Electrolytic partial fluorination of organic compounds. 36

Article abstract of DOI:10.1016/S0022-1139(99)00179-7

The anodic fluorination of 3-phenylthio-2-benzofuranones and α-phenylthio-2-benzothiazolylacetonitrile was investigated. Both derivatives were selectively fluorinated in good yields at the carbon α to the sulfur atoms in Et₄NF·3HF/DME using a p

Full text of DOI:10.1016/S0022-1139(99)00179-7

Journal of Fluorine Chemistry 99 (1999) 189±195
Electrolytic partial ¯uorination of organic compounds. 36 [1].
Regioselective anodic ¯uorination of phenylthiolated
benzofuranone and benzothiazole derivatives
Seiichiro Higashiya, Kamal M. Dawood1,
Toshio Fuchigami*
Department of Electronic Chemistry, Tokyo Institute of Technology, 4259, Nagatsuta,
Midori-ku, Yokohama 226-8502, Japan
Received 2 June 1999; received in revised form 23 June 1999; accepted 23 July 1999
Dedicated to the 75th birthday of Dr. Yoshiro Kobayashi, Emeritus Professor of Tokyo
University of Pharmacy and Life Science
Abstract
The anodic ¯uorination of 3-phenylthio-2-benzofuranones and a-phenylthio-2-benzothiazolylacetonitrile was investigated. Both
derivatives were selectively ¯uorinated in good yields at the carbon a to the sulfur atoms in Et4NFÁ3HF/DME using a platinum anode and
an undivided cell. The ¯uorination yields of the benzofuranone derivatives were improved by the addition of Ph2S, which was not effective
in the case of the benzothiazole derivative. The ¯uorination yield of the benzothiazole derivative was strongly affected by the stirring state
of the electrolytic solution or the applied anode potential. # 1999 Elsevier Science S.A. All rights reserved.
Keywords: Selective anodic ¯uorination; Benzofuranone; Benzothiazole; Phenylthio group; Electroauxiliary; Mediator
1. Introduction
2. Results and discussion
The incorporation of ¯uorine atom(s) into organic or
bioorganic compounds sometimes drastically changes their
physical, chemical, and biological properties [2,3]. We have
been investigating the oxidative incorporation of ¯uorine
atom(s), especially, using an electrochemical method, i.e.,
anodic ¯uorination to synthesize potent biologically active
compounds [4±10]. In these studies, organic molecules were
regioselectively ¯uorinated in excellent to good yields under
very mild conditions.
In this paper, we report the selective anodic ¯u-
orination of biologically active benzofuranone [11] and
benzothiazole derivatives [12,13] to provide more potent
active analogs.
2.1. Synthesis, electrochemical and chemical properties
of phenylthiolated benzofuranone 2 and
benzothiazolylacetonitrile derivatives 4
5-Chloro-2-benzofuranone 1b was synthesized via the
chlorination of commercially available 2-benzofuranone
(2-coumaranone) 1a by N-chlorosuccinimide (NCS) without
any radical initiators in a polar solvent as CH3CN. The
synthesis of the 3-phenylthiolated 2-benzofuranones (2) and
a-phenylthiolated 2-benzothiazolylacetonitrile (4) were
achieved via phenylthiolation of 1 and 3, respectively, by
diphenyl disul®de in the presence of a base (Scheme 1).
In the case of 2, the yields were not so high, because the
parent benzofuranones 1 easily underwent the Claisen con-
densation to give dimerized product 5 under basic conditions
[11,14]. The methine protons of these phenylthiolated com-
pounds 2 and 4 seems to be acidic, because their extraction
*Corresponding author. Fax: +81-45-924-5406
1
from alkaline aqueous solutions was not ef®cient. The H
NMR of the methine proton of 4 in DMSO appeared in a
very low ®eld around 12.5 ppm as two broad singlets,
E-mail address: fuchi@echem.titech.ac.jp (T. Fuchigami)
1UNESCO Research Fellow (1997±1998). Present address: Department
of Chemistry, Faculty of Science, Cairo University, Giza, Egypt.
0022-1139/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 9 9 ) 0 0 1 7 9 - 7

190
S. Higashiya et al. / Journal of Fluorine Chemistry 99 (1999) 189±195
Scheme 1.
instead of the usual ®eld around 5±6 ppm, possibly due to
tautomers 40 and 400 in a very polar solvent like DMSO as
described in Scheme 1.
Prior to the anodic ¯uorination of 2 and 4, we measured
the oxidation peak potentials by cyclic voltammetry (Table
1). Compound 4 showed a prepeak at 0.95 V vs. a sodium
saturated calomel electrode (SSCE). This prepeak was
found to be related to the yield of the anodic ¯uorination
of 4, as described later (Section 2.3).
(run 1), and the addition of Ph2S [15] also improved the
yield from 76% to 84% (run 3). Potentiostatic electrolysis
did not signi®cantly improve the yield (run 4). The product
6a was unstable, especially in the crude and concentrated
state. It rapidly decomposed at temperature higher than
508C and gradually decomposed even at room temperature.
Compound 6a also decomposed by eliminating hydrogen
¯uoride and the PhS group to produce an unidenti®ed
products and a dithioacetal derivative 7 as denoted in
Scheme 2, during the removal of the electrolyte by extrac-
tion or passing through a silica gel column if the silica gel
was not well-dried. Such migration of a PhS group was
previously reported by our group [16].
2.2. Anodic fluorination of 3-phenylthiolated
benzofuranone derivatives 2
First of all, we attempted anodic ¯uorination of 3-phe-
nylthio-2-benzofuranone (2a) using 1 M Et4NFÁ3HF solu-
tions (Table 2).
1,2-Dimethoxyethane (DME, run 2) gave the correspond-
ing a-¯uorinated product 6a in a higher yield than CH3CN
A dimerized compound 8 was also found. It seems to be
formed via the dimerization of the anodically generated
radical intermediate A, which should be stabilized by
captodative and resonance effects.
Finally, the product 6a was partly puri®ed using the
silica gel which was well-dried by heating in vacuo and
then deactivated by ethyl acetate in order to reduce the
heat generated when the substrate was adsorbed on the silica
gel.
Table 1
Oxidation peak potentials (Epox) of phenylthiolated benzofuranone and
benzothiazolylacetonitrile derivatives 2, 4a
This unstability of 6a could be attributed to the stabiliza-
tion of the benzylic cation by the phenolic oxygen atom.
Considering this point, we next tried the anodic ¯uorination
of 2b which has a chlorine atom on the benzene ring to
destabilize the corresponding benzyl cation generated from
the ¯uorinated product 6b. As expected, 6b was more stable
than 6a, but the yield was much lower under the same
conditions used for the anodic ¯uorination of 2a (Table 2,
run 5). However, when the stirring of the solution was
stopped during the electrolysis (still condition), the yield
of 6b was signi®cantly increased (run 6). Use of
Et4NFÁ4HF/DME and Ph2S also improved markedly the
Substrate
X
Epox (V vs. SSCEb)
2a
2b
4
H
Cl
±
1.85, 1.98
1.88, 2.72
0.95, 2.8 (sh)
a In 0.1 M Et4NClO4/CH3CN. Sweep rate: 100 mV s
b Sodium saturated calomel electrode.
.
1

S. Higashiya et al. / Journal of Fluorine Chemistry 99 (1999) 189±195
191
Table 2
Anodic fluorination of 3-phenylthiolated benzofuranone derivatives 2
Run
Substrate
Fluoride Salt/electrolytic
solvent
Additive (equiv.)
Other conditions
Electricity
1
Yield of 6
(%)a
(F mol
)
1
2
3
4
2a (X = H)
Et4NFÁ3HF/CH3CN
Et4NFÁ3HF/DME
Et4NFÁ3HF/DME
Et4NFÁ3HF/DME
±
5 mA cm 2b, stirr
3.0
2.2
2.5
2.2
40
±
5 mA cm 2b, stirr
76 (23)
84
76
Ph2S (0.5)
Ph2S (0.5)
5 mA cm 2b, stirr
1.6 V vs. Ag/0.01 M Ag+c
5
6
7
8
9
2b (X = Cl)
Et4NFÁ3HF/DME
Et4NFÁ3HF/DME
Et4NFÁ4HF/CH3CN
Et4NFÁ4HF/DME
Et4NFÁ4HF/DME
±
5 mA cm 2b, stirr
5 mA cm 2b, stirr
5 mA cm 2b, stirr
5 mA cm 2b, stirr
5 mA cm 2b, stirr
3.0
3.5
3.5
3.0
3.5
14
±
49
49
±
±
61 (42)
74
Ph2S (0.5)
a Determined by 19FNMR; isolated yields are denoted in parentheses.
b Potentiostatic electrolysis.
c Galvanostatic electrolysis.
Scheme 2.
yields of 6b (runs 8 and 9), but when the solvent was
changed to CH3CN, the yield was decreased (run 7).
CH3CN (run 1) similar to the case of compounds 2.
Et4NFÁ4HF (run 2) and Et4NFÁ3HF (run 3) gave almost
the same results, but the current ef®ciency of the latter was
better, and Et4NFÁ3HF is less corrosive to the glassware
compared to the former. The addition of Ph2S (run 4) or the
use of a divided cell (run 5) had almost no effect on the
yields, but when the electrolytic solution was not stirred
during the electrolysis (run 6), the yield of 9 signi®cantly
increased. These results implied that a higher anodic poten-
tial gave the better yield in this case. Therefore, we carried
out the anodic ¯uorination of 4 at various anodic potentials
and the resulting yield-anodic potential relationship (runs 7±
13) was compared with the linear sweep voltammogram of
the substrate 4 (Fig. 1).
2.3. Anodic fluorination of a-phenylthiolated
benzothiazolylacetonitrile 4
Next, a-phenylthiolated benzothiazolylacetonitrile 4 was
subjected to anodic ¯uorination under various electrolytic
conditions (Table 3).
In almost all the cases, the a-¯uorinated product 9 was
formed with a trace amount of the desulfurizatively ¯uori-
nated product 10 (the maximum yield was 5% (run 12)).
Compound 9 was much more stable than the a-¯uorinated
benzofuranone derivatives 6. DME gave better yields than

192
S. Higashiya et al. / Journal of Fluorine Chemistry 99 (1999) 189±195
Table 3
Anodic fluorination of a-phenylthiolated benzothiazolylacetonitrile 4
1
)
Run
Electrolyte
Solvent
Other conditions
Electricity (F mol
Yield of 9 (%)a
2
Galvanostatic, 5 mA cm
1
2
3
4
5
6
1 M Et4NFÁ3HF
CH3CN
DME
3.0
6.0
3.0
3.5
3.0
3.5
4
1 M Et4NFÁ4HF
1 M Et4NFÁ3HF
11
11
12
14
52
Ph2S (0.5 equiv.)
Divided cellb
Still
Potentiostatic, vs. Ag/0.01 M Ag
7
0.6 V
1.0 V
1.5
1.4
1.2
2.8
4.0
4.0
8.0
0
8
9
8
1.4 V
16
39
39
53c
33
10
11
12
13
1.8 V
2.1 V
2.1 V, still
2.4 V
a Determined by 19F NMR.
b The cell was divided using an anion exchange membrane.
c 10 was formed in 5% yield.
solubility even in DMSO, but the result of the elemental
analysis predicted the structure as the oxidatively desulfur-
izative dimer 11 denoted in Scheme 3.
After the ®rst oxidation step, if the anodic potential is not
high enough or the intermediate cation radical B migrates to
the bulk from the anodic surface, the second oxidation does
not take place and the cation radical intermediate B releases
a proton and the phenylthio radical. The latter radical
dimerizes to diphenyl disul®de and in some cases, diphenyl
disul®de is further oxidized to S-phenyl thiobenzenesulfo-
nate. The resulting benzothiazolylacetonitrile carbene C
seems to dimerize to yield 11.
Fig. 1. Yield-potential plot and linear sweep voltammogram of a-
phenylthiolated benzothiazolylacetonitrile 4 (electrolytic solution: 1 M
Et4NFÁ3HF/DME; Pt electrodes; yield-potential plot, & : yield of 9; *:
yield of 10; notched line: linear sweep voltammogram of 4 at a sweep rate
Under still conditions, 10 was formed in a maximum
yield as 5%. Therefore, the proposed mechanism as shown
in Scheme 3 would be reasonable.
1
of 50 mV s with stirring).
As expected, the yield increased as the anodic potential
increased, but the yields in the stirring cases (runs 7±11, 13)
were lower than those in the still cases (runs 6,12). Even
when the anodic ¯uorination was carried out at 0.6 V vs. Ag/
0.01 M Ag+ which corresponded to the prepeak potential
(ca. 0.9 V vs. SSCE), the substrate was almost consumed,
but the desired product 9 was not formed. In the linear sweep
voltammogram, two waves were observed at 0.5 and 1.0 V,
and the ¯uorinated product could be obtained in moderate
yield above the potential of the second wave.
3. Experimental
3.1. General
Caution: Et4NFÁ4HF is toxic and may cause serious burns
if it comes in contact with unprotected skin, while
Et4NFÁ3HF is much less aggressive, so proper safety pre-
cautions should be taken at all times. Therefore, the use of
rubber gloves is recommended to protect the hands.[17]
1H NMR, 19F NMR, and 13C NMR spectra were recorded
at 270, 254, and 68 MHz, respectively, in CDCl3 as the
solvent using a JEOL EX-270 spectrometer. The chemical
shifts for the 1H and 13C NMRs are given in ꢀ ppm down®eld
During the electrolysis, a needle-like, highly crystalline
reddish-orange precipitate began to deposit from the solu-
1
tion after the charge of ca. 0.2F mol was passed. This
compound was not yet well-de®ned because of its quite low

S. Higashiya et al. / Journal of Fluorine Chemistry 99 (1999) 189±195
193
Scheme 3.
from internal TMS and the 19F NMR chemical shifts are
3.3. Preparation of 3-phenylthio-2-benzofuranone
derivatives 2a,b
given in ꢀ ppm down®eld from external CF3COOH. To
determine the crude yield of the ¯uorinated products, a
certain amount of mono¯uorobenzene was added to the
crude solution, and the yield was calculated by comparison
between the integration values of the ¯uorine NMR signals
of the ¯uorinated products and mono¯uorobenzene. Mass
spectra were obtained with Shimadzu GCMS-QP2000A and
JEOL JMS-700 mass spectrometers. Cyclic voltammetry
was performed using a Hokuto Denko Potentiostat/Galva-
To a two-necked 200-ml round ¯ask ®tted with a dropping
funnelequippedwithathree-waycockonthetop(oneofwhich
wasarubberballoon®lledwithnitrogen),andaseptumrubber
cap, diphenyl disul®de (2.84 g, 13 mmol, 1.3 equiv.) and 60%
NaH (0.60 g, 15 mmol, 1.5 equiv.) was added and purged by
nitrogen. To the ¯ask, anhydrous THF or DME (50 ml) was
added through the septum cap, and to the dropping funnel, 2-
benzofuranone 1a (1.34 g, 10 mmol) dissolved in the same
solvent (50 ml) was added. The solution of 1a was slowly
added for 1 h and stirred for additional 1 h. The solution was
diluted with toluene (150 ml) and then 1 M aq. H2SO4 was
slowlyadded to this solution. This mixturewas separated, and
theorganicphasewaswashedtwicewithH2O, thendriedover
anhydrous Na2SO4. The volatile solvent was evaporated and
the residue was puri®ed on the silica gel column chromato-
graphy (100 g). At ®rst, the by-products were washed out by
hexane then the product was eluted out using 5% ethyl acetate
in hexane, to give the crude product in 49% yield (1.177 g).
After recrystallization from ethyl acetate/hexane, the analy-
tically pure product 3-phenylthio-2-benzofuranone 2a was
obtained in 47% yield (1.135 g). m.p. 82±838C; Anal. Calcd.
for C14H10O2S: C, 69.40%; H, 4.16%; S, 13.23%. Found C,
69.47%;H,4.07%;S,13.42%;1HNMRꢀ 7.4(m,3H),7.3±7.1
(m, 6H), 6.91 (d, J = 7.9 Hz, 1H), 4.77 (s, 1H); 13C NMR ꢀ
173.69, 153.41, 134.65, 129.94, 129.74, 129.36, 129.02,
125.45, 124.46, 110.71, 47.32; MS m/e 242 (M+), 133
(M+±PhS), 109, 105, 77.
1
nostat HA 6-151 at a scan speed of 100 mV s in 0.1 M
Et4NClO4/CH3CN. Preparative electrolysis experiments
were carried out using a Potentiostat/Galvanostat HA-501
and a Coulomb/Amperehour meter HF-201 (Hokuto
Denko,) with a reference electrode (Ag wire/0.01 M
AgNO3, 0.1 M Et4NBF4 in CH3CN) for the potentiostatic
electrolysis, and a Metronix Corp. (Tokyo) constant current
power supply for the galvanostatic electrolysis.
3.2. Preparation of 5-chloro-2-benzofuranone 1b
To a 100-ml round ¯ask, 2-benzofuranone 1a (2-coumar-
anone, 1.92 g, 14.3 mmol), N-chlorosuccinimide (5.72 g,
42.6 mmol) and anhydrous CH3CN (50 ml) were added
and the solution was vigorously stirred for 1 week. CH3CN
was then evaporated and the residue was diluted with
toluene. The organic solution was washed with one portion
of aq. Na2S2O3 and two portions of H2O, then dried over
MgSO4. After removal of the MgSO4, the solvent was
evaporated and the residue was puri®ed by silica gel column
chromatography using a linear gradient of 0±50% toluene in
hexane. After removal of the solvent, the residue was
recrystallized from Et2O/hexane to give the product 1b in
74% yield (1.78 g). m.p. 126±1278C (lit. 127±1298C [11]);
Anal. Calcd. for C8H5ClO2: C, 57.00%; H, 2.99%; Cl,
21.03%. Found C, 56.99%; H, 3.05%; Cl, 21.00%; 1H
NMR ꢀ 7.3 ꢀ 7.2(m, 2H), 7.0 (m, 1H), 3.74 (s, 2H); 13C
NMR ꢀ 173.10, 152.97, 129.20, 128.81, 124.82, 124.67,
111.73, 32.87; MS m/e 168 (M+), 140, 112, 77.
Based on almost the same procedure, 3-phenylthio-5-
chloro-2-benzofuranone 2b was obtained in 52% yield
(5.76 g) from 5-chloro-2-benzofuranone 1b (6.78 g,
40.2 mmol),diphenyldisul®de(17.57 g,80.5 mmol,2equiv.),
and 60% NaH (2.41 g, 60.3 mmol, 1.5 equiv.). m.p. 67±688C;
Anal. Calcd. for C14H9ClO2S: C, 60.76%; H, 3.28%; Cl,
12.81%; S, 11.59%. Found C, 61.04%; H, 3.35%; Cl,
1
12.60%; S, 11.33%; H NMR ꢀ 7.5ꢀ7.1 (m, 7H), 6.84 (d,
1H, J = 5.8 Hz), 4.74 (s, 1H); 13C NMR ꢀ 172.90, 151.68,

194
S. Higashiya et al. / Journal of Fluorine Chemistry 99 (1999) 189±195
134.72, 129.92, 129.63, 129.58, 129.18, 129.09, 126.24,
125.54, 125.50, 111.82, 47.26; MS m/e 276 (M+), 167 (M+±
S), 109 (PhS+).
was allowed to pass through a short column of the silica gel
which had been dried in vacuo and immersed in ethyl acetate
before use. The eluent was evaporated (ca. 10% of 2 was lost
during this procedure) and the residue was further puri®ed by
column chromatography using the above-mentioned dried
silica gel which was deactivated by ethyl acetate, then the
eluent was displaced by hexane. The product was eluted out
usingalineargradientof0±50%tolueneinhexaneasrapidlyas
possible. Compounds2wereimmediatelydecomposedonthe
silica gel TLC, therefore, they appearedas spotsatthestarting
point after the development.
3-Fluoro-3-phenylthio-2-benzofuranones (6a): 1H NMR ꢀ
7.62 (d, 2H, J = 7.3 Hz), 7.56±7.40 (m, 4H), 7.24±7.12 (m,
3H);19FNMRꢀ-56.90(s);13CNMRꢀ166.67(d,J = 61.3 Hz),
151.87(d,J = 6.1 Hz),136.57,136.53,132.65(d,J = 2.4 Hz),
130.69, 129.18, 126.60, 124.83 (d, J = 8.5 Hz), 123.20 (d,
J = 22.0 Hz), 111.56, 95.18 (d, J = 247.8 Hz),; MS m/e 260
(M+), 151 (M+±PhS), 109 (PhS+); HRMS Calcd. for
C14H9FO2S: m/e 260.0607. Observed 260.0608.
3,3-Di(phenylthio)-2-benzofuranone (7): 1H NMR ꢀ
7.40±7.34 (m, 4H),7.32±7.28 (m, 2H), 7.24±7.14 (m,
6H), 7.10±7.04 (m, 1H), 6.78±6.74 (m, 1H); 13C NMR ꢀ
172.61, 151.86, 136.75, 130.28, 128.86, 128.64, 126.60,
125.52, 124.26, 110.51, 61.04; MS m/e 350 (M+), 241 (M+±
PhS), 213, 184, 152, 133, 109, 77. HRMS Calcd. for
C20H14O2S2: m/e 350.0435. Observed 350.0436.
3,30-Di(phenylthio-2-benzofuranonyl) (8): 1H NMR ꢀ
7.55 (m, 2H), 7.2 (m, 6H), 7.3±7.0 (m, 8H), 6.5 (m, 2H);
13C NMR ꢀ 171.51, 151.86, 137.14, 137.07, 130.46, 130.19,
128.41, 127.89125.25, 124.74, 110.24, 62.50; MS m/e 482
(M+), 373 (M+±PhS), 264 (M+±PhSSPh), 241 (M/2+), 218
(PhSSPh). HRMS Calcd. for C28H18O4S2: m/e 482.0647.
Observed 482.0645.
3.4. Preparation of a-phenylthio-2-
benzothiazolylacetonitrile 4
Toa200-mlround¯ask,2-benzothiazolylacetonitrile3[18]
(2.96 g, 16.6 mmol), diphenyl disul®de (4.45 g, 20.6 mmol,
1.2 equiv.), KOH (3.73 g, 66.4 mmol, 4 equiv.), and THF
(80 ml) were added and stirred overnight. The solvent was
partly evaporated and the residue was dissolved in a 1 : 1
mixtureoftolueneandethylacetate,thensequentiallywashed
with 2 M aq. HCl and H2O. The organic phase was dried over
MgSO4andthesolventwasremovedinvacuo.Theresiduewas
recrystallized from MeOH and dried in vacuo at 1008C to
remove the diphenyl disul®de. The dried product was recrys-
tallized again to give the product 4 in 72% yield (3.41 g). m.p.
181±1828C; Anal. Calcd. for C15H10N2S2: C, 63.80%; H,
3.57%; N, 9.92%; S, 22.71%. Found C, 63.89%; H, 3.52%;
N, 9.96%; S, 21.78%; 1H NMR (in DMSO-d6) ꢀ 12.69, 12.36
(2s, 1H), 7.72, 7.61 (2d, 1H, J = 7.9 Hz), 7.34 (m, 8H), 7.19,
7.12 (t and m, 1H, J = 6.8 Hz); 13H NMR (in DMSO-d6) ꢀ
172.20, 168.18, 142.25, 140.94, 136.89, 136.03, 129.40,
127.03, 126.60, 125.82, 124.96, 124.87, 124.75, 123.04,
122.72, 122.46, 122.10, 121.48, 119.86, 112.76, 112.56,
53.23, 52.74; MS m/e 282 (M+), 173 (M+±PhS), 146, 109
(PhS+).
3.5. Synthesis of the fluorinated products by anodic
fluorination
3.5.1. Anodic fluorination of 3-phenylthio-2-
benzofuranone derivatives 2a,b and a-phenylthio-2-
benzothiazolylacetonitrile 4. General procedure
5-Chloro-3-¯uoro-3-phenylthio-2-benzofuranone (6b):
Anal. Calcd. for C14H8ClFO2S: C, 57.05%; H, 2.74%; Cl,
12.03%;F,6.45%;S,10.88%.FoundC,57.31%;H,2.78%;Cl,
1
Under a nitrogen atmosphere, electrolysis was carried out
a 1 M
12.05%; F, 6.44%; S, 10.97%; H NMR ꢀ 7.60 (d, 2H,
with platinum electrodes (2 cm  2 cm) in
J = 7.6 Hz), 7.51 (d, 1H, J = 7.3 Hz), 7.43 (m, 3H), 7.07 (d,
2H, J = 8.6 Hz); 13H NMR ꢀ 166.49 (d, J = 31.7 Hz), 150.57
(d, J = 4.9 Hz), 137.09, 133.03, 131.43, 130.67, 129.76,
126.51, 125.43, 124.94 (d, J = 22.0 Hz), 113.30, 95.47 (d,
J = 249.1 Hz); 19F NMR ꢀ-58.17 (s); MS m/e 294 (M+), 185
(M+±PhS),129, 109(PhS+). HRMSCalcd.forC14H8ClFO2S:
m/e 293.9918. Observed 293.9932.
Et4NFÁnHF (n = 3,4) electrolytic solution (15 ml) contain-
ing the substrate (1.5 mmol) and in the presence or absence
of diphenyl sul®de (0.75 mmol) using a cylindrical undi-
vided cell or H-type divided cell with an anion-exchange
membrane (IE-DF 34-5 TOSOH) at ambient temperature. In
the cases of constant potential electrolysis and the linear
sweep voltammetry of 4, a reference electrode (Ag wire/
0.01 M AgNO3, 0.1 M Et4NBF4 in CH3CN) was used. After
the starting material was almost consumed (determined by
silica gel TLC), the solvent was evaporated and the 19F
NMR was measured to estimated the product yield.
3.5.3. Isolation and identification of the products of the
anodic fluorination of a-phenylthio-2-
benzothiazolylacetonitrile 4
After the electrolysis, the solution was ®ltered to separate
the reddish-orange precipitate, i.e., 11, and the ®ltrate was
diluted with cold ethyl acetate. To remove the electrolyte,
the other polymeric and highly polar compounds, the cold
solution was allowed to pass through a short column of the
silica gel. The eluent was evaporated and the residue was
further puri®ed by silica gel column chromatography using
a linear gradient of 0±20% ethyl acetate in hexane.
3.5.2. Isolation and identification of the products of the
anodic fluorination of 3-phenylthio-2-
benzofuranone derivatives 2a,b
After the electrolysis, the solution was diluted with cold
ethylacetate.Inordertoremovethesupportingelectrolyte,the
otherpolymericandhighlypolarcompounds,thecoldsolution

S. Higashiya et al. / Journal of Fluorine Chemistry 99 (1999) 189±195
195
ꢁ-¯uoro-ꢁ-phenylthio-2-benzothiazolylacetonitrile (9):
References
m.p. 103±1048C; Anal. Calcd. for C15H9FN2S2: C, 59.98%;
H, 3.02%; N, 9.33%; F, 6.33%; S, 21.35%. Found C, 60.25%;
H, 2.89%; N, 9.31%; F, 6.42%; S, 21.30%; 1H NMR ꢀ 8.20 (d,
1H, J = 8.3 Hz), 7.95 (d, 1H, J = 7.9 Hz), 7.78 (d, 2H,
J = 7.3 Hz), 7.64±7.42 (m, 5H); 13C NMR ꢀ 160.74 (d,
J = 31.7 Hz), 152.17, 136.78, 135.54, 131.54, 129.69,
127.20, 127.01, 126.58, 124.71, 121.87, 112.44 (d,
J = 44.0 Hz), 94.86 (d, J = 227.1 Hz); 19F NMR ꢀ -33.63
(s); MS m/e 300 (M+), 191 (M+±SPh), 134 (M+±CFSPhCN),
109 (PhS+), 102; HRMS Calcd. for C15H9FN2S2: m/e
300.0191. Observed 300.0200.
ꢁ-¯uoro-2-benzothiazolylacetonitrile(10):1HNMRꢀ 8.16
(d,1H,J = 7.6 Hz),7.99(dd,1H,J = 7.1,1.3 Hz),7.61(td,1H,
J = 7.4, 1.3 Hz), 7.54 (td, 1H, J = 7.4, 1.3 Hz), 6.49 (d, 1H,
J = 46.2 Hz); 13C NMR ꢀ 158.89 (d, J = 26.8 Hz), 152.34,
135.58, 127.22, 127.10, 124.55, 122.09, 112.99 (d,
J = 31.7 Hz), 77.29 (d, J = 185.6 Hz); 19F NMR ꢀ -97.63 (d,
J = 45.9 Hz);MSm/e192(M+);HRMSCalcd.forC9H5FN2S:
192.0157. Observed 192.0155.
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We are grateful to Dr. K. Momota of Morita Chemical
Industries Co. for his kind gifts of Et4NFÁnHF (n = 3, 4).