021/jo971173i

J . Org. Chem. 1997, 62, 8773-8776
8773
Electr olytic P a r tia l F lu or in a tion of Or ga n ic Com p ou n d s. 22.1
High ly Regioselective An od ic Mon oflu or in a tion of Oxin d ole a n d
3-Oxo-1,2,3,4-tetr a h yd r oisoqu in olin e Der iva tives: Effects of
Su p p or tin g F lu or id e Sa lts a n d An od e Ma ter ia ls
Yankun Hou, Seiichiro Higashiya, and Toshio Fuchigami*
Department of Electronic Chemistry, Tokyo Institute of Technology, Midori-ku, Yokohama 226, J apan
Received J une 27, 1997X
Highly regioselective monofluorination of 1-aryl-3-(phenylthio)oxindoles and 2-substituted-3-oxo-
4-(phenylthio)-1,2,3,4-tetrahydroisoquinolines can be successfully carried out in the presence of
Me4NF‚4HF or Et4NF‚3HF as a supporting electrolyte to provide the corresponding 3-fluorinated
oxindole and 4-fluorinated isoquinoline derivatives in good yields. Carbon anodes as well as a
platinum anode were found to be effective for the fluorination when Me4NF‚4HF was used as the
supporting electrolyte.
In tr od u ction
aliphatic nitrogen- and/or sulfur-containing heterocycles11
together with heterocyclic sulfides.12 Among the anodi-
cally fluorinated heterocycles, monofluorinated 3-thiolan-
one derivatives showed marked biological activity such
as PLA2 inhibition.13 On the other hand, oxindole and
3-oxo-1,2,3,4-tetrahydroisoquinoline are commonly used
as starting materials and intermediates for many phar-
maceutical products. These facts prompted us to attempt
anodic monofluorination of oxindoles and 3-oxo-1,2,3,4-
tetrahydroisoquinolines having a phenylthio group R to
the carbonyl group. Furthermore, the effects of support-
ing fluoride salts and anode materials on the anodic
fluorination were also investigated in this work.
Fluoroorganic compounds have rather unique chemical,
physical, and biological properties. For instance, many
important biological activities have been found in a
number of fluorinated heterocyclic compounds.2-5 The
synthesis of ring-fluorinated heterocyclic systems has
been rather limited although a number of new methods
for the preparation of fluoroorganics have been developed
to date. Direct fluorination is the most simple way to
prepare fluorinated heterocyclic compounds. However,
direct fluorination is not always straightforward because
conventional methods require hazardous, poisonous, or
costly fluorinating reagents.2,5 On the other hand, elec-
trochemical partial fluorination seems to be promising
for the synthesis of fluorinated heterocyclic compounds
because this method does not require any hazardous
reagents.6,7 However, few examples of anodic fluorina-
tion of heterocycles have been reported to date,8 and the
yields were unsatisfactory in all cases.
Resu lts a n d Discu ssion
P r ep a r a tion of Oxin d ole a n d 3-Oxo-1,2,3,4-tet-
r a h yd r oisoqu in olin e Der iva tives. The starting ox-
indole and 3-oxo-1,2,3,4-tetrahydroisoquinoline deriva-
tives bearing a phenylthio group at the position R to the
carbonyl group were synthesized as shown in Scheme 1
in a manner similar to the procedure for the preparation
of the corresponding heterocycles having a methylthio
group.14
Recently, electrochemical fluorination of sulfides has
been proven to be an elegant and efficient way for the
preparation of R-monofluorinated sulfides as reported by
Laurent et al.9 and our group10 independently. In a
preceding papers, we have reported a successful applica-
tion of this electrochemical monofluorination to various
Oxid a tion P oten tia ls of Oxin d ole a n d Isoqu in o-
lin e Der iva tives. The oxidation potentials of oxindole
and isoquinoline derivatives were measured by means
of cyclic voltammetry using a divided cell with platinum
electrodes in 0.1 M Bu4N‚BF4/anhydrous acetonitrile. All
the compounds chosen in the present study showed
irreversible oxidation waves. The peak potentials for the
first stage of oxidation are summarized in Table 1.
* Corresponding author: tel, +81 45 924 5406; fax, +81 45 921 1089;
e-mail, fuchi@echem.titech.ac.jp.
X Abstract published in Advance ACS Abstracts, November 15, 1997.
(1) For part 21, see: Hou, Y.; Higashiya, S.; Fuchigami, T. Synlett
1997, 655.
(2) Purrington, S. T.; Kagen, B. S.; Partrick, T. B. Chem. Rev. 1986,
86, 997.
(3) (a) Biomedicinal Aspects of Fluorine Chemistry; Filler, R.,
Kobyashi, Y., Eds.; Kodansha & Elsevier Biomedical: Tokyo, 1982.
(b) Fluorine in Bioorganic Chemistry; Welch, J . T., Eswarakrishnan,
S., Eds.; Wiley: New York, 1991.
In comparing compound 1a with 1b, we found that
substitution at the benzene rings with two electron-
(4) Silvester, M. J . Aldrichim. Acta 1991, 24, 32.
(5) Selective Fluorination in Organic and Bioorganic Chemistry;
Welch, J . T., Ed.; American Chemical Society: Washington, DC, 1991.
(6) Childs, W. V.; Christensen, L.; Klink, F. W.; Koipin, C. F. In
Organic Electrochemistry, 3rd ed.; Lund, H., Baizer, M. M., Eds.;
Marcel Dekker: New York, 1991; Chapter 24.
(7) (a) Fuchigami, T. Rev. Heteroatom. Chem. 1994, 10, 155. (b)
Fuchigami, T.; Konno, A. J . Org. Synth. Chem. J pn. 1997, 55, 301. (c)
Fuchigami, T.; Nishiyama, S. J . Electrochem. Soc. J pn. 1997, 65, 626.
(8) (a) Gambaretto, G. P.; Napoli, M.; Franccarro, C.; Conte, L. J .
Fluorine Chem. 1982, 19, 427. (b) Ballinger, J . R.; Teare, F. W.
Electrochim. Acta 1985, 30, 1075. (c) Makino, K.; Yoshioka, H. J .
Fluorine Chem. 1988, 39, 435. (d) Meurs, J . H. H.; Eilenberg, W.
Tetrahedron 1991, 47, 705. (e) Sono, M.; Morita, N.; Shimizu, Y.; Tori,
M. Tetrahedron Lett. 1994, 35, 9237.
(10) Fuchigami, T.; Shimojo, M.; Konno, A.; Nakazawa, K. J . Org.
Chem. 1990, 55, 6074.
(11) (a) Fuchigami, T.; Narizuka, S.; Konno, A. J . Org. Chem. 1992,
57, 3755. (b) Konno, A.; Naito, W.; Fuchigami, T. Tetrahedron Lett.
1992, 33, 7017. (c) Narizuka, S.; Fuchigami, T. J . Org. Chem. 1993,
58, 4200. (d) Konno, A.; Shimojo, M.; Fuchigami, T. J . Fluorine Chem.,
in press. (e) Fuchigami, T.; Narizuka, S.; Konno, A.; Momota, K.
Electrochim. Acta, in press.
(12) Erian, A. W.; Konno, A.; Fuchigami, T. J . Org. Chem. 1995,
60, 7654.
(13) Narizuka, S.; Fuchigami, T. Bioorg. Med. Chem. Lett. 1995, 5,
1293.
(14) Tamura, Y.; Uenishi, J . I.; Maeda, H.; Choi, H. D.; Ishibashi,
H. Synthesis 1981, 534.
(9) Brigand, J .; Laurent, E. Tetrahedron Lett. 1990, 31, 2287.
S0022-3263(97)01173-0 CCC: $14.00 © 1997 American Chemical Society

8774 J . Org. Chem., Vol. 62, No. 25, 1997
Hou et al.
Ta ble 1. Oxid a tion P oten tia ls (P ea k P oten tia ls, Ep ox) of
Ta ble 3. Effect of Electr od e Ma ter ia ls on An od ic
Oxin d ole a n d Tetr a h yd r oisoqu in olin e Der iva tivesa
Mon oflu or in a tion of Oxin d ole 1a a
yield (%)
anode
Pt
C-plate
C-sheet
C-felt
Et4NF‚3HF
Me4NF‚4HF
58
64
60
59
42
2
28b
36b
21b
24b
substrate
ox
Ep
Ebonex
no.
n
R
R′
(V vs SSCE)
a
Solvent: CH3CN. Cathode: Pt. Current density: 4 mA/cm2.
1a
1b
1c
1d
0
0
1
1
H
CH3
H
Ph
1.75
1.55
1.75
1.62
b
Charge passed: 4 F/mol. Starting material 1a was recovered.
CH3C6H4
Ph
C6H5CH2
the fluorides, Me4NF‚4HF15 gave the best result and
Et4NF‚3HF was also effective. Although Et3N‚3HF has
been shown to be the most effective for anodic fluorina-
tion of organic sulfur compounds, owing to its strong
nucleophilicity,7 this fluoride salt gave a much lower yield
compared with Et4NF‚3HF and Me4NF‚4HF. Since the
oxidation potential of Et3N‚3HF is lower than those of
Et4NF‚3HF and Me4NF‚4HF, Et3N‚3HF seems to be
easily oxidized during the anodic fluorination of 1a . In
fact, a large excess amount of electricity was required
until the starting 1a was completely consumed when
Et3N‚3HF was used. This probably caused a decrease
of the yield of the fluorinated product 2a . When the
content (n) of HF in R4NF‚nHF (R ) Me, Et) increased,
the oxidation potential of the fluoride salts became more
positive. Therefore, it is reasonable that a higher yield
of 2a is obtained with an increase of the HF content (n).
Thus, Et4NF‚3HF or Me4NF‚4HF were found to be
suitable for the fluorination of such an oxindole deriva-
tive.
H
a
In 0.1 M Bu4N‚BF4/CH3CN. Sweep rate: 100 mV/s.
Ta ble 2. Effect of Su p p or tin g Electr olyte on An od ic
Mon oflu or in a tion of 1-P h en yl-3-(p h en ylth io)oxin d ole (1a )
supporting
electrolyte
charge passed
(F/mol)
yield
(%)
run
1
2
3
4
5
Et3N‚2HF
Et3N‚3HF
Et4NF‚2HF
Et4NF‚3HF
Me4NF‚4HF
6
6
4
3.7
3.5
3
30
41
58
64
Sch em e 1
Next, the effect of anodic materials on the anodic
fluorination was investigated. Anodic fluorination of 1a
as a model compound was carried out at various anode
materials as shown in Table 3. The starting 1a was
completely consumed when 4 F/mol of electricity was
passed at a platinum anode in Et4NF‚3HF and Me4NF‚
4HF. Therefore, to compare the electrolytic results, the
electrolysis was stopped when 4 F/mol was passed. The
results are summarized in Table 3.
Sch em e 2
Anodic fluorination proceeded regardless of anodic
materials expect for one: An Ebonex anode was not
effective in Me4NF‚4HF/MeCN, whereas in Et3NF‚3HF/
MeCN this anode provided the fluorinated product 2a in
a reasonable yield. Thus, the Ebonex anode was not so
effective for anodic fluorination although this anodic
material is known to be stable in a strongly acidic
electrolytic solution. A platinum anode was the most
suitable for the fluorination regardless of supporting
electrolytes. When Me4NF‚4HF was used, carbon plate
and sheet anodes as well as a platinum anode were
effective for this fluorination. Since the former anodes
are much cheaper than the latter one, this finding is quite
important from a practical aspect.
Then, this anodic fluorination was extended to the
other oxindole derivative 1b, which has methyl groups
on the benzene rings. Even in this case, a fluorine atom
was introduced into the 3-position exclusively. Although
benzylic anodic nucleophilic substitutions are well-known
to take place easily, no benzylic fluorination was observed
in the case of 1b.
donating methyl groups affected the oxidation potentials
significantly, causing the oxidation peak to shift to less
positive potentials. Interestingly, isoquinoline 1c showed
the same oxidation potential as oxindole 1a , although
their ring systems are different.
An odic Flu or in ation of Oxin dole an d 3-Oxo-1,2,3,4-
tetr a h yd r oisoqu in olin e Der iva tives. Anodic fluori-
nation was carried out mainly at platinum electrodes in
anhydrous acetonitrile with an undivided cell at constant
current. Various fluoride salts were used as both the
supporting electrolyte and the fluorine source. We de-
termined the optimal experimental conditions by exam-
ining the details of electrolysis of 1-phenyl-3-(phenyl-
thio)oxindole (1a ) as a model compound. The results of
anodic fluorination of 1a are summarized in Table 2 and
Scheme 2.
Next, we successfully extended this fluorination to
3-oxo-1,2,3,4-tetrahydroisoquinoline derivatives 1c,d as
As shown in Table 2, anodic fluorination of 1-phenyl-
3-(phenylthio)oxindole (1a ) proceeded smoothly to give
the corresponding 3-fluorinated product 2a regardless of
the supporting electrolytes except for Et3N‚2HF. Among
(15) Momota, K.; Morita, M.; Matsuda, Y. Electrochim. Acta 1993,
38, 619.

Highly Regioselective Anodic Monofluorination
J . Org. Chem., Vol. 62, No. 25, 1997 8775
Ta ble 4. An od ic Mon oflu or in a tion of Oxin d ole a n d
3-Oxo-1,2,3,4-tetr a h yd r oisoqu in olin e Der iva tives
Sch em e 5
charge
passed yield
(F/mol) (%)
substrate
supporting
electrolyte
run no.
n
R
R′
1
2
3
4
1a
1b
1c
1d
0
0
1
1
H
Ph
Me4NF‚4HF
3.5
3
2.6
2
64
50
71
70
CH3 p-CH3C6H4 Me4NF‚4HF
H
H
Ph
C6H5CH2
Et4NF‚3HF
Et4NF‚3HF
Sch em e 3
Sch em e 4
Sch em e 6
shown in Table 4. In these cases, even Et4NF‚3HF
provided the corresponding desired fluorinated products
2c,d in good yields and with rather good current efficien-
cies. Although 1d has three kinds of benzylic carbons,
the fluorination took place at the 4-position exclusively.16
Therefore, it is noted that this anodic fluorination is
highly regioselective.
An ECEC mechanism is widely accepted for electro-
chemical nucleophilic substitution reactions. To clarify
the fluorination mechanism in this case, we studied the
influence of the phenylthio group on the fluorination
reaction. In contrast to the case of 1, the corresponding
oxindole and 3-oxo-1,2,3,4-tetrahydroisoquinoline deriva-
tives devoid of a phenylthio group did not undergo
selective anodic fluorination, and complicated products
arising from fluorination of the benzene rings were
formed as shown in Scheme 4.17 This clearly suggests
that the phenylthio group plays an important role during
anodic fluorination.
We have already proposed a Pummerer-type mecha-
nism via a fluorosulfonium ion for the anodic fluorination
of sulfides.18 Therefore, the high regioselectivity of this
anodic fluorination can be explained as follows. Since
the phenylthio group is the most easily oxidized, anodic
oxidation takes place at the sulfur atom selectively to
generate the radical cation intermediate A as shown in
Scheme 5. Elimination of the R-proton should be facili-
tated by the adjacent electron-withdrawing carbonyl
group to form the cationic intermediate B, which provides
the fluorinated product 2 predominantly.
It is well-known that methods for the introduction of
fluorine into organosulfur compounds require expensive
and dangerous reagents such as xenon difluoride19 or
DAST.20 In recent years, N-fluoropyridinium triflates
and tetrafluoroborates have been developed as effective
fluorinating reagents with variable fluorinating power.21
However, fluorination of compound 1 as model com-
pounds with various types of N-fluoropyridinium triflates
resulted in no formation of desired products as shown in
Scheme 6. In the case of N-fluoro-2,4,6-trimethylpyri-
dinium and N-fluoropyridinium triflates, the starting 1
was almost completely recovered, whereas decomposition
of 1 took place in the reaction with N-fluoro-2,6-dichlo-
ropyridium triflate. Therefore, this electrochemical fluo-
rination is much superior to conventional chemical
methods.
In summary, this work reveals that N-aryloxindole and
3-oxo-1,2,3,4-tetrahydroisoquinoline derivatives bearing
a phenylthio group can be electrochemically fluorinated
efficiently in good yields and with high regioselectivity.
Thus, we have demonstrated that the electrochemical
method is highly promising for direct fluorination of such
biologically interesting heterocycles.
Exp er im en ta l Section
Ca u tion : Me4NF‚4HF is toxic and if in contact with skin
causes serious burns. Et4NF‚3HF, Et3N‚3HF, and Et3N‚2HF
are much less aggressive. However, proper safety precautions
should be taken at all times. It is therefore recommended that
hands be protected with rubber gloves. These fluoride salts
were obtained from Morita Chemical Industries Co. Ltd.
(J apan).
(16) The regioselectivity for the fluorination of 1c,d was determined
using 19F NMR, 13CNMR, and DEPT (distortionless enhancement by
polarization transfer). In DEPT, primary and tertiary carbon atoms
appear with positive phase, while a secondary carbon atom appears
in negative phase. Accordingly, by comparing the DEPT spectra of
the starting materials with those of their products, we easily deter-
mined which carbon was substituted by a fluorine atom.
(17) In the case of anodic fluorination of isoquinolines in Et4NF‚4HF/
MeCN, polyfluorination took place at the benzene ring predominantly
but the heterocyclic moiety was not fluorinated at all. Kato, K.;
Momota, K. The 18th Symposium on Electroorganic Chemistry,
Nagoya, J apan, 1995; Abstract 101.
1H NMR, 19F NMR, and 13C NMR spectra were recorded at
270, 254, and 68 MHz, respectively, with CDCl3 as a solvent.
The chemical shifts for 1H and 19F NMR are given in δ (ppm)
(19) (a) Zupan, M. J . Fluorine Chem. 1976, 8, 305. (b) Marat, R. K.;
J amzen, A. F. Can. J . Chem. 1977, 55, 3031. (c) J anzen, A. F.; Wang,
P. M. C.; Lemire, A. E. J . Fluorine Chem. 1983, 22, 557.
(20) McCarthy, J . R.; Peet, N. P.; LeTourneau, M. E.; Inbasekaran,
M. J . Am. Chem. Soc. 1985, 107, 735.
(18) Fuchigami, T.; Konno, A.; Nakagawa, K.; Shimojo, M. J . Org.
Chem. 1994, 59, 5937.
(21) (a) Umemoto, T.; Tomizawqa, G. Bull. Chem. Soc. J pn. 1986,
59, 3625. (b) Umemoto, T.; Tomizawa, G. J . Org. Chem. 1995, 60, 6563.

8776 J . Org. Chem., Vol. 62, No. 25, 1997
Hou et al.
downfield from internal Me4Si and perfluorobenzene, respec-
tively. High-resolution mass spectra were obtained with a
J EOL J MS-700 mass spectrometer. Cyclic voltammetry was
performed with a Hokutodenko potentiostat/galvanostat HA
6-151, and preparative electrolysis experiments were carried
out with a Metronix Corp. Tokyo constant-current power
supply.
oxidation of 1a (1 mmol) was carried out with platinum-plate
electrodes (2 × 2 cm2) in 0.25 M Me4NF‚4HF15 (10 equiv of F-
to 1a )/MeCN (10 mL) in an undivided cell under a nitrogen
atmosphere at room temperature. Constant current (4 mA/
cm2) was passed until the starting material 1a was consumed
(checked by TLC). After the electrolysis, the electrolyte was
neutralized with 10% aqueous ammonia solution and the
resulting aqueous solution was extracted with ether repeat-
edly. After the combined extracts were dried over anhydrous
MgSO4, 1-phenyl-3-(phenylthio)-3-fluorooxindole (2a ) was iso-
lated by silica gel chromatography (hexane:AcOEt ) 5:1).
1-P h en yl-3-(ph en ylth io)-3-flu or ooxin dole (2a): 1H NMR
δ 6.80-7.65 (m, 14H); 19F NMR δ -62.1 (s); MS (CI) m/z 336
(M + H+), 316 (M+ - F), 226 (M+ - SPh). Anal. Calcd for
C20H14FNOS: C, 71.62; H, 4.21; N, 4.18. Found: C, 71.71; H,
4.21; N, 3.97.
1-(p -Tolyl)-3-flu or o-3-(p h en ylt h io)-5-m et h yloxin d ole
(2b): 1H NMR δ 2.25 (s, 3H), 2.40 (s, 3H), 6.60-7.65 (m, 12H);
19F NMR δ -62.0 (s); MS m/z 363 (M+), 344 (M+ - F), 254
(M+ - SPh). HRMS: m/z calcd for C22H18FNOS, 363.1093;
found, 363.1069.
2-P h en yl-3-oxo-4-flu or o-4-(p h en ylth io)-1,2,3,4-tetr a h y-
d r oisoqu in olin e (2c): 1H NMR δ 4.78 (d, 1H, J ) 16.4 Hz),
4.98 (d, 1H, J ) 16.4 Hz), 6.66-7.62 (m, 14H); 19F NMR δ
-62.9 (s); MS m/z 349 (M+), 330 (M+ - F), 240 (M+ - SPh).
Anal. Calcd for C21H16FNOS: C, 72.18; H, 4.62; N, 4.01.
Found: C, 72.21; H, 4.45; N, 4.02. HRMS: m/z calcd for
C21H16FNOS, 349.0937; found, 349.0924.
P r ep a r a tion of Sta r tin g Ma ter ia ls. Oxindole and 3-oxo-
1,2,3,4-tetrahydroisoquinoline derivatives 1a -d were prepared
in
a
manner similar to the reported method.14 Typical
synthetic procedure: N-Acylation of N-phenylaniline with
R-(phenylthio)acetyl chloride22 followed by oxidation of the
resulting N-phenyl-R-(phenylthio)acetanilide with 3-chloroben-
zoperoxic acid gave N-phenyl-R-(phenylsulfinyl)acetanilide in
48% yield. Treatment of the sulfoxide thus formed with 2
equiv of p-toluenesulfonic acid in boiling carbon tetrachloride
provided 1-phenyl-3-(phenylthio)oxindole (1a ) in 61% yield.
1a : 1H NMR δ 4.68 (s, 1H), 6.52-7.54 (m, 14H). Anal. Calcd
for C20H15NSO: C, 75.68; H, 4.76; N, 4.41. Found: C, 75.57;
H, 4.75; N, 4.34.
1-(p-Tolyl)-3-(p h en ylth io)-5-m eth yloxin d ole (1b): 1H
NMR δ 2.39 (s, 3H), 4.65 (s, 1H), 6.40-7.38 (m, 12H); MS m/z
345 (M+), 236 (M+ - SPh). Anal. Calcd for C22H19NSO: C,
76.49; H, 5.54; N, 4.05. Found: C, 76.18; H, 5.61; N, 4.03.
HRMS: m/z calcd for C22H19NSO, 345.1221; found, 345.1214.
2-P h en yl-3-oxo-4-(p h en ylt h io)-1,2,3,4-t et r a h yd r oiso-
qu in olin e (1c): 1H NMR δ 4.63 (s, 1H), 4.60 (d, 1H, J ) 16.1
Hz), 4.90 (d, 1H, J ) 16.1 Hz), 6.48-7.48 (m, 14H); MS (FAB)
m/z 332 (M + H+), 222 (M+ - SPh). Anal. Calcd for
C21H17NSO: C, 76.10; H, 5.17; N, 4.23. Found: C, 76.65; H,
5.17; N, 4.09. HRMS (FAB): m/z (M + H+) calcd for
C21H17NSO, 332.1109; found, 332.1116.
2-Ben zyl-3-oxo-4-(p h en ylt h io)-1,2,3,4-t et r a h yd r oiso-
qu in olin e (1d ): 1H NMR δ 3.98 (s, 1H), 4.62 (d, 1H, J ) 14.5
Hz), 4.71 (d, 1H, J ) 14.8 Hz), 4.87 (s, 1H), 6.87-7.36 (m, 14H);
MS m/z 345 (M+), 236 (M+ - SPh). Anal. Calcd for
C22H19NSO: C, 75.68; H, 5.54; N, 4.05. Found: C, 76.24; H,
5.44; N, 3.92: HRMS m/z calcd for C22H19NSO, 345.1187;
found, 345.1187.
2-Ben zyl-3-oxo-4-(p h en ylth io)-4-flu or o-1,2,3,4-tetr a h y-
d r oisoqu in olin e (2d ): 1H NMR δ 4.20 (d, 1H), 4.58 (d, 1H),
4.70 (d, 1H), 4.82 (d, 1H), 6.94-7.40 (m, 14H); 19F NMR δ
-60.8 (s); MS (CI) m/z 364 (M + H+), 344 (M+ - F), 254 (M+
- SPh). Anal. Calcd for C22H18FNOS: C, 72.70; H, 4.99; N,
3.85. Found: C, 73.42; H, 5.15; N, 3.85. HRMS: m/z calcd
for C22H18FNOS, 363.1093; found, 363.1091.
Ack n ow led gm en t. This study was financially sup-
ported by a Grant-in-Aid for Developmental Scientific
Research and Ciba-Geigy Foundation (J apan) for the
Promotion of Science. We also thank Dr. K. Momota of
Morita Chemical Industries Co. Ltd. for his generous
gifts of Et4NF‚3HF and Me4NF‚4HF. We are also
grateful to Chichibu Onoda Cement Co. for generous
gifts of N-fluoropyridinium triflates.
An od ic F lu or in a tion of Oxin d ole a n d 3-Oxo-1,2,3,4-
tetr a h yd r oisoqu in olin e Der iva tives. A typical procedure
for the anodic fluorination of oxindoles 1 is as follows. Anodic
(22) Mooradian, A.; Cavalltito, C. J .; Bergman, A. J .; Lawson, E. J .;
Suter, C. M. J . Am. Chem. Soc. 1949, 71, 3372.
J O971173I