Carbonylation of Polyfluorobenzocyclobutenones in a SbF5 Medium

Article abstract of DOI:10.1134/S1070428019080086

The carbonylation of perfluoro-2-R-benzocyclobutenones (R = F, CF₃, C₂F₅, C₆F₅) in a CO-SbF₅ system is accompanied by transformations of the four-membered cycle in the substrate to form polyfluorinated 1H-isochromene derivatives. The reaction of perfluoro-2-R-benzocyclobutenes (R = F, CF₃, C₂F₅) with (CF₃CO)₂O or CF₃COOH in a SbF₅ medium in a sealed ampule involves formation of polyfluorobenzocyclobutenones and their carbonylation under the reaction conditions.

Full text of DOI:10.1134/S1070428019080086

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2019, Vol. 55, No. 8, pp. 1103–1111. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Organicheskoi Khimii, 2019, Vol. 55, No. 8, pp. 1193–1202.
Carbonylation of Polyfluorobenzocyclobutenones
in a SbF5 Medium
Ya. V. Zonova,b,*, V. M. Karpova, and T. V. Mezhenkovaa
a Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia
*e-mail: yzonov@nioch.nsc.ru
b Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090 Russia
Received January 31, 2019; revised March 6, 2019; accepted March 15, 2019
The carbonylation of perfluoro-2-R-benzocyclobutenones (R = F, CF3, C2F5, C6F5) in a CO–SbF5 system is
accompanied by transformations of the four-membered cycle in the substrate to form polyfluorinated 1H-
isochromene derivatives. The reaction of perfluoro-2-R-benzocyclobutenes (R = F, CF3, C2F5) with (CF3CO)2O
or CF3COOH in a SbF5 medium in a sealed ampule involves formation of polyfluorobenzocyclobutenones and
their carbonylation under the reaction conditions.
Keywords: carbonylation, polyfluorinated benzocyclobutenones, isochromenone, antimony pentafluoride
DOI: 10.1134/S1070428019080086
Earlier we used the example of perfluorobenzo-
cyclobutene and its perfluoroalkyl and pentafluoro-
phenyl derivatives to accomplish for the first time the
carbonylation of perfluorinated organic compounds
with carbon monoxide in a SbF5 medium [1, 2]. The
irreversible transformations of the four-membered ring
in the adduct of CO with the polyfluorobenzocyclo-
butenyl cation favor the process and lead to the
formation of 2-arylalkenoic acids derived from iso-
chromene and indan-2-one [1, 2].
with polyfluorinated benzocyclobutenes [1, 2], carbo-
nylation is accompanied by transformation of the four-
membered cycle and forms perfluoro-1H-isochromen-
1-one 2. Along with compound 2, we detected among
the products obtained after hydrolysis of the reaction
mixture small amounts of perfluorinated benzo-
cyclobutenedione 3, 2-methylbenzoic acid 4 (2 : 3 : 4 =
95 : 3 : 2, 19F NMR), and phthalic acid 5 (Scheme 1).
The transformation of ketone 1 into compound 2 is
likely to occur in the following way. Cation А
generated from compound 1 takes up a molecule of
СО, after which the four-membered cycle in the
resulting acyl cation undergoes opening to form
intermediate B. Heterocyclization of the latter
followed by F–addition gives product 2 (Scheme 1).
The reaction was later extended to polyfluorinated
indanes and tetralins, which in the CO–SbF5 system
take up one or two CO molecules at the benzylic
position of the substrate to form the corresponding
carbonyl fluorides [3]. Prior to our works [1–3], only
the reverse reaction was reported in the literature,
specifically, the decarbonylation of fluorinated
carboxylic acid halides under the action of Lewis acids
[4–6]. To find out the possibility of carbonylation of
functional derivatives of polyfluorobenzocycloalkenes,
in the present work we have studied the behavior of a
series of perfluoro-2-R-benzocyclobutenones (R = F,
CF3, C2F5, C6F5) in the CO – SbF5 system.
The reaction of perfluoro-2-methylbenzocyclo-
butenоne 6 with CO–SbF5 under the same conditions is
slower compared to ketone 1. The reaction mixture
before its treatment with water contained perfluoro-4-
methyl-1H-isochromen-1-one (7) along with salts of
perfluoro-(1Н-isochromen-4-yl)oxomethyl 8 and 4-
(fluorocarbonyl)perfluoro-1H-isochromen-1-yl cations
9 (Scheme 2). Compounds 7–9 in SbF5 are in
equilibrium with each other, as we showed earlier [1]
in our study on the carbonylation of perfluoroben-
zocyclobutene in the CO–SbF5 system [1].
In was shown that perfluorocyclobutenone 1 readily
reacts with СО in the presence of SbF5 at room
temperature and atmospheric pressure. Therewith, like
1103

ZONOV et al.
1104
Scheme 1.
1. CO, SbF5, 20oC
2. H2O
O
O
COOH
COOH
CF3
F
F
F
F
F
+
F
F
+
+
O
COOH
O
O
5, 10%
1
2, 67%
3
4
F
F
+
F
CO
_
F
F
+
SbF5
C
CO
+
F
2
F
F
F
_
O
_F
O
+
C
O
O
A
O
B
O
Hydrolysis of the reaction mixture forms a mixture
containing compound 7, perfluoro-1Н-isochromene-4-
carboxylic acid (10), and 2-(carboxymethyl)-3,4,5,6-
tetrafluorobenzoic acid (11). The latter is likely to be
formed from salts 8 and 9 via their hydrolytic
transformations and decarboxylation of intermediate
products.
cation isomerizes into cation E, the cyclization of
which gives cation 13.
Unlike methyl- and ethylbenzocyclobutenones 6
and 12, perfluoro-2-isopropylbenzocyclobutenоne 16
forms an acyclic product under the same conditions.
Thus, its reaction with CO–SbF5 gave, after the
reaction mixture had been treated with methanol,
methyl 2-[1-(methoxycarbonyl)-2-(trifluoromethyl)tri-
fluoroprop-1-enyl]-3,4,5,6-tetrafluorobenzoate 17,
Perfluoro-2-ethylbenzocyclobutene 12 reacts with
CO–SbF5, yielding, unlike 6, only one products,
namely a salt of perfluoro-3-methyl-4-(fluorocarbonyl)
isochromenyl cation 13. Hydrolysis of the reaction
mixture gives a mixture of perfluorinated 4-(fluoro-
carbonyl-3-methyl- and 4-carboxy-3-methylisochro-
men-1-ones 14 and 15 (Scheme 3). Cation 13 in this
reaction is likely to be formed in the following way.
The initial carbonylation product С undergoes opening
of the four-membered ring to afford cation D. This
probably, as
a result of methanolysis of the
corresponding fluoride F (Scheme 3).
The reaction of perfluoro-2-phenylbenzocyclo-
butenоne 18 with CO–SbF5 at 20°С results in
preferential formation of perfluoro-4-phenylisochro-
men-1-one (19). Along with this product, the mixture
obtained after hydrolysis of the reaction mixture,
Scheme 2.
+
CO
CF3
COF
F
CF3
F
CO, SbF5
20oC
F
F
F
F
F
F
O
O
O
O
+
O
8
6
7
9
:
16
76
:
8
COOH
CH2COOH
COOH
H2O
F
F
F
+
+
7
O
14%
10, 50%
11, 27%
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 8 2019

CARBONYLATION OF POLYFLUOROBENZOCYCLOBUTENONES IN A SbF5 MEDIUM
1105
Scheme 3.
COF
COOH
COF
CF2CF3
F
CF3
CF3
CF3
H2O
CO, SbF5
20oC
F
F
F
F
+
O
O
O
+
F
O
O
O
12
13
14
15
+
CO
CO
CF2CF3
CO
+
_
F
CF2CF3
CFCF3
_
+
CO, SbF5
F
F
F
13
O
+
CO
O
F
D
C
E
COF
COOCH3
CF3
CF(CF3)2
CF3
CH3OH
CO, SbF5
20oC
F
F
F
F
CF3
COF
CF3
COOCH3
O
16
F
17, 70%
contains 2-[carboxy(pentafluorophenyl)methyl]-3,4,5,6-
tetrafluorobenzoic and perfluoro-2-benzoylbenzoic
acids 20 and 21 (Scheme 4).
whereas holding a mixture of compound 19 with SbF5
at 20°С for 20 h followed by hydrolysis yields acid 21.
The possible way of formation of the latter involves
fluorination of compound 19 followed by generation of
cation G, opening of the six-membered in the latter to
form cation H. This cation undergoes isomerization
Separate experiments showed that hydrolysis of
compound 19 in an acidic medium provides acid 20,
Scheme 4.
1. SbF5, 2. H2O
C6F5
C6F5
C6F5
C6F5
1. CO, SbF5, 20oC
2. H2O
F
CHCOOH
F
O
F
F
+
F
+
F
O
COOH
COOH
O
HCl_H2O_Et2O
O
18
19, 46%
_SbF3
20, 8%
21, 23%
SbF5
_
H2O
+
_F
C6F5
CF
C6F5
CF
C6F5
CF
C6F5
_
+
+
_
+
COF
F
CO
F
F
F
F
F
_CO
O
+
CO
COF
COF
O
G
H
I
J
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 8 2019

ZONOV et al.
1106
Scheme 5.
1. CF3COOH, SbF5 or
(CF3CO)2O, SbF5,
sealed ampule
2. H2O
CF3
F
F
F
F
6
7
10
11
+
+
+
+
O
22
23
CF3COOH
1 equiv, 20oC, 70 h
_
26%
41%
8%
10%
1.1 equiv, 70oC, 8 h
2 equiv, 70oC, 8 h
15%
_
32%
30%
2%
2%
35%
52%
4%
1%
(CF3CO)2O
1 equiv, 20oC, 70 h
_
_
_
23%
_
20%
_
50%
_
1.2 equiv, 20oC, 2 h, open flask
87%
into acyl cation I, decarbonylation of the latter leads to
diarylmethyl cation J, whose hydrolysis provides acid
21 (Scheme 4).
compound 22 with 2 equiv of CF3COOH and SbF5 at
70°C, no ketone 6 was detected in the mixture of
products 7, 10, and 11, and, therewith, the fraction of
acid 11. In this case, it cannot be ruled out that an
additional amount of CO is formed as a result of
reaction of excess CF3COOH with the carbonylation
products of ketone 6.
We earlier developed a method of synthesis
carbonyl derivatives of polyfluorinated benzocyclo-
alkenes involving selective conversion of the CF2
group in the benzylic position of the benzocycloalkene
into carbonyl under the action of CF3COOH–SbF5 [7].
This method gave good results, including the synthesis
of ketones 1, 6, and 12 from the corresponding
polyfluorinated benzocyclobutenes.
It was shown in the present work that poly-
fluorobenzocycloalkenes can be converted into
ketones, if CF3COOH is replaced by its anhydride.
Thus, the reaction of compound 22 with (CF3CO)2O–
SbF5 in an open flask forms ketone 6 in a good yield
(Scheme 5). By stoichiometry, the formation of 1 mol
of ketone 6 should be accompanied by the formation of
2 mol of CF3COF and, correspondingly, 2 mol of CO
should be evolved. Therefore, the reaction of
compound 22 with (CF3CO)2O (1 equiv) in SbF5 in a
sealed ampule followed hydrolysis forms compounds
7, 10, and 11 and no ketone 6.
It the present work we showed that the resulting
polyfluorinated benzocyclobutenоnes undergo further
carbonylation, when the reaction is performed in a
closed volume. The carbon monoxide necessary for
this reaction is generated in situ, because during the
reaction CF3COOH converts into CF3COF [7], and the
latter decomposes into СО and CF4 under the action of
SbF5 [8].
The reaction of perfluoro-1-ethylbenzocyclobutene
24 with (CF3CO)2O in SbF5 in a sealed ampule 20°C
provides, after hydrolysis of the reaction mixture, a
mixture of isochromenоnes 14 and 15 (Scheme 6). The
same products are formed by the reaction of compound
24 with CF3COOH–SbF5 at 70°C. These results are
concide with those obtained for the carbonylation of
ketone 12 in CO–SbF5 (Scheme 3).
Thus, the reaction of perfluoro-1-methylbenzo-
cyclobutene 22 with CF3COOH (1 equiv) in SbF5 in a
sealed ampule at 20°C for 70 h followed by hydrolysis
of the reaction mixture forms a mixture of compounds
7, 10, and 11 as result of carbonylation of ketone 6
(Scheme 5). However, complete conversion of ketone
6 is not observed, probably, because of the lack of
excess СО over the stoichiometric amount. Increasing
the temperature to 70°C reduces the reaction time, but
the post mixture, too, contains ketone 6 and, in
addition, a small amount of its isomerization product
perfluoroindan-1-one 23 [9]. After the reaction of
The reaction of perfluoro-1-phenylbenzocyclo-
butene 25 with (CF3CO)2O in SbF5 in a sealed ampule
at 70°C and subsequent hydrolysis of the reaction
mixture yields a mixture of compounds 19 and 21,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 8 2019

CARBONYLATION OF POLYFLUOROBENZOCYCLOBUTENONES IN A SbF5 MEDIUM
1107
Scheme 6.
COF
COOH
1. CF3COOH, SbF5,
70oC, 8 h
2. H2O
1. (CF3CO)2O, SbF5,
20oC, 70 h
2. H2O
C2F5
CF3
CF3
F
F
24
F
F
+
O
O
O
O
24
14
15
C6F5
C6F5
1. CF3COOH, SbF5,
70oC, 8 h
2. H2O
1. (CF3CO)2O, SbF5,
70oC, 8 h
2. H2O
C6F5
F
O
25
F
F
F
F
+
O
COOH
O
25
19
21
with the former prevailing (Scheme 6). The same
result was obtained in the reaction of compound 25
with CF3COOH–SbF5 at 70°C. It is not excluded that
these two reactions, carbonylation involves not only
ketone 18, but also unreacted phenylbenzocyclobutene
25, whose reaction with CO–SbF5 at 70°C gives
product 19 [1].
The example of compound 22 was further used to
study, whether other carboxylic acids than CF3COOH
and its anhydride are applicable to prepare and carbo-
nylate polyfluorocyclobenzocyclobutenones in SbF5.
Reasonable results were obtained with HCOOH, which
decomposed on contact with SbF5 with CO evolution.
Thus, after the reaction of compound 22 with
HCOOH–SbF5in a sealed ampule we isolated, after
hydrolysis of the reaction mixture, preferentially
compounds 7 and 11, along with a small amount of
acid 10 (Scheme 8).
Perfluorobenzocyclobutene 26 in the (CF3CO)2O–
SbF5 system in a sealed ampule at 20°C, like ketone 1
in the CO–SbF5 system (Scheme 1), forms isochro-
menоne 2 along with compounds 3–5 (Scheme 7). The
only difference is that in the latter case more
admixtures 3–5 are formed that in the reaction of
ketone 1 with CO.
Noteworthy is the prevalence among the reaction
products of compound 7, the share of which decreases
in going from HCOOH (Scheme 8) to CF3COOH and
Scheme 7.
1. (CF3CO)2O, SbF5,
20oC, 75 h
2. H2O
O
CF3
COOH
COOH
F
F
F
F
F
F
F
+
+
F
+
O
COOH
O
O
26
2, 61%
3, 2%
4, 5%
5, 14%
Scheme 8.
1. RCOOH, SbF5,
70oC, 8 h
CF2
CF3
CF3
H
2. H2O
O
O
+
10
11
F
22
6
23
+
+
F
O
7
F
+
+
+
+
O
O
O
27
28
29
_
_
_
_
_
60%
4%
20%
HCOOH, 2 equiv
_
_
_
_
C2F5COOH, 1.9 equiv
CH3COOH, 2 equiv
49%
31%
10%
31%
31%
5%
_
_
_
11%
5%
11%
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 8 2019

ZONOV et al.
1108
further to (CF3CO)2O (Scheme 5). This tendency may
be explained in terms of the quantity of HF formed in
the system and its effect on the equilibrium between
compounds 7, 8, and 9 (Scheme 2). It should be noted
that the reaction of compound 22 with HCOOH forms
2 mol of HF per mol acid, the reaction with
CF3COOH, 1 mol of HF, while the reaction with
(CF3CO)2O forms no НF.
Reaction of perfluorocyclobutenone 1 with СО–
SbF5. A mixture of 0.51 g (2.24 mmol) of compound 1
and 2.85 g (13.18 mmol) of SbF5 was vigorously
stirred in a СО atmosphere at 20°С for 3 h, after which
it was poured into 5% HCl at 0°С, successively
extracted with CH2Cl2 and Et2O, and the extracts were
dried over MgSO4. According to 19F NMR, the ether
extract contained 0.055 g of acid 5 (yield 10%). The
CH2Cl2 extract was evaporated to leave 0.42 g of a
mixture containing 95% of compounds 2, 3, and 4 in a
95 : 2 : 3 ratio. The mixture was dissolved in a small
amount of CH2Cl2, washed with saturated aqueous
NaHCO3, dried over MgSO4, and transferred onto a
watch glass to obtain 0.38 g (yield 67%) of compound 2.
The analytical sample (0.23 g) was obtained by
recrystallization from hexane followed by vacuum
sublimation (90°С, 20 mmHg).
Unlike the above-described examples, in the
reaction of compound 22 with C2F5COOH–SbF5 in a
sealed ampule, the degree of carbonylation of ketone 6
formed from compound 22 was low even at 70°C. The
reaction mixture contained ketones 6 and 23 and small
amounts of acid 11 and perfluoro-3-methylphthalide
(27) (Scheme 8).
No carbonylation products were detected in the
reaction of compound 22 with CH3COOH–SbF5 at
70°C. The water-treated reaction mixture contained
compounds 6 and 23, perfluoro-3-methylphthalide
(27), as well as 3-(trifluoromethyl)-4,5,6,7-tetrafluoro-
phthalide (28) and perfluoro-3-methylenephthalide
(29) (Scheme 8). This result is probably explained by
that the corresponding acids are quite highly resistant
to decomposition with СО evolution as compared to
CF3COF [5, 8].
Perfluoroisochromen-1-one (2), mp 130–132°С.
IR spectrum (KBr), ν, cm–1: 1795 (C=O), 1728 (C=C),
1513, 1499 (fluorinated aromatic ring). 19F NMR
spectrum (CDCl3), δ, ppm: 62.3 (1F, F3), 30.9 (1F, F8),
22.0 (1F, F6), 17.4 (1F, F5), 9.6 (1F, F7), –22.8 (1F,
F4); JFF, Hz: J3,4 8, J3,5 5, J3,6 2.5, J3,7 6.5, J3,8 3.5, J4,5
46, J4,6 1, J4,7 3.5, J4,8 3.5, J5,6 20, J5,7 2.5, J5,8 14.5, J6,7
20.5, J6,8 13.5, J7,8 20. Found, %: C 42.45; F 45.09.
[M]+ 253.9795. C9F6О2. Calculated, %: C 42.54; F
44.86. M 253.9797.
The composition and structure of the reaction
products were established by elemental analysis, high-
resolution mass spectrometry, and IR and 19F NMR
spectroscopy, and compounds 3 [10], 7, 11 [11], 8, 9,
10, 19 [1], 13, 14, 15 [12], 18, 21 [13], 4, 23, 28, 29
[14], and 27 [15] were identified by a comparison of
their 19F NMR spectra with the spectra of authentic
samples.
Reaction of perfluoro-2-methylbenzocyclo-
butenоne (6) with СО–SbF5. A mixture of 0.84 g
(3.03 mmol) of compound 6 and 3.94 g (18.18 mmol)
of SbF5 was vigorously stirred in a СО atmosphere at
20°С for 24 h. The 19F NMR spectrum showed signals
of cations 8 and 9 and compound 7 in a 76 : 8 : 16
ratio. The solution was poured into 5% HCl at 0°С,
successively extracted with CH2Cl2 and Et2O, and the
extract was dried over MgSO4. According to 19F NMR,
the ether extract contained 0.21 g of acid 11 (yield
27%). The CH2Cl2 extract was evaporated to leave
0.62 g of a mixture containing ~95% of compounds 6,
7, and 10 in a 1 : 21 : 78 ratio. The mixture was
dissolved in a small amount of CH2Cl2, washed with
saturated NaHCO3, dried over MgSO4, and transferred
onto a watch glass to obtain 0.13 g of compound 7
(yield 15%). The aqueous part was acidified with HCl
and then extracted with CH2Cl2, dried over MgSO4,
and transferred onto a watch glass to obtain 0.46 g
(yield 50%) of acid 10.
EXPERIMENTAL
The IR spectra were registered on a Bruker Vector 22
spectrometer. The 19F and 1Н NMR spectra were
obtained on a Bruker AV-300 spectrometer at 282.4
and 300 MHz, respectively. The chemical shifts were
measured downfield from C6F6 (19F) and TMS (1Н),
internal standards C6F6, SO2ClF (262.8 ppm against
C6F6), and CHCl3 (7.24 ppm against TMS). Elemental
analysis was performed using high-resolution mass
spectrometry on a Thermo Electron Corporation DFS
instrument. The compositions of the reaction mixtures
were established by 19F NMR spectroscopy using
C6F5CF3 as the quantification internal standard for
estimating the yields of some compounds.
Reaction of perfluoro-2-ethylbenzocyclobutenone
(12) with СО–SbF5. A mixture of 0.76 g (2.32 mmol)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 8 2019

CARBONYLATION OF POLYFLUOROBENZOCYCLOBUTENONES IN A SbF5 MEDIUM
1109
of compound 12 and 3.23 g (14.93 mmol) of SbF5 was
vigorously stirred in a СО atmosphere at 20°С for 24 h.
The 19F NMR spectrum of the mixture displayed
signals of cation 13. The solution was poured into 5%
HCl at 0°С, extracted with CH2Cl2, and the extract was
dried over MgSO4. The solvent was distilled off to
leave 0.74 g of a mixture of compounds 14 and 15
(total yield 96%) in a 60 : 40 ratio.
95%). The analytical sample of the product (0.24 g)
was obtained by recrystallization from CHCl3.
2-[Carboxy(pentafluorophenyl)methyl]-3,4,5,6-
tetrafluorobenzoic acid (20), mp 152–157°С
(decomp.). IR spectrum (KBr), ν, cm–1: 1717 (С=О),
1525, 1507, 1484 (fluorinated aromatic ring). 1H NMR
spectrum [(CD3)2CO], δ, ppm: 9.1 br.s (2H, OH), 5.90
s (1H, CH). 19F NMR spectrum [(CD3)2CO], δ, ppm:
28.2 (1F, F3), 25.1 (1F, F6), 23.7 (2F, Fortho), 10.4 (1F,
F4), 8.7 (1F, F5), 8.1 (1F, Fpara), 0.1 (2F, Fmeta); JFF, Hz:
Jpara,meta 20.5, Jpara,ortho 2.5, J3,ortho 22.5, J3,4 20, J3,5 5.5,
Reaction of perfluoro-2-isopropylbenzocyclo-
butenоne (16) with СО–SbF5. A mixture of 0.61 g
(1.62 mmol) of compound 16 and 2.49 g (11.51 mmol)
of SbF5 was vigorously stirred in a СО atmosphere at
20°С for 6 h. The solution was poured into 30 mL of
methanol at 0°С, kept at 20°С for 10 min, transferred
into 250 mL of 5% HCl, extracted with CH2Cl2, and
dried over MgSO4. The extract contained compounds
16 and 17 in a 10 : 90 ratio (19F NMR). The solvent
was distilled off, and the residue was subjected to
column chromatography on silica gel (eluent CHCl3)
to obtain 0.48 g (yield 70%) of compound 17.
J
3,6 11, J4,5 20, J4,6 5.5, J5,6 21.5. Found [M]+ 417.9889.
C15H3F9O4. Calculated M 417.9888.
Reaction of perfluoro-4-phenylisochromen-1-one
(19) with SbF5. To 1.08 g (4.99 mmol) of SbF5, a
solution of 0.16 g (0.4 mmol) of compound 19 in
0.3 mL of C6F6 was added. The mixture was kept at
20°С for 20 h, poured into 5% HCl at 0°С, extracted
with CH2Cl2, and dried over MgSO4. The solvent and
C6F6 were removed to obtain 0.15 g of a mixture
containing ~90% of compounds 19 and 21 in a 30 : 70
ratio.
Methyl 2-[1-(methoxycarbonyl)-2-(trifluorome-
thyl)trifluoroprop-1-en-1-yl]-3,4,5,6-tetrafluoroben-
zoate (17). Liquid. IR spectrum (KBr), ν, cm–1: 2957
(С–Н), 1753 (С=О), 1516, 1481 (fluorinated aromatic
ring). 1H NMR spectrum (CDCl3), δ, ppm: 3.91 s (3H,
CH3), 3.81 s (3H, CH3). 19F NMR spectrum (CDCl3),
δ, ppm: 101.5 (3F, CF3Z), 101.2 (3F, CF3E), 27.7 (1F,
F6), 26.2 (1F, F3), 14.6 (1F, F4), 12.2 (1F, F5); JFF, Hz:
JCF3(E),CF3(Z) 8, JCF3(E),3 3, J3,4 21.5, J3,5 5, J3,6 11.5, J4,5
20, J4,6 8.5, J5,6 21.5. Found [M]+ 428.0106.
C14H6F10O4. Calculated M 428.0101.
Reaction of perfluoro-1-methylbenzocyclobutene
(22) with (CF3СО)2O–SbF5 in an open tube. A glass
beaker with 0.43 g (2.05 mmol) of (CF3СО)2O was put
into a glass tube charged with a solution of 0.5 g
(1.67 mmol) of compound 22 in 1.09 g (5 mmol) of
SbF5. To avoid a loss of (CF3СО)2O, the tube was
sealed and turn upside down to mix the reagents. The
ampule was then immediately opened, purged with air,
kept at 20°С for 2 h, transferred into 5% HCl at 0°С,
extracted with CH2Cl2, and dried over MgSO4. The
solvent was distilled off to obtain 0.4 g of ketone 6
(yield 87%).
Reaction of perfluoro-2-phenylbenzocyclobute-
nоne (18) with СО–SbF5. A solution of 0.51 g
(1.36 mmol) of compound 18 in 1 mL of C6F6 was
added dropwise to a stirred solution of 2.29 g
(10.59 mmol) of SbF5. The mixture was vigorously
stirred in a СО atmosphere at 20°С for 30 h, poured
into 5% HCl at 0°С, extracted with CH2Cl2, and dried
over MgSO4. The solvent and C6F6 were distilled off to
obtain 0.49 g of a mixture containing ~85% of
compounds 19, 20, and 21 (total yield 77%) in a
60 : 10 : 30 ratio (19F NMR).
Experiments in sealed ampules. A glass beaker
with (CF3СО)2O or carboxylic acid was placed into a
glass tube containing a solution of polyfluorobenzo-
cyclobutene in SbF5. The tube was sealed and turned
upside down to mix the reagents. The mixture was kept
at a required temperature, after which the tube was
opened, its content was transferred into 5% HCl at
0°С, successively extracted with CH2Cl2 and Et2O, and
the extracts were dried over MgSO4.
Hydrolysis of perfluoro-4-phenylisochromen-1-
one (19). To a solution of 0.49 g (1.22 mmol) of
compound 19 in 7 mL of ether, 7 mL of 10% HCl was
added, and the mixture was stirred for 17 days. The
ether layer was dried over MgSO4, and the solvent was
removed in a vacuum to obtain 0.49 g of acid 20 (yield
Reaction perfluoro-1-methylbenzocyclobutene (22)
with (CF3СО)2O–SbF5 (experiment no. 1). From 0.61 g
(2.05 mmol) of compound 22, 2.65 g (12.2 mmol) of
SbF5, and 0.43 g (2.05 mmol) of (CF3СО)2O (20°С, 70 h)
we obtained 0.28 g of a mixture containing ~95% of
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 8 2019

ZONOV et al.
1110
compounds 7 and 10 (total yield 43%) in a 53 : 47 ratio
from the CH2Cl2 extract. The ether extract contained,
according to 19F NMR, 0.26 g of acid 11 (yield 50%).
Reaction perfluoro-1-ethylbenzocyclobutene (24)
with (CF3СО)2O–SbF5 (experiment no. 6). From 0.82 g
(2.36 mmol) of compound 24, 3.1 g (14.32 mmol) of
SbF5, and 0.5 g (2.38 mmol) of (CF3СО)2O (20°С, 70 h)
we obtained 0.7 g of a mixture of compounds 14 and
15 (total yield 90%) in a 85 : 15 ratio from the CH2Cl2
extract.
Reaction perfluoro-1-methylbenzocyclobutene (22)
with CF3СОOH–SbF5 (experiment no. 2). а. from
0.76 g (2.53 mmol) of compound 22, 3.29 g (15.2 mmol)
of SbF5, and 0.3 g (2.61 mmol) of CF3СОOH (20°С,
70 h) we obtained 0.07 g of acid 11 (yield 10%) from
the ether extract and 0.59 g of a mixture containing
~95% of compounds 6, 7, and 10 (total yield 75%) in a
35 : 55 : 10 ratio from the CH2Cl2 extract.
Reaction perfluoro-1-methylbenzocyclobutene (22)
with CF3СОOH–SbF5 (experiment no. 7). From 0.54 g
(1.55 mmol) of compound 24, 2.03 g (9.37 mmol) of
SbF5, and 0.36 g (3.12 mmol) of CF3СОOH (70°С, 8 h)
we obtained 0.47 g of a mixture of compounds 14 and
15 (total yield 92%) in a 50 : 50 ratio from the CH2Cl2
extract.
b. From 0.67 g (2.23 mmol) of compound 22, 2.94 g
(13.56 mmol) of SbF5, and 0.28 g (2.46 mmol) of
CF3СОOH (70°С, 8 h) we obtained 0.2 g of acid 11
(yield 35%) from the ether extract and 0.34 g of a
mixture containing ~95% compounds 6, 7, 10 and 23
(total yield 53%) in a 29 : 60 : 4 : 7 ratio from the
CH2Cl2 extract.
Reaction of perfluorobenzocyclobutene (26) with
(CF3СО)2O–SbF5 (experiment no. 8). From 0.65 g
(2.61 mmol) of compound 26, 3.38 g (15.57 mmol) of
SbF5, and 0.54 g (2.59 mmol) of (CF3СО)2O (20°С, 75 h)
we obtained 0.09 g of acid 5 (yield 14%) from the ether
extract and 0.47 g of a mixture containing ~95% of
compounds 2, 3, and 4 (total yield 68%) in a 90 : 3 : 7
ratio from the CH2Cl2 extract.
c. From 0.78 g (2.61 mmol) compound 22, 3.32 g
(15.3 mmol) of SbF5, and 0.6 g (5.24 mmol) of
CF3СОOH (70°С, 8 h) we obtained 0.34 g of acid 11
(yield 52%) from the ether extract and 0.33 g of a
mixture containing ~80% of compounds 7, 10, and 23
(total yield 33%) in a 91 : 7 : 2 ratio from the CH2Cl2
extract.
Reaction perfluoro-1-phenylbenzocyclobutene (25)
with (CF3СО)2O–SbF5 (experiment no. 9). From
compound 25, obtained from 0.62 g (2.52 mmol) of
compound 26 and 0.42 g (2.52 mmol) of C6F5H in 3.28 g
(15.11 mmol) of SbF5 [16], and 0.56 g (2.64 mmol) of
(CF3СО)2O (70°С, 8 h) we obtained a mixture, which
was transferred into 5% HCl at 0°С, extracted with
CH2Cl2–Et2O (2 : 1), the extract was dried over
MgSO4, and the solvent was distilled off. The residue
was sublimed in a vacuum (100–150°С, 2 mmHg) to
obtain 0.98 g of a mixture containing ~90% of
compounds 19 and 21 (total yield 88%) in a 60 : 40
ratio.
Reaction perfluoro-1-methylbenzocyclobutene (22)
with HСОOH–SbF5 (experiment no. 3). From 0.68 g
(2.28 mmol) of compound 22, 2.88 g (13.28 mmol) of
SbF5, and 0.21 g (4.61 mmol) of HCОOH (70°С, 8 h)
we obtained 0.14 g of acid 11 (yield 24%) from the
ether extract and 0.49 g of a mixture containing ~90%
of compounds 7 and 10 (total yield 64%) in a 94 : 6
ratio from the CH2Cl2 extract.
Reaction perfluoro-1-methylbenzocyclobutene (22)
with C2F5СОOH–SbF5 (experiment no. 4). From 0.72 g
(2.42 mmol) of compound 22, 3.07 g (14.17 mmol) of
SbF5, and 0.74 g (4.48 mmol) of C2F5CОOH (70°С, 8 h)
we obtained 0.06 g of acid 11 (yield 10%) from the
ether extract and 0.57 g of a mixture of compounds 6,
23, and 27 (total yield 85%) in a 57 : 37 : 6 ratio from
the CH2Cl2 extract.
Reaction perfluoro-1-phenylbenzocyclobutene (25)
with CF3СОOH–SbF5 (experiment no. 10). In a
similar way, from 0.51 g (2.06 mmol) of compound
26, 0.35 g (2.1 mmol) of C6F5H, 2.68 g (12.37 mmol)
of SbF5, and 0.47 g (4.15 mmol) of CF3СОOH (70°С,
8 h) we obtained a CH2Cl2 extract, which was dried
over MgSO4. The solvent was distilled off to obtain
0.8 g of a mixture containing ~80% of compounds 19
and 21 (total yield 78%) in a 71 : 29 ratio.
Reaction perfluoro-1-methylbenzocyclobutene (22)
with CH3СОOH–SbF5 (experiment no. 5). From 0.74 g
(2.48 mmol) of compound 7, 3.24 g (14.93 mmol) of
SbF5, and 0.3 g (5.05 mmol) of CH3CОOH (70°С, 8 h)
we obtained 0.6 g of a mixture of compounds 6, 23, 27,
28, and 29 (total yield 88%) in a 35 : 35 : 12 : 12 : 6
from the CH2Cl2 extract.
ACKNOWLEDGMENTS
The authors are grateful to the Chemical Research
Center for Collective Use, Siberian Branch, Russian
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 8 2019

CARBONYLATION OF POLYFLUOROBENZOCYCLOBUTENONES IN A SbF5 MEDIUM
1111
8. Olah, G.A., Germain, A., and Lin, H.C., J. Am.
Chem. Soc., 1975, vol. 97, p. 5481. doi 10.1021/
ja00852a028
Academy of Sciences, for spectral and analytical
measurements.
CONFLICT OF INTEREST
The authors declare no conflict of interest.
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