Reactions of 4-hydroxy-5,6,7,8-tetrafluorocoumarin derivatives with S-nucleophiles

Article abstract of DOI:10.1016/S0022-1139(99)00210-9

In the reactions with o-aminothiophenol, 4-hydroxy-(3-(imino)acetyl)-5,6,7,8-tetrafluorocoumarins give products of S-substitution at the C-7 atom. 7-Substituted 5,6,8-trifluorocoumarins form benzothiazole as a result of heterocyclic ring opening; 3-ethoxycarbonyl-2-methyl-5,6,7,8-tetrafluorochromone undergoes acid splitting to 2-(2-hydroxy-3,4,5,6-tetrafluorophenyl)benzothiazole. Under alkaline conditions, S-substituted coumarins decompose to acetophenone. In an acid medium, 4-hydroxy-3-iminoacetyl-5,6,8-trifluoro-7-(2-aminophenylthio)coumarin affords 7-(2-aminophenylthio)-2-methyl-5,6,8-trifluorochromone. 4-Hydroxy-5,6-difluoro-2-H-pyrano[6,5-a]phenothiazin-2-one was isolated from condensation of 7-(2-aminophenylthio)-4-hydroxy-5,6,8-trifluorocoumarin in the presence of NaH. Reactions of 3-acetyl(iminoacetyl)-4-hydroxy-5,6,7,8-tetrafluorocoumarins and 3-ethoxycarbonyl-2-methyl-5,6,7,8-tetrafluorochromone with 2-mercaptoethanol result in the formation of 5,7,8-trisubstituted derivatives. Interaction of 3-ethoxycarbonyl-2-methyl-5,6,7,8-tetrafluorochromone with 2-mercaptoethanol, mercaptoacetic acid and 1,2-ethanedithiol leads to the formation of the 7-substituted products. Acyl-lactone rearrangement of mono- and trisubstituted chromones gives the corresponding coumarins.

Full text of DOI:10.1016/S0022-1139(99)00210-9

Journal of Fluorine Chemistry 103 (2000) 3±12
Reactions of 4-hydroxy-5,6,7,8-tetra¯uorocoumarin
derivatives with S-nucleophiles
I.T. Bazyl0, S.P. Kisil0, Ya.V. Burgart, V.I. Saloutin*
Institute of Organic Synthesis, Urals Division, Russian Academy of Sciences, 620219, GSP-147,
Ekaterinburg, Russia
Received 1 June 1999; accepted 23 August 1999
Abstract
In the reactions with o-aminothiophenol, 4-hydroxy-(3-(imino)acetyl)-5,6,7,8-tetra¯uorocoumarins give products of S-substitution at the
C-7 atom. 7-Substituted 5,6,8-tri¯uorocoumarins form benzothiazole as a result of heterocyclic ring opening; 3-ethoxycarbonyl-2-methyl-
5,6,7,8-tetra¯uorochromone undergoes acid splitting to 2-(2-hydroxy-3,4,5,6-tetra¯uorophenyl)benzothiazole. Under alkaline conditions,
S-substituted coumarins decompose to acetophenone. In an acid medium, 4-hydroxy-3-iminoacetyl-5,6,8-tri¯uoro-7-(2-aminophenylthio)-
coumarin affords 7-(2-aminophenylthio)-2-methyl-5,6,8-tri¯uorochromone. 4-Hydroxy-5,6-di¯uoro-2-H-pyrano[6,5-a]phenothiazin-2-one
was isolated from condensation of 7-(2-aminophenylthio)-4-hydroxy-5,6,8-tri¯uorocoumarin in the presence of NaH.
Reactions of 3-acetyl(iminoacetyl)-4-hydroxy-5,6,7,8-tetra¯uorocoumarins and 3-ethoxycarbonyl-2-methyl-5,6,7,8-tetra¯uorochromone
with 2-mercaptoethanol result in the formation of 5,7,8-trisubstituted derivatives. Interaction of 3-ethoxycarbonyl-2-methyl-5,6,7,8-
tetra¯uorochromone with 2-mercaptoethanol, mercaptoacetic acid and 1,2-ethanedithiol leads to the formation of the 7-substituted
products. Acyl-lactone rearrangement of mono- and trisubstituted chromones gives the corresponding coumarins. # 2000 Elsevier Science
S.A. All rights reserved.
Keywords: Fluorocoumarin; Fluorochromone; S-nucleophile; o-Aminothiophenol; 2-Mercaptoethanol; Displacement; Opening of cycle; Acid splitting;
Cyclization; Acyl-lactone rearrangement
1. Introduction
Mono-substituted products are formed in the reactions of
6,7-di¯uoro- and 6,7,8-tri¯uoroquinolones with 2-mercap-
toethanol and o-aminothiophenol [7]. Displacement of the
¯uorine atom at the position 5 or 8 in quinolones is possible
when the heterocycle already has the substituent at the C-7
atom [8±10].
In this paper, reactions of 4-hydroxy-5,6,7,8-tetra¯uoro-
coumarin derivatives with o-aminothiophenol and 2-mer-
captoethanol is described.
Coumarin derivatives are of signi®cant interest for study
as so many of them are biologically active compounds [1]. 4-
Hydroxy-5,6,7,8-tetra¯uorocoumarin derivatives were
synthesized previously [2] and their reactions with amines
were studied [3]. Thus, 3-acetyl- and 3-iminoacetyl-4-
hydroxy-5,6,7,8-tetra¯uorocoumarins react with ammonia
and morpholine to form 7-substituted products. Under simi-
lar conditions, 3-methyl-6,7,8,9-tetra¯uorobenzopyranoi-
soxazole-4-one undergoes opening of the pyrone ring to
give the corresponding amides [3]. Data on the reactions
of 4-hydroxy-5,6,7,8-tetra¯uorocoumarin derivatives with
S-nucleophiles are absent.
The reactions of ¯uoroquinoline-3-carboxylic acids
with S-nucleophiles are known to result in the formation
of 7-substituted quinolinones. Thus, interaction of 4-oxo-
5,6,7-tri¯uoro-1-ethylquinoline-3-carboxylic acid with
2-mercaptoethanol leads to 7-alkylthio-derivatives [4±6].
2. Experimental details
Melting points were measured in open capillaries and are
reported uncorrected. Infrared spectra were measured on a
Specord 75 IR spectrometer.1H- and 19F-NMR spectra were
recorded on a Tesla BS-587A instrument (1H: 80 MHz,
using TMS as an internal standard, 19F: 75 MHz, using
CFCl3 as an internal standard). Microanalyses were per-
formed with a Carlo Erba CHNS-O EA 1108 elemental
analyzer. Thin-layer chromatography was performed on
`Silufol-UV 254' plates.
* Corresponding author. Fax: ‡7-3432-745954.
E-mail address: fc@ios.uran.ru (V.I. Saloutin).
0022-1139/00/$ ± see front matter # 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 9 9 ) 0 0 2 1 0 - 9

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I.T. Bazyl0 et al. / Journal of Fluorine Chemistry 103 (2000) 3±12
2.1. Materials
2.2.3. Reaction of 3-methyl-6,7,8,9-tetrafluoro-4H-
benzopyrano[3,4-d]isoxazol-4-one (4) with
o-aminothiophenol
Coumarins 1±4 were prepared by the method described
previously [2]. Compound 7 was prepared from coumarin 1
via a described procedure [3]. Chromone 10 was prepared
according to the literature methods [11].
A mixture of compound 4 (0.55 g, 2.01 mmol) and o-
aminothiophenol (0.3 g, 2.42 mmol) was re¯uxed in 20 ml
of benzene for 5 h. The solvent was removed. A solution of
HCl (10 ml, 10%) was added to the resulting oil. The
precipitate was collected by ®ltration, dried and recrystal-
lized from toluene to give compound 3 (0.2 g, 36%) as white
crystals (m.p. 171±1728C; compare Ref. [2]).
2.2. Reactions of 4-hydroxy-5,6,7,8-tetrafluorocoumarin
derivatives with o-aminothiophenol
2.2.1. 7-(2-Aminophenylthio)-4-hydroxy-5,6,8-
trifluorocoumarin (5) (nc)
2.2.4. 2-(2-Hydroxy-2-(2-hydroxy-(2-aminophenylthio)-
3,5,6-trifluoro)phenyl)vinylbenzothiazole (8) (nc)
(a) o-Aminothiophenol (4.5 g, 36 mmol) was added to a
solution of coumarin 1 (2.3 g, 10 mmol) in 100 ml of
methanol. The mixture was re¯uxed for 1 h. The resulting
precipitate was ®ltered off, washed with hot methanol and
dried in vacuum to give compound 5 (1.38 g, 41%) as white
A mixture of compound 5 (1 g, 2.95 mmol) and o-ami-
nothiophenol (1.84 g, 14.7 mmol) in 30 ml of toluene
was re¯uxed for 3 h. The resulting precipitate was collected
by ®ltration, dried and recrystallized from isopropyl alcohol
to give compound 8 (1.1 g, 83%) as white crystals (m.p.
1
crystals (m.p. 263±2658C). H NMR ((CD3)2SO) d: 5.31
1
(2H, s, NH2); 5.64 (1H, s, =CH); 6.43±7.60 (4H, m, C6H4);
11.03 (1H, br.s, OH) ppm. 19F NMR ((CD3)2SO) d: 143.40
(1F, d-d, F-5, J(5-6) ˆ 23.4, J(5-8) ˆ 14.7 Hz); 138.65
(1F, d, F-6, J(6-5) ˆ 23.4, J(6-8) ˆ 0 Hz); 131.94 (1F, d,
F-8, J(8-5) ˆ 14.7, J(8-6) ˆ 0 Hz) ppm. IR: 3340, 3280
(NH2); 3070 (=CH); 1720 (C=O); 1600, 1540 (C=C,
C=N, NH); 1000 (CF) cm 1. Analysis: Found: C, 53.16;
H, 2.48; F, 16.69; N, 4.33. Calc. for C15H8F3NO3S: C,
53.10; H, 2.38; F, 16.80; N, 4.14%.
268±2708C). H NMR ((CD3)2SO) d: 5.64 (1H, s, =CH);
6.43±7.38 (10 H, m, 2 C6H4, NH2) ppm. 19F NMR
((CD3)2SO) d: 143. 40 (1F, d-d, F-6, J(6-5) ˆ 23.0,
J(6-3) ˆ 14.4 Hz);
J(5-3) ˆ 0 Hz);
138.64 (1F, d, F-5, J(5-6) ˆ 23.0,
132.95 (1F, d, F-3, J(3-6) ˆ 14.4,
J(3-5) ˆ 0 Hz) ppm. IR: 3350, 3280 (NH2); 1630, 1530
(C=C, C=N); 990 (CF) cm 1. Analysis: Found: C, 56.42;
H, 3.05; F, 12.89; N, 5.91; S, 14.01. Calc. for
C21H13F3N2O2S2: C, 56.37; H, 3.15; F, 12.74; N, 6.26; S,
14.33%.
(b) In a similar manner, compound 5 (1.7 g, 50%) was
obtained from coumarin 2 (2.76 g, 10 mmol). The physi-
cochemical data were identical to those listed above.
2.2.5. 2-(2-Hydroxy-2-(2-hydroxy-4-(4-morpholinyl)-
3,5,6-trifluoro)phenyl)vinylbenzothiazole (9) (nc)
2.2.2. 7-(2-Aminophenylthio)-4-hydroxy-3-iminoacetyl-
5,6,8-trifluorocoumarin (6) (nc)
In a similar manner, compound 9 (0.6 g, 50%) as
white crystals (m.p. 222±2248C) was obtained from com-
pound 7 (1 g, 2.92 mmol) and o-aminothiophenol (2.1 g,
(a) A mixture of coumarin 3 (3.9 g, 14.2 mmol) and o-
aminothiophenol (5.3 g, 42.4 mmol) in 50 ml of methanol
was re¯uxed for 3 h. After cooling, the resulting precipitate
was collected by ®ltration. Recrystallization of ppt from
methanol gave 6 (3.0 g, 56%) as white crystals (m.p. 221±
1
16.8 mmol). H NMR ((CD3)2SO) d: 3.20±3.43 (4H, m,
CH2±N±CH2); 3.64±3.76 (4H, m, CH2±O±CH2); 6.73 (1H,
br.s, =CH); 7.20±7.93 (4H, m, C6H4); 13.24, 14.95 (2H, br.s,
2 OH) ppm. 19F NMR ((CD3)2SO) d: 161.55 (1F, d, F-5,
1
2238C). H NMR ((CD3)2SO) d: 2.54 (3H, s, CH3); 5.41
J(5-6) ˆ 22.5, J(5-3) ˆ 0 Hz); 153.48 (1F, d, F-3, J(3-6) ˆ
(2H, s, NH2); 6.43±7.37 (4H, m, C6H4); 10.14 (1H, br.s,
=NH); 11.73 (1H, br.s, OH) ppm. 19F NMR ((CD3)2SO)
d: 147.07 (1F, d-d, F-5, J(5-6) ˆ 23.0, J(5-8) ˆ 15.6 Hz);
139.86 (1F, d-d, F-6, J(6-5) ˆ 23.0, J(6-8) ˆ 2.0 Hz);
132.77 (1F, d-d, F-8, J(8-5) ˆ 15.6, J(8-6) ˆ 2.0 Hz) ppm.
IR: 3360, 3285 (NH2); 1715 (C=O); 1630, 1600, 1550 (C=C,
C=N, NH); 1000 (CF) cm 1. Analysis: Found: C, 53.62; H,
3.11; F, 14.76; N, 7.45. Calc. for C17H11F3N2O3S: C, 53.68;
H, 2.92; F, 14.99; N, 7.51%.
(b) A mixture of compound 4 (0.55 g, 2.01 mmol) and
o-aminothiophenol (1.2 g, 9.68 mmol) was re¯uxed in
30 ml of benzene for 6 h. The solvent was removed. A
solution of 10% HCl acid (10 ml) was added to the resulting
oil. The precipitate was ®ltered off, dried and recrystallized
from methanol to give compound 6 (2.7 g, 50%).
The physicochemical data were identical to those listed
above.
11.0, J(3-5) ˆ 0 Hz); 141.65 (1F, d-d, F-6, J(6-5) ˆ 22.5,
J(6-3) ˆ 11.0 Hz) ppm. IR: 3220±3000 (OH); 1630, 1530
(C=C, C=N); 990 (CF) cm 1. Analysis: Found: C, 55.92; H,
3.73; F, 14.28; N, 7.07; S, 7.69. Calc. for C19H15F3N2O3S:
C, 55.93; H, 3.68; F, 13.97; N, 6.86; S, 7.89%.
2.2.6. 2-(2-Hydroxy-3,4,5,6-tetrafluorophenyl)-
benzothiazole (11) (nc)
A mixture of compound 10 (0.5 g, 1.64 mmol) and o-
aminothiophenol (0.8 g, 6.4 mmol) was re¯uxed in 20 ml of
toluene for 6 h. After cooling, the resulting precipitate was
®ltered off and recrystallized from toluene to give com-
pound 11 (0.2 g, 41%) as white crystals (m.p. 193±1958C).
1H NMR ((CD3)2SO) d: 7.0±8.3 (4H, m, C6H4); 12.1, 13.7
(2H, br.s, 2OH) ppm. 19F NMR ((CD3)2SO) d: 171.17 (1F,
d-d-d); 162.58 (1F, d-d-d); 153.07 (1F, d-d-d); 140.15
(1F, d-d-d) ppm. IR: 2770 (OH); 1510, 1500 (C=C, C=N);

I.T. Bazyl0 et al. / Journal of Fluorine Chemistry 103 (2000) 3±12
5
990 (CF) cm 1. Analysis: Found: C, 52.12; H, 1.64; F,
25.64; N, 4.80; S, 10.86. Calc. for C13H5F4NOS: C, 52.17;
H, 1.67; F, 25.42; N, 4.62; S, 10.70%.
2.2.10. 4-Hydroxy-5,6-difluoro-2-H-pyrano[6,5-
a]phenothiazin-2-one (14) (nc)
The mixture of compounds 14 and 15 (0.5 g, 1.5 mmol)
was dissolved in 10 ml of o-xylene and re¯uxed for 5 min.
The reaction mixture was cooled to 108C. The resulting
precipitate was collected by ®ltration and dried to
give compound 14 (0.2 g, 21%) as white crystals
(m.p. > 2708C). 1H NMR ((CD3)2SO) d: 5.66 (1H, s,
=CH); 6.8±7.4 (4H, m, C6H4); 8.7 (2H, br.s, OH, NH)
ppm. 19F NMR ((CD3)2SO) d: 150.07 (1F, d, J(ortho-F-F)
ˆ 22.0 Hz); 145.46 (1F, d, J(ortho-F-F) ˆ 22.0 Hz) ppm. IR:
3280 (NH); 3070 (=CH); 1710 (C=O); 1640, 1600, 1510
(C=C, NH); 1000 (CF) cm 1. Analysis: Found: C, 56.16; H,
2.54; F, 11.17; N, 4.53; S, 10.22. Calc. for C15H7F2NO3S: C,
56.43; H, 2.21; F, 11.90; N, 4.38; S, 10.44%.
2.2.7. 4-(2-Aminophenylthio)-2-hydroxy-3,5,6-
trifluoroacetophenone (12) (nc)
(a) Compound 5 (0.5 g, 1.47 mmol) was dissolved in
10 ml of 10% aqueous solution of NaOH. The mixture
was re¯uxed for 2 h. After cooling, the resulting precipitate
was dissolved in water. The solution was treated with
conc. HCl to pH ꢀ 2. The resulting precipitate was collected
by ®ltration and recrystallized from heptane to give
compound 12 (0.2 g, 43%) as white crystals (m.p. 89±
1
908C). H NMR ((CD3)2SO) d: 2.66 (3H, s, CH3); 4.17
(2H, br.s, NH2); 6.57±7.59 (4H, m, C6H4); 12.39 (1H,
br.s, OH) ppm. 19F NMR ((CD3)2SO) d: 145.24 (1F, d-
d, F-5, J(5-6) ˆ 24.4, J(5-3) ˆ 3.9 Hz); 138.1 (1F, d-d, F-6,
J(6-3) ˆ 13.6, J(6-5) ˆ 24.4 Hz); 134.87 (1F, d-d, F-3,
J(3-6) ˆ 13.6, J(3-5) ˆ 3.9 Hz) ppm. IR: 3460, 3370 (NH2);
1650 (C=O); 1550 (C=C, NH); 1000 (CF) cm 1. Analysis:
Found: C, 53.76; H, 3.34; F, 18.54; N, 4.58; S, 10.44. Calc.
for C14H10F3NO2S: C, 53.67; H, 3.19; F, 18.21; N, 4.47; S,
10.22%.
2.3. Reactions 4-hydroxy-5,6,7,8-tetrafluorocoumarin
derivatives with 2-mercaptoethanol
2.3.1. 4-Hydroxy-7-(2-hydroxyethylthio)-5,6,8-
trifluorocoumarin (16) (nc)
To a solution of coumarin 1 (1.15 g, 4.78 mmol) in 16 ml
of DMSO, 2-mercaptoethanol (3.7 g, 47.8 mmol) and
triethylamine (3.7 ml) were added. The reaction mixture
was heated at 808C for 3 h, cooled to 208C and poured into a
solution of conc. HCl (15 ml) in 70 ml of water. The
solution was extracted by ether (3Â 20 ml). The extract
was washed with water and dried under MgSO4. The solvent
was removed in vacuum. The residue was recrystallized
from acetonitrile to give compound 16 (0.25 g, 18%) as
white crystals (m.p. 160±1658C). 1H NMR ((CD3)2SO)
d: 3.07±3.20 (2H, m, SCH2); 3.50±3.63 (2H, m, OCH2);
5.64 (1H, s, =CH); 9.6, 11.4 (2H, br.s, 2OH) ppm. 19F NMR
(b) By analogy, product 12 (0.12 g, 48%) was obtained
from compound 6 (0.3 g, 0.79 mmol). The physicochemical
data were identical to those listed above.
2.2.8. 7-(2-Aminophenylthio)-2-methyl-5,6,8-
trifluorocoumarin (13) (nc)
A mixture of compound 6 (0.5 g, 1.31 mmol), conc.
H2SO4 (5 ml) and water (5 ml) was re¯uxed for 4 h. The
reaction mass was cooled and treated with 10% aqueous
solution of NaOH to pH ꢀ 7. The resulting precipitate
was ®ltered off, dried and recrystallized from heptane to
give compound 13 (0.15 g, 34%) as white crystals (m.p.
((CD3)2SO) d: 143.7 (1F, d-d, F-5, J(5-6) ˆ 23.4, J(5-8)
ˆ
14.6 Hz); 137.7 (1F, d, F-6, J(6-5) ˆ 23.4, J(6-8) ˆ 0 Hz);
131.1 (1F, d, F-8, J(8-5) ˆ 14.6, J(8-6) ˆ 0 Hz) ppm. IR:
3240, 2640 (OH); 1700, 1680 (C=O); 1620, 1600, 1550
(C=C); 1000 (CF) cm 1. Analysis: Found: C, 45.09; H,
2.37; F, 19.46; S, 10.63. Calc. for C11H7F3O4S: C, 45.21; H,
2.41; F, 19.50; S, 10.97%.
1
162±1648C). H NMR ((CD3)2SO) d: 2.34 (3H, s, CH3);
4.38 (2H, br.s, NH2); 6.07 (1H, s, =CH); 6.57±7.61 (4H, m,
C6H4) ppm. 19F NMR ((CD3)2SO) d: 144.80 (1F, d-d,
F-5, J(5-6) ˆ 21.0, J(5-8) ˆ 16.5 Hz); 135.78 (1F, d, F-6,
J(6-5) ˆ 21.0, J(6-8) ˆ 0 Hz); 130.40 (1F, d, F-8, J(8-5)
ˆ
16.5, J(8-6) ˆ 0 Hz) ppm. IR: 3350, 3270 (NH2); 3070
(=CH); 1640 (C=O); 1510 (C=C); 1000 (CF) cm 1. Ana-
lysis: Found: C, 56.85; H, 2.89; F, 16.89; N, 4.17; S, 9.88.
Calc. for C16H10F3NO2S: C, 56.97; H, 2.99; F, 16.90; N,
4.15; S, 9.50%.
2.3.2. 3-Acetyl-4-hydroxy-5,7,8-tri(2-hydroxyethylthio)-6-
fluorocoumarin (17) (nc)
In a similar manner, compound 17 (0.4 g, 23%), white
crystals (m.p. 165±1708C) from coumarin 2 (1.15 g,
4.16 mmol), 2-mercaptoethanol (3.7 g, 47.8 mmol) and
triethylamine (3.7 ml). 1H NMR ((CD3)2SO coumarin,
chromone isomers (see text) ratio 1:2)d: 2.57, 2.67 (1H,
s, CH3); 2.96±3.26 (6H, m, SCH2); 3.47±3.60 (6H, m,
OCH2); 4.7 (3H, br.s, 3OH); 9.9, 11.6 (2H, br.s, 2OH)
ppm. 19F NMR ((CD3)2SO) d: 99.7, 101.6 (1F, s)
ppm. IR: 3250, 2700 (OH); 1700, 1680 (C=O); 1600,
1550 (C=C); 1030±1000 (CF) cm 1. Analysis: Found: C,
45.75; H, 4.35; F, 4.13; S, 21.23. Calc. for C17H19FO7S3: C,
45.32; H, 4.25; F, 4.22; S, 21.35%.
2.2.9. Cyclization of compound (5)
Finely ground NaH (0.3 g, 12.5 mmol) was added to a
solution of compound 5 (1 g, 2.95 mmol) in 15 ml of
anhydrous DMF under argon. The reaction mixture was
heated at 808C under argon for 3 h, then cooled to 208C and
poured into a mixture of conc. HCl (20 ml) and water
(100 ml). The resulting precipitate was collected by ®ltra-
tion and dried in vacuum at 908C to give a mixture of
compounds 14 and 15 (0.75 g, 80%).

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I.T. Bazyl0 et al. / Journal of Fluorine Chemistry 103 (2000) 3±12
2.3.3. 4-Hydroxy-3-iminoacetyl-5,7,8-tri-
(2-hydroxyethylthio)-6-fluorocoumarin (18) (nc)
SCH2); 3.5±3.62 (6H, m, OCH2); 4.30 (2H, q, OCH2CH3);
4.6 (3H, br.s, OH) ppm. 19F NMR ((CD3)2SO) d: 107.9
(1F, s) ppm. IR: 3500±3200 (OH); 1730 (CO2Et); 1620
(C=O); 1540, 1500 (C=C); 990 (CF) cm 1. Analysis:
Found: C, 47.90; H, 4.76; F, 3.84. Calc. for C19H23FO7S3:
C, 47.69; H, 4.84; F, 3.97%.
(b) By analogy, compound 20 (3.8 g, 80%) was obtained
from chromone 19 (3.62 g, 10 mmol), 2-mercaptoethanol
(7.8 g, 100 mmol) and triethylamine (5 ml). The physico-
chemical data were identical to those listed above.
(a) To a solution of coumarin 3 (5.7 g, 20.7 mmol) in
80 ml of DMSO, 2-mercaptoethanol (18 g, 231 mmol) and
triethylamine (18 ml) were added. The reaction mixture was
heated at 808C for 3 h, cooled to 208C and poured into a
solution of conc. HCl (50 ml) in 300 ml of water. The
solution was stored at 208C for 24 h. The resulting pre-
cipitate was ®ltered off, dried and recrystallized from
acetonitrile to give compound 18 (8.0 g, 86%) as white
1
crystals (m.p. 186±1908C). H NMR ((CD3)2SO) d: 2.55
(3H, s, CH3); 3.03±3.16 (6H, m, SCH2); 3.4±3.6 (6H, m,
OCH2); 4.4 (3H, br.s, OH); 9.98 (1H, br.s, NH); 11.8 (1H,
br.s, OH) ppm. 19F NMR ((CD3)2SO) d: 101.5 (1F, s) ppm.
IR: 3500±3000 (OH, NH); 1680 (C=O); 1600, 1550, 1510
(C=C, C=N); 990 (CF) cm 1. Analysis: Found: C, 45.05; H,
4.63; F, 3.97; N, 2.85. Calc. for C17H20FNO6S3: C, 45.42; H,
4.48; F, 4.23; N, 3.11%.
(b) A solution of compound 20 (0.45 g, 0.94 mmol) in
30 ml of 25% aqueous NH4OH was stirred for 48 h at 188C.
The resulting precipitate was collected by ®ltration and
dried to give compound 18 (0.3 g, 71%). The physicochem-
ical data were identical to those listed above.
2.3.6. 4-Hydroxy-7-(2-hydroxyethylthio)-3-iminoacetyl-
5,6,8-trifluorocoumarin (21) (nc)
A solution of compound 19 (10 g, 27.6 mmol) in 200 ml
of 25% aqueous NH4OH was stirred at 208C for 48 h. The
resulting precipitate was ®ltered off and dried to give
compound 21 (7.0 g, 76%) as white crystals (m.p. 186±
1
1918C). H NMR ((CD3)2SO) d: 2.55 (3H, s, CH3); 3.12
(2H, s, SCH2); 3.55 (2H, m, OCH2); 4.93 (1H, br.s, OH);
10.15 (1H, br.s, NH); 11.74 (1H, br.s, OH) ppm. 19F NMR
((CD3)2SO) d: 147.36 (1F, d-d, F-5, J(5-6) ˆ 23.5, J(5-8)
15.0 Hz); 138.91 (1F, d-d, F-6, J(6-5) ˆ 23.5, J(6-8)
ˆ
ˆ
0 Hz); 131.94 (1F, d-d, F-8, J(8-5) ˆ 15.0, J(8-6) ˆ 0 Hz)
ppm. IR: 3340, 3180 (OH); 1680 (C=O); 1610, 1550 (C=C,
C=N); 980 (CF) cm 1. Analysis: Found: C, 46.73; H, 3.12;
F, 17.06; N, 4.28. Calc. for C13H10F3NO4S: C, 46.85; H,
3.02; F, 15.73; N, 4.20%.
2.3.4. 3-Ethoxycarbonyl-7-(2-hydroxyethylthio)-2-methyl-
5,6,8-trifluorochromone (19) (nc)
2-Mercaptoethanol (3.8 g, 48.7 mmol) was added to a
solution of chromone 10 (3.8 g, 12.5 mmol) in 70 ml of
DMSO. The reaction mixture was cooled to 208C, 2 ml of
triethylamine added and stored at 208C for 2 min. The
reaction mixture was poured into a solution of conc. HCl
(120 ml) in 130 ml of water. The resulting precipitate was
collected by ®ltration, dried and recrystallized form CCl4 to
give compound 19 (3.7 g, 82%) as white crystals (m.p. 121±
2.3.7. 3-Ethoxycarbonyl-7-carboxymethylthio-2-methyl-
5,6,8-trifluorochromone (22) (nc)
To a solution of chromone 10 (2 g, 6.58 mmol) in 30 ml
of DMSO, mercaptoacetic acid (3.8 g, 41.3 mmol) and
triethylamine (0.3 ml) were added. The mixture was stored
at 188C for 20 min and then poured into a mixture of 150 ml
of water and 10 ml of conc. HCl. The resulting precipitate
was ®ltered off, washed with water and recrystallized from
toluene to give compound 22 (1.3 g, 53%) as white crystals
1
1238C). H NMR ((CD3)2SO) d: 1.29 (3H, t, OCH2CH3),
2.46 (3H, s, CH3); 3.18 (2H, s, SCH2); 3.59 (2H, m, OCH2);
4.31 (2H, q, OCH2CH3); 4.96 (1H, br.s, OH) ppm. 19F NMR
1
((CD3)2SO) d: 146.22 (1F, d-d, F-5, J(5-6) ˆ 22.4, J(5-8)
ˆ
(m.p. 161±1638C). H NMR ((CD3)2SO) d: 1.29 (3H, t,
OCH2CH3); 2.46 (3H, s, CH3); 3.95 (2H, s, SCH2); 4.31
15.5 Hz); 135.75 (1F, d-d, F-6, J(6-5) ˆ 22.4, J(6-8)
ˆ
0 Hz); 129.78 (1F, d-d, F-8, J(8-5) ˆ 15.5, J(8-6) ˆ 0 Hz)
ppm. IR: 3510, 3450 (OH); 1720, 1710 (CO2Et); 1640
(C=O); 1540 (C=C); 990 (CF) cm 1. Analysis: Found: C,
49.73; H, 3.71; F, 15.74. Calc. for C15H13F3O5S: C, 49.73;
H, 3.62; F, 15.73%.
(2H, q, OCH2CH3); 13.0 (1H, br.s, COOH) ppm. 19F NMR
((CD3)2SO) d: 146.18 (1F, d-d, F-5, J(5-6) ˆ 22.0, J(5-8)
15.6 Hz); 136.07 (1F, d-d, F-6, J(6-5) ˆ 22.0, J(6-8)
ˆ
ˆ
0 Hz); 130.13 (1F, d-d, F-8, J(8-5) ˆ 15.6, J(8-6) ˆ 0 Hz)
ppm. IR: 3300±3000 (OH); 1720 (CO2Et); 1670 (CO2H);
1630 (C=O); 1550 (C=C); 990 (CF) cm 1. Analysis: Found:
C, 48.04; H, 2.83; F, 15.01. Calc. for C15H11F3O6S: C,
47.88; H, 2.95; F, 15.15%
2.3.5. 3-Ethoxycarbonyl-5,7,8-tri(2-hydroxyethylthio)-2-
methyl-6-fluorochromone (20) (nc)
(a) To a solution of chromone 10 (8.4 g, 27.6 mmol) in
150 ml of DMSO, 2-mercaptoethanol (16 g, 205 mmol) and
triethylamine (16 ml) were added. The reaction mixture was
heated at 808C for 3 h, cooled and poured into a solution of
conc. HCl (50 ml) in 300 ml of water. The resulting pre-
cipitate was ®ltered off, dried and recrystallized from
acetonitrile to give compound 20 (7.0 g, 53%) as white
2.3.8. 1,2-Bis((3-ethoxycarbonyl-2-methyl-5,6,8-
trifluorochromone-7-yl)thio)ethane (23) (nc)
To a solution of chromone 10 (3 g, 9.87 mmol) in 60 ml
of DMSO, 1,2-ethanedithiol (0.5 g, 5.32 mmol) and triethy-
lamine (0.3 ml) were added. The reaction mixture was
stored at 188C for 10 min. The resulting precipitate was
®ltered off, washed with water and recrystallized from CCl4
to give compound 23 (2.5 g, 76%) as white crystals (m.p.
1
crystals (m.p. 133±1378C). H NMR ((CD3)2SO) d: 1.30
(3H, t, OCH2CH3), 2.46 (3H, s, CH3); 3.0±3.2 (6H, m,

I.T. Bazyl0 et al. / Journal of Fluorine Chemistry 103 (2000) 3±12
7
204±2068C). 1H NMR ((CD3)2SO) d: 1.39 (3H, t,
OCH2CH3); 2.51 (3H, s, CH3); 3.27 (2H, s, SCH2); 4.31
(2H, q, OCH2CH3) ppm. 19F NMR ((CD3)2SO) d: 143.73
(1F, d-d, F-5, J(5-6) ˆ 22.0, J(5-8) ˆ 16.6 Hz); 134.75 (1F,
d-d, F-6, J(6-5) ˆ 22.0, J(6-8) ˆ 0 Hz); 130.16 (1F, d-d, F-8,
J(8-5) ˆ 16.6, J(8-6) ˆ 0 Hz) ppm. IR: 1730 (CO2Et); 1645
(C ˆ O); 1560 (C ˆ C); 990 (CF) cm 1. Analysis: Found:
C, 50.74; H, 3.06; F, 17.17. Calc. for C28H20F6O8S2: C,
50.76; H, 3.04; F, 17.21%.
(b) By analogy, product 25 (0.28 g, 80%) was obtained
from compound 24 (0.40 g, 1.2 mmol). The physicochem-
ical data were identical to those listed above.
3. Results and discussion
3.1. Reaction of 4-hydroxy-5,6,7,8-tetrafluorocoumarin
derivatives with o-aminothiophenol
In the present work, it has been found that coumarin 1
reacts with o-aminothiophenol in re¯uxing methanol to
form product 5. The structure of the compound results from
nucleophilic displacement of the C-7 ¯uorine atom in the
heterocycle. Under analogous conditions, 3-acetyl-substi-
tuted coumarin 2 with o-aminothophenol also affords com-
pound 5. Probably, in this case the displacement is
accompanied by deacylation. Coumarin 3 with an iminoa-
cetyl group at the C-3 position on reaction with o-ami-
nothiophenol gives the corresponding 7-substituted product
6 (Scheme 1). It should be noted that the reactions described
do not require the addition of base as catalyst and are carried
out in methanol rather than DMSO unlike the interaction of
¯uoroquinolone-carboxylic acid derivatives with o-ami-
nothiophenol [4]. The use of DMSO as a solvent in the
reactions of coumarins 1±3 with o-aminothiophenol
decreases the selectivity of these transformations and leads
to a mixture of products that is dif®cult to separate.
Interaction of benzopyranoisoxazole 4 with an equimolar
amount of o-aminothiophenol leads to coumarin 3 as a result
of the reductive splitting of the isoxazole ring (Scheme 1).
The lability of isoxazoles under treatment with such bases as
hydrazine, phenylhydrazine is known [12]. However, such a
result in the reaction with o-aminothiophenol was obtained
for the ®rst time. Benzopyranoisoxazole 4 with an excess of
o-aminothiophenol forms compound 6 which was obtained
from coumarin 3.
2.3.9. 7-(2-Hydroxyethylthio)-2-methyl-5,6,8-
trifluorochromone-3-carboxylic acid (24) (nc)
a. A solution of compound 21 (0.45 g, 1.24 mmol) in
40 ml of 25% aqueous NH4OH was re¯uxed for 2 h, then
treated with conc. HCl to pH ˆ 1±2. The resulting preci-
pitate was collected by ®ltration, dried and recrystallized
from a mixture of heptane and CCl4 (1:1) to give compound
24 (0.1 g, 24%) as white crystals (m.p. 1358C decomp.). 1H
NMR ((CD3)2SO) d: 2.68 (3H, s, CH3); 3.22 (2H, s, SCH2);
3.61 (2H, s, OCH2), 6.6 (1H, br.s, OH) ppm. 19F NMR
((CD3)2SO) d: 142.40 (1F, d-d, F-5, J(5-6) ˆ 23.0, J(5-8)
ˆ
15.0 Hz); 137.55 (1F, d-d, F-6, J(6-5) ˆ 23.0, J(6-8)
ˆ
0 Hz); 131.48 (1F, d-d, F-8, J(8-5) ˆ 15.0, J(8-6) ˆ 0 Hz)
ppm. IR: 3300 (OH); 1730 (CO2H); 1630 (C=O); 1600,
1535 (C=C); 1010±990 (CF) cm 1. Analysis: Found: C,
46.74; H, 2.89; F, 17.16. Calc. for C13H9F3O5S: C, 46.71; H,
2.71; F, 17.05%.
(b) A solution of compound 19 (6 g, 18 mmol) and NaOH
(7 g, 175 mmol) in 200 ml of water was stirred at 208C for
2 h and treated with conc. HCl to pH ˆ 2±3. The resulting
precipitate was ®ltered off, washed with water, dried and
recrystallized from CCl4 to give compound 24 (2.5 g, 86%).
The physicochemical data were identical to those listed
above.
2.3.10. 7-(2-Acetoxyethylthio)-2-methyl-5,6,7-
trifluorochromone (25) (nc)
In contrast to the above-mentioned transformations, inter-
action of compound 4 with ammonia and morpholine
(which do not possess reducing properties) leads to the
splitting of pyrone ring with retention of the isoxazole ring
[3].
(a) A solution of compound 19 (0.65 g, 1.79 mmol) in a
mixture of conc. acetic acid (15 ml) and conc. HCl (3 ml)
was re¯uxed for 15 h, then poured into 100 ml of water. The
resulting precipitate was collected by ®ltration, washed with
water, dried and then dissolved in 10 ml of heptane. The
resulting solution was ®ltered from small amounts of inso-
luble material. The solvent was removed in vacuum to give
compound 25 (0.4 g, 67%) as white crystals (m.p. 87±908C).
1H NMR ((CD3)2SO) d: 2.03 (3H, s, CH3CO); 2.40 (3H, s,
CH3); 3.28 (2H, s, SCH2); 4.24 (2H, s, OCH2), 6.1 (1H, br.s,
OH) ppm. 19F NMR ((CD3)2SO) d: 143.73 (1F, d-d, F-5,
J(5-6) ˆ 22.0, J(5-8) ˆ 16.6 Hz); 134.75 (1F, d-d, F-6, J(6-5)
ˆ 22.0, J(6-8) ˆ 0 Hz); 130.16 (1F, d-d, F-8, J(8-5) ˆ 16.6,
J(8-6) ˆ 0 Hz) ppm. IR: 1730 (CO2Et); 1630 (C=O); 1600,
1530 (C=C); 1000 (CF) cm 1. Analysis: Found: C, 50.41;
H, 3.26; F, 17.26. Calc. for C14H11F3O4S: C, 50.60; H, 3.34;
F, 17.15%.
Coumarins 5, 7 with substituents at the C-7 atom inert to
nucleophilic displacement do not react with o-aminothio-
phenol on re¯uxing in methanol. Under more severe con-
ditions on re¯uxing in toluene, coumarins 5, 7 with o-
aminothiophenol form benzothiazole derivatives 8, 9
(Scheme 2) as a result of the reaction of the nucleophile
at the lactone ring followed by cleavage of the C±O bond.
Interaction of 3-ethoxycarbonyl-2-methyl-5,6,7,8-tetra-
¯uorochromone 10 (that is the precursor of coumarin 3 in
an acyl-lactone rearrangement [2]) with o-aminothiophenol
results in the formation of benzothiazole 11 on re¯uxing in
toluene (Scheme 3). A similar benzimidazole was obtained
in the reaction of the chromone 10 with o-phenylenediamine
[2]. Obviously, cleavage of the pyrone ring proceeds as the

8
I.T. Bazyl0 et al. / Journal of Fluorine Chemistry 103 (2000) 3±12
Scheme 1.
®rst step of these transformations to form a 2-acylsubsti-
tuted 3-oxoester as an intermediate. Under reaction condi-
tions, the latter undergo acid splitting to give the
corresponding heterocycles. It is known that acid splitting
is typical for the interaction of ¯uorine-containing 2-acyl-3-
oxoesters with amines to form derivatives of ¯uorine-con-
taining carboxylic acid Ð amides and 2-¯uoroalkylbenzi-
midazole [13,14].
The behavior of S-substituted coumarins 5, 6 have been
studied in various mediums. It has been found that hetero-
cycle of compounds 5, 6 is destroyed to acetophenone 12 on
re¯uxing in aqueous solution of NaOH (Scheme 4). Similar
Scheme 2.

I.T. Bazyl0 et al. / Journal of Fluorine Chemistry 103 (2000) 3±12
9
Scheme 3.
splitting was observed for 7-amino-4-hydroxy-3-iminoace-
tyl-5,6,8-tri¯uorocoumarin [3].
the mixture in DMF-d7 showed aromatic protons as a
multiplet between d 6.8 and 7.4 ppm; protons of amino-
and hydroxygroups as a broad signal at d 8.7 ppm. Two
singlet signals at d 5.66 and 5.62 ppm were assigned
to methine protons of phenothiazines 14 and 15. In the
19F NMR spectrum of the mixture, two doublet signals at d
150.07 and 145.46 ppm with coupling constant of 22 Hz
between ortho-atoms of ¯uorine were assigned to phe-
nothiazine 15; the doublet at d ±139.88 ppm, doublet of
doublets d ±138.77 ppm with coupling constants of 14 and
3 Hz between para-atoms of ¯uorine and the F-5 atom and
NH-group, respectively, were assigned to phenothiazine
14. Only product 14 was isolated by recrystallization from
o-xylene as a pure substance.
In an acid medium, compound 6 gives chromone 12 as a
result of a process that is inverse to a coumarin rearrange-
ment followed by decarboxylation (Scheme 4). Analogous
transformations were described for the reaction of non-
substituted coumarin 3 [2].
Intramolecular heterocyclization is possible for coumarin
5 due to the nucleophilic displacement of a ¯uorine atom by
an aminogroup of 2-aminophenylthio-substituent. The
attack of nucleophile may occur either at atom C-8 to form
phenothiazine 14 or at atom C-6 to give phenothiazine 15.
Intramolecular displacement at both positions is known for
quinolones [4,15]. The reaction is carried out in the presence
of NaH or NaOH as condensing reagents in anhydrous DMF
under argon. The product isolated in the reaction has a
microanalysis that corresponded to both phenothiazine 14
3.2. Reaction of 4-hydroxy-5,6,7,8-tetrafluorocoumarin
derivatives with 2-mercaptoethanol
1
and its isomer 15. H- and 19F NMR-spectra indicate that
the product is a mixture of phenothiazines 14 and 15
1
(Scheme 5) in the ratio 3:1. The H NMR spectrum of
Interaction of coumarin 1 with 2-mercaptoethanol in
DMSO in the presence of an excess of Et3N at 808C for
Scheme 4.

10
I.T. Bazyl0 et al. / Journal of Fluorine Chemistry 103 (2000) 3±12
Scheme 5.
3 h results in product 16. The structure of the compound
results from displacement of ¯uoride by an S-nucleophile.
Under similar conditions, coumarins 2, 3 in the reaction
with 2-mercaptoethanol afford the tri-substituted products
17, 19 (Scheme 6). IR and NMR spectra of compound 17
indicate that the product exists as a mixture of two tautomers
(coumarin A and chromone B) unlike coumarins 16, 19.
Under analogous conditions, interaction of chromone
10 with 2-mercaptoethanol, leads to the formation of the
tri-substituted compound 19 (Scheme 7). When the reaction
is carried out at room temperature for a shorter period
(3 min), product of mono-displacement 20 can be obtained
(Scheme 8). Chromone 20 reacts with 2-mercaptoethanol to
afford compound 19.
The above-mentioned reactions require the presence of
Et3N as a catalyst. Thus, heating chromone 10 with an
excess of 2-mercaptoethanol for 10 h without a basic cat-
alyst does not give any products.
Treatment of chromones 19, 20 with aqueous ammonia at
room temperature affords coumarins 21, 18, respectively
(Scheme 7). These compounds may result from the addition
of amine at the C-2 atom with opening of pyrone ring
Scheme 6.

I.T. Bazyl0 et al. / Journal of Fluorine Chemistry 103 (2000) 3±12
11
Scheme 7.
followed by intramolecular cyclization. Thus, acyl-lactone
rearrangement in basic medium is typical for mono- and tri-
substituted chromones 19, 20 like starting non-substituted
chromones [2].
In contrast to the reaction of chromone 10 with o-phe-
nylenediamine (Scheme 8), interaction of compound 10
with 2-mercaptoethanol affords the products of ¯uorine
atom displacement rather than product of pyrone ring open-
ing followed by splitting.
For comparison the reactions of chromone 10 with other
S-nucleophiles have been studied. Thus, chromone 10 reacts
with mercaptoacetic acid in DMSO in the presence of a
catalytic amount of Et3N at 188C for 20 min to form the
substituted product 22. Under analogous conditions, the
interaction of chromone 10 with 1,2-ethanedithiol also
yields the substituted compound 23. The latter results from
displacement of a ¯uorine atom of two-chromone molecule
at the C-7 position by one S-dinucleophile. A similar
product was obtained by the reaction of 2-etoxycarbonyl-
5,6,7,8-tetra¯uorochromone with ethylenediamine in
DMSO [16].
Displacement of a ¯uorine atom by an S-nucleophile
(2-mercaptoethanol) in coumarin 21 changes the chemical
properties of the heterocycle. Thus, compound 21 on boiling
in aqueous ammonia is converted into chromone-carboxylic
acid 24 (Scheme 9) that does not occur in case of non-
substituted coumarin 3 [3]. It is known that 2-methyl-
5,6,7,8-tetra¯uorochromone-3-carboxylic acid readily
undergoes heterocyclic opening and decarboxylation when
treated with aqueous ammonia [2]. Under similar condi-
tions, acid 24 is stable.
IR and NMR spectroscopies and microanalysis of com-
pound 24 makes it possible to consider alternative structure
for 3-acetylcoumarin C.
The structure of compound 24 was proved by the che-
mical transformations. Thus, hydrolysis of ester of chro-
Scheme 8.

12
I.T. Bazyl0 et al. / Journal of Fluorine Chemistry 103 (2000) 3±12
Scheme 9.
[2] V.I. Saloutin, I.T. Bazyl, Z.E. Skryabina, S.P. Kisil, Zh. Org.
Khim. 33 (1997) 1241 [Russ. J. Org. Chem. (1997) 33 (Engl.
Transl.)].
mone 19 results in acid 24. Both acid 24 and its ester 19 give
the same product 25 when treated with a mixture of acetic
and hydrochloric acids. Compound 25 results from decar-
boxylation and acylation of the hydroxyl group of the
mercaptoethanol fragment (Scheme 9). This product cannot
be obtained from coumarin C.
[3] I.T. Bazyl, S.P. Kisil, A.E. Sharapko, Y.V. Burgart, V.I. Saloutin,
O.N. Chupakhin, Zh. Org. Chem. 34 (1998) 394 [Russ. J. Org.
Chem. (1998) 34 (Engl. Transl.)].
[4] G.A. Mokrushina, S.G. Alekseev, V.N. Charushin, O.N. Chupakhin,
Zh. Vses. Khim. Obsch. (1991) 447.
In general, interaction of coumarins 1±3 and chromone 10
with S-nucleophiles leads to displacement of ¯uorine atoms
but not the opening of sensitive heterocycle rings that occur
in reactions with N-nucleophiles [2]. Similar reactions of
¯uorine-containing quinoline-3-carboxylic acids with 2-
mercaptoethanol are known to result in 7-monosubstituted
quinolinones [4±6]. Displacement of the ¯uorine atom at the
position 5 or 8 in quinolones is possible when the hetero-
cycle already has the substituent at the C-7 atom [8±10].
The formation of tri-substituted products in the reaction
of ¯uorinated coumarins 2, 3 and chromone 10 with S-
nucleophiles was found for the ®rst time. The attempts to
obtain mono-substituted products in the reactions of cou-
marins 2, 3 with 2-mercaptoethanol were unsuccessful.
Such an activating effect of the thioalkyl group on displace-
ment of ¯uorine atoms may compare to that of electron-
withdrawing groups (CF3, NO2) [17,18]. This is due to high
polarizability of the S±ArF bond unlike other donating
substituents X±ArF (X ˆ OAlk, OH, NH2, CH3 et al.).
[5] M. Ohta, H. Koga, J. Med. Chem. 31 (1991) 131.
[6] Japan Patent 156 961, 1989 [Chem. Abst. 112 (1990) 20980].
[7] T. Yoshida, Y. Yamamoto, N. Yagi, Yakugaku Zasshi. 110 (1990)
258.
[8] T. Uno, M. Takamatsu, Y. Inoue, J. Med. Chem. 30 (1987) 2163.
[9] US Patent 4 767 762, 1988 [Chem. Abst. 107 (1988) 217616t].
[10] T. Miyamoto, J.-I. Matsumoto, K. Chiba, J. Med. Chem. 33 (1990)
1645.
[11] N.N. Voroschzov, V.A. Barhash, A.T. Prudchenko, T.I. Homenko,
Dokl. Akad. Nauk SSSR 164 (1965) 1046.
[12] R. Elderfild, Heterocyclic Compounds, Moscow, 1961, V. 5 (in
Russian).
[13] K.I. Pashkevich, V.M. Krohalev, V.I. Saloutin, Izv. Akad. Nauk SSSR
Otd. Khim. Nauk (1988) 1367 [Russ. Bull. Acad. Sci., Div. Chem.
Sci. (1988) (Engl. Transl.)].
[14] V.M. Krohalev, V.I. Saloutin, A.D. Ramas0, B.A. Ershov,
K.I. Pashkevich, Izv. Akad. Nauk SSSR Otd. Khim. Nauk (1990)
376 [Russ. Bull. Acad. Sci., Div. Chem. Sci. (1990) (Engl.
Transl.)].
[15] D.T.W. Chu, R.E. Maleczka, C.W. Nordeen, J. Heterocyclic. Chem.
25 (1988) 927.
[16] V.I. Saloutin, I.T. Bazyl, Z.E. Skryabina, O.N. Chupakhin, Izv. Akad.
Nauk. Otd. Khim. Nauk (1994) 904 [Russ. Bull. Acad. Sci., Div.
Chem. Sci. (1994) (Engl. Transl.)].
References
[17] G.G. Yakobson, Reactivity of Polyfluoroaromatic Compounds,
Nauka, Novosibirsk, 1983 (in Russian).
[18] L.S. Cobrina, Fluor. Chem. Rev. 7 (1974) 1.
[1] D. Barton, W.D. Ollis, Comprehensive Organic Chemistry, Part 9,
Khimiya, Moscow, 1984, p. 40 (in Russian).